Mass spectrometer signal enhancement

Abstract

To provide a mass spectrometer that is not affected by the presence of constituents other than a subject to be analyzed in a sample, a mass spectrometer, and a method for operating inductively coupled plasma emission spectrometry.SOLUTION: A method for operating a mass spectrometer having a skimmer and a circuit that is constituted to apply electric potential to the skimmer includes a process of acquiring a first mass spectrum of a sample, where the method includes the processes of: measuring a value of a first mass spectrum obtained, in which the value shows ion beam intensity of one or more kinds of ion species; applying various DC electric potential to the skimmer to specify an operating potential, in which DC electric potential is allowed to vary until a value showing the ion beam intensity of one or more kinds of ion species changes by a predetermined amount; and presenting an output value including a mass spectrum by the an operating potential applied to the skimmer.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to mass spectrometers and methods of operating mass spectrometers, particularly inductively coupled plasma mass spectrometry (ICP-MS).

Background Art

[0002] Data generated by a mass spectrometer regarding a particular analyte may be affected by the presence of other constituent substances in the sample other than the analyte. This may be referred to as matrix effect or matrix interference. Generally, this may suppress the ion intensity signal within the mass spectrum, which can lead to a decrease in sensitivity, inaccuracy of quantitative results, and other errors.

[0003] One type of matrix effect is the physical suppression of the signal of the analyte caused by the level of total dissolved solids (TDS) or acid concentration in the sample. Another type of matrix effect is induced when matrix components affect the ionization conditions in the plasma discharge, resulting in various amounts of signal suppression depending on the concentration of the matrix components. A further mechanism that results in signal suppression is the matrix-induced effect that causes a decrease in the signal of the analyte, known as the space charge effect. This is a type of matrix-induced interference that causes suppression of the signal of the analyte. This space charge effect may cause a shift in the focus of the ion beam. Thus, very abundant matrix elements occupy the ion beam, pushing the analyte ions out of their paths, usually resulting in a decrease in sensitivity.

[0004] Furthermore, matrix components may accumulate around the skimmer or sampler orifice due to prolonged instrument operation. This can lead to long-term instability in the measured ionic intensity values. Internal standards may be used to correct for matrix interference, ideally having a similar mass and sample composition to the analyte, although this is limited to the study of similar analytes. However, in particular, there is a need to improve results regarding matrix effects in the case of long-term experiments where drift effects still occur due to deposition in the sampling area and elsewhere.

[0005] Some configurations of a mass spectrometer offer greater sensitivity, but they can also make the spectrometer more susceptible to matrix effects. Switching between a configuration that is more robust to matrix effects and one that offers improved sensitivity may require hardware modifications, which can be time-consuming, present other challenges, and require skilled personnel.

[0006] Therefore, methods and systems are needed to overcome these challenges. [Overview of the project]

[0007] Mass spectrometers, such as liquid chromatography-mass spectrometers (LC-MS) or inductively coupled plasma-mass spectrometers (ICP-MS), can be configured, calibrated, or otherwise optimized for use with specific samples or sample types. For example, a sample may contain the analyte but also a matrix (e.g., contaminants or other constituent materials that may interfere with the ion beam intensity signal of the analyte). Mass spectrometers may also have a skimmer, which can be used to skim off the boundary region of the plasma plume and form an ion beam as it enters the mass spectrometer.

[0008] The matrix can occupy a much larger proportion of the total ion flow than the analyte, and therefore, in the mass spectrum, may be represented by a much higher signal intensity than the analyte. One example of a matrix effect is a decrease in the amount of analyte ions detected by the mass spectrometer. Another matrix effect is caused, for example, by space charges that shield the voltage of the extraction lens. This can affect the focusing of the ion optics. In either case, the presence of a matrix can alter the expected value of the ion beam intensity for at least one analyte, which is a result of a particular matrix concentration. This can lead to inaccurate results that indicate an incorrect concentration of the analyte in the sample.

[0009] However, applying a potential (preferably a negative DC potential) to the skimmer can reduce matrix dependence and diminish the effectiveness of matrix control, even though this may (but not always) reduce the overall signal intensity from both the analyte and the matrix.

[0010] A further advantage of applying an electric potential to the skimmer is that it helps keep the components clean by deflecting contaminants (preferably a positive DC potential for this purpose). This is particularly advantageous because the small size of the skimmer opening can easily lead to clogging.

[0011] This system and method involves finding improvements or optimizations to the voltage applied to the skimmer (usually a negative voltage, but in some cases a positive voltage may be used) by setting the voltage, resulting in a change (increase or decrease) of the mass spectrometer signal of one or more ion species by a specific amount or proportion (e.g., 3 / 4).

[0012] This can be described as an adjustment or operation of the method for setting up a mass spectrometer for a particular sample or sample type. This technique improves the immediate signal recovery rate of the device for a particular sample. This adjustment method may be performed, for example, by automation and using computer control (communicating with the mass spectrometer), or by using a dedicated control unit having firmware configured to perform this method.

[0013] To improve long-term stability (e.g., when the device is used for several hours), instead of applying a voltage (e.g., a negative voltage) to the skimmer, or simultaneously, a higher or increased pressure can be applied inside the mass spectrometer. Both techniques can alter the overall signal intensity, and thus reduce the overall signal intensity in two ways. Applying a voltage (e.g., a negative DC voltage) to the skimmer improves the instantaneous recovery of the matrix, and the increased pressure in the beam path (e.g., in the skimmer or extraction region) improves long-term stability. Therefore, both techniques complement each other.

[0014] In summary, optimal matrix stability / tolerance is ensured by using increased pressure in the skimmer and / or by applying voltage to the skimmer of the mass spectrometer and / or by applying increased pressure.

[0015] Against this backdrop, and according to the first aspect, a method for operating a mass spectrometer having a skimmer and a circuit configured to apply an electric potential to the skimmer, The process of obtaining the initial mass spectrum of the sample, A step of measuring the value of the first mass spectrum obtained, wherein the value indicates, for example, the ion beam intensity of one or more ion masses or ion species. A step of determining the operating potential by applying various DC potentials to a skimmer, wherein the DC potential is changed until the value indicating the ion beam intensity of one or more ion species changes by a predetermined amount. A method is provided which includes the step of presenting an output value including a mass spectrum using an operating potential applied to a skimmer.

[0016] Therefore, matrix effects can be reduced, partially eliminated, or completely eliminated. Thus, more consistent or more accurate quantitative measurements can be obtained. When the intensity of one or more ion species changes by a predetermined amount, the potential applied to the skimmer can be recorded (e.g., for a specific sample and other operating conditions) and the change can be terminated. This potential becomes the operating potential or manipulative potential for one or more mass spectra that can be obtained from the mass spectrometer. The mass spectra may be stored along with the data indicating the operating potential. This process can be performed once for a specific series of measurements or before all mass spectra to be obtained.

[0017] Various methods may exist to determine a value that indicates a predetermined change in ion beam intensity. For example, the amplitude for a particular ion in the mass spectrum can be reduced by a specific percentage, absolute value, or ratio (original value versus new value). Other conditions indicating that the value has fluctuated or changed by a predetermined amount may be reached directly or indirectly. The potential may be set relative to other parts or components of the mass spectrometer. These other components may, for example, normally be grounded or earthed. If an output value is obtained in the final method step of obtaining the mass spectrum at the operating potential applied to the skimmer, the further output value may include the initial mass spectrum, and as a result, both mass spectra, i.e., with and without the potential applied to the skimmer, can be compared.

[0018] Preferably, the step of obtaining the initial mass spectrum of the sample is performed without potential (using a floating skimmer) or using the ground potential (i.e., 0V) applied to the skimmer. A constant non-zero voltage may be applied to the skimmer for the initial mass spectrum, but typically the skimmer is initially grounded.

[0019] Depending on the circumstances, the method may further include increasing or decreasing the pressure at the interface between the sampling aperture (of the mass spectrometer) and the skimmer to change (increase or decrease) a value indicating the ion beam intensity of one or more ion species, and as a result, a combination of increasing or decreasing pressure and potential is obtained to obtain a value indicating the ion beam intensity of one or more ion species at a predetermined amount. Once the value has changed by the predetermined amount, the pressure may be recorded and set as the operating pressure or control pressure, and used together with the operating potential for one or more mass spectra. The mass spectra may be recorded together with the values ​​of the operating pressure and / or operating potential. For example, the pressure may be increased or changed within the extended region (interface region) located between the sampler and the skimmer. Generally, as the pressure increases (from an extended vacuum of about 2.9 mbar (Ar) or less), the signal from the mass spectrometer decreases.

[0020] Here, only given pressure values ​​should be adopted as illustrative values. Furthermore, these values ​​are typically measured using a Pirani (thermal conduction) pressure gauge calibrated for nitrogen. To convert these values ​​to physical pressure (expressed as force divided by area), they must be corrected according to the type of gas. This is not easy, as the inventors are dealing with gas mixtures. Therefore, although Pirani output values ​​are used in the described systems and methods, the physical pressure values ​​may deviate slightly from the Pirani output values.

[0021] The voltage applied to the skimmer may increase or decrease the ion intensity signal. When both effects occur, the overall result will be a change (e.g., decrease) in the signal by a predetermined amount (e.g., 3 / 4 or 1 / 2) compared to the value obtained without applying voltage to the skimmer and using the normal operating pressure. The pressure may be measured, configured, or regulated by a pressure regulator or control unit. The pressure may be measured in the expansion region, or downstream of the skimmer in the extraction region. Pressure changes may also be managed automatically, for example, by computer control or by a dedicated control unit with suitable firmware. The interface between the sampler (or the inlet to the mass spectrometer) and the skimmer may be the region directly in front of the skimmer cone. The interface pressure may be varied using a pump and measured using a pressure sensor. The interface pressure can be changed, for example, by changing the speed of a rotary pump, by changing the conductance (e.g., by using a control valve or otherwise changing the gas flow rate), by switching between different conductances, and / or by turning the power on and off of a further pump system.

[0022] Depending on the circumstances, the value indicating ion beam intensity may be one or more of the amplitudes of one or more peaks in the mass spectrum and one or more measured values ​​of the total current (e.g., total ion current). The ion current can be measured, for example, using an ion optical lens. Other values ​​or characteristics of the mass spectrum or signal may also be used.

[0023] Preferably, the predetermined amount may be a decrease in percentage or a decrease in fraction. The predetermined level may be selected from, for example, a series of predetermined amounts or one of several levels specific to various experimental conditions, samples, sample types, or matrix types.

[0024] Depending on the circumstances, the specified amount may be expressed as a percentage change or a fractional change in the value.

[0025] In some cases, the predetermined amount may be a decrease in value.

[0026] In some cases, the decrease (predetermined amount) may be a decrease of about one-third (1 / 3) to one-tenth (1 / 10). However, a smaller decrease in value may also be used (e.g., a decrease of about half or three-fourths).

[0027] In some cases, the method further includes repeating the steps (i.e., any or all of the acquisition step, measurement step, application step, and presentation step, and optional steps) using various samples having known compositions, and recording the potential required to change the value indicating the ion beam intensity for each known composition by a predetermined amount. The potential applied to the skimmer to change or decrease the value or signal by a predetermined amount can be recorded for each of the known compositions. This may take the form of a calibration process for a series of known compositions and may be part of an automated computer-controlled process. These values may be stored and retrieved when a sample having an expected composition in a known calibration composition or an expected composition close to a known calibration composition is investigated. Thus, the retrieved potential may be immediately applied (without requiring other steps) to such a sample.

[0028] Preferably, the potential may be a negative potential (e.g., with respect to a sampling cone or other components of the spectrometer that can be grounded or earthed). For most samples, a negative voltage may be appropriate, but in some cases, a positive voltage may also be used. By this method, it may be scanned over a range of voltages (e.g., +10V to -10V, +5V to -5V, +4V to -4V, +3V to -3V or any other range). Any or all of that range can have, as an upper limit value, 10V, 9V, 8V, 7V, 6V, 5V, 4V, 3V, 2V, 1V, 0V. Any or all of that range can have, as a lower limit value, -10V, -9V, -8V, -7V, -6V, -5V, -4V, -3V, -2V, -1V, 0V. The range can be set based on the sample or matrix type and the ion mass of the target analyte.

[0029] Preferably, the method can further include presenting a further output value including a mass spectrum by an operating potential applied to the skimmer. One or more additional data sets (mass spectra) can be collected together with the potential of the skimmer set at the operating potential. These can be used as data for further analysis.

[0030] In some cases, the potential may be -1V to -4V. Other values or ranges may be used (e.g., 0V to -5V).

[0031] In some cases, the method can further include the step of storing the potential required to vary a value indicating the ion beam intensity of one or more ion species to a predetermined amount for various sample types and compositions. Thus, a database or data store of values can be developed.

[0032] Depending on the circumstances, this method may further include the step of applying an AC current to the skimmer simultaneously with applying a DC potential. The AC current may be variable or fixed. A suitable frequency can be, for example, 50 to 60 Hz. In summary, the DC potential and AC current applied to the skimmer can be varied up to predetermined values. The AC RMS range (fixed or variable) can be, for example, + / - 1V, 2V, 3V, 4V, 5V, and up to 10V.

[0033] Depending on the circumstances, this method may be The process of releasing the application of the electric potential, The process may further include the step of presenting further output values, including a mass spectrum, without a potential applied to the skimmer (e.g., using a grounded or 0V-set skimmer). Acquiring data with and without a potential applied to the skimmer can provide further information about the sample. Thus, this can constitute a further exploration technique in which additional information about the sample can be collected by comparing the mass spectrum with and without a potential applied to the skimmer. This process may also be used to verify that the operating potential is correct and does not require re-evaluation or reset.

[0034] According to a second aspect, a method for operating a mass spectrometer, The process of obtaining the initial mass spectrum of the sample, A step of measuring the value of the first mass spectrum obtained, wherein the value indicates the ion beam intensity of one or more ion species, A step of determining the operating pressure by changing the pressure inside a mass spectrometer, wherein the pressure is changed until the value indicating the ion beam intensity of one or more ion species changes by a predetermined amount. A method is provided which includes the step of presenting an output value, including a mass spectrum, based on the pressure inside a mass spectrometer at the operating pressure.

[0035] Depending on the circumstances, this method may further include a step of applying various DC potentials to the skimmer of a mass spectrometer to determine the operating potential, wherein the DC potential changes, and as a result, by combining the operating pressure and the application of the potential to the skimmer, the value indicating the ion beam intensity of at least one or more ion species changes to a predetermined amount. An AC current (as described above) may also be applied to the skimmer.

[0036] Preferably, the operating potential may be a negative potential. A positive potential may also be used. Preferably, the skimmer may be electrically insulated from other components, and the support and inlet to the system may be grounded or earthed.

[0037] Preferably, the predetermined amount may be a decrease in the value indicating the ion beam intensity of one or more ion species.

[0038] Preferably, the pressure may be increased.

[0039] Preferably, the pressure may be the pressure at the interface between the sampler and the skimmer of the mass spectrometer. This is the pressure just upstream of the cone or at the tip of the skimmer. This interface region may be maintained, or its pressure may be changed using a pump and pressure sensors.

[0040] According to a third aspect, a mass spectrometer is provided having a skimmer and means configured to carry out the steps of the method described.

[0041] Preferably, the mass spectrometer is an inductively coupled plasma mass spectrometer, i.e., ICP-MS. Other mass spectrometers may be used. This technique may also be used in conjunction with liquid chromatography-mass spectrometry (LC-MS) and / or laser ablation.

[0042] In some cases, the mass spectrometer may further include a bipolar (or four-quadrant) power supply configured to apply a potential to the skimmer. The four-quadrant power supply may operate, for example, as both an electron source and an electron sink (e.g., while maintaining a fixed potential).

[0043] In some cases, the skimmer may be formed from platinum, aluminum, titanium, or nickel (or any combination thereof). Other materials may be used (e.g., conductive or semiconductive). Preferably, the skimmer may include a cone.

[0044] Depending on the circumstances, the mass spectrometer may further include a device or setting configured to maintain the skimmer at a temperature of 450°C to 650°C (or more generally, 200°C to 750°C). Other temperatures and temperature ranges may be used (e.g., up to 1000°C). This may include passive heating (i.e., by plasma) but may also be regulated by a suitable thermal coupling (e.g., active or passive). A temperature gradient may exist throughout the skimmer, resulting in a tip (cone) temperature of, for example, 450°C to 750°C.

[0045] In a further embodiment, a method is provided for operating a mass spectrometer having a skimmer and a circuit configured to apply a potential to the skimmer, thereby presenting an output value including a mass spectrum based on the operating potential applied to the skimmer.

[0046] The method for determining the operating potential in a skimmer is: The process of obtaining the initial mass spectrum of the sample, A step of measuring the value of the first mass spectrum obtained, wherein the value indicates the ion beam intensity of one or more ion masses or ion species, A step of determining the operating potential by applying various DC potentials to a skimmer may include a step of changing the DC potential until a value indicating the ion beam intensity of one or more ion masses satisfies a predetermined condition.

[0047] In a further embodiment, a method for operating a mass spectrometer, The process of obtaining the initial mass spectrum of the sample, A step of measuring the value of the first mass spectrum obtained, wherein the value indicates the ion beam intensity of one or more ion masses or ion species, A step of determining the operating pressure by changing the pressure inside a mass spectrometer, wherein the pressure is changed until a value indicating the ion beam intensity of one or more ion masses satisfies a predetermined condition. A method is provided which includes the step of presenting an output value, including a mass spectrum, based on the pressure inside a mass spectrometer at the operating pressure.

[0048] The above method may be implemented as a computer program containing program instructions for operating a computer. The computer program may be stored on a computer-readable medium. The computer may form part of a mass spectrometer or be a separate device.

[0049] A computer system may include one or more processors (e.g., local, virtual, or cloud-based), such as a central processing unit (CPU), and / or a single graphics processing unit (GPU) or a collection thereof. The processors may execute logic in the form of software programs. The computer system may include memory, including volatile and non-volatile storage media. It may also include computer-readable media for storing logic or program instructions. Different parts of the system may be connected using networks (e.g., wireless and wired networks). The computer system may include one or more interfaces. The computer system may include a suitable operating system, such as UNIX®, Windows®, or Linux®.

[0050] It should be noted that any of the above features may be used in conjunction with any particular aspect or embodiment of the present invention.

[0051] The present invention can be implemented in many ways, and embodiments are described below with reference to the accompanying drawings, merely as examples. [Brief explanation of the drawing]

[0052] [Figure 1] This figure shows a schematic diagram of a mass spectrometer system. The skimmer potential Vsk, interface pressure Psk, internal pressure Pint, and skimmer tip temperature Tsk are shown in this figure. [Figure 2] This is a flowchart illustrating how to operate the system shown in Figure 1, presented as a mere example. [Figure 3] This diagram shows a flowchart illustrating further methods for operating the system in Figure 1, which is presented merely as an example. [Figure 4] This diagram shows a flowchart illustrating further methods for operating the system in Figure 1, which is presented merely as an example. [Figure 5] This figure shows a graph displaying the changes in ionic intensity of the mass spectrum obtained from the system in Figure 1 when different voltages are applied to the skimmer. [Figure 6] This figure shows a graph illustrating the operating modes of a typical four-quadrant power supply. [Figure 7] Figure 6 shows a graph displaying the changes in ionic intensity of the mass spectrum obtained from the system in Figure 1 when different DC and AC voltages are applied to the skimmer using a four-quadrant power supply operating as shown in Figure 6. [Figure 8] This figure shows a further graphical representation of the changes in the ion intensity of the analyte obtained from the system in Figure 1 using samples of different matrix concentrations when different DC voltages are applied to the skimmer. [Figure 9] This figure shows a graphical representation of the ion signals obtained from the system in Figure 1, using various interface pressures to select the ion mass. [Figure 10] This figure shows a graphical representation of the ion signals obtained from the system in Figure 1, using various skimmer voltages and specific interface pressures to select ion masses. [Figure 11] This figure shows a graph of the recovery rates obtained using various instrument settings, particularly by using different skimmer voltages and specific interface pressures, in order to select the ion mass.

[0053] Please note that the diagrams are provided for simplicity and are not necessarily drawn to a specific scale. Similar features are given the same reference number. [Modes for carrying out the invention]

[0054] The system described improves the matrix tolerance of mass spectrometers, particularly inductively coupled plasma mass spectrometers (ICP-MS).

[0055] In ICP-MS, the sample is introduced into a plasma where it is vaporized and ionized. Ions of the sample are sampled from the plasma near the interface and introduced into the mass spectrometer. The plasma sampling interface typically includes a sampler and a skimmer. These elements may be grounded. However, improvements are shown when either a positive or negative voltage (depending on the sample, analyte, and / or matrix) is applied to the skimmer, which is also electrically isolated from the ground.

[0056] Preferably, ions can be generated in an ICP torch (however, other techniques may be used), introduced into a vacuum through the interface, and guided to a mass separation device via an ion optical system. The plasma sampling interface typically includes a sampler and an insulating skimmer. Figure 1 shows a schematic diagram of a simplified system 10. The sampler 50 separates atmospheric pressure (approximately 1000 mbar) from a lower pressure region in front of the skimmer 30 (interface pressure, 2.5–4.0 mbar (Ar)). The mass spectrometer 20 operates in a high vacuum, and the vacuum level depends on the specific measurement mode, e.g., whether or not a collision gas is used.

[0057] The potential is controlled by a control unit 40 (e.g., a four-quadrant power supply), which is adjusted using a digital port and can be operated by suitable software (e.g., Qtegra® software). The control unit 40 may also be controlled by a computer 60. A manual power supply may also be used. A specific voltage may be selected using a slider or other user interface, or this may be computer-controlled by suitable software. A selectable voltage range (e.g., -10V to +10V) may be presented within the instrument control window of the control unit 40 or the control software. The voltage may be selected to adjust the recovery rate of a specific required analyte.

[0058] The potential 30 applied to the skimmer depends on specific operating requirements that can be selected by the user. For example, the voltage setting of the control unit 40 may be configured to achieve high sensitivity or optimal matrix robustness for each analyte mass (i.e., dynamic lens adjustment). A description of the adjustment method used to select a specific potential to apply to the skimmer is given below.

[0059] In Figure 1, the ion beam moves from left to right. However, the components of the mass spectrometer and the ion beam may move in different directions. Behind the ICP torch (not shown in this figure) is a sampler 50 which is grounded and introduces ions into an intermediate vacuum. The cone region of the skimmer 30 is connected to a voltage source of a control unit 40 for controlling the potential. The skimmer 30 introduces ions from an intermediate (boundary) region with pressure Psk (e.g., 2.5 mbar(Ar) or less) to a high vacuum region with pressure Pint where the mass spectrometer 20 is located. The mass spectrometer 20 has data and control connections to an operating processor or computer 60. The computer 60 may be a separate device from the mass spectrometer 20, or they may form an integrated unit. The computer is connected to a data store or database 70 used to store mass spectra, operating parameters, or other parameters used in the operation of the mass spectrometer. The computer 60 can also automate the operation of the mass spectrometer.

[0060] Therefore, the skimmer 30 is insulated (for example, using Kapton® or polyimide foil) and its surface is electrically isolated from any support or cooling plate (not shown in this figure).

[0061] Figure 2 shows a flowchart of an example method 100 used to determine the potential difference or voltage applied to the skimmer 30. In step 110, the initial mass spectrum of the sample is obtained using the grounded skimmer 30 (e.g., achieved by the control unit 40). The mass spectrum includes one or more ion mass peaks with amplitudes indicating the ion beam intensity. The ion beam intensity or amplitude of these one or more peaks is measured in step 120 (e.g., by the computer 60).

[0062] In step 130, as the mass spectrometer operates and the ion beam generates a signal from the mass spectrometer 20, the voltage or potential applied to the skimmer 30 is changed using the control unit 40. This may be controlled by the computer 60 or by other means. The ion beam intensity changes with the change in the voltage applied to the skimmer 30 (usually decreasing at least as the ion mass decreases). This is evident from the signal from the mass spectrometer 20. System 10 stores data that defines predetermined levels of change or decrease in ion beam intensity. The applied voltage is changed until this predetermined amount of change or decrease is achieved or other intensity conditions are met. This may be an absolute change, a relative change, or a proportional change. This determines the operating voltage or running voltage applied to the skimmer 30 (i.e., when the desired change in value is achieved). The mass spectrum is generated using the operating voltage applied to the skimmer 30, and this is output in step 140 (e.g., output from the computer 60 and / or stored with the database 70).

[0063] Applying an electric potential (Vsk) to the skimmer 30 can reduce or cancel out matrix effects, but additional techniques may be used instead of, or in addition to, applying an electric potential. Instead of applying an electric potential to alter or reduce the signal in the ion mass from the mass spectrometer 20, the pressure Pint within the mass spectrometer (e.g., between the skimmer 30 and the mass spectrometer 20) may be varied. Typically, increasing this pressure reduces the ion beam intensity. Figure 3 shows a flowchart of method 200 illustrating such a technique (pressure variation only).

[0064] In step 210, the initial mass spectrum is acquired, similar to method 100 as described with reference to Figure 2. This is obtained using the pressure within the mass spectrometer (e.g., the interface between the sampling aperture and the skimmer) at the default or normal pressure level (i.e., interface vacuum of 2.5 mbar(Ar) or less).

[0065] Furthermore, the ion beam intensity is measured in step 220 at the minimum or default pressure level (intermediate vacuum). This measurement is taken from the amplitude of the signal from the mass spectrometer 20. The pressure within the interface region of the mass spectrometer increases while the signal is being generated. This may be controlled by the computer 60 or by other means. This continues until the signal value indicating the ion beam intensity at one or more ion masses changes (decreases or increases) by a predetermined level, the same or similar to that described with reference to the method in Figure 2, or until another intensity condition is met. This interface pressure becomes the new operating pressure. Following this pressure adjustment, in step 235, the remaining instrument parameters are optimized for performance at the new pressure. In step 240a, the mass spectrum is obtained as the output value from the mass spectrometer 20 at the operating pressure. Further mass spectra can be obtained from this sample or a similar sample without changing the pressure.

[0066] The sampler 50 separates atmospheric pressure (approximately 1000 mbar) from a lower pressure region in front of the skimmer 30 (typically set to 2.9–3.1 mbar (Ar) Psk) (interface region). The pressure within the interface region can be controlled, and the vacuum level can be adjusted, preferably operating under a computer-controlled vacuum.

[0067] The combined method 300 is described with reference to Figure 4. The initial mass spectrum is obtained in step 310. This is obtained using the pressure inside the mass spectrometer (e.g., between the sample cone 50 and the skimmer 30) at the default pressure level (i.e., intermediate vacuum of 3.1 mbar(Ar) or less).

[0068] Next, in step 320, the ion beam intensity is measured at the default pressure level (interface vacuum). This measurement is taken from the amplitude of the signal from the mass spectrometer 20. The pressure inside the mass spectrometer increases while the signal is being generated. This continues until the signal value indicating the ion beam intensity at one or more ion masses decreases by a predetermined level similar to that described with reference to the method in Figure 4 (step 330). This pressure becomes the operating pressure. Following this pressure adjustment, the remaining instrument parameters, except for the skimmer potential which is grounded, are optimized in step 335 to perform at the new pressure.

[0069] Next, in step 340, the mass spectrometer is operated so that the ion beam generates a signal from the mass spectrometer 20, and the voltage or potential applied to the skimmer 30 is changed using the control unit 40. The applied voltage is changed until a predetermined change or decrease is achieved. This determines the operating voltage or operating voltage applied to the skimmer 30 (i.e., when the desired change in value is achieved).

[0070] In step 350a, a mass spectrum is obtained as an output value from the mass spectrometer 20 at the operating pressure. Further mass spectra can be obtained from this sample or a similar sample without changing the pressure.

[0071] In Figures 3 and 4, the process for “optimizing the instrument” includes a procedure for searching for instrument parameters (i.e., lens voltage) that maximize ion transmission, starting with a first ion optical element (e.g., an electrostatic lens) behind the grounded skimmer and ending with the last ion optical element before the inlet of the analyzer of the mass spectrometer.

[0072] The specific conditions that define the maximization of ion transmission can vary from lens to lens and from iteration to iteration, and may have additional lateral conditions. It is common to repeat this process twice. The optimization process can be performed manually or automatically, for example, by using an algorithm that defines the computer-controlled "auto-adjustment" of the instrument.

[0073] Figure 5 shows two graphical datasets for selected example ion masses. The y-axis represents the ion beam intensity. The voltage applied to skimmer 30 is shown on the x-axis. These datasets show the direct effect of the skimmer potential on the ion signal intensity in the calibration solution (without matrix). Furthermore, these plots show that the optimal setting for maximum intensity (i.e., the optimal setting for applied voltage) differs with changes in ion mass.

[0074] For example, a given condition in the ion mass intensity signal might be to maximize this signal for a particular mass ion. The example ion 59Co requires a positive skimmer voltage (approximately 4.5V), while the example ion 209Bi requires a slightly negative voltage (-1V to -2V). This indicates that there may not be an optimal skimmer potential that yields intensity gain for all analytes and sample types (at least to maximize sensitivity), and for all purposes. Since higher mass ions may require more negative voltages than lower mass ions, the required skimmer operating voltage should ideally vary between analytes and sample types. This can be described as an adaptive lens adjustment process and a dynamic lens adjustment process.

[0075] The matrix effect reduces the ion signal intensity obtained from low-concentration samples (e.g., 1 ppb). This reduction may be due to space charge effects within or after the skimmer 30. In this region of system 10, whenever the Debye length is no longer small compared to the skimmer dimensions, charge separation occurs and electrons are lost. The space charge of the remaining cations (i.e., Coulomb forces between ions) causes the ion beam to shift focus or ions to be emitted from the ion beam. This effect may be enhanced in the presence of a larger number of ions (e.g., due to a higher matrix content), and increasing matrix content results in a greater suppression of the signal. If a small negative voltage is applied to the skimmer, electron loss is reduced, so this effect may be reduced, avoided, or at least weakened. However, it is also important to determine the precise or optimal applied potential to the skimmer 30 by varying the voltage and monitoring the signal until it reaches a percentage of its original value.

[0076] Figure 6 shows a chart illustrating the operation of a four-quadrant power supply. Each quadrant yields either a positive or negative voltage and either a source current or a sink current.

[0077] Figure 7 shows a graph illustrating the change in ionic intensity of the mass spectra obtained from the system in Figure 1 when the sample contains different amounts of matrix components and different voltages are applied to the skimmer.

[0078] The plot of the graph in Figure 7 is very similar to a conventional Langmuir plot. However, there are some differences, including the fact that the skimmer is larger in terms of plasma size scale compared to a Langmuir probe, and that the plasma is moving toward the skimmer ("probe") at ultrasonic velocity. Nevertheless, several plasma parameters can be determined, as shown by the data presented in the graph in Figure 7.

[0079] In Figure 7, the four quadrants of the I (current) vs. U (voltage) plot are labeled 1 to 4. The measured relationship between U and I is in three quadrants: 1, 4, and 3. Line 8 shows the range where the electron current is dominant, while line 9 shows the range where the sum of the ion current and the photoelectron current exiting the skimmer is dominant. A transitional range exists between these two, as shown by line 6.

[0080] The voltage at which no net current flows is the stray potential. The voltage indicated by arrow 7 is a good approximation of the plasma potential.

[0081] Alternatively or additionally, the potential applied to the skimmer 30 may be modified by applying a smaller AC voltage above the DC voltage (x-axis in Figure 7). The measured current (y-axis in Figure 7) gives the slope of the Langmuir curve and, combined with the absolute current, indicates the position on the Langmuir curve.

[0082] In the results shown in Figure 7, it can be seen that curve 5 does not pass through the origin of the coordinate system, but crosses three of the four quadrants of the coordinate system. Therefore, in order to set the skimmer potential to any desired value, it should be driven by a four-quadrant power supply or a bipolar power supply. This power supply can operate as both a source and a sink. Thus, providing a bipolar power supply or a four-quadrant power supply (as the control unit 40) can bring further advantages to the system 10. Quadrants 1, 3, and 4 (from Figures 6 and 7) are used in this system.

[0083] It may also be useful to provide the system with means or a switch to switch the operation of system 10 between a high-sensitivity setting mode (achieving the highest signal) and a matrix robustness setting mode (for matrix samples, the signal is lower, but a better signal recovery rate is achieved). Therefore, voltage and pressure (and other parameters) can preferably be switched during the same measurement or experiment. Such a configuration of mode switching may be automated and controlled by a computer 60 or a control unit.

[0084] Applying a DC voltage (and especially a negative voltage) achieves the described benefit of reducing matrix effects, but this voltage allows for further improvements to the operation of the mass spectrometer. When the system 10 is operated with a positive voltage applied to the skimmer 30, the deflection effect induced by the voltage keeps the skimmer cleaner or cleans it more effectively. This can be improved by applying an AC current exceeding the DC offset. Under normal operation of the mass spectrometer, the skimmer is the component that requires cleaning more frequently than other components. This effort can be reduced by the improvements described herein. This can be particularly advantageous in the case of a nickel skimmer, where deposits may accumulate over time in high-matrix samples.

[0085] Aside from maximizing the signal for a specific analyte's mass, skimmer potential can be used to improve the response of a mass spectrometer signal to samples containing high levels of matrix components. Figure 8 shows, firstly, the dependence of the signal of 115In as a function of skimmer potential, and secondly, its dependence on the amount of matrix content in the sample. In this case, the matrix consists of increasing concentrations of a mixture of Fe, Ni, Mg, Ca, and other elements. This plot shows that the response of the 115In analyte is asymmetric with respect to the ground potential on the skimmer. It also shows that the higher the matrix content, the more of the 115In analyte signal is lost.

[0086] However, when a sufficiently negative skimmer potential is selected, Figure 8 shows that the signal loss of the 115In analyte becomes increasingly independent of the amount of matrix content in the solution. When the skimmer potential is set to approximately -2.5V, the signal of the 115In analyte does not change up to a matrix content of 1000 ppm, but a matrix concentration of 2000 ppm still results in a significant signal loss. This residual signal loss can still be reduced when the skimmer potential is set to -4.0V. In Figure 8, the signal loss for a matrix-free sample is only 10% at a skimmer potential of -4.0V, compared to approximately 25% at a skimmer potential of -2.5V. At the same time, the measured 115In signal intensity decreases by approximately half from -2.5V to -4.0V.

[0087] In summary, Figure 8 shows that two effects can be observed by setting a negative skimmer potential. 1) Overall strength decreases. 2) Even in samples with high matrix content, signal recovery is improved.

[0088] Referring to the method outlined in Figure 2, Figure 8 shows that this was determined by using a skimmer potential of -2.5V, employing conditions that reduce the signal to one-quarter in the case of a grounded skimmer, and using a clean sample. When this skimmer potential of -2.5V is used to analyze a sample with a matrix content of 2000 ppm, the signal recovery rate of the 115In signal is improved to 75%, compared to a 30% recovery rate in the case of a grounded skimmer. The signal recovery rate can be further improved by using a higher signal reduction factor of approximately 6 or 7 as the conditions in the method shown in Figure 2. This determines a skimmer potential of -4.0V and further improves the signal recovery rate in a 2000 ppm matrix sample from 75% to 90%. Therefore, applying an appropriate voltage to the skimmer 30 can lead to more accurate quantitative results. The optimal potential is as follows: The elements being measured Matrix type and concentration in the sample, Plasma conditions, The condition of the skimmer cone may change with use. Use or purpose of the results, It depends on various factors, including those mentioned above.

[0089] One method for finding the optimal voltage is to vary the skimmer voltage until the signal from the target ion mass changes or decreases by a predetermined amount. The best value for this predetermined amount can be found from a plot such as the one shown in Figure 8.

[0090] Additional information may be considered when determining the appropriate skimmer potential. This includes: 1) Measure plasma-related ions (Ar2, Ar, ArO, O2, etc.), and their relationships, interactions, and proportions. 2) Measurement of the total (ionic and electronic) current affecting ion optical elements such as lenses, dedicated electrodes inserted into the beam path for this purpose, or the skimmer itself.

[0091] Figure 9 shows a second mechanism that can be used to improve signal recovery in a matrix sample. The pressure at the plasma sampling interface between the sample cone and the skimmer cone has a strong effect on ion transmission to the mass spectrometer. It can also be used to control the intensity of the ion beam entering the mass spectrometer. In Figure 9, the ion signals of three different analytes are shown for five different interface pressures. As the interface pressure increases, the signal decreases. According to the method outlined in Figure 3, the interface pressure can be increased, for example, until the signal of one of the analytes in Figure 9 decreases by a predetermined coefficient. For 115In, this coefficient can be 2 when the pressure is limited to the range shown in Figure 9. If the pressure range is extended beyond these values, the pressure can become even higher.

[0092] The method of reducing ion beam intensity by increasing interface pressure is even more limited to a smaller reduction factor than the method using skimmer potential. Combining both methods—first by increasing pressure and then by using skimmer potential—can achieve an even higher reduction factor, thereby enabling the achievement of a better matrix recovery value. As outlined in Figure 4, the advantage of using the combined method is that the improvement in matrix recovery is more stable in long-term behavior.

[0093] Figure 10 shows selected signals measured using a mass spectrometer configured as described in Figures 2-4, with the prior art settings being (a) Vsk = 0V; (b) Vsk = -4.5V; c) Psk higher than 0.7 mbar(Ar); and d) Psk higher than 0.4 mbar(Ar) and conforming to Vsk = -2.5V. With respect to the prior art settings, the 115In signal is approximately three times higher than in the case of the other three improved matrix settings. In this case, the data was acquired using a different system than the one in Figure 8, and the skimmer potential found when reducing a given signal by a quarter was already determined to be Vsk = -2.5V. This reflects the importance of instrument-specific adjustments induced by the signal reduction coefficient, rather than by applying a skimmer potential shift to a fixed negative voltage.

[0094] Similarly, Figure 10 shows the specific differences between the method in Figure 2 (Vsk = -4.5V) and the method in Figure 3 (Psk is 0.7 mbar(Ar) higher). The first method also suppresses light mass analytes such as 9Be much more strongly compared to the prior art, while the second method hardly alters the intensity of light ions. Since light ions are generally underestimated due to the mass bias of the ICP-MS instrument, using increased interface pressure is advantageous for light ions. A similar advantage, albeit to a lesser degree, is observed for high mass ions such as 238U when increased interface pressure is used.

[0095] Finally, Figure 11 shows the results using the four different instrument settings in Figure 9 with a high-matrix sample. The sample contains the same matrix component mixture as used in Figure 8. The bar graph shows the recovery rate (%) of the three ion signals shown in Figure 10 in a 1000 ppm matrix solution.

[0096] Conventional settings achieve recovery rates of only 80%, 50%, and less than 30%, but the settings found in Figures 2, 3, and 4 all typically perform better depending on the specific analyte. Both methods in Figures 2 and 4 achieve recovery rates of 80% to 120% for all indicated analytes. For the 238U, using the method in Figure 4 results in a significant improvement in recovery rate from 30% to 90%, with only a 20% loss of signal intensity from the analyte.

[0097] In summary, Figures 8-11 show that controlling the beam intensity reduction is advantageous for analyte signal recovery across the total elemental mass range in high-matrix samples. To control the beam intensity reduction, a negative potential applied to an electrically insulated skimmer and an increase in interface pressure can be used. A predetermined reduction in the analyte signal in a clean sample simultaneously achieves improved analyte recovery in high-matrix samples. Controlling the beam intensity reduction is considered substantially optimal in the mass range of such analytes, for example, in the major matrix components such as Mg, Ca, Fe, and Ni, with average ionic masses of 24.31u, 40.08u, 55.85u, and 58.71u, respectively.

[0098] Furthermore, when certain skimmer materials, particularly those with low thermal conductivity, are used, the cone of the skimmer 30 can reach very high temperatures (e.g., 1000°C)-Tsk. While high tip temperatures can help avoid deposit buildup, oxidation can rapidly lead to decomposition, which degrades the operation of the mass spectrometer. Applying an electric potential to the skimmer can also reduce oxidation, which is often caused by aggressive plasma conditions, providing additional advantages, particularly for skimmer materials such as titanium, nickel, or aluminum.

[0099] Different values ​​of the skimmer potential may be used for each (different) sample type. The optimal skimmer potential (for a particular sample type and a particular analyte) is when the signal recovery remains as close to 100% as possible. Therefore, the skimmer potential can be varied depending on whether a matrix is ​​present or absent.

[0100] The optimal skimmer potential may also depend on the ion mass. Therefore, the operating skimmer potential that achieves optimal sensitivity and / or robustness to matrix effects can be determined using the desired ion mass of a particular analyte. In other words, method 100 may use intensity values ​​of one or more ion masses within a specific range to determine the operating skimmer voltage.

[0101] Advantages include improved analytical robustness of the instrument for high total dissolved solids (TDS) samples, (possible) improved sensitivity which can be adjusted or set by the skimmer potential, and avoidance of hardware changes when switching between high-sensitivity and high-matrix modes. Furthermore, long-term signal stability can be improved due to reduced coating or deposition.

[0102] The expansion chamber pressure between the sampler cone and skimmer cone at the plasma interface is critical to the overall beam intensity. Generally, lower pressures in this region allow more ions to enter the mass spectrometer, while higher pressures suppress ionic intensity. The graph shown in Figure 9 illustrates that low-to-medium mass ions benefit most at low pressures, while higher pressures primarily reduce overall intensity. The results were obtained with the skimmer grounded. The transmission optics were optimized for individual interface pressures.

[0103] Generally, the signal being analyzed decreases at pressures above 3.5 mbar(Ar). This tendency is used to reduce the total beam intensity entering the skimmer cone and can also occur downstream of the skimmer within the extraction region. This decrease can be more than half.

[0104] An equipment adjustment scheme may be implemented. This may include the following steps: 1. Weakening of the ion beam / space charge is achieved by increasing the interface pressure. 2. Optimize the voltage of the transmission optical system to suit the high interface pressure. The lens voltage after readjustment will be one of the following: a. Static; or b. Mass dependent (scanning). The optimal lens voltage offers advantages and further improves the stability of the signal being analyzed. 3. Set a negative skimmer potential to shift the focus by a specified percentage of the beam intensity.

[0105] This further weakens the beam intensity and, as described above, improves the signal recovery rate in matrix-loaded samples. A negative potential may require about half the amount needed to change the ion intensity by a predetermined amount compared to when the pressure is maintained at a standard value (e.g., approximately 2.9–3.1 mbar(Ar) or less). Therefore, the voltage value (with increasing pressure up to 4.3 mbar(Ar)) may be in the range of -0.5V to -3V.

[0106] Optimizing the transmission optical system after the skimmer potential has been set to a negative voltage may degrade matrix suppression, so it is preferable to follow the steps in this order.

[0107] Improved long-term stability and matrix suppression are also achievable. The improvement in matrix suppression remains equivalent to that achieved when only a negative skimmer potential is used. Furthermore, the long-term stability of the signal in matrix-containing samples can be improved by increasing the pressure at the interface and within the extraction region compared to when the skimmer potential is applied without using higher pressures. The signal drift over time decreases with increasing interface pressure. In this example, the highest stability is observed at a high interface pressure of 3.8 mbar(Ar) and a negative skimmer potential of -2.2 V. Even better long-term stability can reduce the need to actively control parameters during measurement.

[0108] Low mass sensitivity is also a factor. When using high interface pressure in conjunction with a negative skimmer potential, sensitivity to low-mass ions can be twice as high as when operating at a standard interface or atmospheric pressure (approximately 3.0 mbar(Ar)). Current mass spectrometers sometimes attempt to compensate for matrix effects by using different operating modes.

[0109] The optimal parameters can be determined. This allows for the finding of an improved or optimal combination of interface pressure and skimmer potential values. Both can be highly dependent on the size, condition, and circumstances of the individual skimmer and sample cone. The important parameters are as follows: 1. Sample cone orifice size (nominal) 2. Covering of the sample cone (matrix deposits) 3. Skimmer cone orifice size (nominal) 4. Skimmer covering (matrix sediment) 5. Skimmer shape 6. Torch position (sampling depth) 7. Corn temperature 8. Corn ingredients

[0110] When setting up an improved matrix mode (by selecting interface pressure and skimmer potential), the "intra-matrix adjustment" technique cannot be used because the unknown sample may contain an unknown amount of matrix. This also requires at least two standards, not just one, for adjustment.

[0111] A two-step approach may be used when complete preparation is performed using only one clean sample. The first step is to prepare the initial set of parameters. The second step is to actively stabilize the signal throughout the analysis. This can be an optional feature of the preparation strategy.

[0112] Let's continue with the explanation of the first step. The initial adjustment of parameters is performed before the analytical measurements are taken.

[0113] Step 1: 1. At a specified voltage on the skimmer (e.g., 0 or a positive value), increase the interface pressure while monitoring the intensity of the standard analyte. 2. Record pressure measurements (e.g., using a pressure sensor) when the intensity (ion mass) of one or more analytes changes by the following amounts: a. Less than 70% (or 60%, 50%, 40%, 30%) and b. Over 65% (or 55%, 45%, 35%, 25%) 3. Optimize the instrument sensitivity (lens voltage of the transmission optical system). a. Save optimized static voltage b. Preserve mass-dependent voltage correction (if applicable). 4. Reduce the skimmer potential. 5. Maintain and store the skimmer potential (operating potential) with the following intensity levels for one or more analytes. a. Less than 70% (or 60%, 50%, 40%, 30%) and b.3 More than 65% (or 55%, 45%, 35%, 25%) of the intensity observed after this point

[0114] The overall attenuation or change in the standard analyte being monitored (the ratio of sensitivity after and before performing the adjustment procedure described above) may be in the range of 6% to 50%.

[0115] Step 2: Continuous monitoring and control of voltage and / or pressure during analysis and measurement.

[0116] Since cone conditions can vary throughout the analysis time due to high matrix content, one or more parameters can be measured and kept constant via a feedback loop.

[0117] These parameters can be set as follows: 1. Interface pressure 2. Other system pressure or gas flow rate 3. Plasma-related ion signals such as f.ex.38Ar+, or molecular ions such as 40Ar40Ar+ or others. 4. Measure the ion current (or electron or total current) in the skimmer or in another electrode downstream of skimmer 30. This may be an ion optics component such as a lens or aperture. This component may be located approximately 0.5 mm behind the skimmer, approximately 0.5 mm in front of the first RF multipole of the system, or somewhere in between. 5. Ion signal of the internal standard added to the matrix sample.

[0118] A feedback loop may be configured to monitor and control one or more of these parameters, keeping the variation within a narrow bandwidth around the initial value.

[0119] This is done by controlling a related second system parameter, such as the forward pump speed when controlling the interface pressure. The feedback loop can also control any other of the initially adjusted parameters, such as either the skimmer potential or the potential of the transmission optical system lens, to maintain the monitored system parameter at a constant value.

[0120] As will be understood by those skilled in the art, the details of the above embodiments may be modified without departing from the scope of the invention as defined by the appended claims.

[0121] For example, different voltages may be applied to the skimmer. Different types of mass spectrometers may be used. It is preferable to derive the ion beam intensity from the intensity (amplitude) of the peak in the mass spectrum, but other options exist, such as measuring the total ion current using an ion optical lens. The mass spectrum may consist of only a single mass. The matrix components may include nickel and seawater components. Other samples of interest may include wastewater, exploration geological samples (minerals after desolvation), and laser-ablated solid surfaces (e.g., minerals and glass). Although a cone skimmer is illustrated and described, a flat skimmer (simply a disk with holes therein) or a skimmer with a flat cone may also be used, although the performance may be inferior if a flatter skimmer is used. A predetermined change in ion beam intensity (e.g., indicated by the ion mass signal or amplitude) may be determined each time and at the start of the method. For example, various conditions, parameters, samples, sample types, and matrix types may affect predetermined values.

[0122] When this method is repeated using different samples with various known compositions, and the required potential is recorded for each known composition, this information can be used to find the optimal settings for the mass spectrometer. This allows for the creation of a lookup table that can be referenced using new samples with known (similar) matrix compositions. However, parameters for similar compositions may also be used.

[0123] When ionic species are mentioned, they are sometimes also called ionic masses. When ionic masses are mentioned, they are also sometimes referred to as ionic species.

[0124] A value indicating that the ion beam intensity of one or more ion species changes by a predetermined amount may also be described as a value indicating that the ion beam intensity of one or more ion species satisfies a predetermined condition, in which case a specific level value is one example.

[0125] Those skilled in the art will readily recognize many combinations, changes, or modifications of the features of the embodiments described above, which are intended to form part of the present invention. Any feature specifically described in relation to one embodiment or example can be used in any other embodiment with appropriate modifications.

Claims

1. A method for operating a mass spectrometer having a skimmer and a circuit configured to apply an electric potential to the skimmer, The process of obtaining the initial mass spectrum of the sample, A step of measuring the value of the initial mass spectrum, wherein the value indicates the ion beam intensity of one or more ion species, A step of determining the operating potential by applying various positive or negative DC potentials to the skimmer using a control unit, wherein the DC potential is changed until the value indicating the ion beam intensity of one or more ion species changes by a predetermined amount, the predetermined amount being a decrease of a percentage or fraction of the value, and being a decrease of one-third to one-tenth, A method comprising the step of obtaining an output value including a mass spectrum using the operating potential applied to the skimmer.

2. The method according to claim 1, wherein the step of obtaining the first mass spectrum of the sample is performed without an electric potential or using a ground potential applied to the skimmer.

3. The method according to claim 1 or 2, further comprising the step of increasing or decreasing the pressure at the interface between the sampling opening and the skimmer to change the value indicating the ion beam intensity for one or more ion species, and as a result, obtaining the value indicating the ion beam intensity for one or more ion species in a predetermined amount by combining the increase or decrease in pressure and potential.

4. The method according to claim 1 or 2, wherein the value indicating the ion beam intensity is one or more of the amplitudes of one or more peaks in the mass spectrum and the measured values ​​of the total current.

5. The method according to claim 1 or 2, wherein the predetermined amount is a percentage change or fraction change of the value.

6. The method according to claim 5, wherein the predetermined amount is a decrease in the value.

7. The method according to claim 6, wherein the reduction is one-third to one-tenth.

8. The method according to claim 1 or 2, further comprising the steps of: repeating the step described in claim 1 using various samples having known compositions; and recording the potential required to change the value indicating the ion beam intensity for each known composition by a predetermined amount.

9. The method according to claim 1 or 2, further comprising the step of presenting a further output value including a mass spectrum based on the operating potential applied to the skimmer.

10. The method according to claim 1 or 2, wherein the potential is a negative potential.

11. The method according to claim 10, wherein the potential is -1V to -4V.

12. The method according to claim 1 or 2, further comprising the step of storing the potential necessary to change the value indicating the ion beam intensity of one or more ion species to a predetermined amount for various sample types and compositions.

13. The method according to claim 1 or 2, further comprising the step of applying an AC current to the skimmer at the same time as applying the DC potential.

14. The steps include releasing the application of the aforementioned potential, The method according to claim 1 or 2, further comprising the step of providing a further output value including the mass spectrum without the potential applied to the skimmer.

15. A mass spectrometer having a skimmer and means configured to perform the steps described in claim 1 or 2.

16. The mass spectrometer according to claim 15, which is an inductively coupled plasma mass spectrometer, i.e., an ICP-MS.

17. The mass spectrometer according to claim 15, further comprising a bipolar power supply configured to apply an electric potential to the skimmer.

18. A method for operating a mass spectrometer, The process of obtaining the initial mass spectrum of the sample, A step of measuring the value of the initial mass spectrum, wherein the value indicates the ion beam intensity of one or more ion species, A step of determining the operating pressure by changing the pressure inside the mass spectrometer using a control unit, wherein the pressure is changed until the value indicating the ion beam intensity of one or more ion species changes by a predetermined amount, the predetermined amount being a decrease of a percentage or fraction of the value, and being a decrease of one-third to one-tenth, A method comprising the step of presenting an output value including a mass spectrum based on the pressure in the mass spectrometer at the operating pressure.

19. The method according to claim 18, further comprising the step of applying various DC potentials to the skimmer of the mass spectrometer to determine the operating potential, wherein the DC potential changes, and as a result, by combining the operating pressure and the application of the potential to the skimmer, the value indicating the ion beam intensity of one or more ion species changes to a predetermined amount.

20. The method according to claim 19, wherein the operating potential is a negative potential.

21. The method according to any one of claims 18 to 20, wherein the predetermined amount is a decrease in the value indicating the ion beam intensity of one or more ion species.

22. The method according to any one of claims 18 to 20, wherein the pressure increases.

23. The method according to any one of claims 18 to 20, wherein the pressure is the pressure at the interface between the sampling opening of the mass spectrometer and the skimmer.

24. A mass spectrometer having a skimmer and means configured to perform the steps described in any one of claims 18 to 20.

25. The mass spectrometer according to claim 24, which is an inductively coupled plasma mass spectrometer, i.e., an ICP-MS.

26. The mass spectrometer according to claim 24, wherein the skimmer is formed from platinum, aluminum, titanium, nickel, or any combination thereof.

27. The mass spectrometer according to claim 24, further comprising a heater configured to maintain the skimmer at a temperature of 200°C to 750°C.

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