Quadrupole rod mass analyzer based on nonlinear dynamic change of resolution and application of quadrupole rod mass analyzer

Abstract

The invention relates to a quadrupole rod mass analyzer based on nonlinear dynamic change of resolution and application thereof, the quadrupole rod mass analyzer comprises an FPGA (Field Programmable Gate Array), a digital-to-analog converter, a comparator, a chopping differential converter, a power amplifier and a high-voltage converter which are connected in sequence, and the output of the high-voltage converter is also connected to the comparator through a feedback attenuation circuit; the FPGA and digital-to-analog converter is used for setting the output voltage of the radio frequency power supply and converting and outputting the output voltage; the comparator is used for carrying out error comparison on the preset voltage and the voltage fed back by the radio frequency high voltage so as to output error voltage; the chopping differential converter is used for chopping the error voltage and filtering to screen out a fundamental frequency signal; the power amplifier is used for performing power amplification on the fundamental frequency signal, and a primary coil of the high-voltage converter is driven by a half bridge; and the feedback attenuation circuit is used for attenuating AM amplitude modulation signals of the high-voltage converter, detecting and feeding back the AM amplitude modulation signals to the comparator for comparison. According to the invention, the non-linear relation between RF and DC voltage is precisely controlled, so that the resolution capability of different mass intervals is dynamically optimized.

Description

Technical Field

[0001] This invention belongs to the field of mass spectrometry analysis technology, specifically relating to a quadrupole mass analyzer based on nonlinear dynamic changes in resolution and its applications. Background Technology

[0002] A quadrupole consists of four parallel electrodes, and the applied RF and DC voltages create a hyperboloid electric field. The motion of ions in this electric field follows the Mathieu equation, and the stability parameters a and q determine whether they pass through; only ions that satisfy the stability condition (…) a / q (≈ 0.168 is located in the stable region) to pass through the quadrupole.

[0003] Resolution R is defined as R = m / Δ m In other words, resolution is the ability to distinguish between adjacent mass numbers. In a quadrupole, resolution is primarily determined by the following factors: U / V ratio: directly affects the stability condition of a / q, and the formula is approximately: ; In traditional linear mode, the U / V ratio is fixed, and U and V are increased synchronously proportionally during scanning so that ions of different masses pass through in sequence, thus maintaining a constant resolution.

[0004] RF frequency ω: Higher frequencies can improve resolution but reduce sensitivity; Quadrupole length L: Longer quadrupoles can improve resolution, but size and cost must be weighed.

[0005] Traditional quadrupole quality analyzers employ a linear resolution mode with a constant U / V ratio, meaning quality screening is achieved by adjusting the DC voltage U and the RF voltage V in a fixed proportional relationship. This mode has the following drawbacks: (1) When analyzing over a wide quality range (e.g., m / z=5-250), it is difficult to simultaneously meet the high resolution requirements of the low quality region (<80 amu) and the sensitivity requirements of the high quality region; (2) The linear parameter setting leads to an excessively large resolution difference between adjacent mass numbers, resulting in measurement error of isotope ratio; (3) The mass discrimination effect is significant, especially when analyzing samples with severe polyatomic ion interference (such as biological / environmental samples), making it impossible to achieve continuous and smooth resolution control, which leads to difficulties in mass axis calibration. Summary of the Invention

[0006] Based on the aforementioned shortcomings and deficiencies in the prior art, one of the objectives of this invention is to at least solve one or more of the aforementioned problems in the prior art. In other words, one of the objectives of this invention is to provide a quadrupole mass analyzer based on nonlinear dynamic variation of resolution and its application that meets one or more of the aforementioned requirements.

[0007] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: A quadrupole quality analyzer based on nonlinear dynamic resolution variation consists of four parallel metal rods. A DC voltage and an RF voltage are applied to the four poles. The analyzer also includes an FPGA, a digital-to-analog converter, a comparator, a chopper differential converter, a power amplifier, and a high-voltage converter connected in sequence. The output of the high-voltage converter is also connected to the comparator through a feedback attenuation circuit. The FPGA and digital-to-analog converter are used to set the RF power supply output voltage and perform conversion output. The comparator is used to compare the preset voltage with the voltage fed back from the radio frequency high voltage to output an error voltage; The chopper differential converter is used to chop the error voltage and filter it to extract the fundamental frequency signal. The power amplifier is used to amplify the power of the base frequency signal and uses a half-bridge to drive the primary coil of the high-voltage converter. The feedback attenuation circuit is used to attenuate the AM amplitude modulation signal of the high-voltage converter, and the detection feedback is sent to the comparator for comparison.

[0008] As a preferred embodiment, there are several power amplifiers connected in parallel.

[0009] As a preferred option, the quadrupole mass analyzer based on nonlinear dynamic variation of resolution operates as follows: The ratio of DC voltage (DC) to RF voltage (RF) is dynamically adjusted nonlinearly based on the target mass number.

[0010] As a preferred approach, the DC voltage (DC) and RF voltage (RF) corresponding to each m / z are calculated in real time, and the changes in DC voltage (DC) and RF voltage (RF) are adjusted according to a preset nonlinear function to change the resolution at different m / z.

[0011] As a preferred embodiment, the nonlinear function is an exponential, logarithmic, S-curve, or polynomial fitting function.

[0012] As a preferred approach, the mass number is divided into intervals, and different nonlinear functions are used for different mass number intervals.

[0013] As a preferred approach, for mass number ranges less than a preset mass number threshold, the DC voltage (DC) and RF voltage (RF) are adjusted exponentially; for mass number ranges not less than the preset mass number threshold, the DC voltage (DC) and RF voltage (RF) are adjusted using a polynomial fitting function.

[0014] The present invention also provides the application of the quadrupole mass analyzer based on nonlinear dynamic variation of resolution as described in any of the preceding embodiments in ICP-MS.

[0015] Compared with the prior art, the beneficial effects of this invention are: This invention dynamically optimizes the resolution of different quality ranges by precisely controlling the nonlinear relationship between radio frequency (RF) and DC voltage. Attached Figure Description

[0016] Figure 1 This is a control architecture diagram of the quadrupole mass analyzer of the present invention; Figure 2 This is a graph showing the relationship between the mass number and the resolution DC voltage in the low mass number range of this invention; Figure 3 This is a graph showing the relationship between the mass number and the resolution DC voltage fitting within the high mass number range of the present invention. Detailed Implementation

[0017] To more clearly illustrate the embodiments of the present invention, specific implementation methods will be described below with reference to the accompanying drawings. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings and other implementation methods can be obtained based on these drawings without any creative effort.

[0018] In order to overcome the limitations of the traditional quadrupole linear resolution mode, this invention provides a mass spectrometry analysis method that can achieve nonlinear dynamic resolution adjustment.

[0019] The nonlinear mode of this invention is implemented by changing U and V in a nonlinear relationship to dynamically adjust the resolution.

[0020] Specifically, such as Figure 1 As shown, the quadrupole quality analyzer based on nonlinear dynamic resolution variation consists of four parallel metal rods. A DC voltage and an RF voltage are applied to the four poles. It also includes an FPGA, a digital-to-analog converter, a comparator, a chopper differential converter, a power amplifier, and a high-voltage converter connected in sequence. The output of the high-voltage converter is also connected to the comparator through a feedback attenuation circuit. Specifically, the aforementioned FPGA and digital-to-analog converter are used to set the RF power supply output voltage and perform conversion output; The aforementioned comparator is used to compare the preset voltage with the voltage fed back from the RF high voltage to output an error voltage; The above-mentioned chopper differential converter uses differential switch signals to drive high-speed switches to chop the error voltage and filter it to extract the fundamental frequency signal; The aforementioned power amplifier is used to amplify the power of the baseband signal, and employs a half-bridge to drive the primary coil of the high-voltage converter; The aforementioned feedback attenuation circuit is used to attenuate the AM amplitude modulation signal of the high-voltage converter, and the detection feedback is sent to the comparator for comparison.

[0021] The U / V ratio is dynamically adjusted during the scanning process based on the target mass number.

[0022] For example, lower quality number regions require higher resolution (increased U / V), while higher quality number regions require lower resolution (decreased U / V). A digital control system calculates U and V for each m / z in real time and adjusts the ratio according to a preset function (e.g., exponential, polynomial). A nonlinear voltage scanning function is used, where U and V change over time according to a nonlinear function, such as exponential, logarithmic, S-curve, or polynomial fitting curve, thus changing the resolution at different m / z. A high-precision digital-to-analog converter (DAC) generates complex waveforms to ensure the voltage changes precisely according to the preset function. Simultaneously, the ion signal intensity or interference is monitored in real time, and the voltage is dynamically adjusted. For example, when adjacent peak interference is detected, the local U / V is automatically increased to enhance resolution. A high-speed signal processor (e.g., DSP) and feedback algorithm are combined to achieve closed-loop control. Voltage changes must be strictly synchronized with the quality scan, using a high-speed clock and precise timing control. Experimental data is also used to optimize the nonlinear function, balancing resolution, speed, and sensitivity.

[0023] This invention relates to a quadrupole mass analyzer for inductively coupled plasma mass spectrometry (ICP-MS), and particularly to a novel quadrupole mass filtering method that optimizes resolution through nonlinear dynamic parameter control. The method involves applying a DC voltage and an RF voltage to the quadrupole mass analyzer. Unlike conventional quadrupole mass analyzers, the ratio of the applied DC voltage to the RF voltage is not fixed and varies nonlinearly with the mass number of different elements.

[0024] The application of this invention in ICP-MS specifically involves selecting a mixed standard of 16 elements (Li, Al, V, Mn, Co, Cu, Zn, Y, Rh, Ag, In, Ba, Ho, Ta, Pb, U) at 10 ppb, ranging from low to high relative atomic masses, covering a range of 7.02 u to 238.05 u. This covers low, medium, and high mass numbers, ensuring comprehensive and uniform coverage. After the mass spectrometer is started and stabilized for half an hour, the mixed standard is injected into a peristaltic pump tube. The PC scans all the mixed standard resolution spectra using mass spectra. A standard resolution of 0.746 is selected (the standard resolution is between 0.6 and 0.8; other suitable resolutions can also be selected as standard reference resolutions). The resolution DC voltage of each element in the mixed standard is adjusted to achieve a resolution of 0.746 for its corresponding standard element, and so on, until all standard solution elements in the mixed standard have a resolution of 0.746. A segmented fitting method was used in this experiment. The mass number is divided into a low-mass-number fitting interval (5~80u) and a medium-mass-number fitting interval (81~250u), such as Figure 2 As shown, the least squares method is used to fit the function y=ax when the mass number is low. b ,like Figure 3 As shown, the least squares method is used to fit the polynomial function y=ax on high-quality numbers. 3 +bx 2 +cx+d, the resulting standard deviation is R. 2 =0.9975 and R 2 =0.9996.

[0025] The benefit of this experimental example lies in overcoming the limitations of traditional quadrupole linear resolution mode and providing a novel mass spectrometry analysis method that enables nonlinear dynamic resolution adjustment. Furthermore, it can achieve analysis over a wide mass range (e.g., m / z = 5-250), addressing the difficulty of simultaneously meeting the high resolution requirements of the low-mass region (<80 amu) and the sensitivity requirements of the high-mass region. This improves the mass analyzer's accurate resolution of isotopes. Moreover, it enables continuous and smooth resolution control when analyzing samples with severe polyatomic ion interference (such as biological / environmental samples), making the experimental results more accurate and reliable.

[0026] The key to this invention is that the quadrupole resolution nonlinear mode dynamically optimizes the resolution across different quality ranges by precisely controlling the nonlinear relationship between RF and DC voltages. Its core lies in utilizing the stability parameters of the Mathieu equation, combined with advanced algorithms from the electronic control system, and simultaneously optimizing the nonlinear function using experimental data to balance resolution, speed, and sensitivity. This enables flexible quality selection, thereby improving the performance of ICP-MS in complex analytical tasks.

[0027] The above description is merely a detailed explanation of preferred embodiments and principles of the present invention. For those skilled in the art, there may be changes in specific implementation methods based on the ideas provided by the present invention, and these changes should also be considered within the scope of protection of the present invention.

Claims

1. A quadrupole mass analyzer based on nonlinear dynamic variation of resolution, comprising four parallel metal rods, with a DC voltage (DC) and a radio frequency (RF) voltage applied to the four poles, characterized in that, It also includes an FPGA, a digital-to-analog converter, a comparator, a chopper differential converter, a power amplifier, and a high-voltage converter connected in sequence; the output of the high-voltage converter is also connected to the comparator through a feedback attenuation circuit. The FPGA and digital-to-analog converter are used to set the RF power supply output voltage and perform conversion output. The comparator is used to compare the preset voltage with the voltage fed back from the radio frequency high voltage to output an error voltage; The chopper differential converter is used to chop the error voltage and filter it to extract the fundamental frequency signal. The power amplifier is used to amplify the power of the base frequency signal and uses a half-bridge to drive the primary coil of the high-voltage converter. The feedback attenuation circuit is used to attenuate the AM amplitude modulation signal of the high-voltage converter, and the detection feedback is sent to the comparator for comparison.

2. The quadrupole mass analyzer based on nonlinear dynamic variation of resolution according to claim 1, characterized in that, There are several power amplifiers, which are connected in parallel.

3. The quadrupole mass analyzer based on nonlinear dynamic variation of resolution according to claim 1, characterized in that, Its working method is as follows: The ratio of DC voltage (DC) to RF voltage (RF) is dynamically adjusted nonlinearly based on the target mass number.

4. The quadrupole mass analyzer based on nonlinear dynamic variation of resolution according to claim 3, characterized in that, The DC voltage (DC) and RF voltage (RF) corresponding to each m / z are calculated in real time, and the changes in DC voltage (DC) and RF voltage (RF) are adjusted according to a preset nonlinear function to change the resolution at different m / z.

5. The quadrupole mass analyzer based on nonlinear dynamic variation of resolution according to claim 4, characterized in that, The nonlinear function is an exponential, logarithmic, S-curve, or polynomial fitting function.

6. The quadrupole mass analyzer based on nonlinear dynamic variation of resolution according to claim 4, characterized in that, The mass number is divided into intervals, and different nonlinear functions are used for different mass number intervals.

7. The quadrupole mass analyzer based on nonlinear dynamic variation of resolution according to claim 6, characterized in that, For mass numbers less than a preset mass number threshold, the DC voltage (DC) and RF voltage (RF) are adjusted exponentially; for mass numbers not less than the preset mass number threshold, the DC voltage (DC) and RF voltage (RF) are adjusted using a polynomial fitting function.

8. The application of the quadrupole mass analyzer based on nonlinear dynamic variation of resolution as described in any one of claims 1-7 in ICP-MS.

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