Reference-signal-free slope spectral measurement

Abstract

A method includes determining whether a change in probe radiation intensity meets a stability criterion; directing probe radiation through the probe when the probe is disposed in a first location, the first location defining a first path length L1 of the probe radiation through the fluid sample; measuring a transmission intensity I1 of the probe radiation after the probe has passed through the fluid sample when the probe is disposed at the first position; directing probe radiation through the probe when the probe is disposed in a second position, the second position defining a second path length L2 of the probe radiation through the fluid sample; measuring a transmission intensity I2 of the probe radiation after the probe has passed through the fluid sample when the probe is disposed at the second position; and determining a concentration C of the material in the fluid sample based on L1, I1, L2 and I2 when the stability criteria are met.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of priority under 35 U.S.C. §119 to U.S. Provisional Application Serial No. 63 / 343,357, filed on May 18, 2022, entitled “NO-REF-SIGNALSLOPE SPECTROSCOPIC MEASUREMENT,” the entire contents of which are incorporated herein by reference for all purposes. Technical Field

[0003] Embodiments of the present disclosure relate generally to spectral analysis, and more particularly to solution analysis using a light source coupled to a variable path length measurement system. Background Art

[0004] Absorption spectroscopy is used to measure the composition and / or properties of materials in any phase (gas, liquid, solid). For example, the optical absorption spectrum of a liquid substance can be measured to determine the concentration or other properties of a species of interest in the liquid medium. The absorption spectrum can provide a distribution of light attenuation (due to absorbance) as a function of the wavelength of the light. In a known spectrophotometer, the sample material to be studied is placed in a transparent container so that electromagnetic radiation (light) of known wavelength λ (i.e., ultraviolet, infrared, visible, etc.) and intensity I can be measured after passing through the transparent container using a suitable detector.

[0005] Known ultraviolet (UV) / visible spectrophotometers utilize containers such as standard cuvettes, which may have a standard cm path length through which incident light is conducted within a liquid containing the substance to be measured. For a sample consisting of a single homogeneous substance with a concentration c, the light transmitted through the sample will follow a relationship known as Beer's law: A = εCL, where A is the absorbance (also known as the optical density (OD) of the sample at wavelength λ, where OD = the logarithm of the ratio of transmitted light to incident light), ε is the absorption coefficient or extinction coefficient (usually constant at a given wavelength), C is the concentration of the sample, and L is the path length of the light through the sample. Therefore, in principle, information about the concentration of a homogeneous substance can be determined based on the recorded light intensity of the signal passing through the sample container. However, in some cases, the determination of concentration in such an apparatus may be difficult. Compounds of interest in solutions are often highly concentrated. For example, when measuring absorbance, certain biological samples, such as proteins, DNA or RNA, are often separated at concentrations that fall outside the linear range of the spectrophotometer. Therefore, it is usually necessary to dilute the sample to measure an absorbance value that falls within the linear range of the instrument. Multiple dilutions of the sample are often required, which can lead to dilution errors and the removal of the diluted sample for any downstream application. Therefore, it is useful to take existing samples without knowing the likely concentration and measure the absorbance of these samples without dilution. A resulting feature common to these known ultraviolet (UV) / visible spectrophotometers is that the path length L is known very accurately, allowing accurate concentration measurements to be made.

[0006] To address these challenges, a technique based on variable path length spectrophotometers has recently been developed. This type of spectroscopic system can typically employ a known light source, such as a source based on a UV / visible spectrophotometer. The light from the UV / visible spectrophotometer is then directed to a special probe in the analytical instrument, which is arranged to dynamically vary the path length L in a special sample chamber during absorbance measurements. Thus, the intensity of the transmitted radiation generated from the UV / visible spectrophotometer source is detected after passing through the sample chamber, while the movement of the probe changes the path length L through a number of different positions. Thus, a series of measurements are produced that generate different A values ​​for each different l value in a manner that does not require knowledge of any particular path length l in order to determine the concentration C.

[0007] While such variable path length spectroscopy may be suitable for in-line measurement of samples, the instrumentation required for such measurement scenarios may require a significant amount of installation effort and excessive space, for example, when performed by a production system. For example, a UV / visible spectrometer system used as a light source may occupy several cubic feet of space and may have a weight of the order of tens of kilograms. Furthermore, the determination of A typically requires that multiple intensity measurements may be required for each sample measurement performed at a given path length L.

[0008] It is with respect to these and other considerations that the present disclosure is provided. Summary of the invention

[0009] In one embodiment, a method for determining the concentration of a material may include determining whether a change in the intensity of a probe radiation emitted by a light source of an absorbance spectroscopy system satisfies a stability criterion. The method may also include: when the probe is set in a first position, directing the probe radiation through the probe, the first position defining a first path length L1 of the probe radiation through the fluid sample; and measuring the transmission intensity I1 of the probe radiation after passing through the fluid sample when the probe is set in the first position. The method may also include: when the probe is set in a second position, directing the probe radiation through the probe, the second position defining a second path length L2 of the probe radiation through the fluid sample; and measuring the transmission intensity I2 of the probe radiation after passing through the fluid sample when the probe is set in the second position. The method may further include determining the concentration C of the material in the fluid sample based on L1, I1, L2, and I2 when the stability criterion is met.

[0010] In another embodiment, a non-transitory computer-readable storage medium is provided, storing computer-readable program code capable of being executed by a processor to: determine whether a change in the intensity of probe radiation emitted by a light source of an absorbance spectroscopy system satisfies a stability criterion; cause the light source to guide the probe radiation through the probe when the probe is set in a first position, the first position defining a first path length L1 of the probe radiation through a fluid sample; receive a transmitted intensity I1 of the probe radiation after passing through the fluid sample; cause the light source to guide the probe radiation through the probe when the probe is set in a second position, the second position defining a second path length L2 of the probe radiation through the fluid sample; receive a transmitted intensity I2 of the probe radiation after passing through the fluid sample; and when the change in intensity satisfies the stability criterion, determine a concentration C of a material in the fluid sample based on L1, I1, L2 and I2.

[0011] In yet another embodiment, a measuring device is provided, comprising a light source to generate a probe signal; and a measuring instrument to receive the probe signal. The measuring instrument may include a sample container containing a fluid sample, the sample container including a container wall; and a probe arranged to guide the probe signal through the sample container, wherein the probe is movable in a probe direction relative to the container wall so as to change the path length L of the probe signal through the fluid sample. The measuring device may also include a detector, which is arranged to receive the probe signal after passing through the container wall; and a control system. The control system may be arranged to: determine whether a change in the intensity of the probe radiation emitted by the light source meets a stability criterion; and when the change in the intensity meets the stability criterion, calculate the concentration C of the material in the fluid sample based on the change in the measured intensity of the probe signal as a function of the change in the path length L. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The accompanying drawings illustrate preferred embodiments of the disclosed method, as far as has been contemplated for practical application of its principles, and in which:

[0013] Figure 1A depicts an absorption spectroscopy apparatus according to an embodiment of the present disclosure;

[0014] Figure 1B depicts an absorption spectroscopy apparatus according to an embodiment of the present disclosure;

[0015] Figure 1C An arrangement is provided which illustrates the general geometry for determining the concentration of a substance according to the principles of slope spectroscopy.

[0016] Figure 2 depicts an absorption spectroscopy apparatus according to an embodiment of the present disclosure;

[0017] Figure 3 Another absorption spectroscopy apparatus according to an embodiment of the present disclosure is depicted;

[0018] Figure 4 depicts exemplary absorption spectra according to embodiments of the present disclosure;

[0019] Figure 5 An exemplary process flow is presented; and

[0020] Figure 6 Another exemplary process flow is presented. DETAILED DESCRIPTION

[0021] According to an embodiment of the present disclosure, techniques and devices for improving absorbance measurements based on a variable-pathlength-measurement (VPT) device architecture are provided. The present embodiment particularly provides a streamlined and dynamic method for determining the concentration of a material in a fluid sample. The method of the present embodiment employs multiple intensity measurements that are recorded as radiation is transmitted through the fluid sample while the path length of the radiation through the fluid sample changes. As described in detail below, and compared to known absorbance spectroscopy techniques, the present embodiment determines the absorbance change of the fluid sample, and therefore the concentration C of the material within the fluid sample, without having to perform a reference signal measurement.

[0022] Figure 1A An absorption spectroscopy apparatus according to an embodiment of the present disclosure is depicted, shown as system 100. System 100 may include a compact light source 102, a measuring instrument 110 coupled to the compact light source 102, and a detector 112 disposed proximate to the measuring instrument 110. The compact light source 102 may include a light emitting diode (LED) to generate radiation 104 of a target wavelength, such as in the UV to IR range, and in particular in the range of 190nm to 1100nm or 250nm to 1000nm according to various non-limiting embodiments. In some examples, the compact light source 102 may represent a single LED or an array of LEDs that emit radiation of a single wavelength. In other embodiments, a plurality of LEDs may be provided, wherein a given LED emits radiation of a wavelength different from the wavelength of another LED.

[0023] The measuring instrument 110 is arranged to contain a fluid sample including a material of a substance to be measured, wherein details of variations of the measuring instrument 110 are discussed below. The detector 112 is arranged to detect the intensity I of radiation transmitted through a given fluid sample contained in the measuring instrument 110, which is shown as attenuated radiation 111. According to Beer-Lambert's law shown in the following equation, the concentration C of the material in the sample can be determined as A / eL, where A is the absorbance and e is the molar absorptivity.

[0024]

[0025] Then, A is determined as log 10 (I0 / I), where I0 is the intensity of radiation 104 and I is the intensity of attenuated radiation 111. To measure the value of I0, system 100 also includes a reference detector 106 to receive a portion of radiation 104 before it is conducted through measuring instrument 110. This parameter is used to directly calculate absorbance, according to the absorbance equation, Equation 2:

[0026]

[0027] Thus, at a given measurement instant, when detector 112 measures I based on attenuated radiation 111, while reference detector 106 measures I0, the absorbance A will be determined. According to the method of slope spectroscopy, Beer-Lambert's law can be rewritten as A / L,=e C, and further extended to DA / DL,=e C, where the entity DA / DL is considered as the slope parameter m. In operation, system 100 will operate according to the principles of slope spectroscopy to vary the path length L of the distance traveled by radiation 104 in order to determine the variation of absorbance A as a function of the variation of path length L, thus directly determining the value of C for a given substance, given that e for that substance is known.

[0028] Below about Figure 2 and Figure 3 The details of the operation of the variants of the measuring instrument 110 are discussed in detail. However, in brief, the measuring instrument 110 employs a movable optical probe (such as Figure 2 , discussed in more detail below) to change the transmission through a given fluid sample present in the measuring instrument 110 ( Figure 1A Not shown, but see Figure 2 10). The system 100 is a flowmeter that measures the path length L of the radiation 104 passing through the fluid sample 211 in the measuring instrument 110. Because the intensity of the attenuated radiation 111 will change as a function of the change in path length L, the change in I as a function of the change in path length L can be used to directly determine the change in absorbance A as a function of the change in path length L. Thus, knowing I0 (given by the reference detector 106), the system 100 can be used to readily determine the concentration C of a material in a fluid sample by varying the path length of the radiation 104 as it passes through the measuring instrument 110 (to determine D1) and detecting the change in the intensity of the attenuated radiation 111 (to determine DA).

[0029] Figure 1CAn arrangement 180 is provided which shows details of the geometry for determining the concentration of a substance according to the principles of slope spectroscopy. In the arrangement 180, a light source (such as a compact light source 102) directs radiation 104 through a sample 182 (such as a fluid sample). The sample 182 attenuates or absorbs a portion of the radiation 104 so that the attenuated radiation, such as the attenuated radiation 111, will generally exhibit an intensity I that is less than the intensity I0 of the radiation 104. A beam splitter 184 or similar device is provided to direct a portion of the radiation 104 to a reference detector 106 without passing through the sample 182 so that the value of I0 is recorded. As noted above, within the measuring instrument 110, a movable probe can vary the path length L while measuring changes in the absorbance A. For each value of L, a measurement of the intensity I of the attenuated radiation 111 is recorded, and a measurement of the intensity I0 of the radiation 104 is recorded. In this way, for a given change in path length D1, DA is determined as:

[0030]

[0031] Figure 1B An absorption spectroscopic device is depicted, shown as system 150. The system can be operated similarly to system 100 to determine the concentration C of a substance in a measuring instrument 110. Similar components are labeled the same. The difference is that system 100 employs a light source 152, which can be a broad spectrum light source, such as a known UV / vis / IR absorption spectroscopic device, wherein radiation 160 represents light that can be generated over a broad radiation spectrum in intervals of seconds or minutes. Similar to system 100, radiation 160 can be directed to a reference detector 156 to measure I0, while the attenuated radiation 161 is measured at detector 112 after passing through the fluid sample in the measuring instrument 110.

[0032] exist Figure 1A and Figure 1BIn both embodiments, a control system 130 is provided to facilitate simplified and improved operations related to absorbance spectroscopy measurements. In short, the control system 130 may include a non-transitory computer-readable storage medium including instructions that, when executed, such as using an electronic processor, will perform one or more of the operations described below. The control system 130 may include various components, including dedicated electronic controllers, communication interface routines or algorithms to control the operation of various components of the system 100 or system 150. The control system 130 can control the operation of the system 100 or system 150, including the operation of the system in different operating modes. In the "standard" slope spectroscopy mode, the concentration C is determined by determining DA using the I and I0 measurements for each L value, as described above. In the "no reference signal" mode or NRS slope spectroscopy mode, the system 100 or system 150 can be operated to determine the concentration C without measuring I0, as described below. The NRS mode of slope spectroscopy will provide greater flexibility and speed for the measurements performed, as well as potentially higher accuracy.

[0033] According to embodiments of the present disclosure, the NRS slope spectroscopy mode may be used or initiated routinely, or may be initiated when certain stability criteria are met for an operating absorbance spectroscopy system, wherein Equation 3B for determining A may be simplified. For example, the stability criteria may be met when the change in absorbance intensity is below a threshold value, as discussed further below. According to Equation 3B (see above), which summarizes the absorbance calculation according to the known slope spectroscopy method, the change in absorbance DA between a first time instant t1 (corresponding to a first path length L1) and a second time instant t2 (corresponding to a second path length L2) is determined in part by the parameter The value of t1 is determined by the incident intensity at the second moment. Therefore, the ratio of the incident intensity at the second moment to the instantaneous intensity at the first moment is required to calculate DA. These incident intensity measurements using reference detector 106 or reference detector 156 are useful, for example, because the intensity of the incident light generated by the light source will generally change over time, including changes between time t1 and time t2. For example, using a known UV / vis / IR light source, such as light source 152, the acquisition of the transmission spectrum from which I1 or I2 is measured may take many seconds or tens of seconds to complete. Therefore, a known slope spectrum measurement will be performed as follows: a movable probe that directs incident radiation through a fluid sample will be moved to a first position to set a first path length L1, after which a transmission (absorbance) spectrum will be acquired, from which spectrum I1 is determined. Then, the movable probe will be moved to a second position to set a second path length 2, after which a second transmission spectrum will be acquired to determine I2. Therefore, the elapsed time between the measurement of I1 and the measurement of I2, including the time to acquire the transmission spectrum and move the probe, may be long enough that drift in the incident intensity I0 will be expected, requiring the incident intensity to be measured before each measurement of the transmitted intensity I. Furthermore, the stability of the light source may vary from source to source and may change over time, resulting in the need to measure I0 for each measurement of I.

[0034] However, the inventors have realized that in some cases, the term The value of may be small enough that the new NRS slope spectroscopy mode can be used to measure DA, and therefore the concentration C of the substance of interest. In other words, during the setup or calibration process, the incident intensity I0 emitted from the compact light source 102 or light source 152 can be measured continuously or intermittently over a given time span to determine the stability of the light source. If the light source is sufficiently stable, the measurement of the incident intensity, such as I O2 and I O1 The measurement of can be omitted from the slope spectrum measurement process. In particular, to evaluate when to use the NRS slope spectrum mode, the term can be considered as ΔAerr, which means that this term represents the 02 and I 01 When the measurement is not performed, the actual change in absorbance DA (I 02 and I 01 Thus, when a stability measurement of a setup process indicates that the change in I0 value is below a certain value within a certain time span, this change indicates that I0 for a given measurement interval is below a certain value. 02 and I 01 The change between the values ​​may also remain below this value during the actual slope spectrum measurement. Therefore, when I 02 and I 01When the values ​​of are close enough to each other, their ratio is equal to ∼1, which means that ΔAerr is equal to zero. In this case, the actual slope spectrum measurement period I can be omitted. 02 and I 01 The NRSS mode allows the measurement of I and L without unduly affecting the calculated value of C, which is simply calculated as logI1-logI2. Therefore, in NRSS mode, only I and L need to be measured as L changes over time.

[0035] It can be determined from the application when the instability of the incident intensity is low enough to allow the determination of the measured value using the new NRS slope spectroscopy mode. However, in general, for the case where I0 changes only slightly within a predefined time, such changes in the incident intensity can be specified as ±α%. Thus, the term α can be defined as Due to the term This means that ΔAerr = log(1 + α). Alternatively, for determination of the change over any suitable period, involving any suitable number of measurements, a may be defined as (I max -I min ) / I min , where I max is the maximum value of the intensity of the radiation recorded during the appropriate period, and I min is the minimum value of intensity recorded during the period.

[0036] Therefore, depending on the application, a limit on the maximum value of a can be established to determine when the NRS slope spectrum measurement mode is adopted. In one example, for absorbance measurements specified in the United States Pharmacopeia (USP) UV-Vis spectrophotometer operating guidelines, USP requires an absorbance deviation of less than ± 0.01. Therefore, for slope spectrum measurements performed according to the USP guidelines, 0.01>log(1+α), which means |α|<2.33%. Therefore, in some embodiments, the stability standard can be met when the absorbance deviation is less than a specific value, such as less than ± 0.03, less than ± 0.02, or less than ± 0.01. In the latter case, the stability standard corresponds equivalently to |α|<2.33%, where a can be defined by the equation set forth herein.

[0037] In one example, typically according to Figure 1A The slope spectroscopy device (including LED light source) of the embodiment arrangement is used to determine the source stability. During a certain test period, the maximum I max and minimum I min Incident intensity, with the following results:

[0038]

[0039] Thus, in the example above, where the a value is well below the 2.33% limit set by USP, the use of the NRS slope spectrum may be appropriate.

[0040] The use of NRS slope spectroscopy offers advantages for determining the concentration of a material in a fluid sample, including the ability to measure concentration more accurately, more quickly, and in a more dynamic manner. Figure 2 An absorption spectroscopy apparatus according to an embodiment of the present disclosure is depicted, shown as system 200. System 200 may include a compact light source 102, and a variation of a measuring instrument 110 coupled to the compact light source 102, and a detector 112 disposed proximate to the measuring instrument 110. The compact light source 102 may include one or more light emitting diodes to generate radiation 210 of one or more target wavelengths, as described above with respect to Figure 1A discussed.

[0041] In this variation, the measuring instrument 110 includes a movable probe 208, which may be an optical fiber, a fibrette, or a bundle of optical fibers, arranged to conduct radiation 202 to a sample chamber container 215, which includes a fluid sample 211 containing a material of interest, the concentration C of which is to be measured. The radiation 210 is directed into and through the movable probe 208 along a probe axis 206. Figure 2As shown, the movable probe 208 can be translated relative to the container wall 212 of the sample container 210 so as to vary the path length L of the radiation. In particular, the path length L represents the distance between the probe tip 208A and the lower portion of the container wall 212. Therefore, the value of L corresponds to the distance that the radiation can travel through the sample 182 when the fluid sample is disposed in the sample container 215. Note that a window transparent to the radiation 210 can be provided to conduct the radiation out of the sample container 215 as attenuated radiation 220, whose intensity I is detected by the detector 222. Suitable examples of the detector 112 include, among others, a photomultiplier tube, a photodiode, an avalanche photodiode, a charge-coupled device (CCD), and an intensified CCD. Although shown as being disposed in a line-of-sight manner relative to the probe 172, in various embodiments, the detector 112 can be integrated into the measuring instrument 110B, or can be remotely located by operably linking the detector 112 to an optical delivery device (not shown) that can carry the electromagnetic radiation traveling through the sample to the detector. The light delivery device may be fused silica, glass, plastic, or any transmissive material suitable for the wavelength range of the electromagnetic source and detector. The light delivery device may be formed of a single optical fiber or multiple optical fibers, and the optical fibers may have different diameters, depending on the use of the measurement instrument 110. In various non-limiting embodiments, the optical fiber diameter is in the range from about 0.005 mm to about 20.0 mm.

[0042] To facilitate concentration measurements using a method where DA / DL is equal to eC, a drive component (not shown separately) may be a motor that translates the probe tip 208A along the probe axis 206. The drive component may provide continuous motion, or may be configured to change the path length L in precise steps. In various non-limiting embodiments, suitable examples of drive components include stepper motors, servos, piezoelectric, electric and magnetic motors, or any device that can be controlled to provide a variable path length L through a sample. In some embodiments of incremental or step-wise motion, the movable probe 208 moves relative to the sample container 215 in increments ranging from 0.2 μm to 1 cm, and more particularly, in increments ranging from 1 μm to 50 μm. In other embodiments, the movable probe 208 may move in a continuous manner to continuously change L.

[0043] The system 200 also includes a reference detector 204, which can function similarly to the reference detector 106 to measure the incident intensity I0 of the radiation 210, as generally discussed above. In this embodiment, the system 200 can also include a control system 130. Various inputs to the control system 130 can include I0, L, and I. In one example, information about L can be sent from a component 214, which can be a motor assembly, a sensor, or other component that provides position information. In some embodiments, the control system 130 can determine that the change in intensity meets the stability criteria so that the system 200 can operate in an NRS slope spectroscopy mode, in which the position of the movable probe is changed through multiple different locations. Because I0 does not need to be recorded, at each position of the probe, only the L value and the I value of the attenuated radiation 220 are recorded. In this way, the slope parameter m, which is equal to DA / DL or equivalently equal to eC, can be easily calculated as m=

[0044]

[0045] Wherein I1 is the intensity of the attenuated radiation intensity at the first probe position, I2 is the intensity of the attenuated radiation at the second probe position, L1 is the first path length of the incident radiation through the fluid sample being measured at the first probe position, and L2 is the second path length of the incident radiation through the fluid sample being measured at the second probe position, as discussed above.

[0046] Figure 3 An absorption spectroscopy device according to an embodiment of the present disclosure is depicted, shown as system 250. System 250 can be viewed as a variation of system 200 discussed above, with similar components being labeled the same. The difference is that a measuring instrument 256 includes a sample chamber container 260, which includes an inlet port 262 to allow a fluid sample 211 to enter; and an outlet port 264 to conduct the fluid sample 211 out of the sample chamber container 260. Thus, the measuring system 110A can be used to couple to the processing system 270 shown to provide a dynamic measurement of the concentration C of a material in a sample fluid as the sample fluid passes through the measuring instrument 256. Thus, the processing system 270 can represent any suitable system that generates a fluid sample to be measured, such as a chromatography system, a protein purification system, a filtration system, or other fluid processing system. Thus, system 250 provides an architecture for dynamically measuring the concentration in a fluid sample, wherein the fluid sample being measured is flowing and can change, such as in terms of the concentration C of the material to be measured. The advantage provided by the present method is that, under conditions where the change in the intensity of the light source is below a threshold (i.e., a threshold condition or threshold value), since there is no need to measure I0 to determine C, it is only necessary to record the measurement result of the transmitted intensity I in combination with the movement of the probe 208 used to change L, as given by equation (4).

[0047] To further explain the determination of the concentration C of the embodiment using an LED light source, Figure 4 Depicts an exemplary absorption spectrum according to an embodiment of the present disclosure. In this example, Figure 4 The graph of FIG. 40 depicts the detected radiation intensity as a function of wavelength in the near UV range. Three spectra are shown, spectrum 402, spectrum 404, and spectrum 406, each consisting of a single peak representing the detected intensity of UV light emitted from the LED light source.

[0048] Thus, spectrum 402 presents data collected at a first moment in time when the path length of radiation is directed through the probe disposed at a first position, defining a path length L1 through the fluid sample. Similarly, spectrum 404 presents data collected at a second moment in time when the path length of radiation is directed through the probe disposed at a second position, defining a path length L2 through the fluid sample. Spectrum 406 presents data collected at a third moment in time when the path length of radiation is directed through the probe disposed at a second position, defining a path length L3 through the fluid sample. For the time frame represented between the first and second moments in time, given that the concentration C will be equal to DA / (DLe), the determination of the intensity difference between the intensity I2 of spectrum 404 and the intensity I1 of spectrum 402 will directly yield C. This is because, under conditions where the variation in source intensity is below an acceptable threshold, DL is only L2-L1, and DA is only log I1-log I2. Similarly, for the time frame represented between the second and third moments in time, the determination of the intensity difference between the intensity I3 of spectrum 406 and the intensity I2 of spectrum 404 will directly yield C.

[0049] For example, this NRS slope spectroscopy method can be easily extended to record multiple different measurements of I without measuring I0 at multiple different probe positions to more accurately determine the concentration. In other words, I1 and L1 are recorded at the first probe position, I2 and L2 are recorded at the second probe position, I3 and L3 are recorded at the third probe position, and so on. In some embodiments, according to Beer-Lambert's law, the determination of C can be performed as follows, where C = (DA / DL) / e. The intensity data I1, I2, I3 are converted to absorbance data A (equivalent to log I) by determining log I1, log I2, log I3, etc. from the data. A linear regression is performed based on a data set of A plotted as a function of L for three or more probe positions to determine a regression line whose slope is proportional to = (DA / DL). In this case, DA and DL are determined from the corresponding log I and L values ​​at opposite ends of the regression line, rather than, for example, L1, I1, L2. n and log I nIn this way, the calculated concentration C can more accurately reflect the true value than the concentration determined from a pair of intensity and path length measurements performed at only two probe positions.

[0050] Furthermore, since incident intensity measurements are not recorded for different probe positions, the total duration of a set of intensity measurements sufficient to determine C may be shortened to as little as a few seconds in embodiments of compact LED light sources.

[0051] Figure 5 A process flow 500 is presented in accordance with an embodiment of the present disclosure. At box 502, a change in the intensity I0 of incident probe radiation from a light source is measured. In some embodiments, the light source may be a known spectrometer, such as a UV / vis or UV / vis / IR spectrometer, arranged to generate radiation over a wide range of wavelengths. In other embodiments, the light source may be a compact LED light source based on a single LED type that emits radiation in a narrow wavelength range, or based on a plurality of different LEDs that emit radiation in a plurality of different, narrow wavelength ranges. The change in intensity may be specified as ±α%, and may be measured over a given period of time, such as a predetermined interval of a few seconds or up to a few minutes.

[0052] At decision block 504, it is determined whether the change in the intensity of I0 is below a threshold. The threshold may be set based on a standard for measuring a given class of materials, for operating a given type or device, or based on any suitable standard. In some non-limiting embodiments, the threshold for the change in I0 may be ±0.03, ±0.02, or ±0.01. In the latter case, the stability criterion equivalently corresponds to when |α|<2.33%, where a may be defined by the equation set forth herein.

[0053] If so, flow continues to block 506 .

[0054] At block 506, when the probe is disposed at a first position, probe radiation from the light source is directed through the probe. The probe may be an optical fiber, a small optical fiber, an optical fiber bundle, or other suitable structure suitable for conducting the probe radiation. At the first probe position, the probe tip may be disposed near or within the fluid sample, wherein the first probe position is used to define a first path length L1 of the probe radiation through the fluid sample. In particular, the path length L1 may represent the distance between the probe tip and a wall of a sample container or other container containing the fluid sample.

[0055] At block 508, a process is performed to measure the transmitted intensity I1 of the probe radiation after the probe radiation passes through the fluid sample when the probe is disposed in the first position. The transmitted intensity may be measured by any suitable detector, such as an electronic detector adapted to detect radiation within the wavelength range of the probe radiation.

[0056] At block 510, probe radiation from the light source is directed through the probe when the probe is disposed in a second position. The second probe position may define a second path length L2 of the probe radiation through the fluid sample.

[0057] At block 512 , a process is performed to measure a transmitted intensity I 2 of the probe radiation after the probe radiation passes through the fluid sample when the probe is disposed in the second position.

[0058] At block 514, a process is performed to determine the concentration C of the material in the fluid sample based on L1, log I1, L2, and log I2. For example, the concentration C may be calculated according to Beer-Lambert's law as C=(DA / DL) / e, where DL is given by |L1-L2| and DA is given by log I1-log I2.

[0059] If at decision block 504, it is determined that the change in I0 is not below the threshold, then the flow proceeds to block 516. At block 516, the incident intensity I of the probe radiation before passing through the fluid sample to be measured when the probe is set in the first position is measured. 01 For example, the measurement may represent the first measurement in a series of absorbance measurements of a material in a fluid sample.

[0060] In this case, flow continues to block 506A, which is generally performed according to block 506 previously described.

[0061] After block 506A, flow proceeds to block 518 where the transmitted intensity I1 of the probe radiation after passing through the fluid sample when the probe is disposed in the first position is measured. Note that the operations of blocks 516, 518, and 506A may be performed substantially simultaneously.

[0062] The flow then proceeds to block 520 where the incident intensity I of the probe radiation before passing through the fluid sample when the probe is disposed in the second position is measured. 02 The operation is performed.

[0063] In this case, the flow proceeds to block 510A, which is generally performed according to the previously described block 510. After block 510A, the flow proceeds to block 522, where the transmission intensity I2 of the probe radiation after passing through the fluid sample when the probe is set in the second position is measured. Note that the operations of blocks 520, 522, and 510A can be performed substantially simultaneously.

[0064] The process then proceeds to block 524, where the 01 and I 02An operation of determining the concentration C of the material in the fluid sample is performed. For example, the concentration C can be calculated according to Beer-Lambert's law as C=(DA / DL) / e, where DL is given by |L1-L2| and DA is given by log I1–log I 2.+ log(I 01 / I 02 ) is given.

[0065] Figure 6 Another process flow 600 according to an embodiment of the present disclosure is presented. At block 602, the following operations are performed: at a first time, when the probe is disposed at a first position p1, directing probe radiation through the probe, the first position defining a first path length L1 of the probe radiation through the fluid sample. The probe radiation may be generated by a light, such as a known spectrometer, such as a UV / vis or UV / vis / IR spectrometer, arranged to generate radiation over a wide range of wavelengths. In other embodiments, the light source may be a compact LED light source, based on a single LED type emitting radiation in a narrow wavelength range, or based on a plurality of different LEDs emitting radiation in a plurality of different, narrow wavelength ranges.

[0066] At block 604 , a transmitted intensity I1 of the probe radiation after passing through the fluid sample at a first time is measured.

[0067] At block 606 , the following operations are performed: directing probe radiation through the probe at a plurality of additional time instances when the probe is disposed at a plurality of additional positions p2 , p3 , . . . , the plurality of additional positions respectively defining a plurality of additional path lengths L2 , L3 of the probe radiation through the fluid sample.

[0068] At block 608 , the following operations are performed: at a plurality of additional time instants, respectively measure the transmission intensities I2 , I3 , . . . of the probe radiation after passing through the fluid sample.

[0069] At box 610, the operation involves performing a linear regression to determine the slope m of a line that plots a data set of A1, A2, A3, ... as a function of L1, L2, L3, where m is determined from the ratio of the change in absorbance to the change in path length. To determine A1, A2, etc., the intensity data I1, I2, etc. are converted to absorbance data by determining log I1, log I2, etc. In other words, a linear regression is performed on a data set constructed from a plurality of data points, where the data points represent, for example, A1, L1; A2, L2; A3, L3; etc. In particular, the linear regression performed in box 610 is used to define a line that best fits the set of A, L data points, where the slope of the fitted line defines the effective value of m.

[0070] At block 612 , the following operations are performed: determining the concentration C of the material in the fluid sample, where C=m / e, where e is the molar absorptivity of the material, and m is determined as in block 610 .

[0071] Although the present arrangement has been disclosed with reference to certain embodiments, many modifications, changes and variations to the described embodiments are possible without departing from the spirit and scope of the disclosed arrangement, as defined in the appended claims. Therefore, it is intended that the present arrangement not be limited to the described embodiments, but rather have the full scope defined by the language of the following claims and their equivalents.

Claims

1. A method for determining the concentration of a material, comprising: determining whether a change in the intensity of probe radiation emitted by a light source of the absorbance spectroscopy system satisfies a stability criterion; directing said probe radiation through said probe when the probe is disposed in a first position, said first position defining a first path length L1 of said probe radiation through a fluid sample containing said material; measuring a transmission intensity I1 of the probe radiation after passing through the fluid sample when the probe is set at the first position; directing the probe radiation through the probe when the probe is disposed in a second position, the second position defining a second path length L2 for the probe radiation through the fluid sample; measuring a transmission intensity I2 of the probe radiation after passing through the fluid sample when the probe is disposed at the second position; and When the stability criterion is met, a concentration C of a material in the fluid sample is determined based on L1, I1, L2, and I2.

2. The method according to claim 1, wherein: When the stability criterion is met, the concentration C is determined as: C = (DA / DL) / e, where e is the molar absorptivity of the material, DL is the absolute value of the difference between L1 and L2, and ΔA = logI1 - logI2.

3. The method according to claim 1, wherein: The change in the intensity of the probe radiation is given by a, where a=(I max -I min ) / I min , where I max is the maximum value of the intensity of the radiation recorded in a given period, and I min is the minimum value of the intensity recorded during the given period.

4. The method according to claim 3, wherein: The duration of the given period is from 1 second to 100 seconds.

5. The method according to claim 1, wherein: When the stability criterion is met, the incident intensity of the probe radiation at the first position or at the second position prior to passing through the fluid sample is not measured.

6. The method according to claim 1, wherein: The transmission intensity I1 and the transmission intensity I2 are determined by a measuring instrument of the absorbance spectroscopy system, and the measuring instrument comprises: A sample container containing the fluid sample comprises a container wall, wherein the probe is movable relative to the container wall along a probe direction so as to change the path length of the probe signal through the fluid sample from the first path length L1 to the second path length L2.

7. The method according to claim 1, wherein: The stability criterion includes a state of the light source where the change in intensity is below a threshold, the method further comprising, when the change in intensity is greater than the threshold: Measuring the incident intensity I of the probe radiation before passing through the fluid sample when the probe is set in the first position 01 ; Measuring the incident intensity I of the probe radiation before passing through the fluid sample when the probe is set in the second position 02 ;and Based on L1, I1, L2, I2, I 01 and I 02 The concentration C of a material in the fluid sample is determined.

8. The method according to claim 7, wherein: C = (DA / DL) / e, where DL is given by |L1-L2| and DA is given by log I1–log I 2.+ log(I 01 / I 02 ) is given.

9. The method according to claim 1, wherein: The probe is disposed at the first position during a first moment in time and is disposed at the second position during a second moment in time, the method further comprising: For at least one additional time, directing the probe radiation through the probe when the probe is disposed in at least one additional position, the at least one additional position respectively defining at least one additional path length L of the probe radiation through the fluid sample n ; At the at least one additional time, the transmission intensity I of the probe radiation after passing through the fluid sample is measured. n ;and Perform linear regression to determine the plotted as L1, L2, L n The function of A1, A2, A n , …, where A equals logI.

10. A non-transitory computer-readable storage medium storing computer-readable program code executable by a processor to: determining whether a change in the intensity of probe radiation emitted by a light source of the absorbance spectroscopy system satisfies a stability criterion; causing the light source to direct the probe radiation through the probe when the probe is disposed in a first position, the first position defining a first path length L1 of the probe radiation through the fluid sample; receiving a transmission intensity I1 of the probe radiation after passing through the fluid sample; causing the light source to direct the probe radiation through the probe when the probe is disposed in a second position, the second position defining a second path length L2 of the probe radiation through the fluid sample; receiving a transmission intensity I2 of the probe radiation after passing through the fluid sample; and When the change in intensity satisfies the stability criterion, the concentration C of the material in the fluid sample is determined based on L1, I1, L2, and I2.

11. The non-transitory computer-readable storage medium of claim 10, wherein: The concentration C is determined as: C = (DA / DL) / e, where e is the molar absorptivity of the material, DL is the absolute value of the difference between L1 and L2, and ΔA = logI1 - logI2.

12. The non-transitory computer-readable storage medium of claim 10, wherein: The change in the intensity of the probe radiation is given by v, where = (I max -I min ) / I min , where I max is the maximum value of the intensity of the radiation recorded in a given period, and I min is the minimum value of the intensity recorded during the given period, where when v is below a threshold, the stability criterion is met.

13. The non-transitory computer readable storage medium of claim 10, the computer readable program code being executable by a processor to determine the concentration C when the change in the intensity satisfies the stability criterion without receiving an incident intensity I of the probe radiation at the first position prior to passing through the fluid sample. 01 The measurement result is obtained by measuring the incident intensity I of the probe radiation at the second position before passing through the fluid sample. 02 The measurement results.

14. The non-transitory computer readable storage medium of claim 10, the computer readable program code being executable by a processor to, when the change in the intensity does not satisfy the stability criterion: Receive the incident intensity I of the probe radiation before passing through the fluid sample when the probe is set at the first position 01 ; receiving an incident intensity I of the probe radiation before passing through the fluid sample when the probe is set at the second position 02 ;and Based on L1, I1, L2, I2, I 01 and I 02 The concentration C of a material in the fluid sample is determined.

15. The non-transitory computer readable storage medium of claim 14, the computer readable program code being executable by a processor to determine C by calculating a change in absorbance DA from a first moment to a second moment, where C = (DA / DL) / e, where DL is given by |L1-L2|, and DA is given by log I1–log I 2.+ log(I 01 / I 02 ) is given.

16. The non-transitory computer readable storage medium of claim 10, wherein the probe is disposed at the first position during a first moment in time and disposed at the second position during a second moment in time, the computer readable program code being executable by a processor to: For at least one additional time, causing the source to direct the probe radiation through the probe when the probe is disposed in at least one additional position, the at least one additional position respectively defining at least one additional path length L of the probe radiation through the fluid sample n ; At the at least one additional time, the transmission intensity I of the probe radiation after passing through the fluid sample is measured. n ;and Perform linear regression to determine the plotted as L1, L2, L n The function of A1, A2, A n , …, where A equals logI.

17. A measuring device comprising: a light source for generating a probe signal; and A measuring instrument, which is used to receive the probe signal, the measuring instrument comprising: a sample container containing a fluid sample, the sample container comprising a container wall; a probe arranged to guide the probe signal through the sample container, wherein the probe is movable in a probe direction relative to the container wall so as to vary a path length L of the probe signal through the fluid sample; a detector configured to receive a probe signal after passing through the container wall; and A control system which is arranged to: determining whether a change in the intensity of the probe radiation emitted by the light source satisfies a stability criterion; and When the change in intensity satisfies the stability criterion, the concentration C of a material in the fluid sample is calculated based on the change in the measured intensity of the probe signal as a function of the change in the path length L.

18. The measuring device according to claim 17, the control system being arranged as follows: receiving a transmission intensity I1 of the probe radiation after passing through the fluid sample when the probe is set at the first position; receiving a transmission intensity I2 of the probe radiation after passing through the fluid sample when the probe is disposed at the second position; and C is calculated as A / DL) / e, where e is the molar absorptivity of the material, DL is the absolute value of the difference between L1 and L2, and ΔA=logI1-logI2, where L1 is the first path length of the first location and L2 is the second path length of the second location.

19. A measurement device according to claim 18, wherein the control system is arranged to determine the concentration C when the change in the intensity satisfies the stability criterion without receiving an incident intensity I of the probe radiation at the first position before passing through the fluid sample. 01 The measurement result is obtained by measuring the incident intensity I of the probe radiation at the second position before passing through the fluid sample. 02 The measurement results.

20. The measurement device of claim 17, the light source comprising a light emitting diode (LED) to generate radiation of a target wavelength in the range of ultraviolet to infrared.

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