Data processing system and data processing method for chromatograph

Abstract

A data processing system including a sensitivity coefficient holder for holding a value R of a sensitivity coefficient for a wavelength 1 belonging to one peak in a spectrum of a first component and a second wavelength 2 belonging to the same peak and having a lower intensity than 1, the value R defined using the ratio of the peak areas or similar information of two chromatograms respectively obtained at the two wavelengths; a chromatographic detector for spectroscopically analyzing sample components exiting from a component-separating column and for measuring an intensity at the second wavelength 2 of the spectrum of the first component and an intensity at a wavelength 3 of a spectrum of a second component at each point in time; and a concentration ratio calculator for calculating the ratio of concentration between the first component and the second component.

Claims

1. A data processing system for a chromatograph, comprising a memory unit, a single spectroscopic detector, and a central processing unit, wherein: the memory unit holds a value R of a sensitivity coefficient for a first wavelength 1 belonging to one peak in a spectrum of a first component and a second wavelength 2 belonging to the same peak and having a lower intensity than 1, the value R defined using a ratio of peak areas or similar information of two chromatograms respectively obtained at the two wavelengths; the single spectroscopic detector spectroscopically detects the first component and the second component contained in a sample provided for a single analysis exiting from a component-separating column and for measuring an intensity at the second wavelength 2 and an intensity at a third wavelength 3 at each point in time in the single analysis, when an intensity of the first component at the first wavelength 1 is outside of a dynamic range of the single spectroscopic detector; and the central processing unit comprises: a chromatogram creator for creating a chromatogram of the first component based on the intensity measured by the single spectroscopic detector at the second wavelength 2 and a chromatogram of the second component based on the intensity measured by the single spectroscopic detector at the third wavelength 3; and a concentration ratio calculator for: calculating a chromatogram peak height h1 of the first component at the first wavelength 1 from a chromatogram peak height h2 of a chromatogram peak of the first component at the second wavelength 2 and the value R of the sensitivity coefficient, calculating a concentration of the first component from the chromatogram peak height h1, and calculating a concentration of the second component from a peak height h3 of a chromatogram peak at the third wavelength 3 of the second component, or calculating a chromatogram peak area A1 of the first component at the first wavelength 1 from a chromatogram peak area A2 of a chromatogram peak of the first component at the second wavelength 2 and the value R of the sensitivity coefficient, calculating a concentration of the first component from the chromatogram peak area A1, and calculating a concentration of the second component from a peak area A3 of a chromatogram peak at the third wavelength 3 of the second component, and calculating a ratio of concentration between the first component and the second component, and wherein another spectroscopic detector is not used to detect the second component.

2. The data processing system for a chromatograph according to claim 1, wherein the third wavelength 3 coincides with the first wavelength 1.

3. The data processing system for a chromatograph according to claim 1, wherein the third wavelength 3 coincides with the second wavelength 2.

4. The data processing system for a chromatograph according to claim 1, wherein the memory unit further comprises an information of relationship between the concentration and the intensity and the peak height and/or the peak area of the peak in the chromatogram.

5. A data processing method for a chromatograph, comprising steps of: a) determining and holding a value R of a sensitivity coefficient for a first wavelength 1 belonging to one peak in a spectrum of a first component and a second wavelength 2 belonging to the same peak and having a lower intensity than 1, the value R defined using a ratio of a peak areas or similar information of two chromatograms respectively obtained at the two wavelengths; b) spectroscopically detecting, by a single spectroscopic detector, the first component and the second component contained in a sample provided for a single analysis exiting from a component-separating column, and measuring an intensity at the second wavelength 2 of the spectrum of the first component and an intensity at a third wavelength 3 at each point in time in the single analysis, when an intensity of the first component at the first wavelength 1 is outside of a dynamic range of the single spectroscopic detector; c) creating a chromatogram of the first component based on the intensity measured by the single spectroscopic detector at the second wavelength 2 and a chromatogram of the second component based on the intensity measured by the single spectroscopic detector at the third wavelength 3; and d) calculating a chromatogram peak height h1 of the first component at the first wavelength 1 from a chromatogram peak height h2 of a chromatogram peak of the first component at the second wavelength 2 and the value R of the sensitivity coefficient, calculating a concentration of the first component from the chromatogram peak height h1, and calculating a concentration of the second component from a peak height h3 of a chromatogram peak at the third wavelength k3 of the second component, or calculating a chromatogram peak area A1 of the first component at the first wavelength 1 from a chromatogram peak area A2 of a chromatogram peak of the first component at the second wavelength 2 and the value R of the sensitivity coefficient, calculating a concentration of the first component from the chromatogram peak area A1, and calculating a concentration of the second component form a peak area A3 of a chromatogram peak at the third wavelength 3 of the second component, and calculating a ratio of concentration between the first component and the second component, wherein another spectroscopic detector is not used to detect the second component.

6. The data processing method for a chromatograph according to claim 5, wherein the third wavelength 3 coincides with the first wavelength 1.

7. The data processing method for a chromatograph according to claim 5, wherein the third wavelength 3 coincides with the second wavelength 2.

8. The data processing method for a chromatograph according to claim 5, further comprising a step of holding an information of relationship between the concentration and the intensity and the peak height and/or the peak area of the peak in the chromatogram.

9. A data processing system for a chromatograph, comprising a single spectroscopic detector and a central processing unit operating on a basis of three-dimensional data of time, wavelength and intensity obtained with a three-dimensional chromatograph: the single spectroscopic detector for detecting a sample component exiting from a component-separating column, and measuring an intensity at a target wavelength 1 and an intensity at a correction wavelength 2 of the sample component by a single analysis, the correction wavelength 2 being different from the target wavelength 1; the central processing unit comprising: a chromatogram creator for creating a chromatogram based on the intensity measured by the single spectroscopic detector at the target wavelength 1 and a chromatogram based on the intensity measured by the single spectroscopic detector at the correction wavelength 2; a correction-needing peak detector for detecting a correction-needing peak which is a peak having a peak intensity being outside of a dynamic range of the single spectroscopic detector in the chromatogram at the target wavelength 1; a correction value calculator for calculating a corrected peak height and/or corrected peak area which is a peak height and/or peak area of the correction-needing peak in a chromatogram along the correction wavelength 2; a sensitivity coefficient calculator for calculating, from a spectrum of the correction-needing peak obtained at time Ts which is earlier or later than a retention time T1 of the correction-needing peak and which belongs to the correction-needing peak, a value R of a sensitivity coefficient defined using a ratio between an intensity at the target wavelength 1 and an intensity at the correction wavelength 2 or similar information; and a peak value calculator for calculating the peak height and/or peak area of the correction-needing peak, based on the value R of the sensitivity coefficient and the corrected peak height and/or corrected peak area.

10. A data processing method for a chromatograph, comprising following steps performed on a basis of three-dimensional data of time, wavelength and intensity obtained with a three-dimensional chromatograph: a) a single spectroscopic detecting step, in which a sample component exiting from a component-separating column is detected, and an intensity at a target wavelength 1 and an intensity at a correction wavelength 2 of the sample component are measured, the correction wavelength 2 being different from the target wavelength 1; b) a chromatogram creating step, in which a chromatogram is created based on the intensity measured at the target wavelength 1 and a chromatogram is created based on the intensity measured at the correction wavelength 2, respectively; c) a correction-needing peak detection step, in which a correction-needing peak, which is a peak having a peak intensity being outside of a dynamic range of the single spectroscopic detector, is detected in the chromatogram at the target wavelength 1; d) a correction value calculation step, in which a corrected peak height and/or corrected peak area is calculated, which is a peak height and/or peak area of the correction-needing peak in the chromatogram along the correction wavelength 2 which is a wavelength different from the target wavelength 1; e) a sensitivity coefficient calculation step, in which a value R of a sensitivity coefficient defined using a ratio between an intensity at the target wavelength 1 and an intensity at the correction wavelength 2 or similar information is calculated from a spectrum of the correction-needing peak obtained at time Ts which is earlier or later than a retention time T1 of the correction-needing peak and which belongs to the correction-needing peak; and f) a peak value calculation step, in which the peak height and/or peak area of the correction-needing peak is calculated based on the value R of the sensitivity coefficient and the corrected peak height and/or corrected peak area.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIGS. 1A-1C are time-wavelength graphs conceptually showing the process performed by the data processing system and method for a chromatograph according to the first aspect of the present invention, where FIG. 1A is the case where the wavelengths 1 and 2 related to the first component are different from the wavelength 3 related to the second component, FIG. 1B is the case where 1 coincides with 3, and FIG. 1C is the case where 2 coincides with 3.

(2) FIG. 2 is a three-dimensional graph of time, wavelength and intensity conceptually showing the process performed by the data processing system and method for a chromatograph according to the second aspect of the present invention.

(3) FIG. 3 is a schematic configuration diagram of an analyzing system including a data processing system for a chromatograph as the first embodiment.

(4) FIG. 4 is a schematic flowchart of the data processing performed in the data processing system for a chromatograph of the first embodiment.

(5) FIG. 5 shows two chromatograms obtained with the data processing system for a chromatograph of the first embodiment.

(6) FIG. 6 is a schematic configuration diagram of an analyzing system including a data processing system for a chromatograph as an embodiment of the data processing system and method for a chromatograph according to the second aspect of the present invention.

(7) FIG. 7 shows a spectrum of a correction-needing peak to be processed in the embodiment of the second aspect.

(8) FIG. 8 shows a chromatogram including a correction-needing peak.

(9) FIG. 9 shows a sensitivity-corrected spectrum.

(10) FIG. 10 illustrates a dynamic range of a detector.

DESCRIPTION OF EMBODIMENTS

(11) One embodiment of the data processing system for a chromatograph according to the present invention is hereinafter specifically described with reference to the drawings. FIG. 3 is a schematic configuration diagram of an analyzing system including the data processing system for a chromatograph according to the present embodiment.

(12) As shown in FIG. 3, this analyzing system has a liquid chromatograph (LC) 1 for temporally separating the components contained in a liquid sample, a detector 2 for detecting each of the separated components at predetermined wavelengths, and a data processing system 3 for processing the data produced by the detector 2. The data processing system 3 is actually a commonly used computer consisting of a CPU (central processing unit), memory unit, storage device (e.g. hard disc drives or solid state devices) and other components. A dedicated data processing software program is installed on this computer. By executing this software program, the functions of the chromatogram creator 32, concentration ratio calculator 33 and other components shown in the figure are realized. On the other hand, the sensitivity coefficient holder 31 is provided on one area of the storage device included in or connected to the data processing system 3.

(13) Additionally, an operation unit 4 consisting of a keyboard and/or a pointing device (e.g. mouse) and a display unit 5 are connected to the data processing system 3.

(14) In the sensitivity coefficient holder 31, a value R of the sensitivity coefficient for a sample which is known to contain a principal component is stored, with the peak top wavelength 1 of the principal component and a second wavelength 2 having a lower intensity than the peak top wavelength 1 as the target wavelengths. As the sensitivity coefficient R, the area ratio between the chromatograms at wavelengths 1 and 2 may be previously obtained by actually using a standard sample containing the sample to be analyzed, or an intensity ratio between 1 and 2 in the spectrum of the principal component may be used as R. In the present example, the peak top wavelength is selected as one of the two wavelengths, although any wavelength 1 having a comparatively high intensity may be combined with the wavelength 2 having a comparatively low intensity to calculate the ratio. It is also possible to hold a plurality of ratios R1, R2 and so on for three or more wavelengths.

(15) A process of analyzing a sample which contains a principal component and its impurities and determining whether or not the content of the impurities relative to the principal component is equal to or greater than a predetermined upper limit level is hereinafter described with reference to the flowchart shown in FIG. 4.

(16) Initially, the detection wavelengths of the detector 2 are set at the second and third wavelengths 2 and 3, and a sample to be analyzed is passed through the column of the LC1. The components of the sample are temporally separated by the LC1 and individually detected by the detector 2. At each point in time, the intensity values at the second and third wavelengths 2 and 3 are sent to the data processing system 3 (Step S1). Based on the signals successively fed from the detector 2, the chromatogram creator 32 in the data processing system 3 creates a chromatogram, as shown in FIG. 5. In FIG. 5, the left half is the chromatogram obtained at wavelength 2, while the right half is the chromatogram obtained at wavelength 3. In the chromatogram obtained at wavelength 2, the principal component forms a high peak, but its height (intensity) does not exceed the dynamic range (the vertical range in the figure). In the chromatogram obtained at wavelength 3, the peak height (intensity) of the principal component exceeds the dynamic range (the vertical range in the figure), while the impurity peaks show high values within the dynamic range, so that the concentrations of those impurities can be correctly measured using this chromatogram.

(17) In the subsequent Step S2, the concentration ratio calculator 33 computes the chromatogram peak top area A1 of the principal component by multiplying the value R of the sensitivity coefficient stored in the sensitivity coefficient holder 31 and the area A2 of the chromatogram peak corresponding to the aforementioned spectrum peak of the principal component at the second wavelength 2 (i.e. the peak area of the principal component in the left chromatogram in FIG. 5).

(18) In Step S3, the concentration ratio calculator 33 computes the concentration of the impurities based on the total area A3 of the chromatogram peaks at wavelength 3 (i.e. the

(19) Subsequently, in Step S4, the concentration ratio calculator 33 computes the ratio of concentration between the principal component and the impurities based on the concentration of the principal component calculated in Step S2 and that of the impurities calculated in Step S3 (Step S4).

(20) As described thus far, the data processing system for a chromatograph according to the present invention can calculate the ratio of concentration between a principal component and impurities contained in a sample by a single analysis even if the difference in concentration between the principal component and the impurities is too large to determine the ratio between the two concentrations by a single measurement due to the limited dynamic range of the detector 2 or other reasons.

(21) In the previous embodiment, it is previously known that the principal component is a high-concentration component and its peak top intensity at wavelength 1 will exceed the dynamic range of the detector 2. However, there is also the case where the components contained in the sample to be analyzed have unknown concentrations. Such a case can also be handled by simultaneously detecting the intensities of all the wavelength components of the dispersed light using a photodiode array (PDA) detector or the like in the chromatographic measurement and then performing the previously described process based on the obtained three-dimensional data of time, wavelength and intensity.

(22) Specifically, if the peak intensity of the first component at the peak top wavelength 1 has exceeded a predetermined upper limit intensity, a chromatogram is created for wavelength 2 which belongs to the same peak and which does not exceed the upper limit intensity, and its area is measured. By correcting this area with the sensitivity coefficient R, the concentration of the first component can be determined. By comparing this concentration with that of the second component calculated from the area of the chromatogram at the peak top of the second component, the ratio of concentration between the first and second components can be obtained.

(23) A data processing system for a chromatograph according to the second aspect of the present invention is hereinafter specifically described with reference to the drawings. The configuration of the entire system of the present embodiment is the same as that of the previous embodiment, except that a photodiode array (PDA) detector 21 is used as the detector. The data processing system of the present embodiment has a correction-needing peak detector 35, a correction wavelength setter 36, a correction wavelength chromatogram creator 37, a sensitivity-corrected spectrum creator 38, a peak area determiner 39 and other components. Using these components, the present system provides the function of virtually expanding the dynamic range in the detected chromatogram (dynamic range expanding function).

(24) In an analysis of a high-concentration sample, a chromatogram peak may possibly exceed the highest measurable level for the detector or the upper limit of the linearity range of the detector and prevent the peak area value from being correctly obtained. In the PDA dynamic range expanding function of the data processing system for a chromatograph according to the present embodiment, the area value of a target peak is calculated by multiplying a peak area of a chromatogram taken at a wavelength where the linearity is ensured and a sensitivity coefficient R calculated from a spectrum taken at a point in the foot of the peak.

(25) Specifically, the calculation is performed by the following procedure, in which all the peaks found in the chromatogram obtained at the target wavelength 1 are subjected to a correction process as follows:

(26) (1) Detection of Correction-Needing Peak

(27) For every peak belonging to the chromatogram obtained at the target wavelength 1, the correction-needing peak detector 35 obtains the peak intensity value and determines whether or not the intensity value exceeds a predetermined threshold. Any peak exceeding the threshold is identified as a correction-needing peak and is subjected to the correction process. The threshold should be previously set taking into account the dynamic ranges of the PDA, A/D converter and other components.

(28) (2) Determination of Correction Wavelength

(29) The correction wavelength setter 36 sets a correction wavelength 2 which differs from the target wavelength 1 (FIG. 7). The correction wavelength 2 may be set automatically by the system or manually by the user.

(30) following steps:

(31) A spectrum is obtained at the retention time T1 of the correction-needing peak. In this spectrum, a wavelength at which the intensity value becomes equal to a correction wavelength intensity (which is preset by the user) is located on either the plus side (longer-wavelength side) or minus side (shorter-wavelength side) of the absorption wavelength 1 and selected as the correction wavelength 2. The searching direction (plus or minus) may be previously specified by the user or defined beforehand in the system.

(32) (3) Creation of Chromatogram at Correction Wavelength 2

(33) The correction wavelength chromatogram creator 37 creates a chromatogram at the correction wavelength 2 from the three-dimensional data of the time, wavelength and intensity of the chromatogram obtained with the PDA 21, and searches this chromatogram for a peak corresponding to the correction-needing peak. The peak area A2 and peak height h2 of the located peak are adopted as the data for correction.

(34) (4) Creation of Sensitivity-Corrected Spectrum

(35) From the aforementioned three-dimensional data, the sensitivity-corrected spectrum creator 38 creates a spectrum at a point in time Ts (FIG. 8) which is later than the retention time T1 of the correction-needing peak and at which the intensity value becomes equal to a predetermined sensitivity-corrected spectrum extraction intensity (this spectrum is called the sensitivity-corrected spectrum; FIG. 9). A background correction may additionally be performed on the created sensitivity-corrected spectrum.

(36) (5) Calculation of Sensitivity Coefficient

(37) The peak area determiner 39 initially calculates a sensitivity coefficient R, which is the ratio between the intensity I.sub.1 at wavelength 1 and the intensity I.sub.2 at wavelength 2 in the sensitivity-corrected spectrum:
[Sensitivity Coefficient R]=[Intensity I.sub.1 at Wavelength 1]/[Intensity I.sub.2 at Wavelength 2]

(38) (6) Determination of Area and Other Value of Correction-Needing Peak

(39) Next, the peak area determiner 39 replaces the area A1 and height h1 of the correction-needing peak with the values obtained by multiplying the area A2 and height h2 of the peak of the chromatogram at the correction wavelength 1 by the sensitivity coefficient R:
[Area A1 of Correction-Needing Peak]=[Area A2 of Peak at Correction Wavelength 2][Sensitivity Coefficient R]
[Height h1 of Correction-Needing Peak]=[Height h2 of Peak at Correction Wavelength 2][Sensitivity Coefficient R]

(40) Thus far, the data processing system for a chromatograph according to the present invention has been described, illustrating specific examples. It should be noted that the previous embodiments are mere examples and can be appropriately changed, improved or modified within the spirit of the present invention.

(41) For example, it is possible to calculate not only the area of a saturated peak by a conversion from the area of a non-saturated peak as described in the previous embodiment, but also the area of a low peak by a conversion from the area of another peak located at a wavelength with a higher level of sensitivity. The type of chromatograph is not limited to the liquid chromatograph; it may naturally be a gas chromatograph.

REFERENCE SIGNS LIST

(42) 1 . . . Liquid Chromatograph (LC) 2 . . . Detector 21 . . . Photodiode Array (PDA) Detector 3 . . . Data Processing System 31 . . . Sensitivity Coefficient Holder 32 . . . Chromatogram Creator 33 . . . Concentration Ratio Calculator 35 . . . Correction-Needing Peak Detector 36 . . . Correction Wavelength Setter 37 . . . Correction Wavelength Chromatogram Creator 38 . . . Sensitivity-Corrected Spectrum Creator 39 . . . Peak Area Determiner 4 . . . Operation Unit 5 . . . Display Unit