Data processing system and method for chromatograph

Abstract

Based on three-dimensional data of time, wavelength and intensity acquired with a three-dimensional chromatograph, whether or not the peak-top intensity of the peak of a target component exceeds a predetermined upper limit is determined. If the intensity exceeds the limit, two wavelengths λ1 and λ2 are set in a spectrum passing through the peak top, where λ1 is the peak-top wavelength while λ2 is a wavelength which belongs to the peak and at which the intensity is within a predetermined range. For each point in time belonging to the target peak, the ratio between the intensity at λ1 and the intensity at λ2 in the spectrum at that point in time is calculated, and one of the calculated intensity ratios is selected as a correction value. Based on this correction value and a quantitative value calculated from a chromatogram at λ2, the quantitative value of the target component is determined.

Claims

1. A three-dimensional chromatograph, comprising: a three-dimensional chromatograph part that temporally separates components contained in a sample, the separated components including a target component; a detector that detects the separated components; and a data processing system that produces three-dimensional data of time, wavelength and intensity acquired with the three-dimensional chromatograph part based on the detected separated components, the data processing system including, a) a setting section for setting two wavelengths λ1 and λ2 in a spectrum passing through a peak top of a peak of the target component, based on the three-dimensional data, where λ1 is a wavelength of the peak top while λ2 is a wavelength which belongs to the peak and is different from λ1; b) a calculating section for calculating, for each of points in time belonging to the peak, an intensity ratio between an intensity at the peak-top wavelength λ1 and an intensity at the wavelength λ2 in a spectrum obtained at that point in time; c) an automatic correction-value selecting section for selecting, as a correction value, one of the intensity ratios respectively calculated for the aforementioned points in time by the calculating section; and d) a component quantity determining section for determining a quantitative value of the target component, based on the correction value and a quantitative value of the peak in a chromatogram at the wavelength λ2.

2. The three-dimensional chromatograph according to claim 1, wherein: the data processing system further includes a determining section for determining whether or not the peak-top intensity of the peak of the target component exceeds a predetermined upper limit; and the setting section sets the wavelength λ1 of the peak-top and the wavelength λ2 in the case where the peak-top intensity exceeds the upper limit, the wavelength λ2 being set at a wavelength at which the intensity is equal to or lower than the upper limit as well as equal to or higher than a predetermined lower limit.

3. A three-dimensional chromatograph, comprising: a three-dimensional chromatograph part that temporally separates components contained in a sample, the separated components including a target component; a detector that detects the separated components; and a data processing system that produces three-dimensional data of time, wavelength and intensity acquired with the three-dimensional chromatograph part based on the detected separated components, the data processing system including a) a setting section for setting two wavelengths λ1 and λ2 in a spectrum passing through a peak top of a peak of the target component, based on the three-dimensional data, where λ1 is a wavelength of the peak top while λ2 is a wavelength which belongs to the peak and is different from λ1; b) a calculating section for calculating, for each of points in time belonging to the peak, an intensity ratio between an intensity at the peak-top wavelength λ1 and an intensity at the wavelength λ2 in a spectrum obtained at that point in time; c) a graphic displaying section for displaying a graphic image showing a relationship between the intensity ratio and the point in time of the spectrum for which the intensity ratio has been calculated; d) a correction-value selecting section for allowing a user to select, as a correction value, one of the intensity ratios shown on the graphic image; and e) a component quantity determining section for determining a quantitative value of the target component, based on the correction value and a quantitative value of the peak in a chromatogram at the wavelength λ2.

4. The three-dimensional chromatograph according to claim 3, wherein: the data processing system further includes a determining section for determining whether or not the peak-top intensity of the peak of the target component exceeds a predetermined upper limit; and the setting section sets the wavelength λ1 of the peak-top and the wavelength λ2 in the case where the peak-top intensity exceeds the upper limit, the wavelength λ2 being set at a wavelength at which the intensity is equal to or lower than the upper limit as well as equal to or higher than a predetermined lower limit.

5. A three-dimensional chromatography method, comprising: temporally separating components contained in a sample using a chromatograph part, the separated components including a target component; detecting the separated components; producing three-dimensional data of time, wavelength and intensity acquired with a three-dimensional chromatograph based on the detected separated components, a) setting two wavelengths λ1 and λ2 in a spectrum passing through a peak top of a peak of the target component based on the three-dimensional data of time, wavelength and intensity acquired with the three-dimensional chromatograph part, where λ1 is a wavelength of the peak top while λ2 is a wavelength which belongs to the peak and is different from λ1; b) calculating, for each of points in time belonging to the peak, an intensity ratio between an intensity at the peak-top wavelength λ1 and an intensity at the wavelength λ2 in a spectrum obtained at that point in time; c) automatically selecting one of the intensity ratios respectively calculated for the aforementioned points in time as a correction value; and d) determining a quantitative value of the target component based on the correction value and a quantitative value of the peak in a chromatogram at the wavelength λ2.

6. The three-dimensional chromatography method according claim 5, further comprising: determining step whether or not the peak-top intensity of the peak of the target component exceeds a predetermined upper limit; and wherein, in the setting step, the wavelength λ1 of the peak-top and the wavelength λ2 are set in the case where the peak-top intensity exceeds the upper limit, the wavelength λ2 being set at a wavelength at which the intensity is equal to or lower than the upper limit as well as equal to or higher than a predetermined lower limit.

7. A three-dimensional chromatography method, comprising: temporally separating components contained in a sample using a chromatograph, the separated components including a target component; detecting the separated components; producing three-dimensional data of time, wavelength and intensity acquired with a three-dimensional chromatograph based on the detected separated components, a) setting two wavelengths λ1 and λ2 in a spectrum passing through a peak top of a peak of the target component based on the three-dimensional data of time, wavelength and intensity acquired with the three-dimensional chromatograph, where λ1 is a wavelength of the peak top while λ2 is a wavelength which belongs to the peak and is different from λl; b calculating, for each of points in time belonging to the peak, an intensity ratio between an intensity at the peak-top wavelength λ1 and an intensity at the wavelength λ2 in a spectrum obtained at that point in time; c) displaying a graphic image showing a relationship between the intensity ratio and the point in time of the spectrum for which the intensity ratio has been calculated; d) allowing a user is allowed to select, as a correction value, one of the intensity ratios shown on the graphic image; and e) determining a quantitative value of the target component based on the correction value and a quantitative value of the peak in a chromatogram at the wavelength λ2.

8. The three-dimensional chromatography method according claim 7, further comprising: determining whether or not the peak-top intensity of the peak of the target component exceeds a predetermined upper limit; and wherein, in the setting step, the wavelength λ1 of the peak-top and the wavelength λ2 are set in the case where the peak-top intensity exceeds the upper limit, the wavelength λ2 being set at a wavelength at which the intensity is equal to or lower than the upper limit as well as equal to or higher than a predetermined lower limit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic configuration diagram of an analyzing system including a chromatographic data processing system as one embodiment of the present invention.

(2) FIG. 2 is a schematic flowchart of the data processing performed in the chromatographic data processing system of the present embodiment.

(3) FIG. 3 is a contour diagram showing three-dimensional data to be obtained by the chromatographic data processing system of the present embodiment.

(4) FIG. 4 is a spectrum obtained from the three-dimensional data along the line of time=T1.

(5) FIG. 5 is a chromatogram obtained from the three-dimensional data along the line of correction wavelength=λ2.

(6) FIG. 6 is a three-dimensional graph of time-wavelength-intensity showing the concept of the process for calculating an intensity ratio.

(7) FIG. 7 is a spectrum at time t belonging to a target peak.

(8) FIG. 8 is a graph showing a relationship between time and intensity ratio as well as two chromatograms respectively obtained at the peak-top wavelength λ1 and the correction wavelength λ2.

(9) FIG. 9 is an explanatory diagram showing the dynamic range in a detector.

DESCRIPTION OF EMBODIMENTS

(10) One embodiment of the chromatographic data processing system according to the present invention is hereinafter specifically described with reference to the attached drawings.

EXAMPLE

(11) FIG. 1 is a schematic configuration diagram of an analyzing system including a chromatographic data processing system according to the present embodiment. This analyzing system includes a liquid chromatograph (LC) 1 for temporally separating the components contained in a liquid sample, a photo diode array detector (PDA) 2 for detecting spectra of each of the separated components over a predetermined range of wavelengths, and a data processing system 3 for processing data produced by the PDA 2. The substance of the data processing system 3 is a commonly used computer having a CPU (central processing unit), a memory device (e.g. RAM, HDD or SSD) and other devices. This computer has a dedicated data-processing software program installed. By executing this program, various functions as shown in FIG. 1 are realized, such as the intensity determining section 31, the wavelength setting section 32, the correction quantitative value calculating section 33, the intensity ratio calculating section 34, the graphic displaying section 35, the correction value selecting section 36, and the component quantity determining section 37.

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

(13) A process of calculating the quantitative value of a target component is hereinafter described with reference to the flowchart shown in FIG. 2. Initially, a target sample to be analyzed is introduced into the LC 1, which temporally separates the components contained in the sample. The obtained components are individually detected by the PDA 2. The detection data are sequentially sent to the data processing system 3, which produces three-dimensional data of time, wavelength and intensity as shown in FIG. 3 (Step S1). The intensity determining section 31 in the data processing system 3 determines whether or not the peak-top intensity of the peak of the target component in the three-dimensional data (which is hereinafter called the “target peak”) exceeds a predetermined upper limit Pa (Step S2). This upper limit Pa is a value which has been preset in the data processing system 3 taking into account the dynamic range of the PDA 2, the A/D converter (not shown) and other elements. Normally, the upper limit of the dynamic range is used as Pa, although it is possible to use a lower and securer value or a slightly higher value which is practically acceptable.

(14) In Step S2, if the peak-top intensity of the target peak has been found to be equal to or lower than the upper limit Pa, the data processing system 3 calculates the quantitative value (peak area or peak height) of the target component by a normal method from the chromatogram taken along the peak-top wavelength λ1 of the target peak, and completes the entire calculation without performing the processes of Step S3 through S7.

(15) If the peak-top intensity of the target peak has been found to be higher than the upper limit Pa, the quantitative value of the target component calculated from the chromatogram taken along the peak-top wavelength λ1 of the target peak will not be a correct value. Therefore, the operation proceeds to Step S3 to perform a correction of the quantitative value of the target component as follows.

(16) In Step S3, two wavelengths λ1 and λ2 are set within a wavelength range which belongs to the target peak in the spectrum passing through the peak top of the target peak (i.e. the spectrum taken along the line of time=T1 in FIG. 3), where λ1 is the peak-top wavelength and λ2 is another wavelength at which the intensity is equal to or lower than a predetermined upper limit Pb as well as equal to or higher than a predetermined lower limit Pc, as shown in FIG. 4 (λ2 is hereinafter called the “correction wavelength”). Similar to the upper limit Pa, the upper limit Pb is a value which has been preset in the data processing system 3 based on the upper limit of the dynamic range of the PDA 2 and other elements. The upper limits Pa and Pb respectively used in Steps S2 and S3 may be equal to or different from each other. In the present embodiment, Pa=Pb.

(17) The lower limit Pc is a value which has been preset in the data processing system 3 based on the lower limit of the aforementioned dynamic range. Pc should normally be set at the lower limit of the dynamic range, although a slightly higher value may also be used.

(18) The correction quantitative value calculating section 33 creates a chromatogram at the correction wavelength λ2 (correction chromatogram) from the three-dimensional data (FIG. 5), and then calculates, as the correction quantitative value, a quantitative value A2 (peak area or peak height) of the chromatogram peak corresponding to the target peak in this correction chromatogram (Step S4). Since the maximum value of the chromatogram peak is not higher than the upper limit of the dynamic range, the quantitative value of this peak can correctly be calculated.

(19) At each point in time t within a time range of [Ta, Tb] belonging to the target peak (FIGS. 5 and 6), the intensity ratio calculating section 34 acquires an intensity I.sub.1(t) at the wavelength λ1 and an intensity I.sub.2(t) at the correction wavelength λ2 (FIG. 7), and calculates an intensity ratio R(t) as follows (Step S5):
R(t)=I.sub.1(t)/I.sub.2(t)

(20) The graphic displaying section 35 creates a graph of this intensity ratio R(t) and shows it on the display unit 5. As shown in FIG. 8, when at least one of the intensities I.sub.1(t) and I.sub.2(t) is out of the dynamic range, the similarity of the spectrum shape is violated and the intensity ratio R(t) deviates from the constant value. By contrast, when both of the intensities I.sub.1(t) and I.sub.2(t) are within the dynamic range, the intensity ratio R(t) is almost constant. Accordingly, when both of the intensities I.sub.1(t) and I.sub.2(t) are within the dynamic range, the similarity between the spectra is at the highest level, which means that the spectra are highly reliable. In the present embodiment, the correction value selecting section 36 automatically sets, as the correction value Rs, the average (mean, median or mode) of the intensity ratios R(t) obtained within a time range where both of the intensities I.sub.1(t) and I.sub.2(t) are within the dynamic range.

(21) With the correction value Rs thus set, the component quantity determining section 37 calculates the quantity value A1 of the target peak. Specifically, as expressed by the following equation, the quantity value A1 is calculated by multiplying the quantity value A2 obtained from the chromatogram at the correction wavelength λ2 in Step S4 by the correction value Rs (Step S7):
A1=A2×Rs

(22) Thus, a correct quantitative value A1 of the target peak can be calculated using the quantitative value A2 determined within the dynamic range of the PDA 2 and the correction value Rs.

(23) The correction value selecting section 36 may be configured so as to allow users to select one of the intensity ratios on the graph of the intensity ratio R(t) shown on the display unit 5 instead of automatically setting the correction value Rs.

(24) The correction wavelength λ2 may automatically be set by the wavelength setting section 32 based on the three-dimensional data. A method for automatically setting the correction wavelength λ2 is as follows: A spectrum of the target peak at retention time T1 is acquired. In this spectrum, a wavelength at which the intensity value on the positive (longer-wavelength) side or negative (shorter-wavelength) side of the peak-top wavelength λ1 exceeds an “intensity for the correction wavelength” preset by the user is selected as the correction wavelength λ2 (FIG. 4). The searching direction (positive or negative) can be selected previously by the user or preset in the system (in FIG. 4, the search is made in the negative direction).

(25) In the previous embodiment, whether or not the peak-top intensity of the peak of the target component exceeds the upper limit Pa is determined and the processes of Steps S3 through S7 are performed only when the intensity exceeds the upper limit. However, it is also possible to always perform those processes.

REFERENCE SIGNS LIST

(26) 1 . . . Liquid Chromatograph (LC) 2 . . . Photo Diode Array Detector (PDA) 3 . . . Data Processing System

(27) 31 . . . Intensity Determining Section

(28) 32 . . . Wavelength Setting Section

(29) 33 . . . Correction Quantitative Value Calculating Section

(30) 34 . . . Intensity Ratio Calculating Section

(31) 35 . . . Graphic Displaying Section

(32) 36 . . . Correction Value Selecting Section

(33) 37 . . . Component Quantity Determining Section 4 . . . Operation Unit 5 . . . Display Unit