Absorbance detector

Abstract: An absorbance detector comprising a light source 2, a spectroscope 4 to split the light from the light source 2 and lead it to a cell 6, a sensor 8 to detect the light coming through said cell 6 and to measure it absorption constant, a spectroscope controller 10 to make said spectroscope 4 scan with two wavelengths alternately, a pair of absorption constant calculation units 12, 14 synchronizing said spectroscope 4, collecting several past data of absorption constant to calculate a predicted value of absorption constant for a present or future point of time and a chromatograph ratio calculation unit 16 to calculate a ratio of simultaneous absorptional constants of two wavelengths obtained from said pair of absorption constant calculation units 12, 14.

Description: BACKGROUND OF THE INVENTION The present invention relates to absorbance detectors of high-speed liquid chromatography and, more particularly, to an absorbance detector with a function to analyze qualitatively a peak purity of a chromatogram by scanning two wavelengths alternately to calculate a ratio of absorption constants measured by these two wavelengths. An absorbance detector having a spectroscope with alternate scanning by two wavelengths is well known. An absorbance detector is disclosed in DE-A-2 817 333. This type of detector drives a spectroscope scan with two wavelengths λ₁ and λ₂ and measures absorption constants using each of these wavelengths. Given measured data Aλ₁ and Aλ₂, absorption constants are Aλ₁ (n-2), Aλ₂ (n-1), Aλ₁ (n), and the like; thus, the data are obtained alternately with respect to λ₁ and λ₂. Hence, chromatograph ratios are Aλ₁ (n-2)/ Aλ₂ (n-1), Aλ₁ (n)/ Aλ₂ (n+1), and so on. These calculated chromatography ratios uses absorption constants measured at different points of time by λ₁, and λ₂, one at a time. Therefore, these data are not simultaneous. Another absorbance detector uses moving averages of absorption constants measured by wavelengths λ₁ and λ₂ ; a chromatography ratio is given by (Aλ 1 (n-2) + Aλ 1 (n) + ...) / Aλ 2 (n-1) + Aλ 2 (n+1) + ...) A chromatography ratio is to be constant if the ratio is calculated for a single peak. However, a ratio calculated from absorption constants that are not simultaneous is not constant, and therefore, cannot measure peak purity correctly. On the other hand, calculating a moving average needs filtering operation, resulting in the ratio of past data. This causes a time delay of data and is not preferable to a minute-to-minute measurement. OBJECTS AND SUMMARY OF THE INVENTION Accordingly, it is an object of the invention to provide an absorbance detector that is able to obtain a correct peak purity by calculating a present or future absorption constant of each one of different wavelengths and that is applicable to the minute-to-minute measurement by eliminating time delay of the calculated data for a chromatography ratio. BRIEF DESCRIPTION OF THE DRAWINGS Fig.1 is a block diagram to explain the invention. Fig.2 is a graph to show time variations of absorption constants. Fig.3 is a block diagram according to an embodiment of the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to Fig. 1, numeral 2 is a light source, numeral 4 is a spectroscope to split the light from light source 2 and lead it to a cell 6, numeral 8 is a sensor to detect the light coming through cell 6, and numeral 10 is a spectroscope controller to make spectroscope 4 scan with two wavelength alternately. An absorption constant calculation unit 12, synchronizing scans of spectroscope 4, collects data of absorption constants measured at past several points with a wavelength λ₁ and utilize them to predict present or future measurement with wavelength λ₁. An absorption constant calculation unit 14, synchronizing scans of spectroscope 4, collects absorption data measured at past several points with a wavelength λ₂ and utilizes them to predict present or future measurement with wavelength λ₂. A chromatograph ratio calculation unit 16 calculates a ratio of simultaneous absorption constants obtained from absorption constant calculation unit 12 and 14. According to another embodiment of the invention, absorption constant calculation unit 12, synchronizing scans of a spectroscope 4, collects data of absorption constants measured at past several points with a wavelength λ₁ and utilize them to predict an absorption constant at the time when the other absorption constant is measured by wavelength λ₂. Absorption constant calculation unit 14, synchronizing scans of a spectroscope 4, collects data of absorption constants measured at past several points with a wavelength λ₂ and utilize them to predict an absorption constant at the time when the other absorption constant is measured by wavelength λ₁. Chromatograph ratio calculation unit 16, then, calculates a ratio of absorption constant measured by wavelength λ₁ (λ₂) at a certain point of time and absorption constant predicted by absorption constant calculation unit 14(12) for wavelength λ₂ (λ₁) at that same point of time. Fig.2 shows variations of absorption constants with time. A curve A represents absorption constants measured by wavelength λ₁ and a curve B represents absorption constants measured by wavelength λ₂. Spectroscope 4 scans cell 6 with wavelength λ₁ and wavelength λ₂ alternately. If absorption constant measured by λ₁ is denoted by X and absorption constant measured by λ₂ is denoted by Y, then, because of alternate scanning with an equal interval by spectroscope 4, sensor 8 detects absorption constants as X(2n-5), Y(2n-4), X(2n-3), Y(2n-2), and so on. Being detected with the equal interval for each wavelength, absorption constant for a wavelength can be predicted as a linear function of data obtained by past several measurements with that wavelength. According to the invention of claim 1, chromatograph ratio is obtained using the predicted value of each wavelength at the same point of time. According to the invention of claim 2, when a measurement is performed with wavelength λ₁, absorption constant for λ₁, is a measured value at that point of time, which is denoted by Aλ₁ , while absorption constant for λ₂ is a value predicted from past several measurements with λ₂ for that same point of time, which is denoted by Aλ₂*. Then, chromatograph ratio is given by Aλ₁/ Aλ₂*. Similarly, when a measurement is performed by wavelength 2, chromatograph ratio is given by Aλ₁* / Aλ₂ where Aλ₁* is a predicted value for lambda 1 and Aλ₂ is a measured value with λ₂. One way to predict an absorption constant is using an equation X(2n)* = X(2n-1) + X1(2n-1)/2 + X2(2n-1)/2 where X(2n)* is a predicted value of absorption constant for wavelength λ₁ when absorption constant is measured by wavelength λ₂ and X1(m) = X(m) - X(m-2) X2(m) = X1(m) - X1(m-2). When absorption constant is measured by wavelength λ₁ absorption constant for λ₂ is predicted in the same manner. Referring now to Fig.3, a heavy hydrogen lamp can be used as light source 2. Spectroscope 4 scans light having a desired wave length generated by a diffraction grating driven by a motor and leads the light to cell 6. A sample being isolated by a column of high-speed liquid chromatography flows into cell 6 and the light passing through cell 6 is detected by sensor 8. An output of sensor 8 varies according to absorption constant of the sample in cell 6. A CPU 20 receives the output from sensor 8 and processes it. CPU 20 also controls spectroscope 4 by changing scanning wavelength between λ₁ and λ₂ alternately with a certain constant interval. Spectroscope controller 10, absorption constant calculation unit 12, absorption constant calculation unit 14, and chromatograph ratio calculation unit 16 are integrated into CPU 20.

Claims: An absorbance detector comprising a light source (2), a spectroscope (4) for splitting the light from the light source (2) into two components having different wavelengths (λ₁, λ₂) and for directing said components to a sample cell (6), a sensor (8) for detecting the light coming through said cell (6), a spectroscope controller (10) for controlling said spectroscope (4) such that said light components (λ₁, λ₂) are alternately directed to said cell (6), a first absorption constant calculation unit (12) for receiving the output value from said sensor (8) at one wavelength (λ₁) and for calculating the absorption constant by comparing said output value with a reference value as well as for predicting the absorption constant for a future time by extrapolation on the basis of several previously calculated absorption constant values, a second absorption constant calculation unit (14) for receiving the output value from said sensor (8) at the second wavelength (λ₂) and for calculating the absorption constant by comparing said output value with a reference value as well as for predicting the absorption constant for a future time by extrapolation on the basis of several previously calculated absorption constant values and an absorption constant ratio calculation unit (16) for receiving calculated or measured absorption constants for the same point of time from both absorption constant calculation units (12, 14) and for calculating an absorption constant ratio therebetween. An absorbance detector according to claim 1 wherein the future time for which the absorption constant is predicted by one of the first and second absorption constant calculation units (12, 14) is the point of time at which the absorption constant is measured and calculated by the other absorption constant calculation unit (14, 12) respectively.

Inventors: MARUYAMA SHUZO, MARUYAMA, SHUZO, Maruyama, Shuzo, c/o Shimadzu Corp., Sanjo-Factory
Applicants: SHIMADZU CORP, SHIMADZU CORPORATION
Application year: 1991
Main classification: G01N21
IPC codes: G01N21, G01J3