SU892229A1 - Detector for liquid chromatography - Google Patents

Description

(FOR) DETECTOR FOR LIQUID CHROMATOGRAPHY

I

The invention relates to a reference measurement technique, namely, detectors for preparative liquid chromatography, and can be used in automated process control systems as a stand alone concentration meter.

A photoelectric detector is used to record the output of substances separated on a chromatographic column, containing a radiation source, flow cells, a modulator, a converter or a compensating element, a photodetector, and a recording system p.

However, the known detector provides for the registration of changes in only one physical property of the analyzed medium.

The closest technical solution to the invention is a liquid chromatography detector containing a light source sequentially installed on its axis, a cuvette, a linear polarizer, a polarization modulator, a compensator made in the form of two polarization plates, the polarization planes of which are rotated. relative to each other, and the registration system 2j.

A disadvantage of the known detector is that it provides registration of only one physical property of the analyzed medium (refractive index). This does not guarantee against an unregulated pass of the component in the mobile phase at the outlet of the column.

The purpose of the invention is to increase the accuracy of measurements by increasing the number of measured parameters.

The goal is achieved by the fact that in a liquid chromatography detector containing sequentially

A light source, a cuvette, a linear polarizer, a polarization modulator, a compensator made in the form of two polarization plates, the polarization planes of which are rotated relative to each other, and the registration system of the angle between the polarization plates are installed on its axis. the compensator lies in the range of about 80 °, with the 3Tof-o bisector of the angle coinciding with the section of the polarization plates and perpendicular to the polarization plane of the linear polarizer, and the photometric cell is set at an angle to eskoy axis. FIG. 1 shows the block diagram of the proposed detector; FIG. 2 is a schedule on the principle of its work. The detector contains a light source 1, a condenser 2, a diaphragm 3, a filter C, a linear polarizer 5 with a zero setting device, a cell b and a magneto-optical modulator 7, a compensator 8, a recording system including a photocell 9, an amplifier 10, a reversing motor 11, kinetically recorded with a pen of the recorder 12 and a compensator B consisting of polarization plates 13 and 1. Recording changes in optical density, refractive index, fluorescence, rotation of the polarization plane or their combination in the measuring cuvette of proceeds in the following manner .. Elements 1, 2 and 3 form two light beams which pass filter k, the linear polarizer 5, and the measuring cuvette 6 and comparative blowing m Torr 7 wherein they are modulated by variations in the polarization plane. The modulated light beams arrive at the compensator 8, and the beam of light from the measuring cuvette sticks to part 13, and from the comparative one to part 14 of the compensator. A change in the absorption coefficient or fluorescence in the measuring cell causes a change in the intensity of the light flux entering the part 13 of the compressor. A change in the refractive index leads to a shift in the position of the light beam relative to the line of separation of the polarization plates, which is equivalent to a differential change in the intensities of the light fluxes passing through parts 13 and I of the compensator. The change in the optical activity of the solution in the measuring cell entails 8 4 following the rotation of the plane of polarization of the light passing through it, which also leads to a differential change in the intensity of the light flux through part 13 of the capacitor. Taking into account the above, to record the response of the device to a change in any of the listed physical parameters of the medium in the measuring cell, it is sufficient to record the change in the intensity of the light flux through the measuring channel. For the case under consideration, with equal intensities of the light fluxes through the compensator and modulation parts 13 and 14, the total intensity of the light flux at the output of the system also varies according to this law, which is graphically represented by curve 15, and the intensity of the light fluxes from individual parts 13 and 14 along curves 1b and 17 (Fig. 2). If in this system the angle of the polarization plane of the linear polarizer is set, as shown in FIG. 2, and the luminous flux modulates over the oscillations of the polarization plane, the variable cell has a variable component with a doubled modulation frequency (curve 18, Fig. 2). If one of the light fluxes, for example 16, decreases to 16, the total intensity of the light flux will vary along curve 19, and a variable signal with a frequency of modulation will be selected on the photocell (curve 20, fig. 2). When the light flux 17 decreases to 17, the total intensity varies along curve 21, and a variable signal is extracted on the photocell with the same modulation frequency, but opposite to the phase (curve 22, fig. 2). The variable signal from the photocell 9, amplified by the amplifier 10, will force the reversing motor 11 to work and turn the compensator until the original signal phase is restored - until the light fluxes through the equalizer elements 13 and 14 are equal. Thus, the magnitude of the rotation angle of the compensator, which is necessary to restore the original phase of the signal, will determine the change in optical density, refractive index, fluorescence, or optical activity of the solution in the measuring cell.

Placing the photometric cuvette at an angle of 3K to the probing radiation allows the device to respond both to a change in optical density and to a change in the refractive index of the substance dissolved in the test solution if its refractive index differs from the solvent refractive index. In the known photometric devices, the cuvette is located at an angle of 90, with no refraction of light.

If the angle under consideration is greater than 3-5, the probing radiation will be displaced beyond the limits of the photovoltaic device or will not pass through the cell at all.

8, an element consisting of two polarization plates, the polarization planes of which are shifted relative to each other by an angle of 80 °, is used as a compensator, which ensures the maximum amplitude of the variable component of the light flux at the output of the system and, consequently, the possibility of high measurement sensitivity The angle of rotation of the test solution passing through the measuring cuvette. At angles close to 0 or 90, the variable component of the luminous flux at the exit of the system is minimal, and the ability of the device to respond to the optical activity of the monitored solution is practically reduced to zero.

The angle of rotation of the compensator can be measured with an O.OOl accuracy and higher, which provides a very high sensitivity of the proposed device and allows detecting the presence of nanogram quantities of substances in the mobile phase, and providing a response to any of the four physical parameters of the monitored environment practically guarantees from an unrecorded component pass. at the outlet of the liquid chromatographic column.

Claims (2)

1. Dale 3. et al. Liquid column chromatography. M., Mir, 1978, p. 195-217. 2. USSR author's certificate in application N 2739536 / 18-25, cl. G 01 N 21/46, 20.C3.79 (prototype).