JPH06308024A - Measuring apparatus for liquid sample - Google Patents

Abstract

PURPOSE:To provide a highly sensitive and high stable flow cell sensor for liquid chromatograph. CONSTITUTION:In a flow cell part having a reference hole 11 in the vicinity of a sample flow hole 10, wall surfaces in the holes of the sample flow hole 10 and the reference hole 11 are optically polished and cross section diameters of the holes are made equal. A sample light sensor 7 and a reference light sensor 8 for detecting light are placed behind the sample through hole 10 and the reference hole 11, respectively. Response speed of the reference light sensor system circuit is slower than that of the sample light sensor system. Therefore a liquid chromatograph flow cell sensor system which is stable for a long time, without loss in detected light with electric noise reduced is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a measuring device for a fluid sample, and more particularly to a measuring device for optically measuring a liquid whose composition is changing, such as a liquid chromatograph, by flowing it through a flow cell section.

[0002]

2. Description of the Related Art Many conventional liquid chromatograph detectors use a photometer, and such a photometer is provided with a flow cell for guiding the liquid flowing out from a separation column.

Since the light source of an ordinary photometer is not a point light source,
Even if the irradiation light to the flow cell is made into a state close to a parallel light flux by the optical system, it is inevitable that the light flux spreads.
Since the liquid whose composition is changing flows into the flow cell of the liquid chromatograph from the separation column, the irradiation light beam inevitably passes through the part of the component region having a different refractive index, and at this time, the difference in the refractive index is caused. The direction of the light beam is bent in the sample passage hole of the flow cell due to the lens effect based on it.
The irradiation light flux is scattered and absorbed by the inner wall surface of the sample flow hole by the change of the light beam direction. U.S. Pat. No. 4,276,475 takes up this problem and reduces the light absorption by the inner wall surface by making both the sample flow hole and the reference hole of the flow cell into a conical shape that spreads in the traveling direction of the light flux. .

On the other hand, US Pat. No. 4,468,124 discloses a method of reducing shot noise by providing a reference hole having a diameter larger than this hole in the vicinity of a sample flow hole of a flow cell and taking in as much light as possible into the reference hole. Is proposed.

Further, US Pat. No. 4,823,168 discloses forming a light-reflecting layer on the point where two half body members are joined and integrated to form a single flow cell and on the groove formed in each half body. This indicates that the volume of the cell chamber is reduced.

[0006]

Problems to be Solved by the Invention US Pat. No. 4,276,475
In No. 6, the cell body, which is the base material, is only provided with a substantially conical hole, so it is not possible to sufficiently deal with the divergence of light due to the lens effect due to the difference in the refractive index in the flowing liquid, and the cell chamber (hole) The light absorption by the inner wall of the is inevitable. In addition, the cell chamber having such a shape has a large volume.

With the configuration of US Pat. No. 4,468,124, it is difficult to stably measure a liquid sample flowing through the cell chamber (sample passage hole) for a long time. The reason is that the optical axis position changes with time with respect to the sample flow hole and the reference hole.
Also, U.S. Pat. No. 4,823,168 only shows a single cell chamber and does not consider relating the transmitted light obtained through each of the sample flow hole and the reference hole.

An object of the present invention is to change the ratio of the detected sample light signal and the reference light signal even if the position of the optical axis of the irradiation light passing through the sample flow hole and the reference hole of the flow cell portion changes with time. An object of the present invention is to provide a measuring device for a fluid sample, which enables high-accuracy measurement without any need. Another object of the present invention is to be able to follow a state change accompanying the movement of the liquid that is changing the composition flowing in the sample flow hole of the flow cell portion,
An object of the present invention is to provide a fluid sample measuring device capable of reducing noise during measurement.

[0009]

SUMMARY OF THE INVENTION The present invention provides a fluid sample which has a flow cell portion having a sample flow hole and a reference hole, and a fluid sample is passed through the sample flow hole to optically measure the sample. In the measuring device, both the sample flow hole and the reference hole of the flow cell part are formed so as to have a columnar shape having the same hole cross-sectional area, and the inner surfaces of the sample flow hole and the reference hole are mirror-finished, and the transmitted light of the sample flow hole It is characterized in that means for comparing the detection signal with the transmitted light detection signal of the reference hole is provided.

Further, according to the present invention, both the sample flow hole and the reference hole of the flow cell portion are formed so as to have a columnar shape having the same hole cross-sectional area, and the light for detecting the transmitted light of each of the sample flow hole and the reference hole is detected. Connect the preamplifiers to the detectors in correspondence with each other, and provide a reference preamplifier with a time constant larger than that of the sample preamplifier, and output the sample preamplifier and the reference preamplifier. It is characterized in that means for comparing the outputs of the on-amplifiers is provided.

[0011]

In the present invention, since the inner surfaces of both the sample flow hole and the reference hole of the flow cell section are mirror-finished, the conditions of reflection of the irradiation light beam in both holes can be made substantially the same. The light reflected on the inner surface is detected by the photodetector arranged corresponding to each hole. The mirror-like state eliminates the presence of many irregularities on the wall surface. The sample passage hole and the reference hole of the flow cell section are made to have substantially the same size. In particular, both holes have the same cross-sectional area and both holes are columnar. When these holes are cylindrical, the effective diameters are made substantially equal.
As a result, even if the optical axis fluctuates little by little over a long period of time, a stable output can be obtained by taking a ratio in order to compare the two transmitted light signals.

In the light absorption type detector, qualitative and quantitative analysis of the sample is attempted by the light absorption of the sample flowing through the sample flow hole, and the reference light passing through the reference hole is detected as the reference light of zero absorption. It is a thing. In this sense, the detection of the sample light passing through the sample flow hole must respond quickly to the flow of the sample flowing through the hole, but the reference light is much less time-varying than the sample light. It's slow. Paying attention to this, the sample-side time constant setting capacitor that determines the time constant of the sample-side preamplifier has a capacity that can follow the flow of the sample. On the other hand, the capacitance of the reference-side time constant setting capacitor that determines the time constant of the reference-side preamplifier is made larger than that of the sample-side time constant setting capacitor to reduce random noise.

[0013]

FIG. 2 is a schematic configuration diagram of a liquid chromatograph apparatus as an embodiment of the present invention. In FIG. 2, the eluent in the eluent tank 61 is sent by the pump 63 through the flow path 62 toward the separation column 65 at a constant flow rate. The mixture sample liquid containing the test component is introduced into the flow channel system from the sample introducing unit 64, is separated into each component in the separation column 65, and each component region is separated with the passage of time and flows out from the separation column 65, It is supplied to the flow cell section. The flow cell part is formed by forming a sample flow hole 10 and a reference hole in the flow cell block 5, and the effluent from the separation column 65 is introduced into the sample flow hole 10 via the cell inlet 51 and discharged from the cell outlet 52. To be done. Sample is sample flow hole 1
The signal obtained by the photodetector 7 when passing through 0 is processed by the signal processing circuit 30, and the chromatogram and the concentration of each component are displayed on the display device 37.

The optical system of the measuring device will be described with reference to FIGS. A spectroscope 40 is arranged adjacent to the flow cell block 5. The light from the light source 1 is condensed by the condenser mirror 2 on the pair of entrance slits 3 of the spectroscope 40.
The light from the entrance slit 3 is split by the concave diffraction grating 4 whose rotation angle can be changed, and the monochromatic light is extracted from the pair of exit slits 41 of the spectroscope 4 and irradiated on the sample flow hole 10 and the reference hole 11 of the flow cell block 5. To be done. Behind the flow cell block 5, a sample light detector 7 corresponding to the sample light passing through the sample flow hole 10 and a reference light detector 8 corresponding to the reference light passing through the reference hole 11 are arranged. The sample flow hole 10 is connected to the separation column 65 of the liquid chromatograph, but the reference hole 11 is not connected to the flow channel system of the liquid chromatograph.

A fluid such as a buffer solution, water, or air having the same composition as the eluent is enclosed in the reference hole 11, and this fluid does not flow in the reference hole. The sample light signal detected by the detector 7 is compared with the reference light signal detected by the detector 8 in the signal processing circuit 30. The reference light passing through the reference hole 11 has a reference light amount with respect to the sample light. Details of the signal processing circuit 30 will be described later.

A schematic cross-sectional view of the flow cell block 5 is shown in FIG. The flow cell block 5 has a sample flow hole 10 and a reference hole 11 through which the sample flows, and a sample light detector 7 and a reference light detector 8 are arranged after that. The inner surfaces of the sample flow hole 10 and the reference hole 11 are polished into an optical mirror surface. The sample light 12 and the reference light 13 are imaged as convergent light beams on the front surface of the flow cell block 5 corresponding to the exit slit 41. The hole 10 and the hole 11 are long in the depth direction with respect to the hole diameter, and the sample light 12 and the reference light 13 projected therein collide with the inner wall surface of the hole. Since the inner wall surface of each hole is polished to an optical mirror surface, the light hitting the inner wall surface is specularly reflected and advances. This is also effectively exhibited when there is a lens action caused by the difference in the refractive index of the sample whose composition flowing through the sample flow hole 10 is changing. That is, it is assumed that the light beam when the lens action occurs in the fluid is greatly bent, but in this embodiment, since the inner wall surface of the hole is polished to the optical mirror surface, it is incident at any angle. The light that strikes the wall surface is also totally reflected and is effectively captured by the photodetector. Due to this effect, it is possible to obtain a highly sensitive flow cell for a liquid chromatograph without scattering absorption by the wall surface.

Next, the optimum hole diameters of the sample flow hole 10 and the reference hole 11 will be considered with reference to FIG. Sample flow hole 10
The hole cross-section radius of the reference hole 11 is a, and the hole cross-section radius of the reference hole 11 is b. It is assumed that the sample light 12 and the reference light 13 are each shifted by a fixed amount Δt due to time drift. The light initially overlapped with the sample flow hole 10 having the radius a and the light originally overlapped with the reference hole 11 having the radius b are deviated by Δt. At this time, the ratio of the shifted light rays being taken into the sample flow hole 10 and the reference hole 11 is that the sample light 14 after the movement and the reference light 15 after the movement and the common portion of the sample flow hole 10 and the reference hole 11 are It is proportional to the areas Sa (Equation 1) and Sb (Equation 2) shown by hatching in FIG.
The amount taken out as the final chromatographic signal is shown by (Equation 3).

[0018]

[Equation 1]

[0019]

[Equation 2]

[0020]

[Equation 3]

In (Equation 3), Ia is the light intensity of the sample light 12, and Ib is the light intensity of the reference light 13. K _{A / Z} is a lift correction coefficient of the zero point which is usually called an auto-zero correction term. When starting measurement, microscopic Ia and I
In order to correct the shift of zero due to the difference in b, the device side is informed that the current value is set to zero, and the floating amount from zero at that time is subtracted as the K _{A / Z} term. This corrects the zero deviation at the start. With such a function, I
It is easy to think that a and Ib do not have to be equal. However, changing the hole diameter in this manner adversely affects the temporal stability of the device.

This will be described with reference to FIG. 5 and Table 1. Ia and Ib in (Equation 3) are Sa,
Since each is proportional to Sb, (Equation 1) and (Equation 2)
Substituting into (Equation 3), (Equation 3) can be written in the form of (Equation 4).

[0023]

[Equation 4]

[0024]

[Table 1]

In (Equation 4), assuming that a is 1 as a unit unit, b is 1.41 (this corresponds to a ratio of the quantity of light of the sample light Ia to the quantity of the reference light Ib taken in by 1: 2), and Δt is set.
Absorbance signal Abs when changing from 0.0 to 1.0
Table 1 shows a calculation of whether (Equation 4) changes like
Is. The amount of change in luminous flux Δt is changed from 0 to 1 in steps of 0.1. The calculated absorbance signal Abs at this time is the uncorrected absorbance. The absorbance signal Abs is the auto-zero-corrected absorbance when the initial value Δt = 0 for the uncorrected absorbance is corrected by the auto-zero function. As you can see from the auto-zero corrected absorbance column,
It can be seen that the value of the auto-zero-corrected absorbance also changes with the change in the light flux change amount (Δt). It can be seen that when Δt = 1, the auto-zero-corrected absorbance is 0.156, which is a large shift from the zero value. In the usual measurement of the absorbance around 1, this is an error of several tens of percent.
Such an error is caused by making the hole cross-section radius a of the sample flow hole 10 and the hole cross-section radius b of the reference hole 11 different. That is, if a = b in (Equation 1) and (Equation 2), Sa = Sb, Sa / Sb = 1, and the Log of (Equation 4) becomes
The term of (Sa / Sb) becomes 0, and the influence of Δt disappears.
Based on the results of the above consideration, the hole cross-section radius a of the sample flow hole 10 and the hole cross-section radius b of the reference hole 11 were made equal to each other, so that a stable flow cell for a liquid chromatograph was obtained for a long time.

Next, the signal processing circuit 30 will be described with reference to FIG. The sample light 12 is detected by the photoelectric detector 7, and the reference light 13 is detected by the photoelectric detector 8. The output signal of the sample light detector 7 is input to the sample side preamplifier 31, and the output signal of the reference light detector 8 is the reference side preamplifier 32.
Entered in. The output of the amplifier 31 and the output of the amplifier 32 are input to the logarithmic conversion amplifier 35, respectively, and then compared in the zero corrector 36, and the corrected signal is taken out from the output terminal 39. The time constants of the sample side preamplifier 31 and the reference side preamplifier 32 are different. The magnitude of the time constant of the reference side preamplifier 32 is 2 to the time constant of the sample side preamplifier 31.
It is set to 5 times. The time constant of the sample side preamplifier 31 is
The accumulation time is preferably around 0.5 seconds. The time constant of the sample side preamplifier 31 is determined by the capacity of the time constant setting capacitor 33, and the time constant of the reference side preamplifier 32 is determined by the capacity of the time constant setting capacitor 34.
Is larger than that of the capacitor 33.

The detector circuit system on the sample light side for detecting the absorption information of the sample in the multi-beam photometric type for liquid chromatograph which measures the light intensity of the sample light 12 with reference light 13 as a reference is the time of the absorption information of the sample. It is necessary to follow the change promptly according to the change, but it is sufficient for the reference light side to follow the fluctuation of the total light amount caused by the fluctuation of the light source, the thermal distortion of the device, or the like. That is, the time constant of the reference side preamplifier 32 can be made larger than that of the sample side preamplifier 31 to reduce the total noise.

[0028]

According to the present invention, it is possible to obtain a multi-beam photometric system which is stable against long-term drift caused by fluctuations in a light source or thermal distortion. Further, it is possible to reduce noise in the detector system without delaying the signal change based on the sample light.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a signal processing circuit according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of a liquid chromatograph as one embodiment of the present invention.

FIG. 3 is a diagram for explaining an optical system in the embodiment of FIG.

FIG. 4 is a diagram showing a flow cell unit in the embodiment of FIG.

FIG. 5 is a diagram for explaining the relationship between a sample flow hole and a reference hole.

[Explanation of symbols]

5 ... Flow cell block, 7 ... Sample light detector, 8 ... Reference light detector, 10 ... Sample passage hole, 11 ... Reference hole, 12 ... Sample light, 13 ... Reference light, 30 ... Signal processing circuit, 31, 32
... Preamplifier, 33, 34 ... Time constant setting capacitor, 3
6 ... Zero corrector, 40 ... Spectrometer, 65 ... Separation column.

Claims (5)

[Claims] 1. A fluid sample measuring device having a flow cell portion having a sample flow hole and a reference hole, wherein a fluid sample is passed through the sample flow hole to optically measure the sample. And both of the reference holes are formed in a columnar shape having the same hole cross-sectional area, and the inner surfaces of the sample flow hole and the reference hole are mirror-finished, and the transmitted light detection signal of the sample flow hole and the reference hole A device for measuring a fluid sample, characterized in that means for comparing transmitted light detection signals of the above is provided. 2. The device for measuring a fluid sample according to claim 1, wherein the light entrance window of the sample flow hole and the light entrance window of the reference hole are formed of the same member. 3. A fluid sample measuring device having a flow cell portion having a sample flow hole and a reference hole, wherein a fluid sample is passed through the sample flow hole to optically measure the sample. And both of the reference holes are formed in a columnar shape having the same hole cross-sectional area, and a preamplifier is connected to each of the photodetector sections for detecting the transmitted light of the sample flow hole and the reference hole. A reference preamplifier having a time constant larger than that of the sample preamplifier is provided, and means for comparing the output of the sample preamplifier with the output of the reference preamplifier is provided. A device for measuring a fluid sample, characterized in that 4. The apparatus for measuring a fluid sample according to claim 3, wherein the inner surfaces of the sample flow hole and the reference hole are mirror-finished. 5. A device for measuring a fluid sample according to claim 3, wherein the sample preamplifier and the reference preamplifier each have a time constant setting capacitor.