JP5482132B2 - Differential refractometer - Google Patents

Description

  The present invention relates to a differential refractometer that measures the concentration of a solution based on a change in refractive index. In particular, the present invention is useful as a detector for liquid chromatography.

  As a substance dissolves in a solvent, the refractive index of the solvent generally changes. Therefore, in liquid chromatography, as a general-purpose detector for components eluted from a column, the difference in refractive index between a solvent (hereinafter referred to as a reference solution) and a solvent in which the component is dissolved (hereinafter referred to as a sample solution) is measured. A differential refractometer is used. As a differential refractometer, a Fresnel type differential refractometer that detects a change in reflected light intensity due to a refractive index and a deflection type (also referred to as a Bryce type) differential refractometer that detects a change in refraction angle are known. .

  In a normally used deflection type differential refractometer, parallel light generated from a light source is introduced into a flow cell, and the traveling direction of the parallel light is deflected according to the refractive index of the reference liquid and sample liquid passing through the flow cell. The degree of deflection is detected by a position detection light sensor. The flow cell is provided with a flow path having two right-angled triangular sections partitioned by a swash plate inclined with respect to the light traveling direction (optical axis) inside a transparent body such as quartz glass, and the two flow paths The parallel light is transmitted through the sample liquid and the reference liquid respectively. From the magnitude of the change in angle (deflection) in the traveling direction of the transmitted parallel light, the sample concentration in the sample solution that causes the difference in refractive index can be obtained. The deflection-type differential refractometer includes a single-pass method (for example, FIG. 21 of Patent Document 1) that transmits once, and a double-pass method that transmits twice (for example, Patent Document 2), depending on how parallel light is transmitted to the flow cell. Fig. 5).

  In general, in order to obtain a good sensitivity or S / N ratio for an optical analyzer having a light source unit, a measurement cell, and a light receiving unit, the light source unit sends a sufficient amount of light for measurement through the measurement cell. It is necessary to supply the light receiving unit. For example, in the differential refractive index detection device disclosed in Patent Document 2, a light emitting diode having a light emission output inferior to that of a tungsten lamp is used as a light source. However, a condensing lens is interposed between the light source and the aperture. After increasing the amount of light, a configuration is disclosed in which parallel light is transmitted to the flow cell through a collimator lens.

  In order to improve the measurement sensitivity of the differential refractometer, as another method for more efficiently guiding the parallel light generated from the light source unit to the light receiving unit, an aperture opening provided between the light source unit and the flow cell is provided. It is conceivable to expand in a direction orthogonal to the direction of deflection of parallel light due to refraction. When the aperture opening is enlarged in the direction perpendicular to the deflection direction, the irradiation position imaged on the light receiving element surface in the light receiving section increases, but the irradiation position is received as long as the size of the light receiving element is limited. When the element protrudes, the parallel light of the protruding part is wasted. FIG. 1A shows a standard irradiation position 13 when the position detection light sensor 10 in the deflection type differential refractometer is irradiated with parallel light transmitted through the flow cell. When the aperture is expanded in the direction orthogonal to the deflection direction from the state of FIG. 1A, the light receiving element 11 in the position detection light sensor 10 protrudes when the irradiation position 13 expands to the position shown in FIG. Minute parallel light is wasted. Further, it is economically disadvantageous to enlarge the light receiving element to the irradiation position.

  When the irradiation position 13 is expanded to the position shown in FIG. 1B, as a method for accommodating the irradiation position 13 in the light receiving element 11, there is a method of allowing the parallel light that has passed through the aperture to pass through a spherical lens and converge. The irradiation position 13 converged using the above method is schematically shown in FIG. The method is a method of converging while maintaining the aspect ratio of the irradiation position constant. Therefore, when the split photodiode shown in FIG. 1 is used as the position detection light sensor 10, the irradiation position is converged also on the side of the parallel light deflection direction. The ratio of the gap 12 between elements becomes relatively large. That is, the amount of light applied to the light receiving element 11 is reduced, which contributes to a decrease in sensitivity (S / N ratio). Further, if the length of the irradiation position 13 on the deflection direction side of the parallel light is shortened from about 2 to about 3 times the length of the gap 12 between the light receiving elements, it becomes difficult to uniformly enter the light into the two light receiving elements 11. In addition, since it is difficult for light to enter one of the light receiving elements 11, there is a problem that the measurement range becomes narrow. Furthermore, when the aperture is expanded in the direction of deflection of the parallel light, there is a problem that the parallel light may protrude from the effective introduction region of the flow cell, and the measurement range in which the position of the irradiation position 13 imaged on the light receiving element 11 can be detected becomes narrow. It was.

Japanese Examined Patent Publication No. 7-018791 Japanese Patent Publication No. 6-017870

  The present invention provides a differential refractometer that efficiently guides parallel light to a light receiving element and has sufficient measurement sensitivity and measurement range even when a position detection light sensor having a light receiving element of a limited size is used. The purpose is to provide.

  The present inventor has a convergence effect in a direction perpendicular to the deflection direction of the irradiation position in the deflection type differential refractometer when a large amount of light emission output of the light source is collected by the aperture expanded in the direction perpendicular to the deflection direction. By using a cylindrical lens, it has been found that a differential refractometer having a sufficient measurement range can be obtained without impairing measurement sensitivity even if a position detection optical sensor having a light receiving element of a limited size is used. The present invention has been completed.

That is, the first invention is
A light source that generates substantially parallel light;
Aperture,
A flow cell having two hollow portions for allowing a reference solution and a sample solution to pass through, the interior of which is partitioned by a swash plate inclined with respect to the optical axis of parallel light;
A position detection light sensor for detecting the deflection of the parallel light transmitted through the flow cell;
A calculation unit for calculating a refractive index from an output signal of the position detection light sensor;
In a differential refractometer with
Differential refraction, further comprising a cylindrical lens that can converge the irradiation position of parallel light in the position detection light sensor in a direction perpendicular to the deflection direction, between the aperture and the flow cell, or between the flow cell and the position detection light sensor It is a rate meter.

  Moreover, 2nd invention is a differential refractometer as described in 1st invention by which the light source part, the flow cell, and the position detection optical sensor are arrange | positioned in the said order substantially linearly.

In addition, the third invention,
A mirror for reflecting the parallel light transmitted through the flow cell and transmitting the parallel light through the flow cell again;
The differential refractometer according to the first aspect, wherein the position detection light sensor is a sensor that detects the deflection of the parallel light that has again passed through the flow cell.

  Hereinafter, the present invention will be described in detail.

  The differential refractometer of the present invention has an irradiation position 13 shown in FIG. 1B obtained by enlarging the aperture in a direction orthogonal to the direction of deflection of parallel light, in the light receiving element 11 in the position detection light sensor 10. In order to accommodate the above, a cylindrical lens is provided between the aperture and the flow cell, or between the flow cell and the position detection light sensor. To converge the irradiation position 13, there is a method using a normal spherical lens. However, the above method also collects the parallel light deflection direction side of the irradiation position 13 that does not need to be converged. When the split type photodiode shown in FIG. 1 is used as the position detection light sensor 10, when the irradiation position 13 converges in the polarization direction of the parallel light, the ratio of the gap 12 between the light receiving elements of the photodiode relative to the irradiation position 13 is relatively. Therefore, the sensitivity is lowered and the measurement range is reduced (see FIG. 1C). If a cylindrical lens is used, the irradiation position 13 converges only in the direction orthogonal to the deflection direction, so that the influence of the gap 12 between the light receiving elements can be suppressed. The irradiation position 13 obtained by providing the cylindrical lens is schematically shown in FIG. Since the cylindrical lens in the differential refractometer of the present invention is provided so as to exhibit a convergence effect in a direction orthogonal to the deflection direction of the irradiation position 13, the area of the irradiation position 13 obtained is the irradiation position 13 in FIG. The amount of light is the same as the irradiation position 13 in FIG. 1B in which the aperture is enlarged in the direction orthogonal to the deflection direction. Further, since the converging effect by the cylindrical lens does not reach the deflection direction of the parallel light at the irradiation position 13, the influence of the gap 12 between the light receiving elements does not become relatively large, and is sufficient without adversely affecting the measurement range. Measurement sensitivity can be obtained.

As one aspect of the differential refractometer of the present invention,
A light source that generates substantially parallel light;
Aperture,
A flow cell having two hollow portions for allowing a reference solution and a sample solution to pass through, the interior of which is partitioned by a swash plate inclined with respect to the optical axis of parallel light;
A position detection light sensor for detecting the deflection of the parallel light transmitted through the flow cell;
Are arranged in a straight line in the order, so-called single-pass differential refractometer,
A differential refractometer further comprising a cylindrical lens capable of converging the irradiation position of parallel light in the position detection light sensor in a direction orthogonal to the deflection direction, or between the aperture and the flow cell or between the flow cell and the position detection light sensor. Can be given. The above-described aspect has an advantage that the number of parts of the optical system is small and the position and angle of each component are relatively easy to adjust.

As another aspect of the differential refractive index of the present invention,
A light source that generates substantially parallel light;
Aperture,
A flow cell having two hollow portions for allowing a reference solution and a sample solution to pass through, the interior of which is partitioned by a swash plate inclined with respect to the optical axis of parallel light;
A mirror for reflecting the parallel light transmitted through the flow cell and transmitting the parallel light again to the flow cell;
A position detection light sensor for detecting the deflection of the parallel light transmitted through the flow cell again (transmitted twice through the flow cell);
A so-called double-pass differential refractometer comprising a cylindrical lens capable of converging the irradiation position of the parallel light transmitted through the flow cell in the position detection light sensor in a direction perpendicular to the deflection direction, or between the aperture and the flow cell. There is a differential refractometer further provided between the flow cell and the position detection optical sensor. In the above aspect, since parallel light reciprocates in the flow cell, there is an advantage that the angle change of the parallel light due to the change in refractive index is doubled and the sensitivity is improved.

  The cylindrical lens used in the differential refractometer of the present invention may be any lens having a cylindrical surface that has an effect of converging parallel light in at least one direction, that is, a direction orthogonal to the deflection direction of the irradiation position. Examples of cylindrical lenses include cylindrical lenses that have a cylindrical shape, planoconvex cylindrical lenses that have a vertically divided cylindrical shape (cylindrical shape), and cylindrical lenses that have a shape in which the side surfaces of the cylinder are hollowed out in a circular shape. it can. In addition, even with a lens having a toric surface that has different refractive power in the direction in which the parallel light is deflected and in the direction perpendicular to the direction of deflection, the refractive power in the direction in which the parallel light is deflected adversely affects the measurement sensitivity and measurement range. If it does not reach, it can be used as a cylindrical lens in the differential refractometer of the present invention.

In the differential refractometer of the present invention, the light source section needs to generate substantially parallel light. When using a laser light source with good directivity, it may be left as it is, but when using a point light source, it is necessary to convert light emitted from the point light source into parallel light. The following method can be illustrated as a conversion method to parallel light.
(1) A method using a lamp with lens or a light emitting diode with lens.
(2) A method of combining a light source with high brightness and a properly selected lens.
(3) A method of installing the flow cell at a position sufficiently away from the light source.

  Among these, as the conversion method to parallel light in the differential refractometer of the present invention, the method (2) that can obtain high-quality parallel light is most preferable. Examples of the light source used in the method (2) include a tungsten lamp, a halogen-enclosed tungsten lamp, and a light emitting diode. Since the differential refractometer of the present invention can use an aperture that is enlarged in a direction orthogonal to the direction of parallel light deflection, the position detection light sensor can be irradiated with more parallel light from the light source unit. . Therefore, when the light emitting diode having a relatively small light emission output is applied as the light source, the effect of the present invention is particularly exerted. The diameter of the lens used in the method (2) may be appropriately selected so that the effective diameter of the lens includes the transmission part of the aperture. In order to effectively use the light emitted from the light source, it is preferable that the distance between the lens and the light source be as close as possible to widen the effective solid angle. In addition to the spherical lens, the lens used in the method (2) may be an aspherical lens for suppressing spherical aberration or a bonded lens represented by an achromatic lens. Note that the parallel light emitted from the light source unit in the present invention may be substantially parallel light, and may be light that converges slightly with respect to the parallel light or light that diverges slightly. The light intensity distribution in the parallel light section may be substantially uniform with respect to the width direction of the reference liquid channel and the sample liquid channel in the flow cell and the deflection direction of the light transmitted through the flow cell. In order to improve the uniformity of the light intensity distribution, a beam conversion lens or a filter having an absorption characteristic showing a spatial distribution opposite to the intensity distribution of parallel light may be used.

  As an embodiment of the flow cell used in the differential refractometer of the present invention, a flow cell having a pair of hollow portions (liquid channels having a right triangle cross section) for allowing a sample solution and a reference solution to pass through can be mentioned. The material of the flow cell may be appropriately selected in consideration of light transmittance and liquid corrosion resistance. In many cases, transparent quartz glass is used. Further, all or a part other than the part through which light passes may be made of an opaque material such as black quartz glass. Another aspect of the flow cell is a flow cell in which the cross-sectional area of the hollow part through which the sample liquid flows is smaller than the cross-sectional area of the hollow part through which the reference liquid flows in order to prevent the target component dissolved in the sample liquid from spreading.

  As a position detection optical sensor used in the differential refractometer of the present invention, in addition to the photodiode in which the light receiving element shown in FIG. Sensors such as photodiodes, one-dimensional CCD sensors, and one-dimensional CMOS sensors can be used. Furthermore, sensors such as a two-dimensional CCD sensor and a two-dimensional CMOS sensor can also be used as the position detection light sensor in the present invention.

  The parallel light detected by the position detection sensor is obtained by converting the photocurrent generated in each light receiving element into a voltage signal using a current-voltage conversion circuit or the like and then using a difference circuit if there is no change in the light emission amount of the light source. The differential refractive index signal can be obtained as an output. Further, a differential refractive index signal can be obtained as an output by obtaining a difference signal and a sum signal of two elements using a difference circuit and a sum circuit, and further dividing the difference signal by the sum signal using a division circuit. When obtaining the differential refractive index signal, a filter circuit can be appropriately used to suppress the noise signal. In order to reduce noise and drift, it is preferable to use a high-precision operational amplifier with a small offset current and bias current for the current-voltage conversion circuit. Also, instead of using an analog arithmetic circuit, the voltage signal obtained from each light receiving surface is converted to a digital value by an AD converter such as a ΔΣ AD converter, and a division operation is performed by the digital circuit to obtain a differential refractive index. A signal can be obtained. An anti-alias filter circuit can be appropriately inserted in front of the AD converter. Further, after conversion to a digital value, a digital filter may be applied.

  Hereinafter, specific embodiments of the differential refractometer of the present invention will be described with reference to FIGS.

FIG.
A light source unit configured to generate substantially parallel light including the light source 20 and the spherical lens 30;
Aperture 40,
A flow cell 50 having two hollow parts for allowing the reference liquid and the sample liquid to pass through, the interior of which is partitioned by a swash plate inclined with respect to the optical axis of the parallel light;
A position detection light sensor 10 for detecting the deflection of the parallel light transmitted through the flow cell;
Shows a mode in which a cylindrical lens 60 is provided between the position detection optical sensor 10 and the flow cell 50 in a single-pass differential refractometer arranged in a straight line in this order. The light emitted by the light source 20 generates square light by a spherical lens 30 provided immediately thereafter, and then passes through an aperture 40 expanded in a direction orthogonal to the deflection direction. After passing through the aperture, the parallel light passes through the flow cell 50, is converged in a direction orthogonal to the deflection direction by the cylindrical lens 60, and irradiates the position detection light sensor 10. FIG. 3 shows a mode in which the cylindrical lens 60 is provided on the aperture 40 side of the flow cell 50 in FIG. 2.

FIG.
A light source unit configured to generate substantially parallel light including the light source 20 and the spherical lens 30;
Aperture 40,
A flow cell 50 having two hollow parts for allowing the reference liquid and the sample liquid to pass through, the interior of which is partitioned by a swash plate inclined with respect to the optical axis of the parallel light;
A mirror 70 for reflecting the parallel light transmitted through the flow cell 50 and transmitting the parallel light through the flow cell 50 again;
A position detection light sensor 10 for detecting the deflection of parallel light that has passed through the flow cell 50 again (passed through the flow cell 50 twice);
In the so-called double-pass differential refractometer including the above, a mode in which a cylindrical lens 60 is provided between the position detection optical sensor 10 and the flow cell 50 is shown. The light emitted by the light source 20 passes through the spherical lens 30 after passing through the aperture 40 expanded in the direction orthogonal to the deflection direction, thereby generating approximately square light. The parallel light that has passed through the spherical lens 30 passes through the flow cell 50, is reflected by the mirror 70, and passes through the flow cell 50 and the spherical lens 30 again. The parallel light that has passed through the spherical lens 30 passes through the cylindrical lens 60, and further converges in a direction orthogonal to the deflection direction, and is then applied to the position detection light sensor 10. FIG. 5 shows a mode in which the spherical lens 30 is provided immediately after the light source 20 and the cylindrical lens 60 is provided on the aperture 40 side of the flow cell 50 in FIG. 4.

  The differential refractometer of the present invention converges parallel light that has passed through an aperture expanded in a direction orthogonal to the deflection direction in a direction orthogonal to the deflection direction by a cylindrical lens, and passes through the flow cell to the position detection light sensor. Is irradiated. Therefore, when a light receiving element of the same size as the conventional one is used, more light quantity can be irradiated to the light receiving element of the position detection light sensor without adversely affecting the measurement range, and the light source with relatively little light quantity Even so, it is possible to provide a differential refractometer with high measurement sensitivity. On the other hand, when a light source with a sufficient amount of light is used, a differential refractometer can be manufactured at a lower cost because a position detection optical sensor composed of a light receiving element smaller than the conventional one can be used.

It is the figure explaining the irradiation position 13 to the position detection optical sensor 10 in the differential refractometer of this invention compared with the prior art. FIG. 5 is a configuration diagram (side view) showing an aspect of the differential refractometer of the present invention (an aspect in which a cylindrical lens 60 is provided between the flow cell 50 and the position detection optical sensor 10 in the single-pass differential refractometer). is there. It is the block diagram (side view) which showed another aspect (The aspect which provided the cylindrical lens 60 between the aperture 40 and the flow cell 50 in the single-pass-type differential refractometer in the differential refractometer of this invention. FIG. 6 is a configuration diagram (side view) showing another aspect of the differential refractometer of the present invention (an aspect in which a cylindrical lens 60 is provided between the flow cell 50 and the position detection optical sensor 10 in the double-pass differential refractometer). is there. It is the block diagram (side view) which showed another aspect (The aspect which provided the cylindrical lens 60 between the aperture 40 and the flow cell 50 in the double pass system differential refractometer) of the differential refractometer of this invention. In Example 1, it is a figure showing the comparison of the signal base line of the single pass system differential refractometer (with a cylindrical lens) of this invention and the conventional single pass system differential refractometer which does not use a cylindrical lens.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to an Example.

Example 1
A single-pass differential refractometer provided with a cylindrical lens 60 between the flow cell 50 and the position detection optical sensor 10 shown in FIG. 2 and a conventional differential refractometer excluding the cylindrical lens 60 from FIG. 2 are used. The signal baselines were compared. The measurement conditions are shown below.

Measurement condition:
Eluent / sample liquid: both pure water Flow rate: 0.2 ml / min on both sample liquid side / reference liquid side Column: dia. 0.1 × 2m × 2 in series on both sample liquid side / reference liquid side Pump / column / detection Set temperature: 40 ℃
Indoor set temperature: 25 ° C
FIG. 6 shows a chromatogram showing the signal baseline change for 1 minute when each differential refractometer is used. The horizontal axis represents time [minutes], and the vertical axis represents refractive index units [RIU]. Note that the absolute value of the vertical axis is shifted so that a clear comparison can be made (the absolute value of the output signal is meaningless and the amplitude of the signal is a significant value). The differential refractometer of the present invention further provided with a cylindrical lens has reduced noise as compared with the conventional differential refractometer, and can be detected with higher sensitivity than the conventional differential refractometer. confirmed.

DESCRIPTION OF SYMBOLS 10: Position detection light sensor 11: Light receiving element 12: Gap between light receiving elements 13: Irradiation position 20: Light source 30: Spherical lens 40: Aperture 50: Flow cell 60: Cylindrical lens 70: Mirror

Claims (3)

A light source section that generates parallel light , an aperture, and a flow cell that is partitioned by a swash plate whose interior is inclined with respect to the optical axis of the parallel light, and has two hollow parts for allowing the reference liquid and the sample liquid to pass through; a position detecting optical sensor having a light receiving element for detecting the deflection of the collimated light transmitted through the flow cell, in a differential refractive index meter and a calculator for calculating the refractive index from the output signal of the position detection light sensor, the aperture Is expanded in a direction perpendicular to the direction of deflection of the parallel light so that the irradiation position protrudes from the light receiving element with respect to the light receiving element in the position detection light sensor.
A cylindrical lens that can be converged in a direction orthogonal to the deflection direction so that the irradiation position of the parallel light in the position detection light sensor is within the light receiving element is disposed between the aperture and the flow cell, or between the flow cell and the position detection light sensor. A differential refractometer further provided. The differential refractometer according to claim 1, wherein the light source unit, the flow cell, and the position detection light sensor are arranged in a straight line in the order. The mirror for reflecting the parallel light which permeate | transmitted the flow cell, and permeate | transmitting a parallel light again to a flow cell is further provided, and a position detection light sensor is a sensor which detects the deflection | deviation of the parallel light which permeate | transmitted the flow cell again. Differential refractometer.

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