JP3572681B2 - Multi-channel spectrophotometer - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a spectrophotometer used as a general-purpose spectrophotometer or as a liquid chromatograph detector, and more particularly to a multi-channel spectrophotometer having a photodiode array as a detector.
[0002]
[Prior art]
FIG. 5 shows a basic configuration of a conventional multi-channel spectrophotometer having a photodiode array.
In FIG. 5, 1 is a light source, 2 is a condenser lens that collects light from the light source 1 and guides the light to the sample cell, 3 is a shutter, 4 is a sample cell, 5 is an entrance slit of a spectroscope, and 6 is a spectroscope entrance slit. A concave grating as a dispersive element, 7 is a photodiode array as a multi-channel detector provided at the exit position of the spectroscope, 10 is a signal processing / control circuit, and 11 is a memory. The concave grating 6 separates the transmitted light of the sample cell and forms an image of the slit 5 on the surface of the photodiode array 7.
[0003]
The photodiode array 7 includes, for example, 500 light receiving elements. On the surface of the photodiode array 7, 200 nm light of the spectrum of the transmitted light of the sample cell 4 is the first light receiving element, and 700 nm light is the 500th light. It is installed so as to be incident on the light receiving element and detect light of 200 to 700 nm.
[0004]
The shutter 3 is for correcting the dark current of the photodiode array 7. When performing the dark current correction, the shutter 3 is closed to create a dark state, and the drive circuit scans the photodiode array 7, and receives each light. Measure the dark current value of the device. The method of using the multi-channel spectrophotometer will be described. First, the shutter 3 is closed to create a dark state, and the dark current value of each light receiving element is measured and stored in the memory 11. Next, in order to measure the background of the absorption spectrum, the shutter 3 is opened to be in a bright state, the photodiode array 7 is scanned to measure the signal of each light receiving element, and the dark current of each light receiving element is measured from the measured value. By subtracting the value, a background spectrum is obtained and stored in the memory 11.
[0005]
Next, the sample is injected into the sample cell 4, the shutter 3 is also opened to make a bright state, and the light from the light source 1 is condensed by the condenser lens 2 and guided to the sample cell 4. Is split by the concave grating 6 through the slit 5, and an image of the slit 5 is formed on the surface of the photodiode array 7. Then, in this state, the photodiode array 7 is scanned, the signal of each light receiving element is input to the signal processing / control circuit 10, and dark current correction and background correction are performed, whereby the absorption spectrum of the sample is obtained.
[0006]
The conventional multi-channel spectrophotometer is configured as described above. The specific configuration of the photodiode array used at this time will be described in detail with reference to FIG.
[0007]
In FIG. 6, 21 is a shift register, 22 is a photodiode, 23 is a switch, and 24 is a capacitor. When light is applied to each of the photodiodes 22 in a state where the electric charge is accumulated in each capacitor 24, the electric charge accumulated in each capacitor 24 is discharged by the photoelectric effect. Then, the shift register 21 sequentially turns on the switch 23 for each cycle of the clock pulse in FIG. 6, and measures the charge amount charged in each capacitor 24 at this time. The amount of light incident on each photodiode can be known from each charge amount by repeating this measurement.
[0008]
[Problems to be solved by the invention]
The conventional multi-channel spectrophotometer is configured as described above, and a series of measurement procedures of the photodiode array is controlled by a start pulse and a clock pulse shown in FIG. A fixed value is set so that all elements do not exceed the saturation charge amount, that is, the discharge limit amount. That is, in the case of a liquid chromatograph, in order to cover a wide wavelength range, two lamps of a deuterium lamp and a tungsten lamp are used as a light source, and these lamps are simultaneously turned on. The spectrum of this light source is shown in FIG. Become like At this time, as described above, the light receiving time of each light receiving element of the photodiode array, that is, the charge accumulation time of all wavelengths is the same. However, while the charge storage type photoelectric conversion element has a finite saturation charge amount, the spectrum of the light source varies in intensity depending on the wavelength as shown in FIG. 7, so that saturation does not occur at the wavelength with the largest light quantity. Therefore, the charge accumulation time cannot be made too long, and the charge accumulation time is set by the intensity at point A in FIG. On the other hand, the main causes of the noise of the photodiode are circuit noise and reset noise, and this value is constant regardless of the magnitude of the signal. Therefore, if the charge accumulation time is set so that it does not saturate at the point of the wavelength of the highest intensity in the entire wavelength range of the light source spectrum, the signal obtained with this charge accumulation time is small at wavelengths with a small amount of light. There was a problem that it was buried in.
[0009]
This is unavoidable when measuring over the entire wavelength range, but when the measurement wavelength range is limited, for example, when measurement is performed only in the wavelength range from point B to point C in FIG. In spite of the fact that the measurement sensitivity can be improved by increasing the charge accumulation time, conventionally, there has been a problem that the charge accumulation time cannot be increased and high-sensitivity measurement cannot be performed.
[0010]
The present invention has been made in view of such circumstances, and it is an object of the present invention to provide a multi-channel spectrophotometer capable of measuring with high sensitivity while minimizing the influence of noise.
[0011]
[Means for Solving the Problems]
In order to solve the above problems, the present invention provides a light source, a sample cell to which light from the light source is guided, a spectroscope to which light transmitted through the sample cell is guided, and a photodiode array to which light separated by the spectroscope is incident. A multi-channel type spectrophotometer comprising: a measuring wavelength range designating means for designating a measuring wavelength range; a signal processing / control circuit for judging the designated measuring wavelength range and a measured charge amount; Storage time setting means for setting the charge storage time of the photodiode in accordance with a signal from the control circuit, wherein when the measurement wavelength range is determined to be a part of the entire wavelength range by the signal processing / control circuit, the measurement charge The measurement is repeated while changing the accumulation time until the charge exceeds the saturation charge of the photodiode, and when the measured charge exceeds the saturation charge, the storage corresponding to the immediately preceding measurement charge is performed. The time is set to the accumulation time setting means.
[0012]
[Action]
The spectrophotometer of the present invention is configured as described above, and by designating the measurement wavelength range by the measurement wavelength range designation means, the accumulation time setting means automatically sets the accumulation time according to the wavelength range. Since the actual measurement is performed by optimally resetting the two clocks of the photodiode array, the storage time most suitable for the measurement wavelength range can be selected. Measurement can be performed.
[0013]
【Example】
Hereinafter, an embodiment of the multi-channel spectrophotometer of the present invention will be described with reference to FIG.
In FIG. 1, 1 is a light source, 2 is a condenser lens that collects light from the light source and guides the light to the sample cell, 3 is a shutter, 4 is a sample cell, 5 is an entrance slit of a spectroscope, and 6 is dispersion of the spectroscope. A concave grating as an element, 7 is a photodiode array provided at an exit position of the spectroscope, 8 is a measurement wavelength range specifying means, 9 is an accumulation time setting means, 10 is a signal processing / control circuit, 11 is a memory, and 12 is a memory. It is a protection shutter.
[0014]
The operation of the spectrophotometer of FIG. 1 will be described with reference to the flowchart of FIG. 2 and FIGS.
First, when the measurer designates the measurement wavelength range by the measurement wavelength range designation means 8, the signal processing / control circuit 10 determines whether or not the designated measurement wavelength range is the entire range. The standard period corresponding to the accumulation time corresponding to the intensity of the point A of No. 7 is set in the accumulation time setting means 9 as a clock period.
[0015]
On the other hand, when the wavelength range is a part of the entire wavelength range, the signal processing / control circuit 10 sets the clock period as a clock cycle that is slightly longer than the standard cycle corresponding to the standard storage time in the storage time setting unit 9, Perform the measurement. That is, in a state where the sample is not put in the sample cell, the shutter 3 is opened to make the light state, and the switches 23 are sequentially turned on by the shift register 21 to charge the capacitors 24 connected in parallel to the respective photodiodes 22. Is repeatedly measured to obtain the amount of charge discharged from each capacitor 24. Next, the signal processing / control circuit 10 determines whether or not the charge amount of each photodiode has exceeded the saturated charge amount. If the measured charge amount does not exceed the saturated charge amount, the signal processing / control circuit 10 resets the storage time setting means 9 with a slightly longer cycle as the clock cycle. When the measured charge exceeds the saturated charge, the signal processing / control circuit 10 finally sets the immediately preceding clock cycle as the optimum clock cycle in the accumulation time setting means 9.
[0016]
When the setting of the clock cycle is completed, first, the signal processing / control circuit 10 closes the shutter 3 to create a dark state, measures the dark current value of each photodiode, and stores it in the memory 11. Next, the signal processing / control circuit 10 opens the shutter 3 to make it in a bright state in order to measure the background of the absorption spectrum, scans the photodiode array 7 and measures the charge amount of each photodiode. The background spectrum R (n) is obtained by subtracting the dark current value of each photodiode from the value, and is stored in the memory 11.
[0017]
Next, the sample is injected into the sample cell, and the shutter 3 is similarly opened to make a bright state. Then, the light from the light source 1 is condensed by the condensing lens 2 and guided to the sample cell 4, and the transmitted light of the sample is transmitted. Is split by the concave grating 6 through the slit 5, and an image of the slit 5 is formed on the surface of the photodiode array 7. Then, in this state, the signal processing / control circuit 10 scans the photodiode array 7 to measure the charge amount of each photodiode, and performs dark current correction only for signals in the wavelength range set from the measured values. The transmitted light signal S (n) of the sample is calculated by performing background correction, and is stored in the memory 11.
[0018]
Then, using the signal series S (n) and the signal series R (n) measured in advance when there is no sample, the absorbance spectrum A (n) of the sample is calculated as A (n) = − log ₁₀ (S (N) / R (n))
The control and signal processing circuit 10 calculates the absorbance spectrum A (n).
[0019]
The protective shutter 12 movably provided on the front surface of the photodiode array 7 is moved according to the set wavelength range so as to cover photodiodes outside the range. At this time, as shown in FIG. 3, the photodiode in the hatched portion is covered by the protective shutter 12 and is not irradiated with light. This is to prevent the adverse effect on the photodiode array, such as an increase in dark current, if the strong light exceeding the saturation charge is continuously applied.However, strong light, such as when the dark current is small, is used. If the effect is small even if the contact is made, the protective shutter need not be provided.
[0020]
In the above embodiment, the clock cycle as the charge accumulation time is gradually increased to set the optimum clock cycle.However, the light source spectrum is measured before the measurement, and the clock is determined by the peak intensity within the measurement wavelength range. The period can also be set.
[0021]
An embodiment in which the clock cycle is set based on the peak intensity within the measurement wavelength range will be described with reference to the flowcharts of FIGS.
First, in order to measure the signal intensity value in the entire measurement wavelength range, the signal processing / control circuit 10 opens the shutter 3 to make it in the bright state, scans the photodiode array 7 and measures the charge amount of each photodiode. Then, this measured value is stored in the memory 11 as a light source spectrum.
[0022]
Next, when the measurer sets the measurement wavelength range by the measurement wavelength range setting means 8, the signal processing / control circuit 10 sets the measurement wavelength range set from the signal measurement intensity values in the entire measurement wavelength range stored in the memory 11. Find the peak intensity within. Then, for example, the signal processing / control circuit 10 calculates the optimum clock cycle from the ratio of the peak intensity value in the entire wavelength range to the peak intensity value in the measurement wavelength range and the standard clock cycle, and sets the optimum clock cycle in the accumulation time setting means 9. .
[0023]
When the setting of the clock cycle is completed, the signal processing / control circuit 10 performs the dark current measurement and the background measurement, then measures the sample, and performs the measurement in the set wavelength range, as in the first embodiment. The dark current correction and the background correction are performed only on the signal of (i) to obtain the absorbance spectrum of the sample.
[0024]
In the above embodiment, even when the optimum clock cycle is changed, the output of the entire wavelength range is taken out from the photodiode array and only signals within the specified wavelength range are processed. It is also possible to control the shift register so that only the signal inside the shift register is extracted from the photodiode array.
[0025]
In the above embodiment, the case where the present invention is applied to a general-purpose spectrophotometer has been described. However, the present invention can be used as a detector for a liquid chromatograph. That is, the present invention can also be applied to a case where a flow cell is used as a sample cell, an effluent from a column flows into the flow cell, and the spectrum of light transmitted through the flow cell is measured every moment by a photodiode array.
[0026]
Further, in the above embodiment, the condensing lens is used as a means for condensing the light from the light source, but the light from the light source may be condensed using a concave mirror.
[0027]
The embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various changes can be made within the scope of the present invention described in the appended claims. is there. Modified embodiments of the present invention are exemplified below.
[0028]
(1) Multi-channel spectroscopy including a light source, a sample cell to which light from the light source is guided, a spectroscope to which light transmitted through the sample cell is guided, and a photodiode array to which light separated by the spectroscope enters. In a photometer, measurement wavelength range designating means for designating a measurement wavelength range, accumulation time setting means for automatically setting a charge accumulation time of a photodiode according to the designated measurement wavelength range, and a front surface of the photodiode array. And a movable protective shutter provided in the multi-channel spectrophotometer.
[0029]
(2) Multi-channel spectroscopy including a light source, a sample cell to which light from the light source is guided, a spectroscope to which light transmitted through the sample cell is guided, and a photodiode array to which light separated by the spectroscope enters. A photometer, comprising: a measurement wavelength range designating unit for designating a measurement wavelength range; and accumulation time setting unit for automatically setting a charge accumulation time of the photodiode according to the designated measurement wavelength range. A multi-channel spectrophotometer wherein the setting means sets an optimum charge accumulation time by gradually increasing the charge accumulation time.
[0030]
(3) Multi-channel spectroscopy including a light source, a sample cell to which light from the light source is guided, a spectroscope to which light transmitted through the sample cell is guided, and a photodiode array to which light separated by the spectroscope is incident. A photometer, comprising: a measurement wavelength range designating unit for designating a measurement wavelength range; and accumulation time setting unit for automatically setting a charge accumulation time of the photodiode according to the designated measurement wavelength range. A multi-channel spectrophotometer wherein the setting means determines the accumulation time based on a peak intensity within a measurement wavelength range without a sample.
[0031]
【The invention's effect】
The multi-channel spectrophotometer of the present invention is configured as described above, and by specifying the measurement wavelength range by the measurement wavelength range specifying means, the optimal accumulation time for the wavelength range is automatically set. In addition, it is possible to select the accumulation time most suitable for the measurement wavelength range, to minimize the influence of noise, and to perform highly sensitive measurement.
[0032]
Further, in the first embodiment of the present invention, since the clock cycle is gradually increased as the charge accumulation time setting means to set the optimal clock cycle, the peak in the entire wavelength range of the light source spectrum is set. Even if the intensity value is slightly different due to the difference between the lots of the photodiode array, it is possible to set the optimal clock cycle in the measurement wavelength range, and it is also necessary to have the optimal value of the standard clock cycle in the entire wavelength range. It can be set accurately according to.
[Brief description of the drawings]
FIG. 1 is a diagram showing one embodiment of a multi-channel type spectrophotometer of the present invention.
FIG. 2 is a diagram showing a flowchart of clock cycle setting.
FIG. 3 is a diagram illustrating a light blocking state by a protection shutter.
FIG. 4 is a diagram showing a flowchart of clock cycle setting.
FIG. 5 is a diagram showing a conventional multi-channel type spectrophotometer.
FIG. 6 is a diagram showing a specific configuration of a photodiode array.
FIG. 7 is a diagram showing a spectrum of a light source.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Light source 2 Condensing lens 3 Shutter 4 Sample cell 5 Slit 6 Concave grating 7 Photodiode array 8 Measurement wavelength range designation means 9 Storage time setting means 10 Signal processing / control circuit 11 Memory 12 Protection shutter

Claims (1)

In a multi-channel spectrophotometer including a light source, a sample cell into which light from the light source is guided, a spectroscope through which light transmitted through the sample cell is guided, and a photodiode array into which light separated by the spectroscope enters. A measurement wavelength range specifying means for specifying a measurement wavelength range, a signal processing / control circuit for determining the specified measurement wavelength range and the measured charge amount, and a photodiode for controlling the photodiode in accordance with a signal from the signal processing / control circuit. Storage time setting means for setting a charge storage time, and when the signal processing / control circuit determines that the measured wavelength range is part of the entire wavelength range, the measured charge amount exceeds the saturated charge amount of the photodiode. The measurement is repeated while changing the accumulation time, and when the measured charge exceeds the saturation charge, the accumulation time corresponding to the measured charge immediately before is set in the accumulation time setting means. Multi-channel spectrophotometer consisting of Te.

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