JP2560293B2 - Spectrophotometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spectrophotometer suitable for performing a plurality of types of spectroscopic measurements, such as a thin layer chromatograph (TLC) scanner, which greatly differ in required photometric sensitivity.

B. 2. Description of the Related Art A conventional TLC scanner has a structure as shown in FIG. In this figure, 1 is a light source, 2 is a spectroscope, and 3 is a sample TL.
C plate, P1 is a photomultiplier for measuring the absorbance of sample components, P2 is a photomultiplier for measuring the reflection or fluorescence from the sample, and P3 is for monitoring the incident light to the TLC plate. In this photomultiplier tube, a semitransparent mirror 4 inserted between the spectroscope 2 and the TLC plate 3 splits a part of the incident light to the TLC plate and makes it incident. A dimmer 8 is inserted between the semitransparent mirror 4 and the photomultiplier tube P3. This monitor photomultiplier tube
The output of P3 is compared with the reference value by the error amplifier 5, the output of the error amplifier 5 is applied to the negative high voltage generation circuit 6, and the output voltage of the negative high voltage generation circuit 6 is a dynode of each photomultiplier tube P1, P2, P3. Applied to each photomultiplier tube P1, P2, so that the output of the monitor photomultiplier tube P3 is always at the reference value.
The sensitivity of P3 is automatically controlled.

In a TLC scanner spectrophotometer, the photomultiplier tube is required to have high sensitivity at the fluorescence rate as compared with the absorbance measurement. Therefore, in the case of absorbance measurement, the sensitivity of the photomultiplier tube is lowered, and in the case of fluorescence measurement, the sensitivity is maximized.Therefore, it is necessary to switch the voltage applied to the photomultiplier tube when switching from absorbance measurement to fluorescence measurement. There is. Conventionally, this sensitivity switching is performed by switching the gain of the error amplifier 5. At this time, in the absorbance measurement, the monitor photomultiplier tube P3 should be adjusted so that the current flowing through the monitor photomultiplier tube becomes an appropriate value.
If the extinction rate of the dimmer 8 between the semi-transparent mirror 4 and the semi-transparent mirror 4 is set, the sensitivity of P3 increases when switching from absorbance measurement to fluorescence measurement, so an excessive current (eg 50 μA) flows in P3. The operation becomes unstable. Therefore, when a photomultiplier tube is used for a monitor, it is impossible to stably operate the photometric circuit by compensating the difference of 100 times or more in sensitivity by only electric means. For this reason, conventionally, the sensitivity of the photomultiplier tube at the time of fluorescence measurement has been set to be low.

C. Problems to be Solved by the Invention Monitoring the incident light of a sample with a photometer using a photomultiplier tube that performs a plurality of types of measurements with greatly different required photosensitivity, such as a spectrophotometer used in a TLC scanner. With a photomultiplier tube as the photometric element, the operation of the monitor photometry system becomes unstable when switching to high-sensitivity measurement, so it is possible to set the sensitivity of the photomultiplier tube for high-sensitivity measurement sufficiently high. It tries to solve the problem of being unable to do it.

D. Measures for solving problems Using an element that does not have a sensitivity adjustment function such as a silicon photocell as a photodetector for monitoring, the output is converted to a negative high voltage through an input conversion circuit and sample light photometry is performed. Is applied to a photomultiplier for use in the application to compensate for the effect of fluctuations in the incident light of the sample, and the input conversion circuit is provided with means for selecting the output level for the same input. To switch.

E. Suppose now that the incident light intensity of the sample has changed with time by f (t). At this time, the output current i of the silicon photocell for monitoring is
Changes i = kf (t). At this time, in order to make the output of the photomultiplier tube for photometry of the sample constant (assuming no sample), its sensitivity may be changed in proportion to 1 / f (t). The sensitivity G of the photomultiplier tube is a function of the applied voltage V. G = g
(V). Here, V is the output of the above-mentioned input conversion circuit, and when V = h (i) for the input i, the output of the photomultiplier tube is constant when the light intensity changes f (t). , The sensitivity G must have a change of G1 / f (t) = G1 / i with the reference sensitivity of i to the reference value io as G1, so ioG1 / i = g {h (i)} Obtaining (i), h (i) = g ^-1 (ioG1 / i) That is, the function representing the input / output characteristic of the input conversion circuit is in the form of the inverse function of the applied voltage sensitivity characteristic of the photomultiplier tube. To switch the reference sensitivity to G2, h (i) = g ^-1 (ioG2 / i). That is, the measurement sensitivity can be switched by providing a means for switching the coefficient multiplied by 1 / i in the input conversion circuit. In this case, because the sensitivity control of the photomultiplier tube does not use the feedback method as in the conventional example, the output of the silicon photocell for monitoring does not change even if the measurement sensitivity is switched, and the sample light photometry system is switched to high sensitivity. However, the output of the silicon photocell is increased and saturated, and the sensitivity control operation cannot be performed.

F. Embodiment FIG. 1 shows an embodiment of the present invention. 1 is a light source, 2 is a spectroscope, 3 is a sample TLC plate, P1 is a photomultiplier tube for measuring reflected light or fluorescence from the sample, and P2 is a photomultiplier tube for measuring sample transmitted light. Reference numeral 4 denotes a semitransparent mirror that splits the light emitted from the spectroscope 2, and 7 denotes a silicon photocell for monitoring. Part of the sample incident light split by the semitransparent mirror 4 is made incident through the dimmer 8. 9 is a silicon photocell 7
Is an input conversion circuit for converting the output of the above into a negative high voltage and applying it to the dynode of the photomultiplier tube P1, or P2. The input conversion circuit 9 is a logarithmic converter L for logarithmically converting the output current i of the silicon photocell 7 into a voltage signal of (-klogi),
A constant multiplier M for multiplying the output of the logarithmic converter L by a constant number α
And an adder Ad that adds a constant to its output, and a negative high voltage generation circuit 6 that proportionally converts the output v of the adder Ad into a negative high voltage V.

FIG. 2 is a graph showing the relationship between the dynode applied voltage V and the gain (sensitivity) G of the photomultiplier tube. The horizontal axis is V and the vertical axis is io.
It is a drawing of gG. This curve is gently curved, but can be regarded as a straight line in the partial or relatively narrow sensitivity range, and the straight line can be expressed by G = Ke ^αV . As mentioned in the action section,
V = h (i), where G1 is the sensitivity to the reference value io of i, Rewriting the above formula, Can be written. Here, α represents the slope of the curve shown in FIG. 2, and varies depending on the sensitivity range selected. E1 is the monitor output i
Includes sensitivity G1 and α when is a reference value io,
Since G1 is the sensitivity selected according to the type of measurement, E1 can be changed to change the set sensitivity of the photomultiplier tube.

Returning to FIG. 1, the output of the logarithmic converter L is -kiogi with respect to the input i, and k is a value determined by the characteristics of the logarithmic converter L. In the constant multiplier M, the sensitivity β is multiplied by −klogi so that kβ becomes 1 / α. Since the value of α differs depending on the sensitivity range to be selected, there are two resistors, r and r ', which determine the value of β, and one of them is selected by the changeover switch Sw1. The output of the constant multiplier M is added with a constant Ea or Ef by an adder Ad, and the output v of Ad is of the general form v = E−kβlog i, where Ea or Ef is selected depending on the type of measurement. The change-over switches Sw1, Sw2, Sw3 are interlocked and switched between the time of absorbance measurement and the time of fluorescence measurement, and the figure shows the state of switching to the fluorescence measurement side. Feedback resistor r, r ′ of the multiplier
Are adjustable respectively, and the value of β is experimentally determined with respect to the required sensitivity of the photomultiplier tube.

G. In the spectrophotometer of the present invention, the photodetector for monitoring the incident light of the sample is an element having no sensitivity adjusting function such as a silicon photocell instead of the photomultiplier tube, and its output is transmitted through the conversion circuit to the sample. By applying light to the photomultiplier tube to measure the light, the fluctuation of the incident light of the sample is compensated, and the input / output characteristics of the conversion circuit are switched to switch the detection sensitivity of the sample light depending on the type of measurement. Therefore, even if the sensitivity is switched, the monitor photometric output itself does not change, and even if the sample photometric system is switched to high sensitivity, there is no such thing as saturation or operational instability of the monitor photometric system. Since the switching can be performed and an expensive photomultiplier tube is not used for the monitor, the device becomes inexpensive.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention, FIG. 2 is a graph of a relation between a dynode applied voltage of a photomultiplier tube and a gain (sensitivity), and FIG. 3 is a circuit diagram of a conventional example. 1 ... Light source, 2 ... Spectrometer, 3 ... TLC plate, 4 ...
… Semi-transparent mirror, 6 …… Negative high voltage generation circuit, 7 …… Monitor silicon photocell, 8 …… Dimmer, 9 …… Input conversion circuit,
L ... Logarithmic converter, M ... Constant multiplier, Ad ... Adder.

Claims (1)

(57) [Claims] 1. A photomultiplier tube for measuring sample light, a monitor photodetector having no internal sensitivity adjustment function such as a silicon photocell, and a part of sample incident light for the monitor photodetector. A beam splitting means to be incident on, and an input conversion means for compensating for fluctuations in sample incident light by converting the output of the monitor detector into negative high voltage and applying it to the dynode of the photomultiplier, The input conversion means performs logarithmic conversion on the output of the monitor detector, and puts the output into a constant multiple circuit in which the magnification is switched in association with sensitivity switching,
As a result, a spectrophotometer having a configuration in which a constant that can be switched in association with sensitivity switching is added, and the output is input to a negative high voltage generation circuit to switch the sensitivity of the photomultiplier tube.