JPH0522856B2 - - Google Patents

Description

[Detailed description of the invention] B Industrial application field The present invention relates to a dual beam spectrophotometer.

B. Prior art When a spectrophotometer performs wavenumber scanning, the width of the input and output slits of the spectrometer is automatically changed according to the spectral characteristics of the light source so that the energy of the light incident on the spectrophotometer remains approximately constant. The slit width is controlled using a slit program so that the Furthermore, the amount of light that enters the photodetector varies depending on the amount of light absorbed by the sample, but if the amount of light that enters the photodetector is too small, measurement accuracy will decrease. It is desirable to expand the
For this reason, there are several types of slit programs available, including those with generally wide slit widths and those with narrow slit widths, so that the slit width can be selected as appropriate.

On the other hand, in a spectrophotometer, as the wavenumber scanning speed increases, the resolution decreases, so narrowing the slit width to increase the resolution when performing high-speed scanning will simply not improve the resolution. However, in the case of high-speed scanning, it is better to widen the slit width and appropriately adjust the amount of light incident on the photodetector to improve the S/N ratio. In other words, in a spectrophotometer, the resolution improves according to the slit width, but even if the slit width is made narrower than a certain slit width depending on the scanning speed, the resolution does not improve, and the S/N decreases due to the decrease in the amount of incident light. The ratio will only decrease.

However, in the past, there was no mechanism to relate the slit width to the scanning speed, and the operator used an appropriate slit program depending on the sample, and used a narrow slit width for high-speed scanning, resulting in low resolution and S/
There have been cases in which measurements have been made with a poor N ratio, or conversely, unreasonable measurements have been made in which a wide slit width has been selected under conditions that provide high resolution.

The reason why resolution decreases when the wavenumber scanning speed is increased in a spectrophotometer is as follows. In a dual-beam spectrophotometer, the reference light and sample light are separately tapped and incident on the same photodetector, and the contrast and sample light signals are distinguished by the difference in the timing of the chopping, and the ratio of the two is calculated. I'm looking for it. The chopping period is limited by the response speed of the photodetector, and even in high-speed scanning, the chopping period is constant, such as in the case of infrared spectroscopy, about 0.1 seconds.
In normal measurements, signals are sampled at about 20,000 points in the measurement wavenumber range, so it takes more than 30 minutes to make a single measurement. I am trying to see the outline of the absorption spectrum of a sample, but when scanning at high speed, a considerable wave number distance is scanned from one sampling to the next, so the resolution deteriorates. Furthermore, in order to obtain the ratio of the reference signal and the sample signal, each signal is integrated, and when the integration of the reference optical signal exceeds a certain level, the ratio of the integral values of both signals is taken. It has been proposed to prevent the division accuracy from decreasing when the signal is weak, but as the scanning speed becomes faster, the wavenumber scanning distance becomes longer until the integrated value of the reference optical signal reaches a certain level. As the sampling interval increases, the resolution decreases. Generally, when a photometry method is used that increases the measurement sensitivity and improves the S/N by integrating the amount of light, the resolution deteriorates significantly due to the scanning speed.

C. Purpose The present invention is intended to improve the situation in which the slit program is not related to the wave number scanning speed and is selected appropriately, resulting in unreasonable measurements as described above.

D. Configuration The spectrophotometer of the present invention provides a spectrophotometer in which an optimal slit program is automatically selected in relation to the wave number scanning speed. Therefore, in the present invention, the spectrophotometer is provided with a slit width variable means and a control means for controlling the slit width variable means by a slit program that specifies the slit width according to the wave number. In addition to setting a standard slit program, the slit width defined by the standard slit program is multiplied by a coefficient proportional to the square root of the wave number feed rate according to the wave number feed rate, and the result is used as the slit program. The width can now be controlled.

E. Embodiment The drawings show an embodiment of the present invention. L is the light source, R
is a control light flux, S is a sample light flux, 1 and 2 are choppers that intermittent each light flux, and Cr and Cs are a control cell and a sample cell. The two light beams R and S are mirrors 3 and 4.
The beam is made incident on the beam mixer 5, and is made incident on the spectroscope 6 via the beam mixer 5.
In the spectrometer 6, S1 is an entrance slit, and S2 is an exit slit, both of which are driven by a slit motor 7, which is controlled by a control computer 8 according to a predetermined slit program. 9 is a wave number sending motor, which is also controlled by the control computer 8. Spectrometer 6
The light emitted from the detector 10 enters the detector 10 and is converted into an electrical signal. After this signal is amplified by a preamplifier 11, it is passed through frequency discriminators 12 and 13 to R and S.
The signals changing according to the chopping frequencies of both light beams are discriminated into a reference signal and a sample signal, and both signals are integrated by integrators 14 and 15. This integral output is A/D converted and read into the control computer 8, and the control computer 8 outputs the integral output of the control signal.
When Ir exceeds a certain level, the ratio Is/Ir between the sample signal integrated output Is and the reference signal integrated output Ir is calculated, and both integrators 14 and 15 are reset. This operation is repeated while wave number scanning is being performed. The ratio Is/Ir thus obtained is the transmittance of the sample representative of the integral interval. Here, the integration interval is the interval until the integration of the reference light signal exceeds a certain level, so it changes depending on the magnitude of the reference light signal.

Here, the reference optical signal when using the reference slit program is Pr, the wave number scanning speed is V, and the slit opening rate selected at that scanning speed is B. Here, the slit opening ratio is a coefficient that indicates how many times the slit width should be compared to the standard slit width, with the slit width realized by the standard program being called the standard slit width. Now, the integration is continued until the integrated value Ir of the reference optical signal exceeds a certain level, so if that certain level is Ir, then
The integration time Δt is determined by the following formula.

Ir＝∫ ^t+ 〓 ^t _t B Pr dt If the above equation is rewritten as integral by wave number, the wave number distance movement dn in time dt is dn=Vdt, and if the wave number movement in time Δt is ΔW, the above equation becomes Ir= ∫ ^W+ 〓 ^W _W B Pr/Vdn =B Pr/V・∆W...(1) However, Pr is assumed to be constant during ∆W. If the slit width in the standard slit program is S, the slit width in this case is BS, and according to equation (1), ΔW decreases as the slit width increases, but
The resolution is maximum when it is equal to the slit width.
Therefore, if we set ΔW in equation (1) as BS and find B from equation (1), we get becomes. That is, it is preferable to change the slit opening ratio B in proportion to the square root of the wave number scanning speed. in this case,
Since the reference slit width varies depending on the wavelength according to a reference slit program preset according to the spectral characteristics of the light source, the actually selected slit width also varies depending on the wave number. If the standard slit program has a constant slit width with respect to the wave number, the standard slit width will be a constant value, and the actually selected slit width will be a constant value that is B times the standard slit width.

In the figure, reference numeral 16 denotes a keyboard. When the wave number scanning speed V is set, the control computer 8 controls the wave number feed motor 9 according to the set speed, and also slits by a program obtained by multiplying the standard slit program by the opening rate √. Control width.

In the above example, the slit opening ratio changes continuously according to the wave number scanning speed, but the scanning speed may be divided into several ranges and a constant opening ratio may be applied to each range. Furthermore, if there are multiple types of slit programs, the same opening rate may be applied regardless of the type.

Effects According to the present invention, not only can the slit program be selected depending on the light source and the sample, but also the optimal one can be automatically applied according to the scanning speed.
The operator can always perform analysis under appropriate slit conditions without special consideration.

[Brief explanation of drawings]

The drawing is a block diagram of one embodiment of the invention. L...Light source, R...Reference light flux, S...Sample light flux, 1, 2...Chiyotsupa, 5...Beam mixer,
6...Spectrometer, S1...Entrance slit, S2...
Exit slit, 7...Slit drive motor, 10
...Detector, 12, 13...Frequency discriminator, 1
4, 15... Integrator, 8... Control computer,
16...Keyboard.

Claims (1)

[Claims] 1. In a spectrophotometer that performs wave number scanning, a slit width variable means and a reference slit program that defines the slit width according to the wave number are set in advance, and the slit width defined by this reference slit program is set in advance. It is characterized by comprising means for creating a slit program by multiplying the width by a coefficient proportional to the square root of the scanning speed, and a control means for controlling the slit width variable means using the slit program. spectrophotometer.