JP5358527B2 - Spectrophotometer and absorbance measurement method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spectrophotometer which is capable of obtaining absorption spectra in an ultraviolet region and a visible region by preventing the rise of a noise ratio when using a light source of which the amount of light is reduced by changes in wavelength. <P>SOLUTION: A signal from an optical detector for reference light and a signal from an optical detector for sample light transmitted through a sample are integrated to store quantities of light. When the quantity of reference light becomes lower than a preliminarily set threshold, integration times of the optical detector for reference light and the optical detector for sample light transmitted through the sample are extended, and AD conversion periods of a signal of reference light and a signal of sample light, which are obtained by integration, are extended. <P>COPYRIGHT: (C)2012,JPO&amp;INPIT

Description

  The present invention relates to a spectrophotometer and an absorbance measurement method.

  The spectrophotometer measures the proportion of the sample irradiated with light, that is, absorbs the light, that is, absorbs light, creates an absorption spectrum with the wavelength as the horizontal axis, and analyzes the components of the sample.

  The intensity of the reference light irradiated to the sample and the intensity of the sample light transmitted through the sample are measured, and the absorbance is the logarithm with the ratio of the two as the base. The unit is AU (Absorbance Unit), which is called 1 AU for 1/10 and 4 AU for 1 / 10,000. Absorbance is the absorption ratio of sample light to reference light, and in the case of a liquid sample, it is transmittance. The absorbance is proportional to the sample concentration.

  When creating an absorption spectrum having the wavelength as the horizontal axis, if the wavelength changes and the intensity of the reference light decreases, the influence of the measurement error of the photodetector appears and the accuracy of the data decreases. Therefore, it is desirable that the reference light does not change even if the wavelength changes.

  However, the amount of light of a tungsten lamp used as a light source in the visible range varies depending on the wavelength. Also, the amount of light of the deuterium discharge tube used as a light source in the ultraviolet region varies depending on the wavelength. The XeF (xenon fluoride) lamp, which is suitable for repeated blinking, has a spectral distribution in the visible light region close to that of sunlight, but the light intensity difference including the ultraviolet region is large compared to deuterium discharge tubes and tungsten lamps. And there is little absolute light quantity. Further, since the XeF lamp is repeatedly turned on and off, there is a concern that the obtained data may be defective when a lighting error occurs.

  A technique has been proposed in which the resolution of data does not change even if the wavelength changes by integrating the output signal of the light detector and extending the accumulation time even if the light amount of the light source changes (for example, Patent Document 1).

JP-A-5-264352

  Patent Document 1 describes that the integration time of the photodetector is changed according to the output signal level until the integration value becomes a constant value. However, since the integration period is constant, it takes time to obtain data when the amount of light is small.

  The present invention provides a spectrophotometer capable of preventing an increase in the ratio of noise and obtaining a good absorption spectrum in the ultraviolet region and visible region when using a light source that reduces the amount of light due to a change in wavelength. With the goal.

  In order to solve the above-described problems, the embodiment of the present invention integrates the light detector of the reference light and the light detector of the sample light transmitted through the sample to accumulate the light amount, and the light amount of the reference light is previously set. When the threshold value is below the set threshold, the integration time of the reference light detector and the sample light detector that has passed through the sample is expanded, and the reference light signal and sample light signal obtained by integration are expanded. The AD conversion cycle is expanded.

  According to the present invention, there is provided a spectrophotometer capable of preventing an increase in the ratio of noise and obtaining a good absorption spectrum in the ultraviolet region and the visible region when a light source whose amount of light is reduced due to a change in wavelength is used. can do.

It is a block diagram which shows the main structures of a visible ultraviolet spectrophotometer. It is a flowchart which shows the non-lighting process of a light source. It is a flowchart which shows the integration time process when the light quantity of a light source is small. It is a time chart which shows the time change of an output signal.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a configuration diagram showing a main configuration of a visible ultraviolet spectrophotometer as an example of a spectrophotometer. The reference light generated from the light source 2 to which power is supplied from the light source power source 1 is split into a specific wavelength by the diffraction grating 3 in the spectroscope 16 and becomes a single measurement wavelength. The control unit 12 gives a pulsed lighting signal to the light source power source 1, and the light source 2 which is a XeF lamp emits pulses. The diffraction grating 3 is driven by a wavelength driving motor 13 controlled by the control unit 12. The reference light of the measurement wavelength is divided into two directions by a half mirror, detected by the reference light detector 6, and transmitted through the sample cell 5 and detected by the sample light detector 9 as sample light.

  From the reference light detector 6, a pulsed reference light signal is sent to the reference light integrating amplifier 7 and integrated to become a reference light integrating amplifier output signal. The reference light signal AD converter 8 converts the pulse signal from the analog signal to the pulse light. It is converted into a reference light AD conversion signal and stored as reference data in a storage unit (not shown) of the control unit 12.

  The pulsed sample light detected by the sample light detector 9 is integrated by the sample light integration amplifier 10 to become a sample light integration amplifier output signal, and the sample light signal AD converter 11 converts the pulsed sample light from the analog signal. It is converted into an optical AD conversion signal and stored as sample data in a storage unit (not shown) of the control unit 12.

  A computer 15 and a data display device 14 are connected to the control unit 12, and a series of control instructions executed by the control unit 12 or a screen display of measurement data is performed. The controller 12 calculates the absorbance from the stored reference data and sample data, and transmits the absorbance data to the computer 15 and the data display device 14.

  FIG. 2 is a flowchart showing the light source non-lighting process. The light source 2 shown in FIG. 1 performs pulsed lighting in accordance with the lighting signal sent from the control unit 12. However, when an error that does not light is generated, data that is continuously acquired is lost. The control device 12 then executes the programmed procedure shown below. In the initial measurement and condition setting, each instrument of the spectrometer 16 is initialized and the measurement wavelength is set (step 21). Next, as basic data measurement, reference light at a certain measurement wavelength is measured at an appropriate energy level (step 22), and basic data (X) is acquired and stored in a storage unit (not shown) (step 23). Next, actual data measurement is performed for a certain wavelength, and actual data (Yt) of reference light is acquired (step 24). Next, it is determined whether or not there is a light source lighting error (step 25). When the basic data (X) is set as the threshold value X, the actual data (Yt) is compared for each actual data measurement, and the actual data (Yt) is sufficiently small, such as about 1/10 or less of the basic data (X). Determines that a non-lighting error has occurred. Then, a tag indicating non-lighting is attached to the actual data, and collection of the actual data is stopped as necessary (step 26). If there is no light source lighting error in step 25, actual data (Yt) is acquired for the next wavelength. This is repeated below.

  FIG. 3 is a flowchart showing the integration time process when the light amount of the light source is low. In the absorption spectrum, fixed noise of a certain level that cannot be avoided is superimposed. However, if the light amount of the light source is small, the ratio of the fixed noise to the light amount increases, which affects the data accuracy. In the initial measurement and condition setting, each instrument of the spectrometer 16 is initialized and the measurement wavelength is set (step 31). Next, when one wavelength is n, as the basic data measurement, the light quantity in the entire wavelength region where the reference light is set is measured (step 32), and is stored in the storage unit (not shown) as the basic data (Xan). For example, ¼ of the maximum light amount (Xa max.) In the basic data is set as the threshold value E (step 33). As a result, the integration time processing is performed only for the wavelength of light whose actual data is lower than a quarter of the maximum light. Next, the basic data (Xan) stored in the storage unit in step 33 is compared with the threshold value E (step 34). If the basic data (Xan) is equal to or larger than the threshold value E, the integration period is set to the light source 2. The actual data (Yt) is measured (step 36) while keeping the same lighting cycle t as in step 35. When the basic data (Xan) is smaller than the threshold value E, the integration cycle is set to twice the lighting cycle t of the light source 2 (step 37), and actual data (Y2t) is measured (step 38). As described above, the control device 12 determines the threshold value from the measurement of the basic data, and after the light quantity determination, when the light quantity is low, the actual data is measured and integrated by, for example, twice the normal time to perform AD conversion. Since the integration time control is performed, it is possible to prevent an increase in the noise ratio of the signal from the AD converter and to obtain a good absorption spectrum in the ultraviolet region and the visible region.

  FIG. 4 is a time chart showing temporal changes in the output signal. In the normal state other than when the light source 2 is turned on or the light amount is reduced as shown in FIG. 1, the light amount obtained from the light source 2 has a pulse-like waveform with a period t as shown by a waveform 41. As described in FIG. 1, the reference light is integrated by the reference light integrating amplifier 7 and the sample light is integrated by the sample light integrating amplifier 10, and an output signal as shown by the waveform 42 is output. Subsequently, the output from the reference light integrating amplifier 7 is a reference light signal AD converter 8, and the output from the sample light integrating amplifier 10 is a sample light signal AD converter 11. Molded and transmitted to the control unit 12 as reference data and sample data.

  Next, the non-lighting process will be described. As for the waveform 51 of the light source 2, the output signal of the waveform a ′ of the waveform 52 is output from the reference light integrating amplifier 7 and the sample light integrating amplifier 10 with a period t with respect to the normal lighting waveform a. However, since there is no change in the waveform 51 that should be in the period t with respect to the waveform b when the lamp is not lit, the waveform 52 is also represented by the waveform b ′ within the time interval corresponding to the period t. It does not change. When the threshold value X shown in FIG. 2 is superimposed on the waveform 52, the result is as shown in FIG. If not lit, the threshold value X is exceeded in the determination of whether or not the waveform 52 of the actual data (Yt) exceeds the threshold value X in step 25, which is executed every time the actual data (Yt) is measured in step 24 of FIG. Since it is not, it can be judged that it is not lit.

  Next, processing when the light amount of the light source is low will be described. The light source 2 is lit at a period t and becomes a waveform 61. However, when the light amount is small, the waveform 62 in which the reference light is integrated by the reference light integrating amplifier 7 or the waveform in which the sample light is integrated by the sample light integrating amplifier 10 is used. 62 does not exceed the threshold value E defined in step 33 of FIG. 3, it is determined in step 34 that the amount of light is insufficient. In this case, in step 37, the control device 12 sets the integration period in the reference light integrating amplifier 7 or the sample light integrating amplifier 10 to be twice the normal period t, performs AD conversion, and generates the waveform 63. obtain. Thereby, an increase in the noise ratio of the signal from the AD converter can be prevented, and a good absorption spectrum in the ultraviolet region and the visible region can be obtained.

  As described above, the embodiment of the present invention integrates the light detector of the reference light and the light detector of the sample light transmitted through the sample to accumulate the light amount, and sets the light amount of the reference light to a preset threshold value. Below, the integration time of the reference light detector and the sample light detector that has passed through the sample is expanded, and the AD conversion of the reference light signal and the sample light signal obtained by the integration is performed. It is characterized by expanding the period.

  This provides a visible ultraviolet spectrophotometer that can prevent an increase in the ratio of noise and obtain an absorption spectrum in the ultraviolet region and the visible region when using a light source that reduces the amount of light due to a change in wavelength. it can. In addition, when a light source lighting error occurs, a mark indicating that it is a lighting error is added to the data at that time, and measurement of the data is stopped as necessary to distinguish the data at the time of the lighting error from others. Therefore, the effect that the reliability of the entire analysis data is improved can be obtained.

2 light source 3 diffraction grating 6 reference light detector 7 reference light integrating amplifier 8 reference light signal AD converter 9 sample light detector 10 sample light integrating amplifier 11 sample light signal AD converter 12 control unit 14 data display device 15 computer

Claims (4)

In a spectrophotometer that irradiates a sample with light of a specific wavelength at a specific period and obtains the absorbance of the sample when the wavelength is changed,
A half mirror that separates the light into reference light and sample light;
A reference light integrating amplifier that integrates a signal from the photodetector of the reference light;
A reference optical signal AD converter for converting a signal from the reference optical integration amplifier into a digital signal;
A sample light integrating amplifier that integrates the signal from the light detector of the sample light transmitted through the sample;
A sample optical signal AD converter for converting a signal from the sample optical integration amplifier into a digital signal;
When the light amount of the reference light falls below a preset threshold value, the integration time of each of the reference light photodetector and the sample light photodetector transmitted through the sample is expanded and obtained by the integration. A spectrophotometer comprising: a control device that expands the AD conversion period of the reference light signal and the sample light signal. The outer spectrophotometer according to claim 1,
The spectrophotometer characterized in that the integration time is twice the period of light irradiated on the sample, and the period of AD conversion is twice the period of light irradiated on the sample. Total. In the absorbance measurement method of the spectrophotometer that obtains the absorbance of the sample when the wavelength is changed by irradiating the sample with light of a specific wavelength in a specific cycle,
The light is divided into a reference light and a sample light that passes through the sample, and each of the reference light detector and the sample light detector is integrated to accumulate a light amount, and the reference light is accumulated. When the amount of light falls below a preset threshold value, the integration time of each of the reference light photodetector and the sample light photodetector is expanded, and the reference light signal obtained by the integration and A method for measuring absorbance, comprising: expanding an AD conversion cycle of the signal of the sample light. The absorbance measurement method according to claim 3, wherein
The integration time is
The absorbance measurement method characterized in that the period of light irradiated on the sample is twice and the period of AD conversion is twice the period of light irradiated on the sample.

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