JP2008232813A - Interference spectrophotometer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an interference spectrophotometer reducing remarkably a measuring time, when measuring an infrared absorption change. <P>SOLUTION: This interference spectrophotometer is provided with: an interferometer including a light source 11 for generating an infrared ray; a fixed mirror 15; and a movable mirror 16, generates an interference light from the infrared ray, and also provided with: an optical system for irradiating a sample 23 with the interference light; and a detector 25 for detecting a reflected light or a transmission light from the sample 23. The interference spectrophotometer is also provided with: an absorption quantity calculation means for comparing an interferogram obtained by each scanning of the movable mirror 16 with an interferogram serving as a reference, to calculate an infrared absorption quantity based on a shape difference therein; and a movable mirror drive control means for limiting a driving range for the movable mirror 16 in each scanning, to an area required for collecting a data used for the infrared absorption quantity calculation in the absorption quantity calculation means. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an interference spectrophotometer such as a Fourier transform infrared spectrophotometer.

  In a Fourier transform infrared spectrophotometer (hereinafter abbreviated as “FTIR”), a Michelson interferometer including a fixed mirror and a moving mirror generates an interference wave whose amplitude varies with time, and irradiates the sample with this interference wave. The transmitted light or reflected light is detected as an interferogram. Then, by performing Fourier transform on this detection signal, an absorption spectrum having the wave number on the horizontal axis and the intensity (absorbance or transmittance, etc.) on the vertical axis can be obtained. At this time, one interferogram is generated by one scan of the movable mirror, and an absorption spectrum over the entire predetermined wavelength range can be acquired from the interferogram.

  In addition, such FTIR is connected to a chromatograph, the sample components eluted from the chromatograph are sequentially measured by FTIR, and the time change of the infrared absorption amount is quantitatively determined from the shape change of the obtained interferogram. It can also be measured. The time change of the infrared absorption amount is measured, for example, as follows. First, a plurality of scans are performed in advance for a carrier fluid that does not include a sample component, and the obtained plurality of interferograms are stored in a memory as reference interferograms. Thereafter, the sample components sequentially flowing out from the chromatograph are scanned at a predetermined time interval to collect an interferogram, and the difference between the interferogram and each of the plurality of reference interferograms in each scanning cycle is determined by Gram-Schmidt (Gram- It is extracted and digitized by arithmetic processing such as the Schmidt method. Then, by recording the numerical values in time series, a chromatogram indicating a temporal change in the infrared absorption amount is generated (see, for example, Patent Document 1).

  In the conventional FTIR, in order to obtain the optical path difference necessary for spectrum generation, the interferogram is acquired by sampling the photodetection signal at a predetermined interval while moving the movable mirror over a relatively wide range, and the infrared absorption When obtaining a change in quantity, only data of a predetermined region is extracted from the interferogram collected in each scanning cycle and used for arithmetic processing such as the Gram Schmitt method.

JP-A-6-82366

  In the measurement of the change in the infrared absorption amount as described above, in order to detect all the samples that are sequentially eluted from the chromatogram, it is desirable to collect interferograms at as short a time interval as possible. However, as described above, in the conventional FTIR, the movable mirror is driven over the entire region necessary for spectrum generation at each scanning, and thus there is a problem that it takes time for one scanning.

  In addition, although the case where the infrared chromatogram of the chromatograph effluent fluid was produced | generated using FTIR was mentioned here as an example, the above problems may be caused by connecting the FTIR to a thermal analyzer and changing the temperature or chemicals of the substance. This is common when measuring changes in absorption using an interference spectrophotometer, such as when measuring changes in infrared absorption as the change proceeds.

  That is, the problem to be solved by the present invention is to provide an interference spectrophotometer that can significantly reduce the measurement time when measuring the change in the amount of infrared absorption using the interference spectrophotometer. is there.

An interference spectrophotometer according to the present invention, which is made to solve the above problems, includes an interferometer that includes a light source that generates infrared light, a fixed mirror, and a movable mirror, and generates interference light from the infrared light, the interference In an interference spectrophotometer comprising an optical system for irradiating a sample with light, and a detector for detecting reflected light or transmitted light from the sample,
a) comparing the interferogram obtained by each scan of the movable mirror with a reference interferogram, and calculating the amount of infrared absorption from the difference in shape;
b) a movable mirror drive control means for limiting the drive range of the movable mirror in each scan to a region necessary for collecting data used for absorption amount calculation in the absorption amount calculation means;
It is characterized by having.

  Any calculation method may be used to calculate the amount of infrared absorption based on the difference in the shape of the interferogram. However, in order to realize high-speed calculation processing, the above-described Gram Schmitt method should be used. Is desirable.

  According to the interference spectrophotometer according to the present invention having the above-described configuration, the moving mirror drive control means performs control so that the driving range of the moving mirror at the time of measurement is limited to a region necessary for calculating the infrared absorption amount. Therefore, the time required for measuring the amount of infrared absorption can be drastically reduced.

  That is, in the conventional FTIR, as shown in FIG. 5 (a), the movable mirror is scanned over a relatively wide range Ra (the range is determined depending on the wave number decomposition) necessary for calculating the spectrum. An interferogram composed of photometric data of about 1000 to 2000 points sampled at a predetermined interval is acquired. When calculating the infrared absorption change, data of about 100 to 200 points in the predetermined same region Rb is extracted from the interferogram acquired in each scan and calculated by the above-described Gram Schmid method or the like. It is used for. In contrast, as shown in FIG. 5B, the interference spectrophotometer according to the present invention moves from the beginning limited to the range Rb necessary for acquiring the data used for calculating the infrared absorption amount. Since the mirror is driven, it is possible to measure the amount of absorption in a specific wavelength region at a speed several times that of normal spectrum measurement or more.

  In the interferometric spectrophotometer according to the present invention, it is desirable to further provide a band pass filter that allows light in the measurement wavelength range to pass on the optical path from the interferometer to the detector. Thereby, the measurement sensitivity of the target wavelength region can be improved.

  An embodiment of the present invention will be described below with reference to the drawings. In addition, although it demonstrates based on the example which connected the gas chromatograph apparatus and FTIR here, this invention is not limited to the said structure.

  FIG. 1 is a schematic configuration diagram of an FTIR according to the present embodiment. In the FTIR according to the present embodiment, a main interferometer for obtaining an interferogram, and a timing signal for controlling the sliding speed of the moving mirror or sampling a signal obtained by the photodetector of the main interferometer are generated. A control interferometer is provided. The main interferometer includes an infrared light source 11, a condensing mirror 12, a collimator mirror 13, a beam splitter 14, a fixed mirror 15, a moving mirror 16, and the like, and generates interfering infrared light for performing spectrum measurement. That is, the infrared light emitted from the infrared light source 11 is applied to the beam splitter 14 through the condensing mirror 12 and the collimator mirror 13, where it is divided into two directions, the fixed mirror 15 and the movable mirror 16. The lights reflected by the fixed mirror 15 and the movable mirror 16 are combined again by the beam splitter 14 and sent to the optical path toward the parabolic mirror 21. At this time, since the movable mirror 16 is reciprocated back and forth (in the direction of the arrow in FIG. 1) by the movable mirror driving unit 16a, the combined light is interferogram (interferogram) whose amplitude varies with time. ) The light collected by the parabolic mirror 21 is irradiated into the sample chamber 22, and the light that has passed through the gas cell 23 disposed in the sample chamber 22 is collected by the ellipsoidal mirror 24 onto the photodetector 25. The gas cell 23 is connected to a gas chromatograph device (GC) 60 through a heated and insulated introduction pipe, and the sample gas components separated by the gas chromatograph device 60 are sequentially introduced into the gas cell 23 in a gas state. Is done.

  On the other hand, the control interferometer includes a laser light source 17, a mirror 18, a beam splitter 14, a fixed mirror 15, a movable mirror 16, and the like, and generates laser interference light for obtaining an interference fringe signal. That is, the light emitted from the laser light source 17 is applied to the beam splitter 14 through the mirror 18 and is transmitted to the parabolic mirror 21 as interference light similarly to the infrared light. Since this laser interference light travels as a light beam having a very small diameter, it is reflected by the mirror 19 inserted in the optical path and introduced into the photodetector 20.

  A bandpass filter 50 that allows light in a specific wavelength region to pass through is detachably disposed on the optical path from the beam splitter 14 toward the parabolic mirror 21, and according to the target wavelength region as required. By setting an appropriate bandpass filter 50, the measurement sensitivity in a specific wavelength region can be improved. Note that the attachment position of the bandpass filter 50 is not limited to the above, and may be arranged at any position on the optical path from the beam splitter 14 through the sample chamber 22 to the photodetector 25.

  The optical components centering on the main interferometer are arranged in the hermetic chamber 10, and the humidity is controlled in the hermetic chamber 10. This is mainly to protect the beam splitter 14 having KBr having deliquescence as a substrate.

  The light reception signal of the photodetector 20, that is, a laser light interference fringe signal (usually called “fringe signal”) is input to the signal generation unit 29, where a pulse signal for sampling the light reception signal for the infrared interference light is generated. Is done. Further, this laser beam interference fringe signal is also used for performing stable sliding control of the movable mirror 16. As the laser light source 17, a He—Ne laser is generally used, and a pulse signal having the same frequency as the laser light interference fringe signal is generated by the signal generation unit 29.

  The received light signal obtained by the photodetector 25 is amplified by the amplifier 26, sampled by the sample and hold circuit (S / H) 27 at the timing of the pulse signal, and then by the A / D converter (A / D) 28. Converted to digital data. The digital data is sent to the control / processing unit 30 and subjected to data processing described later. The series of measurement operations are executed under the control of the control / processing unit 30.

  Although the control / processing unit 30 can be a dedicated control / processing device, generally, the entity is a personal computer in which dedicated control / processing software is installed, and performs various input operations. An input unit 41 using a keyboard and a pointing device (such as a mouse) and a monitor 40 for displaying measurement results are connected.

  Hereinafter, the operation of FTIR according to the present embodiment will be described with reference to FIGS. FIG. 2 is a functional block diagram of the control / processing unit 30, FIG. 3 is a flowchart showing the FTIR operation of this embodiment, and FIG. 4 is a waveform diagram for explaining the FTIR operation of this embodiment.

(1) Setting measurement conditions First, various measurement conditions are set by the user operating the input unit 41 (step S11). The measurement conditions include at least the number of acquired reference data (reference interferogram) and the driving range of the movable mirror 16.

  Here, assuming that the interferogram obtained by the photodetector 25 with the movement of the movable mirror 16 is as shown in FIG. 4A, it is digitized by the sample hold circuit 27 and the A / D converter 28. The data is as shown in FIG. In such an interferogram, the horizontal axis is the optical path difference (that is, the position of the moving mirror). Accordingly, by specifying the offset data point m from the center burst (maximum measurement point) and the acquired data point n, both end positions of the movable mirror driving range are defined. For example, when the number of offset data points is 20 and the number of acquired data points is 50 points, the position from the position corresponding to the 20th sampling point to the position corresponding to the 70th sampling point is determined from the center burst position. This is the driving range. The number of reference data acquired affects the calculation time required to calculate a quantitative value, which will be described later, and the accuracy of the obtained data.

  Here, the control / processing unit 30 includes a preset storage unit 34 that stores measurement conditions (such as the driving range of the movable mirror) suitable for measurement of changes in infrared absorption in various target samples or wavelength ranges. When the user designates the control sample or the target wavelength region (or the type of the bandpass filter 50 used for measurement) from the input unit 41, an appropriate parameter corresponding to the target sample is automatically set in the preset storage unit 34. Is stored in the setting storage unit 35. It is also possible to set measurement conditions by directly inputting a numerical value or the like from the input unit 41 by the user.

(2) Determination of Center Burst Position Next, prior to measurement, data is collected while moving the movable mirror 16 within a predetermined range, and the position where the measured value is maximum is determined as the center burst position (step S12). .

(3) Acquisition of Reference Data Subsequently, a carrier fluid that does not contain a sample component is introduced into the gas cell 23, and measurement is performed according to the measurement conditions stored in the setting storage unit 35. Thereby, for example, the driving of the movable mirror 16 is started from the position where the data of the m-th sampling point can be acquired in the + direction with the center burst position determined in step S12 as a reference, and then the data for n points is obtained. At the time of acquisition, the drive control unit 36 controls the movable mirror drive unit 16a so that the drive direction of the movable mirror 16 is turned back to the negative direction. Such scanning of the movable mirror 16 is repeatedly executed, and the number (for example, four) of interferograms set in step S11 is stored in the reference data storage unit 31 (step S13). Note that data acquisition can also be performed in the reciprocating direction of the movable mirror 16.

(4) Measurement of sample components to preparation of chromatogram Next, the sample component gases separated by the chromatograph device 60 are sequentially introduced into the gas cell 23, and scanning of the movable mirror 16 in the same range as when the reference data is acquired is performed. Data is collected while being repeatedly executed (step S14). Interferograms (hereinafter referred to as “measurement data”) acquired by each scan are sent to the difference amount calculation unit 32. In the difference amount calculation unit 32, the difference in signal information between the plurality of reference data read from the reference data storage unit 31 and the measurement data is digitized by calculation using the Gram Schmitt method (step S15). The numerical value is sent to the chromatogram creation unit 33, and the quantitative value of the infrared absorption is plotted in time series using the calibration curve obtained in advance, thereby showing the time change of the infrared absorption in the desired wavelength region. An infrared absorption chromatogram is created (step S16). The created infrared absorption chromatogram is displayed on the monitor 40 in almost real time.

  According to the above FTIR according to the present embodiment, the entire range necessary for spectrum generation is not scanned as in the prior art, but the movable mirror is driven only to the range used for quantitative calculation of the change in infrared absorption amount. Therefore, it is possible to measure a change in absorbance in a specific wavelength region at a speed several times faster than general spectrum measurement. As a result, it is possible to scan the sample at shorter time intervals.

  The best mode for carrying out the present invention has been described above using the embodiments. However, the present invention is not limited to the above-described configuration, and appropriate modifications are allowed within the scope of the gist of the present invention. Is. For example, in the above-described embodiment, the normal spectroscopic FTIR is added with the function of performing the high-speed measurement of the change in the infrared absorption amount according to the present invention. It can also be realized as a device dedicated to change measurement.

The schematic block diagram of FTIR which concerns on one Example of this invention. The functional block diagram which shows the control / processing part of FTIR of the Example. The flowchart which shows the measurement procedure of the infrared absorption amount change using FTIR of the Example. The wave form diagram for demonstrating the operation | movement of FTIR which concerns on the Example. It is a conceptual diagram which shows the motion of the movable mirror in an interference spectrophotometer, (a) shows the conventional interference spectrophotometer, (b) shows the interference spectrophotometer which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Airtight chamber 11 ... Infrared light source 12 ... Condensing mirror 13 ... Collimator mirror 14 ... Beam splitter 15 ... Fixed mirror 16 ... Moving mirror 16a ... Moving mirror drive part 17 ... Laser light source 18, 19 ... Mirror 20, 25 ... Light Detector 21 ... Parabolic mirror 22 ... Sample chamber 23 ... Gas cell 24 ... Ellipsoidal mirror 26 ... Amplifier 27 ... Sample hold circuit 28 ... A / D converter 29 ... Signal generator 30 ... Control / processor 31 ... Reference data Storage unit 32 ... Difference calculation unit 33 ... Chromatogram creation unit 34 ... Preset storage unit 35 ... Setting storage unit 36 ... Drive control unit 40 ... Monitor 41 ... Input unit 50 ... Bandpass filter 60 ... Chromatograph device

Claims (3)

An interferometer that includes a light source that generates infrared light, a fixed mirror, and a movable mirror to generate interference light from the infrared light, an optical system that irradiates the sample with the interference light, and reflected or transmitted light from the sample In an interferometric spectrophotometer comprising a detector to detect,
a) comparing the interferogram obtained by each scan of the movable mirror with a reference interferogram, and calculating the amount of infrared absorption from the difference in shape;
b) a movable mirror drive control means for limiting the drive range of the movable mirror in each scan to a region necessary for collecting data used for absorption amount calculation in the absorption amount calculation means;
An interference spectrophotometer characterized by comprising:   2. The interference spectrophotometer according to claim 1, further comprising a bandpass filter that allows light in a measurement wavelength range to pass through an optical path from the interferometer to the detector.   A program for causing a computer to function as the absorption amount calculating means and the moving mirror drive control means according to claim 1.

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