GB/T 6040-2002General rules for infrared analysis (English PDF)

3.1 Transmittance

The ratio OF the radiant energy transmitted through the sample TO the incident radiant energy.

3.2 Baseline

A straight line or curve drawn in a certain way on the absorption spectrum, which is used to represent the background absorption curve in the absence of absorption band.

3.3 Sample thickness

difference calculation, baseline correction, kubelka-munk transformation, kramers-kroning transformation, spectroscopic data retrieval, etc.

4.2.1.6 Display record. DISPLAY the analysis result and data processing result

on the screen. It consists of display and recorder.

4.2.2 Dispersive infrared spectrometer

4.2.2.1 Light source. Same as 4.2.1.1.

4.2.2.2 Sample chamber. The sample chamber consists of a sample cell, a sample holder, and a sample holder for assembling accessories. The dispersive infrared spectrometer is usually a double-beam spectrometer. The sample optical path and the reference optical path are respectively provided with a sample holder.

4.2.2.3 Spectrophotometric part. It consists of dimmer, optical splitter, detector, amplifier, calculator, etc. The optical system of the dispersive infrared spectrometer (optical zero method) is shown in Figure 5.

a) Dimmer. An optical element used for dimming in the optical zero method.

It is set in the reference optical path, to adjust the intensity of the beam passing through the reference optical path to be almost the same as the intensity of the beam passing through the sample optical path.

b) Fan-type mirror. A rotating mirror which switches the sample beam and the reference beam.

c) Optical splitter. An optical system consisting of a slit, a reflector, and a dispersing element. The dispersing element uses a prism, a diffraction grating, or an optical element thereof. A diffraction grating is usually used.

d) Detector. CONVERT the intensity of incident light into an electric signal. A vacuum thermocouple, a thermoelectric detector, or a semiconductor detector, etc. is usually used.

e) Amplifier. To process the signal conveniently, amplify the signal obtained by the detector. In the optical zero method, it consists of a preamplifier, a main amplifier, a synchronous rectifier, a modulator, and a power amplifier.

f) Calculator. In the signal processing system using the electric ratio method, the electric signal of sample beam is separated from the electric signal of reference beam. The intensity ratio of the two signals is calculated.

4.3.6 Temperature change cell. A sample cell used to determine the infrared

absorption of a sample at various temperatures, which can change the sample temperature.

4.3.7 ATR measuring device. A device used to measure the high-absorption

sample or sample surface.

4.3.8 Diffuse reflection measuring device. A device for directly measuring a

powder sample.

4.3.9 Reflection measuring device. A device for measuring the reflection

spectrum, which has the following two types.

a) Reflection measuring device. A device for determining the specular reflection spectrum of a substance having an infrared reflecting surface by means of reflectance spectroscopy.

b) High-sensitivity reflection measuring device. A device used for high- sensitivity measurement of samples with high reflectivity and smooth surface.

4.3.10 Radiation measuring device. A device for determining the radiation

spectrum of a heated sample.

4.3.11 Photoacoustic spectrometric device. A measuring device using a

photoacoustic detector when measuring a high-scattering sample or a sample which is difficult to prepare.

4.3.12 Microscopic infrared measuring device. A device for measuring a very

small amount of sample, which can perform transmittance, reflection, ATR, and high-sensitivity reflection measurement by changing the optical path and the optical mirror.

4.3.13 Gas chromatography infrared (GC-IR) combined device. A device which

uses infrared analysis for components separated by a gas chromatographic column.

4.3.14 Liquid chromatography infrared (LC-IR) combined device. A device

which uses infrared analysis for components separated by a liquid chromatographic column.

4.3.15 Thermogravimetric infrared (TG-IR) measuring device. A device which

uses infrared analysis for the gas component generated by a thermogravimetric device.

4.4 Additional functions

4.4.14 Quantitative calculation. The function of using the absorption intensity to

calculate the concentration of a component.

4.4.15 Data storage. The function of saving measurement results and data

processing results.

5.1 General precautions. When performing infrared analysis, according to the

analysis purpose, sample state, analytical method, and the performance of measuring device, the appropriate sample preparation method must be selected. For qualitative analysis, the concentration of sample shall be adjusted so that the transmittance of the strongest absorption band of the sample is

1%~10%. For quantitative analysis, the appropriate sample concentration, sample thickness, and optical path length of sample cell shall be selected, so that the relationship between the absorbance of the measured absorption band and the sample concentration is in a linear relationship.

5.2 Preparation methods of solid sample

5.2.1 Thin-film method. There are the following four methods.

a) USE a volatile, highly soluble solvent such as methanol, acetone, or trichloromethane to dissolve the sample. The sample solution is dropped on the infrared permeable material plate, expanded. After the solvent is volatilized, a thin film is obtained.

b) A thermally-stable thermoplastic solid sample is sandwiched between two heating plates and pressed to form a thin film.

c) When it is desired not to change the shape of sample as much as possible,

USE a microtome to slice it.

d) For a sample having elasticity such as a rubbery shape or a foamed shape, it is measured by pressurization into a thin film shape using a rhombus frame.

black-body radiation of sample at the same temperature, to correct the intensity of spectrum.

e) Photoacoustic spectrometry. FILL the sample cell with the sample. When the amount of sample is too small, it shall be enriched using a matrix such as potassium bromide powder. The shape of sample has little effect on the determination, but when the space inside the sample cell is too large, the signal-to-noise ratio deteriorates.

f) GC-IR determination. SELECT a solvent which matches the polarity of sample and has a high solubility to dissolve the sample.

g) LC-IR determination. SELECT the LC mobile phase with less infrared absorption and matching the polarity of sample to dissolve the sample.

h) TG-IR determination. When the sample is in the form of lumps or granules, the sample shall be powdered, to ensure accurate measurement.

5.3 Preparation methods of powder sample

5.3.1 Tableting method. Same as 5.2.2.

5.3.2 Solution method. Same as 5.2.3.

5.3.3 Paste method. The powder sample is mixed and ground with the liquid paraffin. The paste is sandwiched between two salt tablets.

5.3.4 Other methods. When using accessories, except for the following

methods, refer to the operating instructions for the accessories.

a) Diffuse reflectance method. The sample is pulverized into a powder having a grain size of several tens of micrometers or less; and laid flat on a sample dish. In order to reduce the influence of specular reflected light, potassium bromide, potassium chloride, or potassium fluoride powder is usually mixed.

b) Photoacoustic spectroscopy. Same as 5.2.5 e).

c) GC-IR method. Same as 5.2.5 f).

d) LC-IR method. Same as 5.2.5 g).

e) TG-IR method. Same as 5.2.5 h).

5.4 Preparation methods of liquid sample

6.3.6 Repeatability. Under the same conditions, in a short period of time, the

same stable sample is measured twice or more, to confirm that the deviation of measured values of wavenumber and transmittance is within a prescribed range.

7.2 When using the above methods to confirm a chemical substance or using

a functional group or atomic group information to speculate a partial structure, it shall pay attention to the following matters.

7.2.1 USE characteristic absorption table and data set for analysis. When

speculating, it shall be noted that the infrared absorption of functional group and atomic group of the substance under determination is affected by the atoms, molecules, etc. adjacent thereto; and the position, intensity, and shape of absorption peak will change.

7.2.2 USE information on known chemical properties, physicochemical

properties, analytical chemistry, etc.

7.2.3 It is difficult to perform qualitative analysis of mixture using only infrared absorption spectral analysis. Chromatography shall be used to separate the mixture into a single component. Combined with information obtained by other analytical chemistry means, analysis shall be performed.

7.2.4 When confirming a compound or using a partial structure to speculate a

compound, it shall be compared with the absorption spectrum measured under associated with the spectroscopic data of the sample under determination.

Calculate the concentration of each component.

8.2.2.2 Factor analysis method. The main component is subjected to matrix transformation by using spectroscopic data group obtained by regression analysis method or PLS regression analysis method, to determine a few quantitatively-necessary spectroscopic data, remove unnecessary factors caused by noise, find the relationship between parameters and concentration, and calculate the concentration of each component.

9.1.3 In accordance with the high-pressure gas treatment method, the high-

pressure gas is operated.

9.1.4 When using liquid nitrogen, protective equipment must be used, to avoid inhalation of high concentrations of gas.

9.1.5 PAY close attention to the safe use of window materials such as thallium, selenium, and arsenic compounds, various hazardous solvents such as halides and carbon disulfide, and the samples. When discarding, perform proper disposal.

9.2 Maintenance. Confirm that the installation site meets the conditions listed

in 6.1.SET inspection items, maintenance items, contents, time, etc.; and

CHECK on time.