红外分光光度法

红外吸收分光光度法

2.2.24. ABSORPTION SPECTROPHOTOMETRY, INFRARED

红外光谱频率在4000～670 cm-1之间（2.5～15.4μm），有时也低至200cm-1 (50μm) 。Infrared spectrophotometers are used for recording spectra in the region of 4000-650 cm−1 (2.5-15.4 μm) or in some cases down to 200 cm−1(50 μm).

仪器设备原理

APPARATUS

记录光谱的分光光度计是由一个合适的光源，单色仪或干涉仪和检测器组成的。傅立叶变换红外分光光度计使用复色光源，利用傅立叶变换计算出随入射光频率变化的原始光谱。也可以使用其他检测领域中配有单色光源系统的红外分光光度计。通常由对比透射光和入射光的强度来获得光谱。

Spectrophotometers for recording spectra consist of a suitable light source, monochromator or interferometer and detector. Fourier transform spectrophotometers use polychromatic radiation and calculate the spectrum in the frequency domain from the original data by Fourier transformation. Spectrophotometers fitted with an optical system capable of producing monochromatic radiation in the measurement region may also be used. Normally the spectrum is given as a function of transmittance, the quotient of the intensity of the transmitted radiation and the incident radiation. It may also be given in absorbance.

吸光率（A）值为透光率（T）的倒数取log10对数的值。

T=I

I0

I0 =入射光强度

I = 透射光强度

Theabsorbance(A) is defined as the logarithm to base 10 of the

reciprocal of the transmittance (T):

,

T=I

I0

I0 = intensity of incident radiation,

I = intensity of transmitted radiation.

制备样品

PREPARATION OF THE SAMPLE

记录吸光率或透光率

FOR RECORDING BY TRANSMISSION OR ABSORPTION

用下列方法制备样品。

Prepare the substance by one of the following methods.

液体：制成两盐片间的液膜或由透明的液体池盛装的样品，也可以直接用红外光照射待测液体。

Liquids. Examine a liquid either in the form of a film between 2 plates transparent to infrared radiation, or in a cell of suitable path length, also transparent to infrared radiation.

悬浊液或乳浊液

Liquids or solids in solution.

用适合的溶剂溶解样品。选择合适的浓度和液体池光程以便得到满意的光谱。通常，液体浓度为10～100g/l，液体池光程为0.1～0.5mm。在参比光路中放入与溶液相同的溶剂池以补偿溶液中溶剂的吸收。如果使用傅里叶变换的红外光谱仪，可以先记录下溶剂以及样品的光谱图，然后通过软件，利用溶剂的系数扣除溶剂的吸收部分。

Prepare a solution in a suitable solvent. Choose a concentration and a path length of the cell which give a satisfactory spectrum. Generally, good results are obtained with concentrations of 10-100 g/L for a path length of 0.5-0.1 mm. Absorption due to the solvent is compensated by placing in the reference beam a similar cell containing the solvent used. If an FT-IR instrument is used, the absorption is compensated by recording the spectra for the solvent and the sample successively. The solvent absorbance, corrected by a compensation factor, is subtracted using calculation software.

固体

使待检物质分散在适合的溶液中（研磨），或者分散在固体中（卤化物压片）；根据专论要求，将熔融的待检物质滴在两盐片之间制成薄膜，然后测定光谱。

Solids. Examine solids dispersed in a suitable liquid (mull) or in a solid (halide disc), as appropriate. If prescribed in the monograph, make a film of a molten mass between 2 plates transparent to infrared radiation.

A研磨法

用少量样品粉末加少量石蜡或者其他适合的液体研磨；通常用5～10mg样品加1滴石蜡研磨，磨好后压入两盐片之间测定光谱。

A. Mull

Triturate a small quantity of the substance to be examined with the minimum quantity of liquid paraffin R or other suitable liquid; 5-10 mg of the substance to be examined is usually sufficient to make an adequate mull using one drop of liquid paraffin R. Compress the mull between 2 plates transparent to infrared radiation.

B压片法

除非另有规定，1～2mg待检测物质加300～400mg干燥的溴化钾或氯化钾细粉，共同磨碎。通常该量的样品足够成压成一个直径为10~15 mm压片，并得到合适的光谱强度。如果检测物质是盐酸盐，推荐使用氯化钾。仔细磨碎混合物，均匀的铺在模子里,在800MPa(8 t·cm−2)压力下压片。导致坏片的原因很多，如过多或太少的研磨，吸潮，分散媒介物中有其他杂质，没有进行充分研磨和颗粒的尺寸不够小等。除非另有规定，不好的压片要弃用：用肉眼观察，压片的透明度不均匀；或没有补偿的情况下，在2000cm-1 (5 µm)左右缺少特殊吸收带，透光率低于60%。

B. Disc

Triturate 1-2 mg of the substance to be examined with 300-400 mg, unless otherwise specified, of finely powdered and dried potassium bromide R or potassium chloride R. These quantities are usually sufficient to give a disc of 10-15 mm diameter and a spectrum of suitable intensity. If the substance is a hydrochloride, it is recommended to use potassium chloride R. Carefully grind the ixture, spread it uniformly in a suitable die, and submit it to a pressure of about 800 MPa (8 t·cm−2). For substances that are unstable under normal atmospheric conditions or are hygroscopic, the disc is pressed in vacuo. Several factors may cause the formationoffaultydiscs,suchasinsufficientorexcessive grinding, humidity or other impurities in the dispersion medium or an insufficient reduction of particle size. A disc is rejected if visual examination shows lack of uniform transparency or when transmittance at about 2000 cm−1 (5 μm)