Determination of Talc in Indomethacin Capsules by Fourier Transform Infrared Spectroscopy

In order to achieve the accurate determination of talc in pharmaceutical preparations, the method mentioned by the title was proposed. Contents of indomethacin capsules containing about 5 mg of talc were taken, and placed into a porcelain crucible with constant weight at 450 ℃, carbonized at 500 ℃ heating plate for 30 min, and then incandesced at 450 ℃ to constant weight. About half of the residue and 100 mg of potassium bromide were taken, and ground in an agate mortar for 5 min. About 50 mg of the mixture was taken, and pressed into a pellet at pressure of 40 kN for 3 min. The absorbance of the characteristic absorption peak of talc at （669±2） cm⁻¹ was measured by Fourier transform infrared spectrometer, and the content of talc in the sample was calculated according to the linear quantitative relationship between the absorbances and mass fractions of talc. It was shown that the linear range of talc was 0.5%‒3.5%, with the detection limit of 0.05%. RSDs （n=6） of absorbance was less than 4.0% for talc reference pellets and sample pellets. Test for recovery was made according to the standard addition method, giving the recovery in the range of 101%‒110%. The proposed method was applied to the analysis of 87 batches of indomethacin capsule samples from 7 enterprises. Talc was detected in the samples produced by 4 enterprises, and the detection amount was 1.90‒12.70 mg·capsule⁻¹, which was inconsistent with the prescription amount provided by the enterprises, and there were significant differences between batches in the samples produced by 3 enterprises.