Talc derived from deposits that are known to contain associated asbestos is not suitable for pharmaceutical use. The manufacturer is responsible for demonstrating by the test for amphiboles and serpentines that the product is free from asbestos. The presence of amphiboles and of serpentines is revealed by X-ray diffraction or by infrared spectrophotometry (see A and B). If detected, the specific morphological criteria of asbestos are investigated by a suitable method of optical microscopy to determine whether tremolite asbestos or chrysotile is present, as described below.
A. Examine by infrared spectrophotometry (2.2.24). In the range 740 cm-1 to 760 cm-1 using scale expansion, any absorption band at 758 cm-1 1 cm-1 may indicate the presence of tremolite or of chlorite. If the absorption band remains after ignition of the substance at 850C for at least 30 min, it indicates the presence of the tremolite. In the range 600 cm-1 to 650 cm-1 using scale expansion, any absorption band or shoulder may indicate the presence of serpentines. Examine the substance prepared as discs using potassium bromide R.
B. Examine by X-ray diffraction employing the following conditions:
Cu Ka monochromatic 40 kV radiation, 24 mA to 30 mA,
incident slit: 1C,
detection slit: 0.2C,
goniometer speed: 1/10C 2q/min,
scanning range: 10C to 13C 2q and 24C to 26C 2q,
the sample is not oriented.
Place the sample on the sample holder; pack and smooth its surface with a polished glass microscope slide.
Record the diffractograms.
The presence of amphiboles is detected by a diffraction peak at 10.5C 0.1C 2q, the presence of serpentines is detected by diffraction peaks at 24.3C 0.1C 2q and at 12.1C 0.1C 2q.
If, by one of the 2 methods, amphiboles and/or serpentine are detected, examine by a suitable method of optical microscopy to determine the asbestos character.
Examined by optical microscopy, the presence of asbestos is shown if the following criteria are met:
a range of length to width ratios of 20:1 to 100:1, or higher for fibres longer than 5 mm,
capability of splitting into very thin fibrils,
and if 2 or more of the following 4 criteria are met:
parallel fibres occurring in bundles,
fibre bundles displaying frayed ends,
fibres in the form of thin needles,
matted masses of individual fibres and/or fibres showing curvature.