Determination of talc in alveolar dusts

Status:

completed 08/1988

Aims:

Talcum powder consists mainly of mineral talcum, a phyllosilicate. As well during the talcum production through grinding of stones as by the utilisation of the powder workers are likely to be exposed to talk. Talcum powders are used in various areas, i.e. as a parting agent in the rubber, asphalt/bitumen, and fodder industries, as a filler or auxiliary product in the plastics or paper processing industries and as an emulsion matrix in the cosmetic or pharmaceutical industry. For talcum (free of asbestos fibres) there is a limit value of 2 mg/m³, measured in the alveolar dust fraction. An analytical method had to be developed for a better control of compliance with the air limit value in the workplace that would allow the talc concentration to be measured on the basis of a respirable dust sample on a membrane filter.

Activities/Methods:

For the quantitative determination of talc an infrared spectrography method was developed using the 3676,6 cm^-1 characteristic absorption band. 50 talc samples were available for the evaluation of the method with partially known mineralogical composition. Out of these samples an optimal sort of talcum was selected for the development and standardisation of a calibration. The following preparation and evaluation approached of air samples was elaborated for routine use: After sampling the filter is dissolved in acetone and the collected mass of dust is separated (centrifugation) and transferred on a fibre glass filter. The loaded fibre glass filter is homogeneously ground with a defined quantity of potassium bromide. The resulting pellet can be analysed by infrared spectrography (determining the integral intensity). The sample preparation can alternatively be made by low-temperature ashing, in which case the sample does not need to be transferred on a fibre glass filter. The presence of anthophylite (a type of amphibole asbestos) disturbs the determination of talc because of overlapping of the characteristic absorption band. An interference in the assessment is also to be expected because of chrysotil, respectively antigorit.

Results:

A method of analysis using infrared spectrograhy was developed for the compliance control of the limit value for talc (free of asbestos fibres) of 2 mg/m³ defined in 1987. The determination of talc takes place with air samples of the alveolar fraction on membrane filters. The absolute detection limit of the method is 0,1 mg. During the talc analysis the presence of asbestos minerals can be controlled within the range of the detection limits of the infrared spectrography. However, with this method it is not possible to determine the presence of the fibrous form of asbestos minerals. Therefore the absence of asbestos fibres cannot be verified.

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