Extracting metalworking fluid aerosol samples in cassettes by provisional ASTM and NIOSH methods

Recent provisional methods for the determination of metalworking fluid aerosol in workplace air involve a solvent extraction procedure to separate the nonvolatile fraction of the fluid from insoluble material such as metal turnings and dirt. The procedure calls for preweighing a filter (W1) and assembling it into a cassette and taking a sample. In the laboratory the filter is removed from the cassette, desiccated to remove any collected water or other volatile substances, and weighed again (W2). The filter is then extracted in an organic solvent blend, allowed to dry, and weighed a final time (W3). The total weight collected by the filter is given by (W2-W1), and the weight of (nonvolatile) metalworking fluid collected is given by (W2-W3). The extraction step can take place within a cassette housing if it is relatively inert to the solvent blend used. The extraction of four metalworking fluids (straight oil, soluble oil, synthetic and semisynthetic) within disposable polypropylene cassettes was investigated using the same protocol used to evaluate the original method. For all fluids the extraction efficiency was greater than 95% with a precision better than 5%. The mean blank contribution to the extraction step was 16 micrograms. Blanks were also evaluated after storage, and after transport and storage. A small additional blank contribution could be removed by desiccation. The limits of detection and quantitation of the extraction step were calculated to be 28 and 94 micrograms, respectively.