Commutability of calibration and control materials for serum lipase.

BACKGROUND: To effectively assess and correct for intermethod variability, calibration and control materials (CCMs) must show the same intermethod behavior as patient sera, i.e., they must be commutable. We describe the commutability of selected CCMs for lipase assays, the impact of noncommutability of CCMs in normalizing patient results, and characteristics of reagents that affect assay specificity and commutability. METHODS: Lipase was measured in 98 patient sera and in 29 commercial CCMs, with 2 commercial methods using different substrates and with 4 experimental methods using 1,2-o-dilauryl-rac-glycero-3-glutaric acid-(6'-methylresorufin) ester as substrate and colipase as cofactor, but differing in the stabilizing proteins used and in the size of the substrate micelles. RESULTS: The noncommutability rate, i.e., the frequency of aberrant intermethod behavior of CCMs in comparison with patient sera, was 27% for liquid CCMs and 47% for lyophilized CCMs. The normalized residuals, measuring the degree of noncommutability, were -2.3 to 2.4 for CCMs with "normal" lipase activity, and -3.5 to 21.7 for CCMs with higher lipase activity. Recalculation of patient results with CCMs as calibrators decreased or increased the original bias according to whether the CCMs were commutable. CONCLUSIONS: For the lipase methods in this study, the frequency of noncommutability of CCMs is affected by assay-specific characteristics, including size of substrate micelles and the presence or absence of added proteins.

Gas chromatography of 4,4'-diphenylmethane diisocyanate in the workplace atmosphere.

A sensitive gas chromatographic procedure for the determination of 4,4'-diphenylmethane diisocyanate concentration in air is described. Traps containing 20-40-mesh silica gel coated with phosphoric acid are used. After the aspiration of the air, the silica gel is eluted with sodium hydroxide in methanol. The amine formed is then separated with a gas chromatograph and measured with a nitrogen-phosphorus detector. This can be performed in 7 min. Virtually no breakthrough occurs if an air concentration of up to 128 nmol in 20 l is sampled. The detection limit based on a 20-1 air sample is 0.7 microgram/m3. Complete analysis requires about 30 min. The method was used to determine the concentration of 4,4'-diphenylmethane diisocyanate in working environments during spraying operations.