SAMPLING INTERCOMPARISONS FOR ALDEHYDES IN SIMULATED WORKPLACE AIR

Thirty one laboratories of various EU Member States have participated in two interlaboratory comparisons in order to assess errors of person al sampling methods associated with both the sampling and the analytic al steps, In contrast to conventional quality control schemes, this pr oject particularly focuses attention on the sampling and identificatio n step; it is executed by means of sampling exercises and has included discussions on potential sources of error, In a sampling exercise, pa rticipants come to a central facility and perform measurements on synt hetic workplace air in a laboratory installation, Concentration levels of formaldehyde, acrolein, glutaraldehyde and acetaldehyde between 0. 1 and 2 times the limit value for workplace air were prepared at vario us humidity levels and with acetone, occasionally, as interferent, Sam pling times varied from 1-4 h. The related analytical work is performe d at the analyst's own laboratory, The intention is for each participa nt to determine the observed value of the delivered standard atmospher e using the sampling method of his own choice, Trueness (bias), precis ion and relative overall uncertainty of each method-laboratory combina tion is calculated and verified towards compliance with EN 482, which outlines minimum performance criteria, The first challenge involved th e precise gas phase generation of the selected analytes in high air fl ows (up to 300 1 min(-1)) and calculating the true value only by direc t reference to primary standards, This was accomplished by modifying t he capillary dosage injection technique so that reactive compounds, li ke low molecular mass aldehydes, could be dosed with the same accuracy and precision as unreactive solvents, A permeation tube with high emi ssion rate was developed for formaldehyde. Up to ten different samplin g techniques were evaluated, The measurement methods used by the major ity of the participants were based on pumped sampling on silica cartri dges (or tubes) and glass fiber filters, coated with 2,4-dinitrophenyl hydrazine. It was observed that for formaldehyde, and in some cases fo r acetaldehyde and glutaraldehyde, the majority of the method-laborato ry combinations complied with an overall uncertainty of 30%. The resul ts for acrolein, however, indicated a systematic negative bias, often larger than minus 50% of the true value, caused by the decomposition o f the acrolein DNPH derivative in the presence of excess acid and exce ss DNPH.