Analytical problems encountered with NIOSH method 5521 for total isocyanates

A recent analysis for total isocyanates in air using National Institute for Occupational Safety and Health Method 5521 presented difficulties in the identification of an oligomeric isocyanate species. Two problems were encountered during the analysis. A false negative response in the high performance liquid chromatography chromatogram was encountered in a majority of the field samples. An anomalous peak served to give a false positive in some of the field blanks and in some of the field samples. Through supplementing the ratio criterion of Method 5521 using the complete UV absorption spectrum from a photodiode array (PDA) UV detector, the two peaks were successfully identified. However, this need for additional data to identify an oligomeric isocyanate species raises the question of whether the ratio criterion of Method 5521 allows the qualitative identification of isocyanate oligomers.