Historically, a large number of alternative methods have been devised for the measurement of airborne isocyanates. Nearly all these methods rely on the derivatization of the reactive isocyanate groups to products that can be analyzed, usually by some form of chromatography. The choice of an ideal method relies partly on the requirements of the regulatory authorities, but there are also technical considerations concerning the validity and reliability of the various methods and the cost and availability of instrumentation. It would be comforting if we had a consistent body of advice from the regulatory authorities concerned. However, NIOSH (USA) recommends three methods, OSHA (USA) recommends two methods, ASTM (USA) recommends three methods, NIWL (Sweden) recommends one method and the HSE (UK) recommends two methods. All of these methods are different, with the exception of the l-(2-methoxyphenyl)piperazine (2-MP) and the l-(2-pyridyl)piperazine (2-PP) methods, which appear twice.
Can the International Standardization Organization help? Actually, ISO is preparing four technical specifications. First, it is preparing a method based on the 2- MP reagent (ISO/FDIS 16207). Second, it is preparing a method based on the 9-(l- methyl-anthracenyl)piperazine reagent (New Work Item). Two further methods, based on the dibutylamine method and the Iso-Chek™ method have been agreed as potential new work items but have not been balloted yet. So many alternative methods would seem inconsistent with the ISO objective of variety reduction. The reason is that, in addition to having different areas of application, all existing methods have some disadvantages. Thus, a fifth (guidance) standard is being developed which will explain in more detail the advantages and disadvantages of each method and it is hoped, will point to the development of a genuinely universal method.