Application of electrochemical detection to the measurement of free monomeric aromatic and aliphatic isocyanates in air by high-performance liquid chromatography
A method based on high-performance liquid chromatography (HPLC) with electrochemical detection is described for the determination of aromatic and aliphatic isocyanates in air. 1-(2-Methoxyphenyl)piperazine is used as the electrogenic reagent. It forms electrochemically active derivatives with all of the isocyanates of occupational hygiene interest that are readily oxidised at carbon electrodes. In addition, these derivatives are strongly absorbing in the ultraviolet region, enabling a combination of electrochemical and ultraviolet detectors to be employed to provide additional qualitative information if required.
Comparison is made between the electrochemical detection method and HPLC-ultraviolet detection methods for isocyanate analysis. The electro-chemical detection method was found to be significantly more sensitive than the ultraviolet detection methods for the determination of phenyl isocyanate, toluene diisocyanate, hexamethylene diisocyanate and (4,4′-diisocyanatodiphenyl)methane in air.