No abstract

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-Methoxypheny1)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 a t 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 HPLCultraviolet detection methods for isocyanate analysis. The electrochemical 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'-diisocyanato-dipheny1)methane in air.

Short Communications 101 8411 01 85 80 70 60 50 40 30 20 1 0 0 TIME (rnin.) Figure 1 HPLC separation of phosphatidic acid dibenzyl esters (PABE), derived from egg yolk phosphatidylcholines (PC). Column: p-Bondapak C-18. Mobile phase: acetonitrile : water (95 : 5, by volume). Flow rate: 2 mllmin at 1,500 psig Detector: UV at 254 nm. Peaks: 1 = 16 : 1/18 : 2 PABEI), 3 = 16 : 0/20 : 4 PABE, 5 = 16 : 0/18 : 2 PABE, 7 = 16 : 0/18 : 1 PABE, 9 = 18 : 0/18 : 1 PABE. 2 = 18 : 2/18 : 2 PABE, 4 = 18 : 1/18 : 2 PABE, 6 = 18 : 1/18 : 1 PABE 8 = 18 : 0118 : 2 PABE,3) An explanation of the chemical notation is given in footnote (2) at the bottom of the text.

The following are summaries of seven of the papers presented at the SAC 80 Conference, which was held on July 20th-25th, 1981, at the University of Lancaster. Further summaries will appear in subsequent issues of Analytical Procsedings.

The United Kingdom Health and Safety Commission has set a 'common control limit' for workplace exposure to all isocyanates. This limit replaces the previous United Kingdom threshold limit values, which were set for just four species of monomeric isocyanate compounds. This new control limit is set at 20 micrograms of isocyanate group per cubic meter of air expressed as an eight-hour weighted average, and 70 micrograms of isocyanate group per cubic meter of air as a 10-minute weighted average. These new control limits make it necessary that analytical methods should be capable of measuring total isocyanate concentration, including monomers and prepolymers. A previously available method for determining isocyanate monomers using 1-(2-methoxyphenyl)piperazine with high performance liquid chromatography (HPLC) has been modified to measure both monomer and prepolymer. A dual detection system employing electrochemical and ultra-violet detectors is used to identify isocyanate-derived HPLC peaks which are then quantified by reference to a monomer standard, thus avoiding the necessity of isolating prepolymer standards. The total isocyanate-in-air concentration is then calculated from the total area of the isocyanate-derived HPLC peaks. The precision of the method is better than 10% over the range 35 to 140 micrograms(NCO)/m3 for a 10 min sample.