Determination of 1-(2-methoxyphenyl)piperazine derivatives of isocyanates at low concentrations by temperature-programmed miniaturized liquid chromatography

A temperature-programmed packed capillary LC method with large-volume injec tion on-column focusing has been developed for screening and determination of 1-(2-methoxyphenyl)piperazine derivatives of airborne toluene-2,4-diisoc yanate, toluene-2, 6-diisocyanate, hexamethylenediisocyanate and methyleneb isphenyl-4,4-diisocyanate, based on sampling methods described in MDHS 25/3 . Injection volumes up to 100 mu l were successfully loaded onto the 250x0. 32 mm I.D. capillary column packed with 3 mu m Hypersil ODS particles. The isocyanate derivatives were loaded at 10 degrees C and eluted by a three-st ep temperature program starting at 10 degrees C for 10 min, followed by a t emperature ramp of 2.5 degrees C min(-1) to 45 degrees C and then 9.9 degre es C min(-1) to 90 degrees C. The mobile phase consisted of acetonitrile-ac etate buffer (3% triethylamine, pH 4.5) (45:55, v/v). The isocyanate deriva tives were dissolved in acetonitrile-acetate buffer (3% triethylamine, pH 4 .5) (30:70, v/v) to achieve sufficient focusing. The concentration limit of detection of the individual derivatives utilizing an "U" shaped flow cell with a 8.0 mm light path and an injection volume of 100 mu l was 44, 87, 43 and 210 pg ml(-1) for toluene-2,6-diisocyanate, hexamethylenediisocyanate, toluene-2,4-diisocyanate and methylenebisphenyl-4,4-diisocyanate, respecti vely. Within the investigated concentration range, 10-500 ng ml(-1), the li near calibration curves gave correlation coefficients ranging from 0.994 to 0.998. The repeatability of the method with regard to retention time and p eak height ranged from 0.3 to 1.1% and 1.1 to 2.3% (n=9) relative standard deviation, respectively. The average recovery of the method, with regard to toluene-2,4-diisocyanate, was 97.7+/-1.6% (n=9). (C) 2000 Elsevier Science B.V. All rights reserved.