Hello
somebody has experience with cysteine derivatization using ethylchloroformate. I'm trying to derivatize cysteine in body fluids. Initially I obtain peaks (m/z 294,m/z 220). After several injections I see no peaks anymore.

I'm trying to use Husek's methodology.

Husek P, Matucha P, Vrankova A, Simek P.
Simple plasma work-up for a fast chromatographic analysis of homocysteine,
cysteine, methionine and aromatic amino acids.
J Chromatogr B Analyt Technol Biomed Life Sci. 2003 Jun 15;789(2):311-22.

- Husek P.
Chloroformates in gas chromatography as general purpose derivatizing agents.
J Chromatogr B Biomed Sci Appl. 1998 Oct 9;717(1-2):57-91. Review.

- Husek P.
Simultaneous profile analysis of plasma amino and organic acids by capillary
gas chromatography.
J Chromatogr B Biomed Appl. 1995 Jul 21;669(2):352-7.

Thank you again.