Toxicology Letters 92 (1997) 139–148 On-line HPLC-tandem mass spectrometry analysis of contaminants of L -tryptophan associated with the onset of the eosinophilia-myalgia syndrome Brian L. Williamson a , Linda M. Benson a , Andy J. Tomlinson a , Arthur N. Mayeno b , Gerald J. Gleich c , Stephen Naylor a,d, * a Biomedical M ass Spectrometry Facility , Department of Biochemistry and M olecular Biology , M ayo Clinic /M ayo Foundation, R ochester, M innesota, 55 905, USA b T suk uba R esearch L aboratories, Pharmacia and Upjohn, 23 W adai, Tsukuba -shi, Ibaraki, 300 -42, Japan c Departments of Immunology and M edicine, M ayo Clinic /Foundation, R ochester, M innesota, 55 905, USA d Department of Pharmacology and Clinical Pharmacology Unit , M ayo Clinic /M ayo Foundation, R ochester, M innesota, 55 905, USA Received 26 March 1997; received in revised form 29 May 1997; accepted 5 June 1997 Abstract The structural characterization of a number of contaminants of L-tryptophan (Trp) associated with eosinophilia myalgia syndrome has been performed for the first time by the powerful structural elucidation technique of tandem mass spectrometry coupled with on-line HPLC (LC-ESI-MS/MS). The identity of the contaminants: peaks UV-5, 3-(phenylamino)alanine, (PAA); E 1,1-ethylidenebis(tryptophan); 200, 2-(3-indolylmethyl)-L-tryptophan; (all iden- tified as case related) and peaks 1, 3-carboxy-1,2,3,4-tetrahydro- -carboline; 2, 3-carboxy-1-methyl-1,2,3,4-tetrahy- dro- -carboline; 100, 2-(2,3 dihydroxy-1-[3-indolyl]propyl)-L-tryptophan; and 300 and 400, diastereomers of 3-carboxy-1-[3-indolyl-methyl]-1,2,3,4-tetrahydro- -carboline, have been confirmed by this technique. By comparison of tandem MS (MS/MS) data from these compounds with the MS/MS data of several other impurities, we have structurally characterized peaks CC, KK and OO, as well as two previously unreported components labeled as peak P18 and peak P31. Peak P18 was unresolved from the large Trp peak and has been characterized as indole-3-ethy- lamine. Peak P31 was previously unresolved from peak 200, a case related compound and therefore its structure is of extreme importance. This compound has been tentatively identified as 2-(3-indolyl)-L-tryptophan. © 1997 Elsevier Science Ireland Ltd. Keywords: Eosinophilia-myalgia syndrome; Tandem mass spectrometry; Liquid chromatography; L-tryptophan *Corresponding author. Tel.: +1 507 2845220; fax: +1 507 2848433; e-mail: naylor.stephen@mayo.edu 0378-4274/97/$17.00 © 1997 Elsevier Science Ireland Ltd. All rights reserved. PII S0378-4274(97)00048-9