Modifications and insights into a method for the analysis of the nitrogen mustard mechlorethamine by high-performance liquid chromatography

Previously, a method was presented for the analysis of mechlorethamine by derivatization of this unstable nitrogen mustard to bis(2-phenylthioethyl)methylamine (PTEMA), a stable compound suitable for analysis by HPLC with UV detection [J.C. Reepmeyer, J. Chromatogr. A, 1085 (2005) 262]. Mechlorethamine HCl served as a reference standard and it was derivatized in situ simultaneously with samples of mechlorethamine HCl in ointment preparations. This paper presents the synthesis of PTEMA on a gram scale, synthesis of its picrate salt, bis(2-phenylthioethyl)methylamine picrate (PTEMAP), and isolation of the picrate as a crystalline solid. PTEMAP may serve as a reference standard replacing the toxic mechlorethamine HCl. Insights into the handling, storage, drying, and hygroscopic properties of mechlorethamine HCl and PTEMAP are discussed. In addition, one step following the derivatization procedure in the original method is recognized as a potential for error, and a procedure relating to the order of addition of reagents is presented to avoid this error. The method has been extended to the analysis of mechlorethamine in aqueous solutions.