Counterfeit homeopathic medicinal products: syrups. A simple and rapid LC-ESI-MS method to detect preservatives not declared in label.

A rapid and simple LC-ESI-MS method for the simultaneous detection and quantitation of six preservatives in homeopathic syrups has been developed. Counterfeit homeopathic syrups are suspected to contain preservatives that are not declared in label. For this reason a method to ascertain the absence of sorbic and benzoic acids, methyl-, ethyl-, propyl- and butyl-parabens, as the most frequently utilised preservatives, has been developed. Analytes were eluted with a linear gradient of acetonitrile-5mM ammonium acetate in 12 min using 2,4-dichlorobenzylalchol as Internal Standard. The HPLC separation was performed on an Eclipse XDB-C18 (2.1 mm x 50 mm-5 microm) column and the ESI-MS detection was performed in negative ion mode. Linearity of the method was studied in the range of 2 pg to 10 ng injected and correlation coefficients r2 > or =0.9992 were obtained. LOD ranged from 0.04 to 0.4 ng mL(-1).