Liquid chromatography analysis of erythromycin A in salmon tissue by electrochemical detection with confirmation by electrospray ionization mass spectrometry

A rapid and sensitive method is described for the quantitation of erythromycin A (EA) in edible salmon tissue by liquid chromatography (LC) analysis using either electrochemical detection (ED) or electrospray ionization mass spectrometric (ESI/MS) detection. The salmon tissue is extracted with 10 mM ammonium formate. The extract is then purified by solid phase extraction using a hydrophilic-lipophilic balanced (HLB) polymeric-based C18 packing, followed by partitioning of EA into methylene chloride at alkaline pH, evaporation, and final dilution. The mean recoveries of EA at 50, 100, 200, and 400 ppb levels in fortified salmon tissue were 63.8 +/- 6.0 and 75.5 +/- 5.4% by LC-ED and LC-ESI/MS, respectively. There was no evidence of formation of the anhydro-EA (m/z 716) decomposition product of EA (m/z 734) that was reported to occur by other published methods.