Prior to extraction, 75 mg ammonium sulfamate is added to the samples to break down any nitrosating components in the sample that could generate false-positive signals on analysis.After adding 1 mL of phosphoric acid (40%) to increase its affinity for the aqueous phase by protonation of NMMO and 2 g of sodium sulfate, 2 mL of a 1: 1 mixture of dichloromethane and ethyl formate are applied.