A measured volume of sample, approximately one-liter, is extracted with chloroform using liquid-liquid extractions in a separatory funnel. The chloroform extract is back-extracted with acid, neutralized, and extracted with chloroform. The chloroform is exchanged to methanol and concentrated using a rotary evaporator and nitrogen blowdown. It is then brought to a volume of 5 mL with an acetate buffer. HPLC conditions are described which permit the separation and measurement of the benzidine compounds using an electrochemical detector.