Minneapolis Veterans Affairs Medical Center, Forensic Toxicology Laboratory Minneapolis, MN 55417, USA
Medtox Laboratories Inc, St. Paul, MN 55112, USA

We have developed a method that uses high performance ion chromatography to quantify the amount of nitrite present in adulterated urine samples. The method uses the IonPac AS 14 analytical column with the Dionex Bio LC AI 450 equipped with an anion self-regenerating suppressor and a conductivity detector. Urine samples are spiked with potassium bromide which serves as an internal standard and diluted with mobile phase. The diluted urine samples are injected into the HPLC system where the anions are resolved isocratically using a mobile phase consisting of 3.5mM sodium carbonate and 1 mM sodium bicarbonate. The nitrite is quantified using a single point calibrator (1000ug/ml).

Using this method we have shown that samples from patients whose urine is infected with bacteria and have a positive reaction on a clinical reagent strip for nitrite have very low to unmeasureable concentration of nitrite. This observation confirms earlier published data. This high performance ion chromatography method has excellent day to day precision with a CV of 6% at concentrations of 1200 ug/ml and 3000 ug/ml. The recovery of nitrite spiked into urine samples at a concentration of 12,000 ug/ml was at 95%. The method is capable of accurately quantifying nitrite up to a concentration of 40,000 ug/ml. Analysis by HPLC of urine samples from Workplace drug testing programs that screened positive by the nT Perfect adulteration detection reagent (Chimera Research & Chemical) showed that the concentration of nitrite in these samples was greater than 1000ug/ml. This method provides definitive confirmation for nitrite.