Spot Test 2

Stock solution: 1% potassium iodide in distilled water.

1. In a test tube add approximately 200 ^L of stock potassium iodide solution (~6-7 drops from a transfer pipette).

2. Add about 100 ^L of urine specimen (~3-4 drops) suspected of nitrite adulteration.

3. Add two drops of 2 N hydrochloric acid. Immediate release of iodine from the colorless potassium iodide solution is observed if nitrite is present in the urine. Shaking of this solution with n-butanol results in the transfer of iodine in the organic phase. If no nitrite is present, the potassium iodide solution remains colorless. There is no interference from high glucose or ketone bodies if present in the urine (26).

3.8.3. Other Tests to Detect Nitrite

Nitrite can also be detected by diazotizing sulfanilamide and coupling the product with N-(1-napthyl) ethylenediamine. The presence of nitrite in urine can also be confirmed by analysis using high performance liquid chromatography using an IonPac AS 14 analytical column with an anion self-generating suppressor and conductivity detector. Using a single-point calibration, the assay was linear up to a nitrite concentration of 12, 000 ^g/mL. The detection limit was 30 ^g/mL (34). Kinkennon et al. described a capillary electrophoresis method for detection of nitrite in urine specimens suspected of adulteration. The method involved separation of nitrite by capillary electrophoresis and direct UV detection at 214nm. Separation was achieved by using a bare fused silica capillary column and 25 mM phosphate buffer at pH 7.5. The method was linear for a nitrite concentration of 80-1500 ^g/mL, with a limit of detection of 20 ^g/mL. However, CrO42- and S2O82- as well as high concentrations of Cl-interfered with the chromatography (35).

3.9. Stealth as a Urinary Adulterant

Stealth is an adulterant advertised as an effective way to escape detection in a urine drug test. Stealth consists of two vials, one containing a powder (peroxidase) and another vial containing a liquid (hydrogen peroxide). Both products should be added to the urine specimen. Stealth is capable of producing false-negative results using Roche ONLINE and Microgenic's CEDIA immunoassay methods when marijuana metabolites, LSD and opiates (morphine) were present in the urine at 125-150% of cut-off values. Adulteration of an authentic positive sample provided by a marijuana user caused that sample to screen negative using these immunoassay reagents (36). Low concentration of morphine (2500 ng/mL) could be effectively masked by Stealth, but higher concentrations (6000 ng/mL) tested positive by immunoassay (Roche ONLINE and Microgenic's CEDIA immunoassay). GC/MS confirmation step can be affected if Stealth is present in the urine. Cody et al. (37) reported that GC/MS analysis of Stealth-adulterated urine using standard procedures proved unsuccessful in several cases, and in 4 of 12 cases, neither the drug nor the internal standard was recovered.

Valtier and Cody described a rapid color test to detect the presence of Stealth in urine. Addition of 10 ^L of urine to 50 ^L of tetramethylbenzidine working solution followed by addition of 500 ^L of 0.1 M phosphate buffer solution caused a dramatic color change of the specimen to dark brown. Peroxidase activity could also be monitored by using a spectrophotometer. Routine specimen integrity check using pH, creatinine, specific gravity and temperature did not detect the presence of Stealth in urine (38). Our experiences show that if a few drops of a urine specimen adulterated with Stealth is added to potassium dichromate followed by a few drops of 2 N hydrochloric acid, a deep blue color develops immediately which usually fades with time.

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