Mechanism Of Action Of Adulterants

Adulterants such as bleach cause a false-positive result in THC radioimmunoassay but false-negative results with both FPIA and EMIT assay. These erroneous results are due to direct effect of bleach on the reagents in the immunoassays (13,43). Adulterants that are strong oxidizing agents such as Klear (potassium nitrite), Urine Luck (PCC) and Stealth (peroxidase and hydrogen peroxide) cause false-negative results in the immunoassays used for screening drugs by directly destroying THC metabolites (THC-COOH). In the GC/MS confirmation stage (GC/MS), these adulterants interfere with confirmation of THC-COOH because of destruction of THC-COOH and internal standard as well as interference during the extraction phase. To overcome this problem, the use of reducing agents such as sodium hydrosulfite or sulfamic acid prior to extraction has been recommended (30). However, such steps can allow detection of remaining THC-COOH but cannot recover the lost concentration of the marijuana metabolite. Most oxidizing agents used as adulterants are more effective if the pH of urine is acidic. To prevent destruction of drugs by oxidizing agents, addition of carbonate as a buffering agent prior to or after urine void has been recommended (44). Other oxidizing agents such as potassium permanganate, hydrogen peroxide/ferrous ammonium sulfate, periodic acid, potassium persulfate, and sodium oxychloride can also destroy THC-COOH within 48 h. The effect of oxidizing agents on THC-COOH primarily depends on the reduction potential (E0 ), pH, temperature, time of reaction and urine constituents. Horseradish peroxidase with hydrogen peroxide, combination of hydrogen peroxide with Japanese radish, and black mustard seed and red radish are all effective in destroying THC-COOH. Interestingly, hydrogen peroxide alone had no effect in destroying any drug (45).

Adulterants can also interfere with the extraction process. Stealth is known to interfere with extraction of codeine and morphine for GC/MS confirmation (37). Our experience indicates that PCC is effective for decreasing the semi-quantitative response rate for THC and opiates using Abuscreen (FPIA). The incubation time played an important role in decreasing the response rate. Nitrite is very effective in reducing the response rate of THC, but PCP assay was also affected.

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