Objectives: To find a suitable method for detecting zinc sulfate in adulterated urine.
Methods: Two rapid spot tests to detect the presence of zinc sulfate in urine were developed.
Results: Addition of 3 to 4 drops of 1N sodium hydroxide solution to approximately 1 mL of urine containing zinc sulfate led to the formation of a white precipitate, which was soluble in excess sodium hydroxide. In the second spot test, addition of 3 to 4 drops of 1% sodium chromate solution to 1 mL of urine containing zinc sulfate followed by the addition of 4 to 5 drops of 1N sodium hydroxide led to formation of a yellow precipitate (zinc chromate). Detection limit of these visual spot tests was 10 mg/mL of zinc sulfate in urine. Twenty drug-free urine specimens and urine containing high amounts of sugar or reducing substances were tested with no false-positive spot test results observed. However, if lead is present in high amounts in urine, it may cause false-positive spot test results. When aliquots of urine controls for drugs of abuse testing were supplemented with different amounts of zinc sulfate, false-negative drug test results were observed except for amphetamine. Zinc sulfate also falsely reduced measured urine alcohol level in urine.
Conclusions: Zinc sulfate can invalidate urine drug and alcohol testing but can be detected using the novel spot tests developed.
Keywords: Adulterated urine; False negative; Spot test; Zinc sulfate.