Novel spot tests for detecting the presence of zinc sulfate in urine, a newly introduced urinary adulterant to invalidate drugs of abuse testing

Am J Clin Pathol. 2013 Oct;140(4):572-8. doi: 10.1309/AJCP2FJ9VBPXJYTQ.


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.

MeSH terms

  • Artifacts
  • Carbohydrates / chemistry
  • Clinical Laboratory Techniques / methods*
  • Drug Contamination
  • False Negative Reactions
  • False Positive Reactions
  • Humans
  • Reducing Agents / chemistry
  • Substance Abuse Detection / methods*
  • Urinalysis / methods*
  • Zinc Sulfate / analysis
  • Zinc Sulfate / urine*


  • Carbohydrates
  • Reducing Agents
  • Zinc Sulfate