False-positive result when a diphenylcarbazide spot test is used on trivalent chromium-passivated zinc surfaces

Research output: Contribution to journalJournal articleResearchpeer-review

Background: A colorimetric 1,5-diphenylcarbazide (DPC)-based spot test can be used to identify hexavalent chromium on various metallic and leather surfaces. DPC testing on trivalent chromium-passivated zinc surfaces has unexpectedly given positive results in some cases, apparently indicating the presence of hexavalent chromium; however, the presence of hexavalent chromium has never been confirmed with more sensitive and accurate test methods. Objectives: To examine the presence of hexavalent chromium on trivalent chromium-passivated zinc surfaces with a DPC-based spot test. Methods: A colorimetric DPC spot test was used for the initial detection of hexavalent chromium on new and 1-year-aged trivalent chromium-passivated zinc surfaces. Then, X-ray photoelectron spectroscopy (XPS) was performed for all samples. Results: The DPC spot test indicated the presence of hexavalent chromium in aged, but not new, trivalent chromium passivation on zinc; however, subsequent analysis by XPS could not confirm the presence of chromium in a hexavalent state. Conclusions: Unintended oxidation of DPC induced by atmospheric corrosion is suggested as a possible reason for the false-positive reaction of the DPC test on a trivalent chromium-passivated zinc surface. Further validation of the use of the DPC test for chromium-containing metallic surfaces is required.

Original languageEnglish
JournalContact Dermatitis
Issue number5
Pages (from-to)315-320
Number of pages6
Publication statusPublished - 2018

    Research areas

  • contact allergy, DPC spot test, EU regulation, false-positive result, hexavalent chromium, trivalent chromium passivation of zinc

ID: 217393694