Analysis of incurred crystal violet in Atlantic salmon (Salmo salar L.): comparison between the analysis of crystal violet as an individual parent and leucocrystal violet and as total crystal violet after oxidation with 2,3-dichloro-5,6-dicyanobenzoquinone

Abstract

Due to on-going concern about the occurrence of triphenylmethane dye residues in fish destined for human consumption, a depletion study of crystal violet in salmon was carried out. Atlantic salmon less than 12 months old were exposed to crystal violet in fresh water at 15°C and subsequently sampled at 1, 7, 14, 28, 63 and 91 days after exposure. The salmon were then analysed by two analytical methods. In the first method, 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) was used to oxidise leucocrystal violet to its parent form. Total parent crystal violet was then analysed by LC-MS/MS. In the second method, crystal violet and leucocrystal violet were analysed individually by LC-MS/MS without oxidation. Both methods gave comparable results for total crystal violet concentrations, with a correlation of r ²= 0.69. Statistical treatment for 88 incurred salmon samples showed no significant difference between the two sets of results with t = 1.68 and t _crit = 1.99. Up to 98% of crystal violet was metabolised to its leuco form in the salmon after 1 day of exposure and could be detected at significant concentrations (approximately 20 µg kg^–1) 91 days after exposure. The depletion data also suggest that crystal violet has a half-life of approximately 15–16 days in salmon.

Keywords:

• fish
• veterinary drug residues
• chromatography – LC/MS
• regulations
• clean-up
• in-house validation

Acknowledgements

The Veterinary Medicines Directorate, an executive agency of the Department for Environment, Food and Rural Affairs (DEFRA), is gratefully acknowledged for funding this work. Salmon dosing was carried out by the Centre of Environment, Fisheries and Aquaculture Science (CEFAS) in Weymouth, UK.