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

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.