Malachite green (MG), originally used as a dyeing agent of textiles [1], was introduced as an ectoparasiticide, fungicide and antiseptic in aquaculture in 1933 [2]. The broad fungicidal and anti-parasitical spectrum, and its efficacy in treating trout suffering from proliferative kidney disease (PKD) has made the drug very popular among fish culturists [1].
After administration, MG is prevalently reduced into leuco-malachite green (LMG) in channel catfish [3] and rainbow trout [4], and deposited in fatty tissue of the fish.
The potential carcinogenic, genotoxic, mutagenic and teratogenic properties were demonstrated in many animal species and cell lines [5]. For that reason, the USA placed MG under scrutiny in 1978, only permitted to specified national fish hatcheries that produced fish for restoration of depleted stocks. As MG is not registered as a veterinary drug, the administration of this antibiotic is not allowed in the European Union either. The ban on its use and its potential adverse effects in humans, necessitated a robust and reliable analytical method for determination of residues of MG in tissues derived from ( cultured ) aquatic animals , which can be used in the control of this drug .
Several analytical approaches for the determination of residues of malachite green have been published. Methods include, for example, HPLC equipped with a post-column unit for oxidation of
LMG and with either an absorbance or MS detector for detection in trout (eggs, fry and muscle), catfish (muscle and plasma) [4,6,7] and in trout muscle [8]. The reactors (from 1032 to 3234 mm) used in these studies were filled with either 100% lead(IV)oxide [7,8] or with a mixture of 10% lead(IV)oxide with celite [4,6]. Other methods include GC–MS of LMG in catfish [9] or LC–APCI-MS in catfish and trout [10] without the use of a reactor for the conversion of LMG. This study aimed at the development and validation of a procedure for sample processing and of an HPLC analysis method for determination of residues of MG in finfish with aquacultural interest
and in prawns. Furthermore, the use of LC–ESI-MS–MS analysis was explored for confirmation of
detected residues of this drug in such matrices.