Development and validation of an analytical method for total amitraz in fruit and honey with quantification by gas chromatography-mass spectrometry

The EU maximum residue limit (MRL) definition for amitraz is 'the sum of amitraz plus all its metabolites containing the 2,4-aniline moiety, expressed as amitraz'. A rapid and sensitive method has been developed and validated in-house for the determination of total amitraz in pears, strawberries, oranges and honey. Samples were hydrolysed (under acidic followed by alkaline conditions) to convert amitraz to 2,4-dimethyaniline, which was then partitioned into 2,2,4-trimethylpentane prior to quantification by gas chromatography-mass spectrometry. The method was validated at 0.02 and 0.1 mg kg^-1 amitraz (well below MRL requirements) with a lowest calibrated level (LCL) for 2,4-dimethylaniline of 0.002 mg kg^-1 (equivalent to 0.0024 mg kg^-1 amitraz). A single partition step yielded recoveries of ∼60% (with % CV values in the range 3.3-8.2), which is satisfactory for screening purposes. A second partition increased recoveries by 10-20%, making the method suitable for the quantification of residues.