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

Abstract

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.

Keywords:

• Amitraz
• 2,4-dimethylaniline
• gas chromatography–mass spectrometry (GC--MS)
• hydrolysis

Acknowledgements

We gratefully acknowledge Defra (Department for Environmental Food and Rural Affairs) for funding and M. Hetmanski for helpful discussions.