Method optimization and validation for multi-class residue analysis in turmeric

Turmeric (Curcuma longa L.) is an economically important food and medicinal plant that grows in tropical and subtropical regions consumed worldwide. Turmeric is a difficult matrix for residue/contaminant analysis due to the high content of potentially interfering polyphenols (curcuminoids) and essential oils with physicochemical properties similar to target analytes. To solve this problem, a simple and straightforward sample preparation protocol based on ethyl acetate extraction and dispersive solid phase clean-up, followed by gas and liquid chromatography coupled to tandem mass spectrometry analysis, was optimized and validated, after selecting a representative blank material using gas chromatography coupled to ion mobility spectrometry and multivariate data analysis. Method validation was performed according to Codex guidelines for 67 pesticide residues, including 12 persistent organic pollutants, 4 aflatoxins and 3 dyes at 0.01, 0.02 and 0.05 mg kg−1level. Recoveries ranged between 60 and 120%, with relative standard deviations for repeatability and reproducibility below 20% and 32% respectively. Method performance was tested collaboratively between laboratories in Austria and Uruguay which helped proving the robustness of the methodology. The method was applied to the analysis of commercial samples and chlorpyrifos was detected in most of them.