Optimization of straightforward methods for the monitoring of organic and inorganic contaminants in strawberries

Abstract

Straightforward methods for the monitoring of chlorothalonil, cyprodinil, fludioxonil, metalaxyl-m, mancozeb and ethylenethiourea in strawberries, based on modified QuEChERS protocols followed by HPLC-DAD, were validated according to DG-SANTE Guidelines. Compounds showed satisfactory recoveries in the range 85.4–100.3% at spiking levels of 0.01, 0.02 and 0.05 mg kg−1, with RSDs below 15 %. LOQs were in the range 0.01 – 0.02 mg kg−1, being below the corresponding maximum residue levels (MRLs). Also, a simple method for the determination of Cd and Pb, based on a microwave-assisted digestion followed by electrothermal atomic absorption spectrometry (ETAAS), was validated according to Eurachem Guide. Trueness and precision were evaluated by analysis of a certified reference material (CRM). Results were statistically equivalent to the certified values at the 95 % significance level, while RSDs were below 5%. Methods were finally applied to the analysis of commercial samples. Residues of mancozeb and ethylenethiourea were detected in some of the samples but below the LOQs. Inorganic contaminants were in the range 0.0031 – 0.0088 mg kg−1 (Cd) and 0.0057 – 0.0212 mg kg−1 (Pb) (fresh weight), being below the corresponding maximum limits established by national regulation. The proposed methods can be easily implemented as routine analysis for food safety monitoring.