Evaluation of an Improved Indirect Method for the Analysis of 3-MCPD Esters Based on Acid Transesterification

The quantification of 3-chloropropane-1,2-diol (3-MCPD) esters in fat-based matrices is currently carried out according to a number of methods that involve either the conversion of all the esters to the free form that is then quantified (indirect methods), or the separation and quantification of the individual esters (direct methods). Indirect methods of analysis show a better sensitivity, however, the series of chemical reactions that take place during sample preparation may affect the reliability of the results because of the potential ex-novo formation of 3-MCPD from precursors present in the sample. This study is focused on the evaluation of the selectivity and robustness of an indirect acid-catalysed method of 3-MCPD esters analysis. The interference of chloride ions and glycidyl esters was evaluated. 3-MCPD esters are overestimated only when high levels of chloride ions (>1.7 mmol/kg oil) were added to the samples. The interference by chloride ions can be easily eliminated by a single extraction step of the samples before analysis. In contrast, glycidyl esters did not interfere with the determination of 3-MCPD esters. Further investigation on the robustness of the method showed that the time allowed for the transesterification, a major drawback of the previous version of the method, can be reduced from 16 to 4 h without any significant reduction of the accuracy and repeatability (RSD = 0.7%).