Tocopherols in espresso coffee: Analytical method development and validation

The present paper reports the development and validation of an analytical micro-method for tocopherols quantification in espresso coffee by normal-phase HPLC with fluorescence detection. The proposed method consists in a liquid-liquid extraction with n-hexane:ethyl acetate, followed by a clean-up with dimethylformamide to eliminate co-eluting interferences. The method showed good intra- and inter-day precisions (coefficient of variation < 6.5%), good accuracies (98 +/- 6%), and high correlation coefficients (r > 0.999) for standards subjected to the entire procedure. Only alpha- and beta-tocopherols were identified in the brews. The detection and quantification limits were 0.5 and 1.4 ng/ml, for alpha-tocopherol, and 0.4 and 1.1 ng/ml, for beta-tocopherol, respectively. A mean total tocopherol content lot (alpha + beta) of 3.5 +/- 0.9 mu g in commercial espresso coffee blends (30 ml) was detected. The proposed method requires low solvent consumption and proved to be sensitive, precise and accurate. (C) 2009 Elsevier Ltd. All rights reserved.