Matrix-specific method validation for quantitative analysis of vitamin C in diverse foods

Vitamin C, assayed as total ascorbic acid (AA), was extracted from foods using HPLC with ultraviolet spectrophotometric detection, including treatment of the extract tris(2-carboxyethyl) phosphine (TCEP) to reduce any dehydroascorbic acid to AA. The method was validated for a variety of matrices including fruits and vegetables, fruit juice, dried spices, and high-starch and high-fat foods, using spike recovery, sequential extractions, analysis of available certified reference materials, and verification of AA peak purity. The limits of detection and quantitation were 0.06-0.09 mg and 0.2 mg AA per 100 g food, respectively. The average recovery of added AA from all matrices was 97-103%. The inter-day relative standard deviation (RSD) for matrices including orange juice, fortified cereal, a fruit and vegetable composite, and freeze-dried vegetables was 1.1-2.0% and 4.8%, and HORRAT values (RSD/predicted RSD) for a wide range of foods were <0.1-0.6. Results for certified reference materials, BCR(R)431 (freeze-dried Brussels sprouts), BCRR 421 (milk powder) and VMA399 (dry breakfast cereal) (465 +/- 4.6, 74.0 +/- 1.1 and 70.5 +/- 1.5 mg/100 g, respectively) were within the certified ranges. Without matrix-specific method adjustments to the method validated for orange juice, extraction problems and interferences in the AA peak for particular matrices lead to over- or underestimation of vitamin C in many foods (0.3-70 mg/100 g; 5.5-64%). (C) 2012 Elsevier Inc.. All rights reserved.