The determination of niacin in selected foods by capillary electrophoresis and high performance liquid chromatography: acid extraction

Abstract

A robust method for the determination of niacin in raw and cooked meat and fish samples using acid extraction to liberate the niacin from the food matrix and capillary electrophoresis (CE) and high performance liquid chromatography (HPLC) as the determinative steps is described. Niacin is liberated from the food matrix by autoclaving in the presence of 0.8 M sulphuric acid at 121°C for 2 h. C18 and cation exchange solid phase extraction (SPE) cartridges were used to isolate and concentrate the niacin before analysis. CE analyses were performed with an uncoated 50 μm extended light path fused silica capillary column and a buffer comprising of 7.5% acetonitrile and 92.5% of a 1:1 mixture of 0.02 M potassium dihydrogen orthophosphate and 0.02 M disodium hydrogen orthophosphate pH 7. Saccharin was used as the internal standard. The levels of niacin determined by CE compared favourably with those determined by HPLC (canned ham CE 3.5 mg/100 g, HPLC 3.3 mg/100 g; raw lamb CE 7.7 mg/100 g, HPLC 7.7 mg/100 g). The average recovery of niacin added to the samples prior to extraction was 103%. The limit of reporting for the determination is 0.5 mg/100 g. The procedure was suitable for only a limited number of other food types (e.g. fruit, vegetables and nuts). Alkali extraction of these foods using saturated calcium hydroxide followed by SPE cleanup and CE determination provided more reliable results. The limit of reporting for this procedure was 0.2 mg/100 g for fruit and 0.5 mg/100 g for vegetables.