Determination of Trigonelline, Nicotinic Acid, and Caffeine in Yunnan Arabica Coffee by Microwave-Assisted Extraction and HPLC with Two Columns in Series

A simple, rapid method was developed for simultaneous extraction of trigonelline, nicotinic acid, and caffeine from coffee, and separation by two chromatographic columns in series. The trigonelline, nicotinic acid, and caffeine were extracted with microwave-assisted extraction (MAE). The optimal conditions selected were 3 min, 200 psi, and 120°C. The chromatographic separation was performed with two columns in series, polyaromatic hydrocarbon C18 (250 × 4.6 mm id, 5 μm particle size) and Bondapak NH2 (300 × 3.9 mm id, 5 μm particle size). Isocratic elution was with 0.02 M phosphoric acid–methanol (70 + 30, v/v) mobile phase at a flow rate of 0.8 mL/min. Good recoveries and RSD values were found for all analytes in the matrix. The LOD of the three compounds was 0.02 mg/L, and the LOQ was 0.005% in the matrix. The concentrations of trigonelline, nicotinic acid, and caffeine in instant coffee, roasted coffee, and raw coffee (Yunnan Arabica coffee) were assessed by MAE and hot water extraction; the correlation coefficients between concentrations of the three compounds obtained were close to 1.