Determination of 9 Organic Acids and 3 Anions in Tea by Ion Chromatography and Differentiation of Different Tea Varieties Based on Multivariate Statistical Analysis

An aliquot (0.25 g) of the tea sample was taken, 50 mL of water was added, and the mixture was extracted by ultrasound at 35 ℃ for 30 min, and settled by 5 min. The supernatant was passed through a 0.22 μm hydrophilic polyethersulfone syringe filter. The filtrate was analyzed by the ion chromatograph. Using the Dionex IonPac AS11-HC chromatographic column as the analytical column, 9 organic acids and 3 anions in the sample solution were separated by gradient elution with potassium hydroxide solution,and determined by suppression type conductivity detector. Cluster analysis was used to distinguish different varieties of tea samples, and principal component analysis was used to identify key factors that affected sample variety differences. It was shown that linear relationships between values of the mass concentration and the peak area of the 12 targets were kept in definite ranges, with detection limits (3S/N) in the range of 0.35-2.31 mg·kg⁻¹. Test for recovery was made according to the standard addition method, giving the recovery in the range of 89.8%-109%, and RSDs（n=6）of the determined values were not greater than 6.0%. The proposed method was used for the analysis of 31 batches of tea samples of different varieties, with higher detection amounts of fumaric acid, citric acid, acetic acid, and PO₄³⁻. The 31 batches of samples was divided into 4 categories by the cluster analysis. Among which, black tea and Pu'er tea could be grouped separately into one category. The anion PO₄³⁻ was extracted by the principal component analysis, which contributed the most to variety differences in tea, followed by the organic acid of malic acid.