Validation of an Ion Chromatographic Method for Determination of Anions in Tea Infusions

The study is focused on the validation of a simple, rapid, and accurate analysis method for the simultaneous determination of F - , Cl - , Br - , NO 2 - , NO 3 - , SO 4 2- and PO 4 3- ions in white, green, black and Pu-erh tea infusions by ion chromatography with conductometric detection. The high levels of organic components were separated using dedicated filter cartridges. Separation was carried out on an anion-exchange column at 30 o C by isocratic elution with an 4.5 mM Na 2 CO 3 + 1.4 mM NaHCO 3 aqueous eluent. The method proved to be selective, and calibration curves are linear for 0.02 – 10 mg L -1 F - , 0.1 - 50 mg L -1 for Cl - , NO 2 - , Br - , NO 3 - , SO 4 2- , and 0.2 – 100 mg L -1 PO 4 3- , characterized by slopes of 0.07 - 0.32, with standard deviations, s b , of 0.03 – 0.14, intercepts of 0.00 – 0.01 mg L -1 , standard deviations of intercepts, s a , of 0.62 - 2.50 mg L -1 , and correlation coefficients of 0.999 for each ion of interest. The calculated limits of detection and quantification for independent fortified samples were in the 0.004 - 0.019 mg L -1 and 0.014 – 0.064 mg L -1 range, respectively. Repeatability and intermediate precision tests gave RDS% between 0.04 % and 0.37 %, values, significantly lower than the imposed limit. The recovery of various anions in spiked tea samples varied in the 95.2 - 114 % range. The method was successfully applied for the anionic content of 60 tea types available in Romanian shops.