Determination of Organic Acids and Inorganic Anions by Gradient Ion Chromatography
有机酸与无机阴离子的梯度离子色谱法分析研究

The chromatographic conditions for separation and detection of organic acids and inorganic anions by gradient ion chromatography with suppressed conductivity detection were studied. The optimized gradient programs were established. Ion chromatography were performed with a DX 100 chromatograph (DIONEX). The separation column is IonPac AS11. Compared with NaHCO 3/Na 2CO 3 and Na 2B 4O 7, NaOH was the optimal eluent. The effect of organic modifier was also studied. Among methanol, 2 propanol and acetonitrile, methanol can make ion pairs such as malate and succinate, malonate and tartrate gaining baseline resolution. By using ion exchange separation, Cl -,NO - 3,malate, succinate, malonate, tartrate, SO 2- 4,oxalate were eluted between 5mmol/L NaOH 16%CH 3OH and 10mmol/L NaOH 16%CH 3OH in 25min. A mobile phase composed of 30mmol/L NaOH, 50%CH 3OH and D.I. water was chosen to elute two groups of organic acids and inorganic anions:(1) quinate, formate, Cl -, malate, malonate, oxalate, citrate, isocitrate, aconitate; (2) lactate, Cl -,SO 2- 4, tartrate,PO 3- 4,citrate,isocitrate, aconitate. The detection limits ( S/N =3) were 0 1625(quinate),0 0691(formate),0 0115(Cl -),0 0886(malate),0 0591(malonate),0 0263(oxalate),0 1147(citrate),0 2017(isocitrate),0 3656( cis aconitate),0 1045( trans aconitate),0 1950(lactate),0 0729(tartrate),0 0224(SO 2- 4) and 0 0692(PO 3- 4) mg/L. The relative standard deviations were lower than 11 9%( n =7) and the correlation coefficients ranged from 0 9212 for Cl - to 0 9999 for formate. The method was applied to determine the organic acids and inorganic anions of beverages and citric acids fermenting medium. The results were satisfactory.