A quick analysis of organic acids by the nonsuppressor-ion chromatography

Organic acids were analyzed by ion chromatography without the suppressor system. A short column (4.6mm ID × 50mm length) of high number of theoretical plates packed with porous silica based on anion-exchange resin which we named a minicolumn was used together with a conductivity detector consisted of five-pole ring electrodes. Considering the effects of pH and concentration of an eluent, it was found that 1.0mM phthalic acid (pH4.0) was the most suitable eluent for separation and that pH3.4 for high sensitivity (for example, 0.01μg/ml for acetic, 0.01μg/ml for lactic, 0.005μg/ml for formic, 0.00514/ml for succinic, and 0.02μg/ml for benzoic acid, respectively). The reproducibility of peak heights from the standard solution was less than 3.3% as the coefficient of variation, except succinic acid (6.9%). The interference of inorganic anions such as nitrate, chloride, and phosphate ions could be eliminated by adjusting pH of the eluent below 3.7. By this method, organic acids in commercial products such as a "SAKE" and "Glucose Injection" could be analyzed within 10min by injecting samples directly without any pretreatment processes.