Abstract:

A method for simultaneous determination of formic acid, acetic acid, propionic acid and nbutyric acid in water sample by ion chromatography was established. The chromatographic instrument used was a Thermo Fisher ICS-5000+ ion chromatograph．An inhibitory conductance detector, Ion Pac AS11HC (250 mm×4 mm I.D.) separation column and Ion Pac AG11HC (50 mm×4 mm I.D.) guard column were used. The temperature of detector and columns were 35 ℃ and 30 ℃, respectively. Gradient elution was conducted with KOH as eluent and the gradient elution conditions were as followings: the concentration of KOH was 1.0 m mol/L at 0 ~17.0 min, 30.0 m mol/L at 17.1~25.0 min, and 1.0 m mol/L at 25.1~30.0 min. When the flow rate was 1.2 ml/min, formic acid, acetic acid，propionic acid and nbutyric acid could meet the requirements of separation, and the detection limit was 0.004, 0.005, 0.004 and 0.005 mg/L, respectively. The four organic acid showed good linear correlation in the range of  0.2 mg/L~3.0 mg/L, and its correlation coefficients was within 0.999 1~0.999 5. Two mixed standard solutions of 0.2 and 1.0 mg /L were detected 11 times and the results showed that the relative standard deviation of formic acid, acetic acid, propionic acid and butyric acid were all less than 2%, and the precision was better. The spike recovery of formic acid, acetic acid, propionic acid and butyric acid ranging from 95.3% to 98.7% was obtained when applying this method to analyze the four organic acids in water samples.

Key words: rate of recovery,  ion chromatography, precision, organic acid