Determination of anions in peptide preparations by ion chromatography.

In many cases, synthetic peptides are formed as their acetates. However, contamination with other anions such as trifluoroacetate and fluoride ion might be caused by synthesis and/or purification processes. Therefore, the analytical method for anions in peptide preparations is required; no study has been reported except for the analysis of acetate by GC. This paper presents a sensitive and reproducible method for determination of anions in the peptide samples by ion chromatography, using an anion exchange column and 0.5 mM sodium bicarbonate (for fluoride ion and acetate) or 4 mM sodium bicarbonate (for trifluoroacetate) as a mobile phase. The calibration curves were linear in the range of 125 μg/ml of fluoride ion, acetic acid or trifluoroacetic acid. The detection limit (S/N=3) was 0.01 μg/ml for fluoride ion, and 0.1 μg/ml for acetic acid and trifluoroacetic acid, respectively. The reletive standard deviation of 5 repeated analyses was 1.3% for 1 μg fluoride ion/ml, 1.2% for 4 μg acetic acid/ml and 1.1 % for 4 μg trifluoroacetic acid/ml, respectively. Several synthetic peptides (growth hormone-releasing factor and its fragment) were analyzed by the present method.