Quantitative determination of valproic acid by means of gas chromatographic headspace analysis

We have developed a simple but accurate procedure to monitor, by means of gas chromatographic headspace analysis, the concentration of valproic acid (VPA) in serum. Unlike previously described gas chromatographic methods, a preanalytical separation step is unnecessary. Irreversible sample loss, a pitfall in gas chromatographic extraction procedures caused by evaporation during the extraction process of this relatively volatile substance, is avoided. After acidifying and adding internal standard (2- ethylbutanoic acid), the serum sample is sealed hermetically in a special headspace tube. After heating, a vapour phase fraction is injected into the chromatographic column. This method reduces sample preparation time to a few minutes. Analysis time is only three minutes, and the method can easily be automated. Contamination of chromatographic columns by higher molecular mass serum ingredients is avoided.