Analysis of phenylcarboxylic acid-type microbial metabolites by microextraction by packed sorbent from blood serum followed by GC–MS detection

A method for analysis of 8 phenylcarboxylic acids in blood serum was developed based on the coupling of microextraction by packed sorbent, derivatization and GC–MS detection. These compounds are low molecular weight aromatic microbial metabolites that are proven and prospective indicators of sepsis in critically ill patients. Recoveries of the phenylcarboxylic acids from serum samples using microextraction by packed sorbent were 30–70%. The present method was linear (R² ≥ 0.9981) over a clinically significant range of concentrations (94–2250 µg L⁻¹/0.5–18 µM). The limits of quantification for the optimized method were 60–100 µg L⁻¹/0.4–0.7 µM for phenylpropionic, phenyllactic, 4-hydroxybenzoic and 4-hydroxyphenylacetic acids, and 160 µg L⁻¹/0.9–1.3 µM for benzoic, 4-hydroxyphenyllactic, homovanillic and 4-hydroxyphenylpropionic acids. The developed conditions were used to determine concentrations of the phenylcarboxylic acids in the most complicated matrix – serum samples of critically ill patients. Results were compared with liquid-liquid extraction and revealed a reduction in the time for sample preparation (45 min vs. 6 min) and serum (200 µL vs. 80 µL) volume. The combination of microextraction by packed sorbent and GC–MS methods, especially when fully automated could be a powerful tool for the clinical diagnosis of sepsis.