Gas chromatography/mass spectrometry analysis of organic acid profiles in human serum: A protocol of direct ultrasound‐assisted derivatization

Rationale Low‐molecular‐weight organic acids that generally contain one to three carboxyl groups are involved in many important biological processes; therefore, it is important to develop a quantitative method for analyzing organic acids in serum in order to allow an evaluation of metabolic changes. In this study, we evaluated a protocol for detecting 26 organic acids in serum based on ultrasound‐assisted derivatization by gas chromatography/mass spectrometry (GC/MS). Methods Serum samples were prepared using ultrasound‐assisted silane derivatization before GC/MS analysis to quantify concentrations of organic acids. Additionally, we investigated the variables affecting derivatization yields, including the extraction solvent, derivatization reagents, and derivatization conditions (reaction temperature, duration, and sonication parameters). The protocol was ultimately applied to detect organic acid profiles related to obesity. Results We used acetone as the extraction solvent and determined suitable derivatization conditions, as follows: BSTFA + 1% TMCS, 50°C, 10 min, and 100% ultrasound power. The protocol showed satisfactory linearity (r = 0.9958–0.9996), a low limit of detection (0.04–0.42 μmol/L), good reproducibility (coefficient of variation (CV) %: 0.32–13.76%), acceptable accuracy (recovery: 82.97–114.96%), and good stability within 5 days (CV%: 1.35–12.01% at room temperature, 1.24–14.09% at 4°C, and 1.01–11.67% at −20°C). Moreover, the protocol was successfully applied to obtain the organic acid profiles from obese and healthy control subjects. Conclusions We identified and validated a protocol for ultrasound‐assisted derivatization prior to GC/MS analysis for detecting 26 kinds of organic acids in serum. The results suggest the efficacy of this protocol for clinical applications to determine metabolic changes related to fluctuations in organic acid profiles.