Microwave-Assisted Derivatization of Bile Acids for Gas Chromatography/Mass Spectrometry Determination

Abstract

Bile acids derived from cholesterol are produced in the liver, and their analysis is difficult due to their complex natures and their low concentrations in biological fluids. Mixtures of various derivatives, created via conventional heating, are used for such analyses. Microwave radiation is proposed to accelerate the derivatization process. This paper presents a mass fragmentation study and microwave-assisted derivatization (MAD) for the silylation of bile acids (cholic and ursodesoxycholic) prior to gas chromatography and mass spectrometry analysis. The derivatization was performed using the two-step process of methoximation and silylation. The reaction time, power, and quantity of N,O-bis-(trimethylsilyl) trifluoroacetamide (BSTFA) + 1% trimethylchlorosilane (TCMS) were optimized to improve the derivatization. The optimized derivatization conditions required 210 W for 3 min. The MAD method exhibited linearity with respect to cholic acid between 0.78 and 20.0 μg mL−1 with an LOQ of 0.23 μg mL−1 and a precision ranging from 1.08% to 9.32% CV. This optimized derivatization method is valid for the analysis of bile acids in different matrices.