Enhanced Gas Chromatography-Mass Spectrometry (GC-MS)-Based Analysis of Metformin and Guanylurea in Water Samples

Metformin is widely used as one of the most effective first-line oral drugs for type 2 diabetes. It is difficult to be metabolized by the human body thus commonly exists in both urine and feces samples. Guanylurea is metformin’s main biotransformation product with increased concentrations in the aquatic environments. Liquid chromatography-tandem mass spectrometry (LC-MS)-based methods used for measuring the two compounds have been well developed, but extremely limited studies have tracked gas chromatography-mass spectrometry (GC-MS)-based analysis. To help better track the occurrence of the two non-volatile biguanide compounds in liquid samples, the improvement of existing GC-MS based methods for reliable metformin and guanylurea analysis is conducted. Derivatization of metformin and guanylurea is the key pretreatment procedure before the associated GC-MS analysis. Four selected factors affecting for the derivatization were evaluated, and the optimal factors include temperature (90°C), reacting time (40 min), solvent (1,4-dioxane), and ratio (1.5:1) of reagent to target component. Buformin and N-methyl-bis(trifluoroacetamide) (MBTFA) were used as the internal standard and the derivatization reagent, respectively. Calibration curves were made based on the optimal conditions of derivatization for metformin and guanylurea with the R² values of calibration linearity achieved as 99.35% and 99.2%, respectively. The values of relative standard deviation (RSD%) of metformin and guanylurea based on seven repeated trails are 2.67% and 15.37%, respectively. The optimal conditions for enhancing the sensitization of metformin and guanylurea derivatization performance were obtained. The improved GC-MS analysis method was eventually applied for metformin and guanylurea analysis in real water samples.