Gas chromatography and mass spectrometry of some trimethylsilyl derivatives of urinary glucuronides

Guidelines are presented to aid the recognition and interpretation of mass spectra for trimethylsilylated (TMS) glucuronides of aromatic acids and substituted phenols. Masses associated with fragmentation of the derivatized glycon include $\text{m}\text{e}$ 465, 464, 449, 392, 375, 359, 333, 331, 319, 305, 257, 243, 217, 204, 169, 147, 143, 129, 117, 103, 95, and 93, with $\text{m}\text{e}$ 375 usually being one of the most abundant masses in the spectrum. Fragmentation of the conjugate after electron impact led to the appearance of a high-abundance fragment of the aglycon having one of the following structures: (a) (TMS)_x-Ar-OTMS⁺, (b) (TMS)_x-Ar-OH⁺, or (e) (TMS)_x-AR-O⁺, where Ar indicates the aromatic ring and (TMS)_x indicates polar hydrogens (OH or NH) on the aglycon replaced by TMS groups. Nine of twelve conjugates studied are ethereally linked through a phenolic hydroxyl group; however, the remaining three are ester linked through an aromatic carboxylate group. The latter appcared to be a more labile linkage, since derivatization apparently cleaved the ester bond, forming appreciable quantities of the fully derivatized aglycon and glucopyranurono-(6→1)-lactone. Gas chromatographic retention (methylene units) and mass spectral data are presented for a number of glucuronides isolated from human urine by high-resolution liquid chromatography.