Directly coupled CZE-NMR and CEC-NMR spectroscopy for metabolite analysis:paracetamol metabolites in human urine

Direct coupling of NMR spectroscopic detection with both capillary zone ele ctrophoresis (CZE) and capillary electrochromatogaphy (CEC) was applied to the separation of metabolites of the drug paracetamol in an extract human u rine. Continuous-flow CZE-NMR and CEC-NMR allowed the detection of the majo r metabolites, the glucuronide and sulfate conjugates of the drug and the e ndogenous material hippurate. Identification of these substances was achiev ed by examination of individual rows of the NMR chromatogram and this also gave estimates of the detection limits. For CEC-NMR, spectra were also obta ined in the stopped-flow mode including a two-dimensional TOCSY NMR experim ent which afforded confirmatory evidence for paracetamol glucuronide. Chara cterisation of drug metabolites using NMR spectroscopy is therefore possibl e with nanolitre sample volumes.