Paired-ion high-performance liquid chromatographic assay for plasma choline.

Choline was isolated from deproteinized plasma by cation-exchange chromatography. Isolated choline was directly converted to the 3,5-dinitrobenzoate derivative and was analyzed by paired-ion high-performance liquid chromatography with UV detection at 254 nm. An internal standard, 3-hydroxy-N,N,N-trimethylpropanaminium iodide was used for quantitation of plasma choline. Linearity was achieved from 1--500 nmole/ml with a reproducibility of +/- 6%. Plasma choline concentrations below 1 nmole/ml could not be accurately measured while plasma choline concentrations in the micromole/ml range deviated from linearity.