Ion-pair Liquid Chromatographic Method Research Articles

Determination of urinary 5-S-cysteinyldopa by high-performance liquid chromatography

A high-performance ion-pair liquid chromatographic method with electrochemical detection is described, which is suitable for routine determination of urinary 5-S-cysteinyldopa. The clean-up procedure includes a first purification step on the cation exchanger AG 50 W (H +). After desorption from the resin at moderately raised pH the catecholic amino acid is adsorbed on alumina at pH 8.6, washed and finally desorbed by elution with perchloric acid. By the combined clean-up procedures, easily oxidized compounds are eliminated, which otherwise cause a number of interfering peaks in the chromatography. The synthesis of 5-S-cysteinyl- l-3,4-dihydroxyphenyl [2,3- 3H] alanine is described, and this tritium-labelled 5-S-cysteinyldopa is used to determine the recovery in the sample. The precision (C.V. = 5.7% at low and C.V. = 4.9% at high 5-S-cysteinyldopa concentration) and recovery (105.0 ± 8.6%) were satisfactory. The mean urinary excretion was 0.34 ± 0.13 (S.D.) μmol per 24 h (range 0.02–0.58 μmol per 24 h) in healthy subjects ( n = 24) and in patients with melanoma metastates ( n = 13) the excretion ranged from 0.9 to 4.8 μmol per 24 h.

Quantitative ion-pair extraction of 4(5)-methylimidazole from caramel colour and its determination by reversed-phase ion-pair liquid chromatography

A procedure for quantitative ion-pair extraction of 4(5)-methylimidazole from caramel colour using bis(2-ethylhexyl)phosphoric acid as ion-pairing agent has been developed. Furthermore, a reversed-phase ion-pair liquid chromatographic separation method has been established to analyse the content of 4(5)-methylimidazole in the extracts. A rapid and adequate separation was achieved on a column of Nucleosil 5 C 8 eluted with methanol—0.2 M potassium dihydrogen phosphate—water (32.5:25:42.5) containing 0.005 M sodium dodecanesulphonate. This method of determination is superior in speed and repeatability to, and at higher contents of 4(5)-methylimidazole gives a better accuracy than, the World Health Organization method currently official in Denmark. The limit of detection is estimated at 4 μg/g.

Reversed-phase, ion-pair liquid chromatography of quaternary ammonium compounds: determination of pyridostigmine, neostigmine and edrophionium in biological fluids.

A reversed-phase, ion-pair liquid chromatographic method for the quantitative determination of quaternary acetylcholinesterase inhibitors is described. The method uses an ion-pair extraction to isolate the drugs from biological material prior to liquid chromatographic separation and online UV detection at 214 nm. Quantiation down to 5 ng/ml and within-day precison with coefficient of variation (C.V.) of 1.5% (n = 10, x = 100 ng/ml) for neostigmine, C.V., 1.7% (n = 10, x = 80 ng/ml) for pyridostigmine and C.V., 1.5% (n = 10, x = 100 ng/ml) for edrophonium have been achieved. The assay was designed for pharmacokinetic studies of these drugs in anesthetized patients.