Ion-pair extraction and high-performance liquid chromatography in pharmaceutical and biomedical analysis

Reversed-phase ion-paired HPLC of purine nucleotides from skeletal muscle, heart and brain of the goldfish, Carassius auratus L.--I. Development of the analytical method

1. A reversed-phase ion-paired liquid chromatographic (HPLC) method was developed to measure AMP, ADP, ATP, IMP, NAD+ and NADP+ levels in white muscle, heart and brain of anoxic goldfish. 2. Mobile phase parameters of the HPLC method (concentrations of buffer, organic modifier and counter-ion, and pH) were varied to establish the optimal conditions for separation of the compounds of interest. 3. The analytical method was evaluated by calculating some relevant chromatographic parameters (reproducibility and linearity). 4. The HPLC method showed sufficient selectivity, high sensitivity and reproducibility, and excellent linearity.

On-line radiometric determination of [14C]-urapidil and its main metabolises in rat plasma, using post-column ion-pair extraction and solvent segmentation techniques

Post-column ion-pair extraction has been applied to the on-line radiometric determination of [(14)C]-urapidil and its main metabolises in reversed-phase liquid chromatography (LC). [(14)C]-remoxipride was used as internal standard. Chromatography was performed isocratically, using acetonitrile-water (pH = 2.2) as eluent on a cyanobonded column. Various ion-pair reagents were tested for their extraction efficiency of the analytes mentioned from the eluent into chloroform. Quantitative extraction was possible using sodium dodecylbenzenesulphonate as ion-pair reagent. The influence of the extraction solvent composition, the percentage organic modifier in the eluent and the flow-rates of eluent and scintillator on the extraction percentage and the (14)C-counting efficiency has been studied. In addition, the enhancement of sensitivity is possible using an on-line radiometric procedure. Finally, the method has been applied to the analysis of rat plasma for [(14)C] -labelled urapidil and its metabolises.

Development of a standardized analysis strategy for basic drugs using ion-pair extraction and high-performance liquid chromatography — VII. Determination of drugs in plasma

A standardized analysis strategy for basic drugs which had been applied previously to pharmaceutical dosage forms, cosmetics and saliva has been applied to plasma. Low extraction recoveries that were obtained at first were shown by protein binding studies to be due to interactions between plasma proteins, the drug and the organic ion-pairing reagent. These interactions could be avoided by removal of the plasma proteins from the sample prior to addition of the counterion solution. The standardized analysis strategy was shown to be applicable to the determination of both polar and non-polar drugs in plasma.

Determination of the theophylline solubilizer salicylamide-O-acetic acid in serum and urine using high-performance liquid chromatography

A high-performance liquid chromatographic method for the determination of the theophylline solubilizer salicylamide-O-acetic acid has been developed in the range 0.5 to 10 microg/ml for human serum and 5 to 400 microg/ml for urine. Reversed-phase ion-pair chromatography was employed with tetrabutylammonium hydrogen sulphate as counterion and 2-nitrophenylacetic acid as internal standard. Preliminary pharmacokinetic single-dose studies show that the sensitivity and the selectivity of the assay are adequate to measure lower concentrations in the late beta-phase.

Determination of amoxycillin in plasma by ion pair column extraction and reversed-phase ion pair high-performance liquid chromatography

A quantitative method is described for the determination of amoxycillin in plasma. The method utilizes ion pair extraction of amoxycillin on disposable columns packed with Baker-10 SPE octadecyl, with tetrabutylammonium ion as the counter ion and methanol as the eluent. Separation and quantitation is performed by reversed-phase ion pair high-performance liquid chromatography (Nucleosil C-18) using the same counter ion and a mobile phase of methanol-phosphate buffer (pH 6.0) (31:69 v/v) with detection at 229 nm.