Catalytic detection principle for high-performance liquid chromatography: Determination of enantiomeric iodinated thyronines in blood serum

Direct separation and quantitative analysis of thyroxine and triiodothyronine enantiomers in pharmaceuticals by high-performance liquid chromatography

A rapid reversed-phase type HPLC method for the simultaneous separation and analysis of D- and L-thyroxine (D- and L-T(4)) and triiodothyronine (T(3)) was developed using a quinine-derived chiral stationary phase and applied for a quantitative assay of the enantiomeric impurity of the drugs in pharmaceutical formulations of levothyroxine. The influence of operating parameters has been studied for the optimization of the separation and also in order to gain an insight into the retention mechanism. Validation of the method included linearity, precision and accuracy which revealed R.S.D. values of <3.3% for intra-assay precision and percent error ranging from -6 to +2.1% for various defined validation samples, proving satisfactory accuracy. Quantitation was performed over the range of 0.5-500 microg ml(-1) with limits of detection and quantitation lower than 0.1 and 0.5 microg ml(-1), respectively, for both analytes. Further, the determination of 0.1% impurity, of D-T(4) as well as L- and D-T(3) in levothyroxine sodium tablets proved to be feasible.

A simple method for the separation and quantitation of radiolabeled thyroid hormones in thyroxine clearance studies

A method was developed to facilitate the separation and quantitation of radiolabeled thyroxine in plasma for thyroxine clearance studies. Following intravenous injection of radioactive thyroxine, the radiolabeled thyroid hormones were isolated from plasma protein and polar metabolites by solid phase extraction on a C18 sorbent bed. The individual thyroid hormones were then separated by ion-pair reversed phase chromatography and sequentially eluted through a UV detector and radiochromatographic detector. The radioactivity of individual radiolabeled thyroid hormones was corrected for recovery of carrier as determined from UV absorbance. The recoveries of thyroxine and 3,5,3'-triiodothyronine (T3) were 96% and 101%, respectively.

Post-column reactors for sensitive and selective detection in high-performance liquid chromatography: categorization and applications

The increasing interest in the rapid trace analysis of large series of biomedical samples using column liquid chromatographic techniques requires the use of well balanced combinations of sample pretreatment, separation and detection techniques. In such work, selectivity, sensitivity and reproducibility are the key parameters. The application of automated or semi-automated on-line pre-column technology and/or post-column reaction detection are excellent ways to meet these requirements. A critical review is presented of the theoretical background of on-line post-column reactors with emphasis on their categorization, viz., open-tubular, packed-bed, segmented-stream and hollow-fibre membrane reactors. The evaluation of these reactor systems is performed by discussing selected applications of, for instance, systems based on electrochemical and redox, hydrolytic, photochemical, ion-pairing, true chemical derivatization, peroxyoxalate chemiluminescence and solid-phase reactions. As automation is becoming even more important, a number of labelling procedures, which can be performed in an on-line pre-column mode, are briefly discussed and a comparison is made between the potential of on-line pre- and post-column procedures.

Determination of iodide and bromide by ion chromatography with post-column reaction detection

During an investigation into the mechanism of the biosynthesis of thyroid hormones, it became necessary to determine traces of iodide and bromide in biological matrices as well as in food. A vydac 302-IC anion-exchange column with methanesulphonic acid as the mobile phase was used for the ion chromatographic separation of iodide and bromide. A post-column reaction detector was developed based on the reaction between iodide or bromide, chloramine-T and 4,4'-bis(dimethylamino)diphenylmethane. Methods with minimal sample preparation are described for determination of iodide or bromide in serum, milk, salt and water. The detection limit is ca. 20 pg iodide and 15 ng bromide injected.

Determination of sodium levothyroxine in bulk, tablet, and injection formulations by high-performance liquid chromatography

Sodium levothyroxine was determined in bulk drugs, tablets, and injections by high-performance liquid chromatography (HPLC). Levothyroxine was separated from excipients and impurities on a 10-microns cyanoalkyl column using an acetonitrile-water-phosphoric acid mobile phase. The HPLC method is shown to be linear, accurate, and precise, and the results obtained by the HPLC and USP XX methods are compared.

High-performance liquid chromatographic separation of iodoamino acids for tracer turnover studies of thyroid hormones in vivo

A reversed-phase high-performance liquid chromatographic technique was developed to separate radioiodinated thyroxine (T4), 3,5,3'-triiodothyronine (T3), 3,3',5'-triiodothyronine (rT3) and two diiodothyronines (3,3'-T2 and 3',5'-T2), in extracts from either serum or urine. Chromatography was performed with 10-micron C18 silica gel, packed in a glass column (3 X 300 mm); the mobile phase was methanol-water (55:45) adjusted to pH 3 with H3PO4, at a flow-rate of 1.2 ml/min and a pressure of 2800 p.s.i. The results demonstrate the ability of the system to yield a clear-cut separation of the iodothyronines involved in in vivo turnover studies, i.e., T4, T3, rT3, and the two T2 compounds together.

High-performance liquid chromatographic assay for sodium levothyroxine in tablet formulations: content uniformity applications

Sodium levothyroxine was quantitated in 25-300 micrograms/tablet formulations. The procedure consisted of pulverization of a suitable sample, extraction into acetonitrile-water (40:60, v/v) containing 0.05% o-phosphoric acid, and injection onto a bonded-phase cyanopropyl column; the effluent was monitored by UV detection at 225 nm. Spiked placebo recovery studies demonstrated the linearity of the method over the range of 80-120% of the label claim. Stability studies indicated that no degradation products or excipients interfered with the quantitation of the intact drug. Data demonstrating the accuracy and precision of this assay are presented, and the method was applied to the measurement of single-tablet content uniformity.

Stability-indicating assay, dissolution, and content uniformity of sodium levothyroxine in tablets

A reverse-phase high-performance liquid chromatographic (HPLC) method for determining sodium levothyroxine in tablet formulations is described. The sodium levothyroxine was extracted from tablets using a mobile phase consisting of 60% acetonitrile and 40% aqueous buffer. After centrifugation 200 microliter of the solution was chromatographed on a 10-micron C18 column. The method gave accurate results when tested against the USP method, by the standard additions method, and by the spiked-placebo method. The method can also be used to determine content uniformity and dissolution of sodium levothyroxine tablets.