Determination of the cardiac glycosides digoxin and digitoxin by liquid chromatography combined with isotope-dilution mass spectrometry (LC-IDMS)--a candidate reference measurement procedure.

This article describes a method of high analytical sensitivity, reproducibility and trueness for the determination of digoxin and digitoxin in serum or plasma at therapeutic levels using a combination of high-pressure liquid chromatography (HPLC), isotope-dilution mass spectrometry (IDMS) and caesium-adduct formation. A method for threefold deuterium substitution in the glycosides was developed, which could be performed within 24 hours without distillation giving yields > 98% of the theoretical value. Extraction from a serum or plasma matrix was performed using a liquid-phase extraction with ammonium acetate buffer/tertiary butylmethyl ether/ethyl acetate at pH 9.

The determination of free and protein-bound haemoglobin in plasma using a combination of HPLC and absorption spectrometry.

The aim of the study was to develop a method for the determination of haemoglobin in plasma suitable for use to set target values for external quality assessment schemes for this analyte using commercially available test kits and equipment. In the early phase of the method development it became clear that the use of a single method, namely HPLC, would not be possible. However, by combining HPLC and absorption spectrophotometry, both qualitative and quantitative rapid determinations of protein-bound and free haemoglobin were able to be performed on equipment present in most routine clinical chemistry laboratories.