On the use of trimethylchlorosilane in methanol for methylation of thyroxine prior to perfluoroacylation and isotope dilution-gas chromatography/mass spectrometry.
Explore the source record for details and available documents.
Acylation↗
Biomedical subjects
V I De Brabandere
Publications and source records attributed to V I De Brabandere.
Isotope dilution-liquid chromatography/electrospray ionization-tandem mass spectrometry for the determination of serum thyroxine as a potential reference method.
A new candidate reference method is presented for the determination of thyroxine in serum. The method is based on isotope dilution-liquid chromatography/tandem mass spectrometry using electrospray for ionization. The internal standard used was 13C6-thyroxine, sample pretreatment consisted of protein precipitation and a two-step liquid/liquid extraction procedure, HPLC was performed on a C-18 column with an eluent containing methanol/water/formic acid (60:40:0.1, by volume), and finally thyroxine and its isotopically labeled analogue were measured in the selected reaction monitoring mode for the transitions m/z 777.7--> 731.7 and m/z 783.7--> 737.7, respectively. The detection limit for thyroxine was 6 pg, the within-run coefficient of variation was 1.1%. The samples were measured in six-fold: in duplicate on three independent days. The mean overall coefficient of variation of the method was 1.6%. The new method was evaluated by measuring nine control sera previously determined by an existing ID-GC/MS method. The differences between the results of the two methods ranged from-1.6% to +3.3%, with a mean of +0.2%.
Calibration↗
13C-NMR and mass spectral data of steroids with a 17,17-dialkyl-18-nor-13(14)-ene substructure.
We present carbon-13 nuclear magnetic resonance (13C-NMR) and mass spectral data for several androstanes and estranes having a 17,17-dialkyl-18-nor-13(14)-ene substructure. These compounds are formed by a Wagner-Meerwein rearrangement of steroids bearing a tertiary 17-hydroxy group during the derivatization reaction with heptafluorobutyric anhydride. The 13C-NMR assignments are compared with those of natural products having a similar substructure. The mass spectra show characteristic fragment ions for which a fragmentation mechanism is proposed.
Carbon Isotopes↗
Candidate reference method for determining serum cortisol based on isotope dilution-gas chromatography/mass spectrometry using heptafluorobutyrilation as derivatization method.
We present a new candidate reference method for determining cortisol in serum. The method is based on isotope dilution-gas chromatography/mass spectrometry and makes use of derivatization with heptafluorobutyric anhydride and selected ion monitoring at m/z 489 and 491. A detection limit of 0.08 pmol (30 pg) was achieved. Twenty-four structurally related steroids were tested for interference and found negative. Verification of the analytical quality specifications was done from measurement in two laboratories of the certified reference materials 192 and 193 of the Bureau Communautaire de Référence and a number of commercial quality control materials. The maximum systematic error was estimated to be 1.0% and the mean imprecision was 1.0%. The total error was lower than 2.05%. The method was applied for target-setting in external quality assessment and internal accuracy control and for measurement of patient samples.
Fluorocarbons↗
Three routine methods for serum cortisol evaluated by comparison with an isotope dilution gas chromatography-mass spectrometry method.
Explore the source record for details and available documents.
Gas Chromatography-Mass Spectrometry↗
Use of cyclodextrins for prepurification of progesterone and testosterone from human serum prior to determination with isotope dilution gas chromatography/mass spectrometry.
A new application of cyclodextrins is presented, being their use for sample purification. This new application is exemplified with a method for the determination of progesterone and testosterone in human serum based on isotope dilution gas chromatography/mass spectrometry. The whole procedure consists of a traditional solvent extraction with hexane for progesterone, respectively dichloromethane for testosterone, followed by a back-extraction of the steroids into a cyclodextrin-water solution. After washing of the aqueous phase with hexane, the steroids are finally extracted with toluene (progesterone) and dichloromethane (testosterone). Different cyclodextrins and cyclodextrin derivatives in various concentrations are investigated. A solution of 150 mmol/L hydroxypropyl beta-cyclodextrin in water is selected. The recovery of progesterone and testosterone is 70 and 80% respectively. The purification effectiveness, accuracy, and precision of the new method are equivalent to a traditional method using gel chromatography for sample purification.
Cyclodextrins↗
Development of a new method for the determination of thyroxine in serum based on isotope dilution gas chromatography mass spectrometry.
A new gas chromatographic/mass spectrometric method in combination with isotope dilution for the determination of thyroxine in serum is described. Special attention was paid to the methylation step of thyroxine, which was investigated using methanolic HCl, dimethylformamide/dimethylacetal and diazomethane, the latter giving the best results in terms of reproducible isotope ratios. For internal standardization, (13C6)-thyroxine was dissolved in fraction V human albumin solution (70 g l-1). The internal standard-in-albumin solution was mixed with known amounts of thyroxine standard, dissolved in 0.05 M Na2HPO4 buffer at pH 11.6, to give isotope ratios of 0.75, 1.00 and 1.25. The same internal standard solution was also used for isotope dilution of the unknown serum samples. The volume of serum was adapted to give a 1:1 isotope ratio. Sample pretreatment consisted of protein precipitation and a two-step liquid/liquid extraction procedure. After methylation of unlabelled and labelled thyroxine with diazomethane and perfluoroacylation with pentafluoropropionic anhydride and heptafluorobutyric anhydride, respectively, mass spectrometric monitoring was done at m/z 951/957 and 1001/1007. Quantitative determination of thyroxine in five serum samples in duplicate, during three consecutive days, showed a mean overall imprecision of 1.0% and a deviation of +0.4% from the target value as determined by a definitive method.
Albumins↗