Determination of plasma dexamethasone by chemical oxidation and electron capture negative ionization mass spectrometry

Determination of betamethasone and betamethasone 17-monopropionate in human plasma by liquid chromatography-positive/negative electrospray ionization tandem mass spectrometry

This study presents a high-performance liquid chromatography-positive/negative electrospray ionization tandem mass spectrometric (LC-ESI(+/-)-MS-MS) method for the determination of betamethasone (BOH) and betamethasone 17-monopropionate (B17P) in human plasma using beclomethasone dipropionate as the internal standard (I.S.). Both compounds were extracted from human plasma with ether-cyclohexane (4:1, v/v) and were separated by HPLC on a Hanbon Lichrospher C(18) column with a mobile phase of methanol-water (85:15, v/v) at a flow rate of 0.7ml/min. Calibration curves were linear over the range of 0.10-50ng/ml for BOH and 0.050-50ng/ml for B17P. The inter-run relative standard deviations were less than 14.4% for BOH and 12.3% for B17P. The intra-run relative standard deviations were less than 9.3% for BOH and 7.9% for B17P. The mean plasma extraction recovery for BOH and B17P were in the ranges of 82.7-85.9% and 83.6-85.3%, respectively. The method was successfully applied to study the pharmacokinetics of a new formulation of betamethasone phosphate/betamethasone dipropionate injection in healthy Chinese volunteers.

Simultaneous analysis of twenty-one glucocorticoids in equine plasma by liquid chromatography/tandem mass spectrometry

A method for the simultaneous separation, identification, quantification and confirmation of the presence of 21 glucocorticoids (GCC) in equine plasma by liquid chromatography coupled with triple stage quadrupole tandem mass spectrometry (LC/TSQ-MS/MS) is described. Plasma sample augmented with the 21 GCC was extracted with methyl tert-butyl ether (MTBE) and analyzed by positive electrospray ionization. Desoxymetasone or dichlorisone acetate was used as the internal standard (IS). Quantification was performed by IS calibration. For each drug, one major product ion was chosen and used for screening for that drug. Analyte confirmation was performed by using the three most intense product ions formed from the precursor ion and the corresponding mass ratios. The recovery of the 21 GCC when spiked into blank plasma at 5 ng/mL was 45-200% with coefficient of variation (CV) from 0.3-18%. The limit of detection (LOD) and that of quantification (LOQ) for most of the analytes were 50-100 pg/mL and 1 ng/mL, respectively, whereas that of confirmation (LOC) was 100-300 pg/mL depending on the analyte. Intra- and inter-day precisions expressed as CV for quantification of 1 and 10 ng/mL was 1.0-17%, and 0.51-19%, respectively, and the accuracy was from 84-110%. The linear concentration range for quantification was 0.1-100 ng/mL (r(2) > 0.997). Estimated measurement uncertainty was from 11-37%. This study was undertaken to develop a method for simultaneous screening, identification, quantification and confirmation of these agents in post-race equine plasma samples. The method has been successfully applied to screening of a large number of plasma samples obtained from racehorses in competition and in pharmacokinetic studies of dexamethasone in the horse and concurrent changes in endogenous GCC, hydrocortisone and cortisone. The method is simple, sensitive, selective and reliably reproducible.

Sensitive liquid chromatographic/tandem mass spectrometric method for the determination of beclomethasone dipropionate and its metabolites in equine plasma and urine

Beclomethasone dipropionate (BDP) is a potent pro-drug to beclomethasone (BOH) and is used in the treatment of chronic and acute respiratory disorders in the horse. The therapeutic dose of BDP (325 microg per horse) by inhalation results in very low plasma and urinary concentrations of BDP and its metabolites that pose a challenge to detection and confirmation by equine forensic laboratories. To solve this problem, a method involving the use of a liquid chromatography coupled with tandem mass spectrometry (LC/MS/MS) was developed for the detection, confirmation and quantification of the analytes in equine samples. Ammonium formate or acetate buffer added to LC mobile phase favored the formation of [M + H](+) ions from BDP and its metabolites, whereas formic acid led to the formation of sodium and potassium adduct ions ([M + Na](+), [M + K](+)) together with [M + H](+) ions. Acetonitrile, on the other hand, favored the formation of abundant solvent adduct ions [M + H + CH(3)CN](+) with the analytes under electrospray ionization (ESI) and atmospheric pressure chemical ionization conditions. In contrast, methanol formed much less solvent adduct ions than acetonitrile. The solvent adduct ions were thermally stable and could not be completely desolvated under the experimental conditions, but they were very fragile to collision-induced dissociation (CID). Interestingly, these solvent adduct ions were observed on a triple-quadrupole mass spectrometry but not on an ion trap instrument where helium used as a damping gas in the ion trap might cause the solvent adduct ions desolvated by collision. By CID studies on the [M + H](+) ions of BDP and its metabolites, their fragmentation paths were proposed. In equine plasma at ambient temperature over 2 h, BDP and B21P were hydrolyzed in part to B17P and BOH, respectively, but B17P was not hydrolyzed. Sodium fluoride added to equine plasma inhibited the hydrolysis of BDP and B21P. The matrix effect in ESI was evaluated in equine plasma and urine samples. The method involved the extraction of BDP and its metabolites from equine plasma and urine samples by methyl tert-butyl ether, resolution on a C(8) column with a mobile phase gradient consisting of methanol and ammonium formate (2 mmol l(-1), pH 3.4) and multiple reaction monitoring for the analytes on a triple-quadrupole mass spectrometer. The detection limit was 13 pg ml(-1) for BDP and B17P, 25 pg ml(-1) for BOH and 50 pg ml(-1) for B21P in plasma and 25 pg ml(-1) for BOH in urine. The method was successfully applied to the analysis of equine plasma and urine samples for the analytes following administration of BDP to horses by inhalation. B17P, the major and active metabolite of BDP, was detected and quantified in equine plasma up to 4 h post-administration by inhalation of a very low therapeutic dose (325 microg per horse) of BDP.

Analysis of corticosteroids in equine urine by liquid chromatography-mass spectrometry

A liquid chromatography-mass spectrometry (LC-MS) method for the analysis of corticosteroids in equine urine was developed. Corticosteroid conjugates were hydrolysed with beta-glucuronidase; free and enzyme-released corticosteroids were then extracted from the samples with ethyl acetate followed by a base wash. The isolated corticosteroids were detected by LC-MS and confirmed by LC-MS-MS in the positive atmospheric pressure chemical ionisation mode. Twenty-three corticosteroids (comprising hydrocortisone, deoxycorticosterone and 21 synthetic corticosteroids), each at 5 ng/ml in urine, could easily be analysed in 10 min.

Collision-induced dissociation of corticosteroids in electrospray tandem mass spectrometry and development of a screening method by high performance liquid chromatography/tandem mass spectrometry

A screening method based on liquid chromatography/electrospray tandem mass spectrometry was developed in order to control the illegal use of corticosteroids as growth promoters in cattle. The objective was the detection of low residue levels of corticosteroids or metabolites in biological matrices. Relative to other studies published on this subject, the present work focused on enhancing specificity and sensitivity. Firstly, fragmentation of corticosteroids by collision-induced dissociation was studied. In positive mode, the losses of H(2)O for each hydroxyl group fixed on the molecule, as well as the loss of HF or HCl for halogenated compounds, were observed. For higher collision energy, fragmentations in the B, C and D rings were induced. The negative mode was found to be more specific, inducing a cleavage of the C(20)-C(21) bond with concomitant loss of formaldehyde (CH(2)O). Secondly, three acquisition methods in the negative mode were studied and evaluated, recorded signals being the parent ion [M + acetate](-) and the two daughter ions, [M - H](-) and [M - H - CH(2)O](-). For dexamethasone, MS/MS instrumental detection limits of fragment ion and neutral loss scans, and of multiple reaction monitoring (MRM), were 250, 20 and 5 pg injected, respectively. The MRM method was then evaluated with the objective of use for the detection of corticosteroid residues in biological samples (urine, hair, muscle) and for a metabolism study.

Determination of dexamethasone in bovine liver by chemiluminescence high-performance liquid chromatography

A new method for the determination of dexamethasone (9alpha-fluoro-11beta,17alpha,21-trihydroxy-16alpha -methylpregna-1, 4-diene-3,20-dione) in bovine liver was developed. This new liquid-liquid extraction method comprises the addition of sodium hydroxide to the tissue sample followed by extraction with ethyl acetate. After centrifugation, the extract is evaporated to dryness and the residue dissolved in acetonitrile. The cleaning of the fat is performed with n-hexane, and the acetonitrile layer is evaporated. Analysis of the extracts is performed using high-performance liquid chromatography with chemiluminescence detection employing luminol as CL reagent. A series of recovery curves performed at spiking levels of 50, 30, 10, 5, and 2.5 ppb show that at least 80% of DEX can be recovered from liver and that the chemiluminescence detection yields satisfactory results with respect to sensitivity (LOD 0.2 ppb), reproducibility (CV% 10.7) and repeatability (CV% 6.2-8.9).

Development of a coupled-column liquid chromatographic-tandem mass spectrometric method for the direct determination of betamethasone in urine

Different hyphenated liquid chromatographic (LC) and mass spectrometric (MS) techniques were investigated in order to set-up a method for the fast, direct analysis of betamethasone in hydrolysed and non-hydrolysed urine using large-volume sample injection. After the optimisation of the LC parameters using a traditional UV detector and of the thermospray and mass spectrometric parameters by flow injection, urine samples (0.5 ml) were submitted to analysis by either LC combined with tandem mass spectrometry (MS-MS), coupled-column LC (LC-LC) combined with single quadrupole MS, and LC-LC-MS-MS. Both the three-step configurations (LC-MS-MS and LC-LC-MS) did not provide satisfactory results: loss of sensitivity was noted in the case of LC-MS-MS (likely due to reduced efficiency in the ionisation of betamethasone in the thermospray owing to the presence of large amounts of matrix interference), while in the case of LC-LC-MS a high chemical noise resulting in insufficient selectivity of detection was observed. On the contrary, LC-LC-MS-MS analysis proved to meet the demand of high speed of analysis (sample throughput, 4.5 h(-1)), selectivity, and sensitivity (LOQ, 1 ng/ml; LOD, 0.2 ng/ml). Notwithstanding the complex analytical system adopted, the developed procedure was manageable and very robust, provided that at the beginning of each analytical session the performance of the system was controlled by checking the retention time of the analytes on the first analytical column with UV detection and by optimising vaporiser temperature of the thermospray by flow injection.

Derivatization procedures for gas chromatographic-mass spectrometric determination of xenobiotics in biological samples, with special attention to drugs of abuse and doping agents

The development of low cost MS detectors in recent years has promoted an important increase in the applicability of GC-MS system to analyze for the presence of foreign substances in the human body. Drugs and toxic agents are in vivo metabolized in such a way that more polar compounds are usually formed. Derivatization of these metabolites is often an unavoidable requirement for gas chromatographic analysis. Application of derivatization methods in recent years has been relevant, especially for silylation, acylation, alkylation and the formation of cyclic or diastereomeric derivatives. Given the relevance of drug of abuse testing in modern toxicology, main derivatization procedures for opiates, cocaine, cannabis, amphetamines, benzodiazepines and LSD have been reviewed. Papers describing the analyses of drugs of abuse in matrixes other than blood, such as hair or sweat, have received special attention. Advances in derivatization for sports drug testing have been particularly relevant for anabolic steroids, diuretics and corticosteroids. Among the several methodologies applied, the formation of trimethylsilyl, perfluoroacyl or methylated derivatives have proved to be both versatile and extensively used. Further advances in derivatization for GC-MS applications in clinical and forensic toxicology will depend on the one hand on the degree of further use of GC-MS for routine applications and, on the other hand, on the alternative progress made for developments in LC-MS or CE-MS. Last but not least, the appearance of comprehensive libraries in which reference spectra for different derivatives of many drugs and their metabolites are collected will have an important impact on the expansion of derivatization in GC-MS for toxicological applications.

Development of an ELISA using a universal method of enzyme-labelling drug-specific antibodies. Part I: Detection of dexamethasone in equine urine

The development, validation, and application of an ELISA for dexamethasone in equine urine is described. The drug-protein conjugate was immobilised in microtitre plate wells and antiserum raised against the same drug-protein conjugate was allowed to compete with sample or standard drug and the immobilised drug-protein conjugate. The proportion of antiserum binding to the immobilised drug-protein conjugate was detected using a biotinylated protein G/extravidin-alkaline phosphatase complex in situ and measurement of the substrate product. The method was used to detect the presence of drug-derived material in unextracted diluted urine after the administration of a single i.m. dose of dexamethasone at approximately 0.04 mg/kg to a thoroughbred horse. Validation of the method was carried out against a radioimmunoassay and GC/MS analysis.

Determination of dexamethasone in urine and faeces of treated cattle with negative chemical ionization-mass spectrometry

For several years, the misuse of dexamethasone and its esters in livestock production has been clearly demonstrated. The first part of the present study deals with the elaboration of a sensitive and specific method for the determination of residues of dexamethasone in excreta at the ppb level. Sample preparation for urine and faeces, including high-performance liquid chromatography (HPLC) fractionation, was carried out. The detection was based on established methodology employing negative chemical ionization-mass spectrometry (NCI-MS) after oxidation of the dexamethasone. In comparison with previous literature, the yield of oxidized dexamethasone was substantially improved and the oxidation procedure was made more simple and robust. In the second part of the study, the relationship between the dose of dexamethasone administered and the levels of the drug in excreta was investigated using this method, as was the ratio between drug levels in urine and faeces. Treatment was carried out for 7 d with an oral dose of 50 mg d-1, the maximum levels found in urine and faeces were 980 and 744 ppb, respectively. While the elimination via faeces responded much slower at the start and the end of treatment, the final part of both excretion profiles were very similar and a level of 1 ppb was reached in both matrices 9 d after the end of treatment. Gas chromatography-mass spectrometry (GC-MS) results obtained for the urine samples were compared with those obtained with direct enzyme immunoassay.

Comparison of immunoaffinity chromatography combined with gas chromatography-negative ion chemical ionisation mass spectrometry and radioimmunoassay for screening dexamethasone in equine urine

A comparison of the sensitive analytical methods of radioimmunoassay (RIA) and immunoaffinity chromatography (IAC) combined with gas chromatography-negative ion chemical ionisation mass spectrometry for the specific and reliable screening of dexamethasone in equine post-race urine is presented. Results from analyses of samples collected from a mare during 144 hours post administration of 26 mg of dexamethasone sodium phosphate are described.

A selective HPLC/RIA for dexamethasone and its prodrug dexamethasone-21-sulphobenzoate sodium in biological fluids

A combined high performance liquid chromatography/radioimmunoassay procedure is described for the simultaneous determination of dexamethasone (DEX) and its prodrug dexamethasone-21-sulphobenzoate sodium (DSS) in plasma. After precipitation of the plasma proteins by acetonitrile, the protein-free supernatant was injected onto a C18 reversed phase liquid chromatographic system and DSS- and DEX-containing fractions were collected. Hydrolysis of DSS by 0.01 N NaOH, followed by fractions extraction of both hydrolysed DSS and DEX fractions with ethyl acetate allowed the use of a dexamethasone-specific radioimmunoassay for the selective determination of both compounds. The method is accurate and reproducible (intraday variability for DSS and DEX < 6%, interday variability for DEX 14%), allowing quantification of DEX and DSS as low as 0.3 ng/mL and 0.7 ng/mL, respectively.

Preliminary studies of 6 beta-hydroxydexamethasone and its importance in the DST

The role of the metabolites of dexamethasone (DEX) in the dexamethasone suppression test (DST) has never been fully elucidated. We report here our preliminary studies of 6 beta-hydroxydexamethasone (6 OH-Dex), a known metabolite of DEX, on the hypothalamic-pituitary-adrenal (HPA) axis of the rat; its activity in the most commonly used radioimmunoassay for plasma DEX; and its plasma concentrations in a normal human subject during the standard 1.0 mg DST. Six OH-Dex administered subcutaneously to rats at a dose of 1 mg/kg was able to completely suppress corticosterone production for at least 3 hr. In the IgG Corp. radioimmunoassay for plasma DEX, 6 OH-Dex was moderately cross-reactive yielding a 50% cross-reactivity of 10%. Gas chromatographic coupled mass spectroscopic analysis of human plasma samples, obtained 12 to 20 hr after the oral ingestion of 1.0 mg DEX, demonstrated similar plasma concentrations for both the parent compound and the 6-hydroxyl metabolite. The relevance of these findings, particularly to pharmacokinetic studies of the DST, is discussed.

A selective LC/RIA for dexamethasone and its prodrug dexamethasone-21-isonicotinate in biological fluids

A combined LC/RIA procedure is described for the selective determination of dexamethasone (DEX) and its prodrug dexamethasone-21-isonicotinate (DIN) in plasma. The low affinity of the employed dexamethasone antiserum for DIN (cross-reactivity less than 0.5%) allowed the direct determination of DEX in plasma extracts. For the determination of DIN, both substances of interest were separated by LC, the DIN containing fraction was collected, hydrolysed and the generated DEX was consequently assayed by radioimmunoassay. The assay detection limits were 0.1 ng ml-1 for DEX and 0.75 ng ml-1 for DIN. For both substances, inter- and intra-day variabilities (RSDs) were 6 and 12%, respectively.