Determination of the acylcoenzyme A cholesterol acyltransferase inhibitor 447C88 in plasma using gas chromatography-mass spectrometry and liquid chromatography atmospheric pressure chemical ionisation tandem mass spectrometry

Two mass spectrometry-based methods are described for the determination of 447C88 (I), a novel inhibitor of acylcoenzyme A cholesterol acyltransferase (ACAT), in rat, dog and human plasma. The first method uses gas chromatography-mass spectrometry (GC-MS) with electron ionisation and selected-ion monitoring. The method employs solid-phase extraction of I from plasma and requires alkylation of I using iodoethane. The second method uses liquid chromatography-tandem mass spectrometry (LC-MS-MS) with atmospheric-pressure chemical-ionisation and selected-reaction monitoring. The LC-MS-MS method uses a simplified version of the extraction procedure used for GC-MS and does not require derivatisation of I. While both methods provide the necessary limit of quantitation of 0.5 ng/ml in human, dog and rat plasma with the required precision and accuracy, the LC-MS-MS assay offers increased sensitivity, selectivity and speed over the GC-MS assay. This allows a same day turn round of results for in excess of 100 samples, including sample preparation and data acquisition and processing.     

Quantitative liquid chromatography-tandem mass spectrometric analysis of 11-dehydro TXB2 in urine

A simple and selective determination method of 11-dehydrothromboxane B2 (11-dehydroTXB2), which is urinary metabolite of TXA2, has been developed employing liquid chromatography-tandem mass spectrometry (LC-MS-MS). 11-DehydroTXB2 and its deuterium-labeled analogue as an internal standard were extracted from urine by simple solid-phase extraction (SPE). These compounds were analyzed using LC-MS-MS in the selected reaction monitoring (SRM) mode, by monitoring the transitions from m/z 367 to m/z 161 for 11-dehydroTXB2 and from m/z 371 to m/z 165 for its internal standard. A good linear response over the range 50 pg-10 ng per tube was demonstrated. The values determined by LC-MS-MS were well validated and closely corresponded to the values determined by gas chromatography-mass spectrometry (GC-MS). The mean concentration of 11-dehydroTXB2 in urine of healthy adults was 635 +/- 427 pg/mg creatinine (mean +/- S.D., n = 13). This simple, accurate and selective determination method described in this study should greatly aid in evaluating the role of TXA2 in vivo.     

Determination of 11-deoxycortisol (Reichstein's compound S) in human plasma by clinical isotope dilution mass spectrometry using benchtop gas chromatography-mass selective detection

A first assay based on stable isotope dilution/gas chromatography-mass spectrometry (ID/GC-MS) has been developed for plasma 11-deoxycortisol (Reichstein's compound S), the leading hormonal marker of 11beta-hydroxylase deficiency. A suitable internal standard being unavailable, we synthesized dideuterated 11-deoxycortisol according to a newly devised synthetic procedure. 17,21-Dihydroxy-pregna-1,4-diene-3,20-dione underwent selective deuteration using Wilkinson's catalyst. Our product [1alpha,2alpha-2H2]11-deoxycortisol was obtained in good yield (35.6%) and high isotopic purity (0.1% 2H0, 99.9% 2H2). Structural confirmation was done by MS and NMR. Our plasma work up consisted of equilibration of plasma with internal standard ([1alpha,2alpha-2H2]11-deoxycortisol), solid phase extraction with Extrelut NT columns, a clean up step using Sephadex LH-20 mini columns and preparation of heptafluorobutyrates as derivatives. Quantification was achieved by selected ion monitoring of m/z 465.40 (analyte) and m/z 467.40 (internal standard). One hundred twenty picograms of 11-deoxycortisol gave a signal to noise ratio of 10. Calibration plot was linear. Spiking experiments showed good accuracy with relative errors <3.0%. Intraassay precision CV was 4.78% and interassay precision CV was 4.56%. We succeeded in integrating our new analyte into our already existing multisteroid ID/GC-MS plasma assay, which now, in its expanded version, is capable of determining all major diagnostic steroids of androgen related disorders in a single profile: 11-deoxycortisol, 17alpha-hydroxyprogesterone, testosterone, 4-androstenedione, 17alpha-hydroxypregnenolone, dehydroepiandrosterone, androstanediol and 5alpha-dihydrotestosterone. The diagnostic potential of our multisteroid ID/GC-MS assay, the small amounts of plasma (0.5 ml) required, the rapid and convenient sample work up, the application of benchtop GC-MS instrumentation, and highest specificity offered by mass spectrometric detection prove our assay suitable for routine clinical use, especially in pediatric endocrinology.     

Rapid quantification of free and esterified phytosterols in human serum using APPI-LC-MS/MS

A novel analytical platform based on liquid chromatography and tandem mass spectrometry using atmospheric pressure photoionization was applied for the simultaneous quantification of free and esterified beta-sitosterol, campesterol, brassicasterol, and stigmasterol. The total time for sample pretreatment and analysis could be reduced from approximately 3 h [gas chromatography-mass spectrometry (GC-MS)] to 15 min. The detection limits of the different phytosterols ranged between 0.25 and 0.68 microg/l. Linear ranges were between 1 and 1,000 microg/l. The within-run and between-run variabilities ranged between 1.4% and 9.9%. The analytical sensitivity was at least 150-fold higher compared with GC-MS. Our new method allows a rapid and simultaneous determination of free and esterified phytosterols in serum.     

Validated method for the determination of risperidone and 9-hydroxyrisperidone in human plasma by liquid chromatography-tandem mass spectrometry

Since the first entry of risperidone on to the market in the early 1990s, investigation of the pharmacokinetic behaviour of the compound for which the availability of a bioanalytical method was a condition sine qua non, has received considerable attention. Most of the published methods, however, did not reach the level of sensitivity and selectivity which can be obtained today since the evolution of liquid chromatography-tandem mass spectrometry (LC-MS-MS) towards a routine technique in the bioanalytical laboratory. Therefore, we developed and validated a new LC-MS-MS method for the determination of risperidone and its active metabolite 9-hydroxyrisperidone in human plasma. This paper describes in detail the bioanalytical procedure and summarizes the validation results obtained. In addition, it focuses on the pitfalls one might encounter when developing similar assays. Despite the particular physicochemical characteristics of risperidone and 9-hydroxyrisperidone, the LC-MS-MS method enabled the quantification of both compounds down to 0.1 ng/ml. The method uses a sample preparation step by solid-phase extraction at pH 6 using a mixed-mode phase. In a short chromatographic run, separation of 9-hydroxyrisperidone from the minor metabolite 7-hydroxyrisperidone is achieved. Detection takes place by (turbo)ionspray tandem mass spectrometry in the positive ion mode. The validated concentration range is from 0.100 to 250 ng/ml, using 500 microliter of sample, with accuracy (bias) and precision (coefficient of variation) being below 15%. Although new developments in equipment will allow us to further improve and speed up the method, the assay reported can be used as a routine method to support a wide range of pharmacokinetic studies.     

On-line sample extraction and enrichment of non-steroidal anti-inflammatory drugs by pre-column in capillary liquid chromatography mass spectrometry

A rapid and sensitive analytical method has been developed for the simultaneous determination of 16 non-steroidal anti-inflammatory drugs (NSAIDs) in human plasma by capillary liquid chromatography (LC) and quadrupole mass spectrometry with electrospray ionization operated in the negative ion mode. The sample clean-up and enrichment on a pre-column were accomplished on-line to improve the sensitivity. This method greatly reduced sample preparation time and sample volume compared with off-line sample extraction methods and conventional LC methods, respectively. The recoveries of NSAIDs from human plasma were 56.7-96.9%. The total analytical time for a single analytical run was approximately 15 min. The detection limits of NSAIDs were 0.001-0.075 microg ml(-1) using a selected ion monitoring mode.     

Validation of a method for quantification of ketobemidone in human plasma with liquid chromatography-tandem mass spectrometry

A liquid chromatography tandem mass spectrometry (LC-MS-MS) method for determination of the analgesic aminophenol ketobemidone in human plasma is presented. Two preparation methods for plasma samples containing ketobemidone were compared, liquid-liquid extraction (LLE) and solid-phase extraction (SPE). Both methods showed good precision (n=10), 1.7% and 2.9%, respectively (0.04 micro M) and 1.1% and 2.5%, respectively (0.14 micro M). The accuracy was 98% and 103%, respectively (0.04 micro M) and 105% and 99%, respectively (0.14 micro M). Ketobemidone could be quantified at 0.43 nM, with a relative standard deviation of 17.5% (n=19) using LLE and 18.6% (n=10) using SPE. This level was an order of magnitude lower than earlier reported quantification limits. Quantitative data from plasma samples analyzed with LC-MS-MS were in good agreement with those obtained by gas chromatography with chemical ionization mass spectrometry (GC-CI/MS). This indicates that LC-MS-MS is a good alternative method to GC-MS as it is more sensitive and time-consuming derivatization can be avoided.     

Validation of a sensitive and automated 96-well solid-phase extraction liquid chromatography-tandem mass spectrometry method for the determination of desloratadine and 3-hydroxydesloratadine in human plasma

To support clinical development, a liquid chromatographic-tandem mass spectrometric (LC-MS-MS) method was developed and validated for the determination of desloratadine (descarboethoxyloratadine) and 3-OH desloratadine (3-hydroxydescarboethoxyloratadine) concentrations in human plasma. The method consisted of automated 96-well solid-phase extraction for sample preparation and liquid chromatography/turbo ionspray tandem mass spectrometry for analysis. [2H(4)]Desloratadine and [2H(4)]3-OH desloratadine were used as internal standards (I.S.). A quadratic regression (weighted 1/concentration(2)) gave the best fit for calibration curves over the concentration range of 25-10000 pg/ml for both desloratadine and 3-OH desloratadine. There was no interference from endogenous components in the blank plasma tested. The accuracy (%bias) at the lower limit of quantitation (LLOQ) was -12.8 and +3.4% for desloratadine and 3-OH desloratadine, respectively. The precision (%CV) for samples at the LLOQ was 15.1 and 10.9% for desloratadine and 3-OH desloratadine, respectively. For quality control samples at 75, 1000 and 7500 pg/ml, the between run %CV was 相似文献   

Determination of cortisol in human saliva using liquid chromatography-electrospray tandem mass spectrometry

The aim of this work was to develop a method for determination of cortisol in saliva by liquid chromatography-tandem mass spectrometry (LC-MS-MS). Saliva was sampled on Salivette tubes. These were centrifuged, deuterium-labeled cortisol was added as internal standard and the proteins precipitated by acetonitrile. The supernatant was evaporated, dissolved in methanol acidified with acetic acid and analyzed by LC-MS-MS. The with-in run precision, tested by pooling saliva samples from volunteers and then analyzing these in a single run, was found to be 7% at 0.7 microgram l(-1). The between-run precision was tested by analysis of the same samples at different days and found to be 11% at 2.5 microgram l(-1). The limit of quantification was 0.5 microgram l(-1). The method was applied for analysis of saliva samples from three volunteers during their last week before vacation and the first and second week on vacation. In addition, the method was compared to analysis by an immunological method. The values from the immunological method were 2.7 times higher than the LC-MS-MS results.     

Comparison of a preliminary procedure for the general unknown screening of drugs and toxic compounds using a quadrupole-linear ion-trap mass spectrometer with a liquid chromatography-mass spectrometry reference technique

Liquid chromatography-tandem mass spectrometry (LC-MS-MS) might be a complement to GC-MS and HPLC-diode array detection for the general unknown screening (GUS) of drugs and toxic compounds, particularly when using information- or data-dependent acquisition (IDA or DDA), an auto-adaptive MS-MS product-ion scan mode where, at each unit time, the m/z ratios above a given intensity threshold are selected for fragmentation. A new quadrupole-linear ion-trap mass spectrometer (LC-QqQlinear ion-trap) was evaluated for GUS using IDA. For the first detection step (so-called "survey scan") the single quadrupole "enhanced" MS mode (EMS), where ions are accumulated then filtered in the Q3-linear ion-trap, was used. The so-called "enhanced" parent ion scan mode (EPI) used at two alternated fragmentation energies gave the best signal intensity and the best mass spectral information when adding mass spectra obtained in low and high fragmentation conditions, respectively, both in the positive (+20 and +50 eV) and negative (-15 and -40 eV) modes. Solid-phase extracts of serum spiked with eight test compounds (chosen for their retention times distributed along the 30-min long chromatogram and for ionising in both the positive and negative modes) were analysed in parallel with this LC-MS-MS technique and with a reference LC-MS method run on a single-quadrupole instrument where low and high in-source fragmentation conditions in the positive and the negative ion modes are alternated. A C(18), 5 microm (150 x 1 mm I.D.) column and a gradient elution of acetonitrile in pH 3, 2 mM ammonium formate, were used for both. Higher signal-to-noise ratios were obtained with the LC-QqQlinear ion-trap instrument than with the reference technique, resulting in mass spectra devoid of contaminant ions and at least as informative as the reconstructed single-MS spectra. After optimisation of the IDA intensity threshold for the detection of tiny chromatographic peaks in noise, five out of the eight compounds (milrinone, lorazepam, fluometuron, piretanide and warfarin) could be unambiguously identified at the concentration of 0.1 mg/l in serum, in the positive or negative modes, or in both, versus only two by LC-MS. All of them could be identified at 1 mg/l by both techniques. These preliminary results show that the sensitivity and mass structural information brought by this new LC-QqQlinear ion-trap instrument may help design an efficient toxicological GUS procedure.     

LC-MS/MS in the Clinical Laboratory – Where to From Here?

Liquid chromatography-tandem mass spectrometry (LC-MS/MS) has seen enormous growth in clinical laboratories during the last 10-15 years. It offers analytical specificity superior to that of immunoassays or conventional high performance/pressure liquid chromatography (HPLC) for low molecular weight analytes and has higher throughput than gas chromatography-mass spectrometry (GC-MS). Drug/Toxicology and Biochemical Genetics/Newborn Screening laboratories were at the vanguard of clinical LC-MS/MS use, but have been eclipsed by Endocrine laboratories. In USA reference/referral laboratories, most steroids and biogenic amines are now assayed by LC-MS/MS, and the technology has started to penetrate into smaller laboratories. Assays for mineralo- and gluco-corticoids and their precursors, sex steroids, metanephrines and 25-hydroxy vitamin D highlight the advantages of LC-MS/MS.However, several limitations of LC-MS/MS have become apparent, centring on the interacting triangle of sensitivity - specificity - throughput. While sample throughput is higher than for conventional HPLC or GC-MS, it lags behind automated immunoassays. Techniques which improve throughput include direct sample injection, LC-multiplexing and samplemultiplexing. Measures to improve specificity and sensitivity include sample clean-up and optimising chromatography to avoid interferences and ion suppression due to sample-matrix components. Next generation instrumentation may offer additional benefits.The next challenge for clinical LC-MS/MS is peptide/protein analysis. The quest for multi-biomarker profiles for various diseases has largely failed, but targeted peptide and protein testing by LC-MS/MS, directed at analytical and clinical questions that need to be answered, is proving highly successful. We anticipate that this will result in similar growth of clinical protein/peptide LC-MS/MS as has been seen for low molecular weight applications.     

A rapid, sensitive and selective liquid chromatography/atmospheric pressure chemical ionization tandem mass spectrometry method for determination of fenretinide (4-HPR) in plasma

A simple and sensitive liquid chromatography/tandem mass spectrometry (LC-MS/MS) method using an atmospheric pressure chemical ionization source (APCI) for the quantification of fenretinide (4-HPR) in mouse plasma was developed and validated. After a simple protein precipitation of plasma sample by acetonitrile, 4-HPR was analyzed by LC-APCI-MS/MS. High-performance liquid chromatography (HPLC) separation was conducted on a Hypurity C18 column (50mmx2.1mm, 5microm) with a flow rate 0.60mL/min using a gradient mobile phase comprised of 0.05% formic acid in water (A) and methanol (B), and a run time of 4.5min. The elimination of a tedious sample preparation process and a shorter run time substantially reduced total analysis time. The method was linear over the range 0.5-100ng/mL, with r>0.998. The intra- and inter-assay precisions were 1.4-9.2% and 5.1-8.2%, respectively, and the intra- and inter-assay accuracies were 93.9-98.6% and 92.7-95.3%, respectively. The absolute recoveries were 90.3% (1.5ng/mL), 97.0% (7.5ng/mL) and 92.1% (75.0ng/mL) for 4-HPR, and 99.1% for the internal standard (150ng/mL). The analytical method had excellent sensitivity using a small sample volume (30microL) with the lower limit of quantification (LLOQ) 0.5ng/mL. This method is robust and has been successfully employed in a pharmacokinetic study of 4-HPR in a mouse xenograft model of neuroblastoma.     

LC-NMR: a new tool to expedite the dereplication and identification of natural products

The rapid identification of known or undesirable compounds from natural products extracts — “dereplication” — is an important step in an efficiently run natural products discovery program. Dereplication strategies use analytical techniques and database searching to determine the identity of an active compound at the earliest possible stage in the discovery process. In the past few years, advances in technology have allowed the development of tandem analytical techniques such as liquid chromatography mass spectrometry (LC-MS), LC-MS-MS, liquid chromatography nuclear magnetic resonance (LC-NMR), and LC-NMR-MS. LC-NMR, despite its lower sensitivity as compared to LC-MS, provides a powerful tool for rapid identification of known compounds and identification of structure classes of novel compounds. LC-NMR is especially useful in instances where the data from LC-MS are incomplete or do not allow confident identification of the active component of a sample. LC-NMR has been used to identify the marine alkaloid aaptamine as the active component in an extract of the sponge Aaptos sp. This extract had been identified as an enzyme inhibitor by a high throughput screening (HTS) effort. Isolated aaptamine exhibited an IC₅₀=120 μM against this enzyme. Strategies for the identification of aaptamine and for the use of LC-NMR in a natural products HTS program are discussed. Journal of Industrial Microbiology & Biotechnology (2000) 25, 342–345. Received 30 March 2000/ Accepted in revised form 03 July 2000     

Field gas chromatography-mass spectrometry for fast analysis

The objective of this presentation is to demonstrate the original device and procedure for fast gas chromatography-mass spectrometry (GC-MS) analysis of gaseous and liquid samples and to discuss its features and capabilities. The concept was developed in order to expand the range of compounds suitable for GC separation and to reduce the time of analysis. Field GC-MS, consisting of original "concentrator-thermodesorber" (CTD) unit, multiple module GC system and compact magnetic mass spectrometer with powerful two-stage vacuum system and multicollector ion detector, is represented. The whole weight of the device is 90 kg. Power consumption is 250 W. The device and analytical procedures allow high speed screening of toxic substances in air and extracts within 100 s per sample. The examples of applications are described, including fast screening of tributyl phosphate (TBP) in air at low ppt level at the rate 1 sample/min.     

Quantitative detection of ketamine, norketamine, and dehydronorketamine in urine using chemical derivatization followed by gas chromatography-mass spectrometry

A repeatable and highly sensitive analytical method using gas chromatography-mass spectrometry (GC-MS) in the selected ion monitoring mode (SIM) is developed for the simultaneous detection of ketamine (KT), norketamine (NK), and newly introduced dehydronorketamine (DHNK) in urine. The test specimen along with the deuterium analogues as internal standards (IS): d4-KT for KT and d4-NK for NK/DHNK, was extracted on an automatic solid-phase extraction (SPE) apparatus. The extracted eluate then was dried and derivatized with N-methyl-bis(trifluoroacetamide) (CF3CONCH3COCF3, MBTFA). Finally, the cooled derivatized solution was directly injected into the GC-MS system for analysis. The proposed process achieves high sensitivity for the detection of KT, NK, and DHNK. Correlation coefficients derived from typical calibration curves in the range of 20-2000 ng/mL are 1.000 for KT and NK, 0.999 for DHNK. The limits of detection (LODs) and limits of quantitation (LOQs) are 0.5-1.0 and 1.5-3.0, respectively. The overall method recoveries of KT, NK, and DHNK are 82.2-93.4. The intra- and inter-day run deviations are smaller than 5.0%. The analytical scheme was also applied to the determination of KT, NK, and DHNK in 20 KT suspected urine specimens, and the results reconfirm that DHNK is a main metabolite of KT.     

Optimized glucuronide hydrolysis for the detection of psilocin in human urine samples

In order to develop a sensitive and reliable analytical method for psilocin (PC) in urine samples, the hydrolysis conditions including the acid, alkaline and enzymatic hydrolyses have been investigated by monitoring not only PC but also psilocin glucuronide (PCG) by liquid chromatography tandem mass spectrometry (LC-MS-MS); PCG was initially identified in a "magic mushroom (MM)" user's urine by liquid chromatography mass spectrometry (LC-MS) and LC-MS-MS. The proposed conditions optimized for the hydrolysis are as follows: hydrolysis, enzymatic hydrolysis; enzyme, Escherichia coli beta-glucuronidase (5000 units/ml urine); incubation, pH 6 at 37 degrees C for 2h. The complete hydrolysis of PCG in urine was obtained under these conditions, while the enzymatic hydrolyses with three types of beta-glucuronidases originated from bovine liver (Type B-1), Helix pomatia (Type H-1) and Ampullaria provided uncompleted hydrolysis of PCG. Also, neither the acid nor alkaline hydrolysis was found to be applicable. According to the present method, 3.55 microg/ml of psilocin was detected in the "magic mushroom" user's urine after the enzymatic hydrolysis, though psilocin was not detected without hydrolysis.     

Liquid chromatography--mass spectrometric method combined with derivatization for determination of 1 alpha-hydroxyvitamin D(3) in human plasma

A stable isotope dilution liquid chromatography-tandem mass spectrometric (LC-MS-MS) method for the determination of plasma 1 alpha-hydroxyvitamin D(3) [1 alpha(OH)D(3)] has been developed. The method employed derivatization, the reaction with 4-[2-(6,7-dimethoxy-4-methyl-3-oxo-3,4-dihydroquinoxalyl)ethyl]-1,2,4-triazoline-3,5-dione and acetylation, which significantly improved the ionization efficiency of 1 alpha(OH)D(3) with a detection limit of 6.3 fmol per injection. The plasma 1 alpha(OH)D(3) was extracted with acetonitrile, purified with disposable cartridges, derivatized and subjected to LC-MS-MS analysis using atmospheric pressure chemical ionization. The intra- and inter-assay coefficients of variation were below 10.6 and 4.7%, respectively, and the analytical recovery of 1 alpha(OH)D(3) was quantitative. The limit of quantitation was 25 pg/ml for a 1.0-ml plasma aliquot. The application of the developed method to the sample of a volunteer orally given 1 alpha(OH)D(3) was also described.     

Quantitative determination of donepezil in human plasma by liquid chromatography/tandem mass spectrometry employing an automated liquid-liquid extraction based on 96-well format plates. Application to a bioequivalence study

An automated high-throughput liquid chromatography/tandem mass spectrometry (LC-MS/MS) method was developed for quantitative determination of donepezil in human plasma. 150 MicroL of plasma samples were placed in 2.2 mL 96-deepwell plates and both donepezil and loratadine (IS) were extracted from human plasma by liquid-liquid extraction (LLE), using hexane as the organic solvent. Robotic liquid handling workstations were employed for all liquid transfer and solution preparation steps and resulted in a short sample preparation time. After vortexing, centrifugation and freezing, the supernatant organic solvent was evaporated and reconstituted in a small volume of reconstitution solution. The method developed, includes a sample analysis performed by reversed phase LC-MS/MS, with positive ion electrospray ionization, using multiple reaction monitoring (MRM). The chromatographic run time was set for 2.0 min with a flow rate of 0.7 mL/min in a C18 analytical column. The method was significantly sensitive, specific, accurate and precise for the determination of donepezil in human plasma and had the shortest run time. The curve was proven to be linear for the concentration range of 0.1-100 ng/mL. After validation, the method was applied to the rapid and reliable quantitative determination of donepezil in a bioequivalence study after per os administration of a 5mg donepezil tablet.     

Gas chromatography mass spectrometry-based metabolite profiling in plants

The concept of metabolite profiling has been around for decades, but technical innovations are now enabling it to be carried out on a large scale with respect to the number of both metabolites measured and experiments carried out. Here we provide a detailed protocol for gas chromatography mass spectrometry (GC-MS)-based metabolite profiling that offers a good balance of sensitivity and reliability, being considerably more sensitive than NMR and more robust than liquid chromatography-linked mass spectrometry. We summarize all steps from collecting plant material and sample handling to derivatization procedures, instrumentation settings and evaluating the resultant chromatograms. We also define the contribution of GC-MS-based metabolite profiling to the fields of diagnostics, gene annotation and systems biology. Using the protocol described here facilitates routine determination of the relative levels of 300-500 analytes of polar and nonpolar extracts in approximately 400 experimental samples per week per machine.     

Analysis of betamethasone in rat plasma using automated solid-phase extraction coupled with liquid chromatography-tandem mass spectrometry. Determination of plasma concentrations in rat following oral and intravenous administration

A method is described for the determination of betamethasone in rat plasma by liquid chromatography-tandem mass spectrometry (LC-MS-MS). The analyte was recovered from plasma by solid-phase extraction and subsequently analyzed by LC-MS-MS. A Packard Multiprobe II, an automated liquid handling system, was employed for the preparation and extraction of a 96-well plate containing unknown plasma samples, standards and quality control samples in an automated fashion. Prednisolone, a structurally related steroid, was used as an internal standard. Using the described approach, a limit of quantitation of 2 ng/ml was achieved with a 50 microl aliquot of rat plasma. The described level of sensitivity allowed the determination of betamethasone concentrations and subsequent measurement of kinetic parameters of betamethasone in rat. Combination of automated plasma extraction and the sensitivity and selectivity of LC-MS-MS offers a valuable alternative to the methodologies currently used for the quantitation of steroids in biological fluids.