Quantitative analysis of short-chain acyl-coenzymeAs in plant tissues by LC–MS–MS electrospray ionization method

Because acyl-CoAs play major roles in numerous anabolic and catabolic pathways, the quantitative determination of these metabolites in biological tissues is paramount to understanding the regulation of these metabolic processes. Here, we report a method for the analysis of a collection of short-chain acyl-CoAs (<6 carbon chain length) from plant extracts. Identification of each individual acyl-CoA was conducted by monitoring specific mass-fragmentation ions that are derived from common chemical moieties of all Coenzyme A (CoA) derivatives, namely the adenosine triphosphate nucleotide, pantothenate and acylated cysteamine. This method is robust and quick, enabling the quantitative analysis of up to 12 different acyl-CoAs in plant metabolite extracts with minimal post-extraction processing, using a 30 min chromatographic run-time.     

An accurate quantitative LC/ESI-MS/MS method for sirolimus in human whole blood

Sirolimus is a widely used immunosuppressant that requires therapeutic drug monitoring (TDM). We optimized a preanalytical procedure that allows for the accurate quantiation of sirolimus in whole blood by LC/ESI-MS/MS with minimal matrix effects. Sirolimus is highly lipophilic, and solvents containing greater than 50% methanol were required to maintain sirolimus recovery. The final pretreatment procedure developed consists of a zinc sulfate protein precipitation, an extraction using octadecyl silyl-silica gel for eliminating water-soluble and hydrophilic compounds, and HybridSPE cartridge treatment to eliminate phospholipids. Using this procedure prior to LC/ESI-MS/MS led to the accurate and reproducible quantitation of sirolimus in human whole blood. The linear range of detection was 0.5-50 ng/mL, a range appropriate for TDM, and the method demonstrated good repeatability and intermediate precision within this quantitative range. In order to investigate the quantitative performance of this method, we compared it to two commercially available sirolimus immunoassays and our previously reported LC/ESI-MS/MS method. The immunoassays gave consistently greater values for the sirolimus concentration, and this may be related to antibody cross-reactivity with sirolimus metabolites and/or other matrix effects. Although our procedure is too long to support real-time TDM for outpatients, it can serve as reference method to assess the performance of other analytical methods that are currently available or may be developed in the future.     

Stereoselective analysis of bupropion and hydroxybupropion in human plasma and urine by LC/MS/MS

A sensitive, stereoselective assay using solid phase extraction and LC-MS-MS was developed and validated for the analysis of (R)- and (S)-bupropion and its major metabolite (R,R)- and (S,S)-hydroxybupropion in human plasma and urine. Plasma or glucuronidase-hydrolyzed urine was acidified, then extracted using a Waters Oasis MCX solid phase 96-well plate. HPLC separation used an alpha(1)-acid glycoprotein column, a gradient mobile phase of methanol and aqueous ammonium formate, and analytes were detected by electrospray ionization and multiple reaction monitoring with an API 4000 Qtrap. The assay was linear in plasma from 0.5 to 200 ng/ml and 2.5 to 1000 ng/ml in each bupropion and hydroxybupropion enantiomer, respectively. The assay was linear in urine from 5 to 2000 ng/ml and 25 to 10,000 ng/ml in each bupropion and hydroxybupropion enantiomer, respectively. Intra- and inter-day accuracy was >98% and intra- and inter-day coefficients of variations were less than 10% for all analytes and concentrations. The assay was applied to a subject dosed with racemic bupropion. The predominant enantiomers in both urine and plasma were (R)-bupropion and (R,R)-hydroxybupropion. This is the first LC-MS/MS assay to analyze the enantiomers of both bupropion and hydroxybupropion in plasma and urine.     

Determination of eprosartan in human plasma and urine by LC/MS/MS

A protein precipitation, liquid chromatography/tandem mass spectrometry (LC/MS/MS) method has been developed and validated for the determination of eprosartan in human plasma and urine. The solvent system also served as a protein precipitation reagent. The chromatographic separation was achieved on a CAPCELL PAK C18 column (50 mmx2.0 mm, 5 microm, Shiseido). A mobile phase was consisted of 0.5% formic acid in water and 0.5% formic acid in acetonitrile (72:28). Detection was by positive ion electrospray tandem mass spectrometry on a Sciex API3000. The standard curves, which ranged from 5 to 2000 ng/mL in human plasma and from 0.25 to 50 microg/mL in urine, were fitted to a 1/x weighted quadratic regression model. The method proved to be accurate, specific and sensitive enough to be successfully applied to a pharmacokinetic study.     

Improved and simplified liquid chromatography/electrospray ionization mass spectrometry method for the analysis of underivatized glucosamine in human plasma

Glucosamine is an amino monosaccharide reagent. It is difficult to assay using typical reversed-phase column due to the early elution, by optimizing the chromatographic conditions, especially the analytical column and the mobile phase composition, an improved analytical method was developed and validated, which offers rapid, sensitive and specific determination of glucosamine in human plasma. Following protein precipitation, the analyte and internal standard (valibose) were separated using an isocratic mobile phase on an Inertsil CN-3 column and detected by mass spectrometry in the multiple reaction monitoring mode using the respective precursor to product ion combinations of m/z 180/72 for glucosamine and m/z 252/198 for valibose. The chromatographic time was just 4.2 min for each sample, which made it possible to analyze more than 120 human plasma samples per day. The method exhibited a linear dynamic range of 4.00-4000 ng/mL for glucosamine in human plasma. The lower limit of quantification (LLOQ) was 4.00 ng/mL with a relative standard deviation of less than 10.9%. Acceptable precision and accuracy were obtained for the plasma concentrations over the standard curve range. By monitoring the two different MRM transitions, it was proved that no endogenous glucosamine was found in human plasma. The validated method has been successfully used to analyze human plasma samples for application in a bioequivalence study.     

High-performance liquid chromatography coupled with electrospray tandem mass spectrometry (LC/MS/MS) method for the simultaneous determination of diazepam, atropine and pralidoxime in human plasma

A high-performance liquid chromatography coupled with electrospray tandem mass spectrometry (LC/MS/MS) procedure for the simultaneous determination of diazepam from avizafone, atropine and pralidoxime in human plasma is described. Sample pretreatment consisted of protein precipitation from 100microl of plasma using acetonitrile containing the internal standard (diazepam D5). Chromatographic separation was performed on a X-Terra MS C8 column (100mmx2.1mm, i.d. 3.5microm), with a quick stepwise gradient using a formate buffer (pH 3, 2mM) and acetonitrile at a flow rate of 0.2ml/min. The triple quadrupole mass spectrometer was operated in positive ion mode and multiple reaction monitoring was used for drug quantification. The method was validated over the concentration ranges of 1-500ng/ml for diazepam, 0.25-50ng/ml for atropine and 5-1000ng/ml for pralidoxime. The coefficients of variation were always <15% for both intra-day and inter-day precision for each analyte. Mean accuracies were also within +/-15%. This method has been successfully applied to a pharmacokinetic study of the three compounds after intramuscular injection of an avizafone-atropine-pralidoxime combination, in healthy subjects.     

Intact glucosinolate analysis in plant extracts by programmed cone voltage electrospray LC/MS: performance and comparison with LC/MS/MS methods

We present a comprehensive, sensitive, and highly specific negative ion electrospray LC/MS method for identifying all structural classes of glucosinolates in crude plant extracts. The technique is based on the observation of simultaneous maxima in the abundances of the m/z 96 and 97 ions, generated by programmed cone voltage fragmentation, in the mass chromatogram. The abundance ratios lie in the range 1:2-1:4 ([m/z 96]/[m/z 97]). Examination of the corresponding full-scan mass spectra allows individual glucosinolates of all structural classes to be identified rapidly and with confidence. The use of linearly programmed cone voltage fragmentation enhances characteristic fragment ions without compromising the abundance of the analytically important [M - H]- ion and its associated (and analytically useful) sulfur isotope peaks. Detection limits are in the low nanogram range for full-scan, programmed cone voltage spectra. Comparison of the technique with LC/MS/MS methods (product ion, precursor ion, and constant neutral loss scans) has shown that the sensitivity and selectivity of the programmed cone voltage method is superior. Data obtained on a variety of plant extracts confirmed that the methodology was robust and reliable.     

Reversed phase LC/MS/MS method for targeted quantification of glycerophospholipid molecular species in plasma

The relationship between lipid status and metabolism, infant development and health has widely been studied, but the importance of individual glycerophospholipid species for biological functions in infants has hardly been considered. We developed a method for quantitative analyses of plasma glycerophospholipids from small sample volume. Proteins were precipitated with methanol, which eliminated further sample preparation. The supernatant was analysed by reversed-phase HPLC using a gradient of water, methanol and isopropanol as mobile phase. Electrospray ionisation in negative mode in combination with tandem mass spectrometry enabled detection of specific fatty acids as fragments of glycerophospholipid species. With this combination of chromatography and mass spectrometry, PC, lyso-PC, PE and lyso-PE species and their relevant isobaric compounds were quantified. Method validation showed a linear working range between 0.05 μmol/L and 10 μmol/L in diluted plasma samples. The intra-assay coefficients of variation (n=6) ranged from 1.1% to 13.9%. Results were comparable with data of the human metabolome database and gas chromatographic fatty acid analyses. All quantitatively important PE and PC species are covered. The method can be applied for investigating dietary effects on plasma GP composition from small plasma volumes.     

Validation of an HPLC/MS/MS method with isotopic dilution for quantitative determination of trans,trans-muconic acid in urine samples of workers exposed to low benzene concentrations

Urinary trans,trans-muconic acid (t,t-MA), a biomarker of benzene exposure, is usually determined by HPLC methods with detection by either UV or, more recently, electrospray tandem mass spectrometry. However, not all these methods have been fully validated for quantitative analysis. This paper presents an HPLC/MS/MS method for reliable quantitative determination of t,t-MA that uses a commercial deuterium-labeled isotope as internal standard; the matrix effect has been evaluated and LOD is 0.22 microg/L. We used this method to test 200 urine samples, 175 of them collected at end-of-shift from workers in an oil refinery.     

Validation study of a method for assaying DE-310, a macromolecular carrier conjugate containing an anti-tumor camptothecin derivative, and the free drug in human plasma by HPLC and LC/MS/MS

DE-310 is a macromolecular carrier conjugate containing an anti-tumor camptothecin derivative, DX-8951, conjugated to a water-soluble polymer by means of a peptide spacer. New assay methods have been developed to determine the polymer-bonded DX-8951 conjugate, free DX-8951, and Glycyl-DX-8951 in human plasma. Solid-phase extraction was used to extract free DX-8951 and Glycyl-DX-8951 from plasma, and LC/MS/MS (Method I) was used to determine the amount of each analyte. Protein precipitation was used to extract Conjugated DX-8951, which was then digested with thermolysin. HPLC (Method II) was used to determine the productive compound (Phenylalanyl-Glycyl-DX-8951). The lower limit of quantitation of DX-8951 was 50 pg/ml, of Glycyl-DX-8951 was 80 pg/ml, and of Conjugated DX-8951 was 100 ng/ml (as DX-8951 equivalent). Both methods showed satisfactory sensitivity, precision, and accuracy.     

Developing a robust ultrafiltration-LC-MS/MS method for quantitative analysis of unbound vadimezan (ASA404) in human plasma

Ultrafiltration of human plasma in combination with LC-MS/MS has been increasingly used in the quantitative analysis of the free fraction of drug candidates for PK/efficacy assessment. In addition to controlling the pre-incubation and centrifugation temperatures, some important factors that must be investigated and addressed include: (1) possible nonspecific binding, (2) possible impact of freeze/thaw cycles of plasma samples and extended storage of plasma samples at room temperature on the analyte recovery prior to ultrafiltration, and (3) identification of the appropriate assay dynamic range to avoid unnecessary dilutions. These factors were explored in the development and validation of a robust LC-MS/MS assay for the quantitative analysis of unbound vadimezan (ASA404) in human plasma. First, to mimic human physiological conditions, all plasma samples were incubated at ~37°C for a minimum of 30 min after thawing and prior to centrifugation to obtain the ultrafiltrate. Second, by passing the calibration standards and QC samples in plasma ultrafiltrate through the ultrafiltration membrane, the observed non-specific binding of the analyte due to the membrane was corrected. Third, the effects of multiple freeze/thaw cycles and/or storage at room temperature for various periods (4, 8, 16 and 24h) were evaluated to determine the impact on analyte concentrations in the ultrafiltrate from the plasma QC samples. Fourth, the appropriate dynamic range was established to accommodate the expected incurred sample free analyte concentrations. The validated assay has a dynamic range of 30.0-30,000 ng/ml for ASA404 in human plasma ultrafiltrate using a sample volume of 30 μl. Quality control pools containing the analyte were prepared at concentrations of 30.0-22,500 ng/ml to cover the assay calibration range. The intra-assay and inter-assay precision and accuracy were ≤ 15% (CV) and within ± 15% (bias) of the nominal values, respectively, for all measured QC concentrations, including the LLOQ. Freeze/thaw for up to three cycles of the plasma samples and/or the extended human plasma sample exposure to room temperature for up to 24h were confirmed to have no impact on the assay results for the free analyte. The validated method was successfully implemented to support clinical studies for the compound.     

Enantioselective LC/MS method for the determination of an antimalarial agent Fenozan B07 in dog plasma

A chiral liquid chromatography/mass spectrometry (LC/MS) bioanalytical procedure has been developed for the analysis of the antimalaric agent Fenozan B07 in dog plasma. Normal-phase chromatography involving a phenylcarbamate derivative of cellulose coated on silica gel as the chiral stationary phase was used to resolve (-)-(S,S)-B07 from (+)-(R,R)-B07. The enantiomers were detected by a mass spectrometer equipped with an atmospheric pressure chemical ionization (APCI) interface operated in the negative ion mode. A mass spectrum, characterized by a base peak of m/z 285, was obtained for each enantiomer. The m/z 285 ion was very specific for the analysis of both enantiomers in the plasma. The selected ion monitoring analysis of the plasma samples was therefore performed at m/z 285 for quantitative purposes. The enantiomers were extracted from the plasma in a basic medium and purified by solid-phase extraction using a hydrophilic-lipophilic balanced sorbent. A lower limit of quantification of 2 ng/mL in plasma was achieved for both enantiomers. The quantitative procedure reported in this study was highly specific and sensitive, and was validated according to the FDA guidance on bioanalytical method validation.     

First LC-MS/MS electrospray ionization validated method for the quantification of perindopril and its metabolite perindoprilat in human plasma and its application to bioequivalence study

A high throughput bioanalytical method based on solid phase extraction and liquid chromatography-tandem mass spectrometry (LC-MS/MS), has been developed for the estimation of perindopril and its metabolite perindoprilat, an angiotensin-converting enzyme inhibitor in human plasma. Ramipril was used as internal standard (IS). The extraction of perindopril, perindoprilat and ramipril from the plasma involved treatment with phosphoric acid followed by solid phase extraction (SPE) using hydrophilic lipophilic balance HLB cartridge. The SPE eluate without drying were analyzed by LC-MS/MS, equipped with turbo ion spray (TIS) source, operating in the negative ion and selective reaction monitoring (SRM) acquisition mode to quantify perindopril and perindoprilat in human plasma. The total chromatographic run time was 1.5 min with retention time for perindopril, perindoprilat and ramipril at 0.33, 0.35 and 0.30 min. The developed method was validated in human plasma matrix, with a sensitivity of 0.5 ng/ml (CV, 7.67%) for perindopril and 0.3 ng/ml (CV, 4.94%) for perindoprilat. This method was extensively validated for its accuracy, precision, recovery, stability studies and matrix effect especially because the pattern of elution of all the analytes appears as flow injection elution. Sample preparation by this method yielded extremely clean extracts with very good and consistent mean recoveries; 78.29% for perindopril, 76.32% for perindoprilat and 77.72% for IS. The response of the LC-MS/MS method for perindopril and perindoprilat was linear over the range 0.5-350.0 ng/ml for perindopril and 0.3-40 ng/ml for perindoprilat with correlation coefficient, r>/=0.9998 and 0.9996, respectively. The method was successfully applied for bioequivalence studies in human subjects samples with 4 mg immediate release (IR) formulations.     

Sensitive assay for determining plasma tenofovir concentrations by LC/MS/MS

An LC/MS/MS assay for the determination of tenofovir (TNF) was developed and validated for use with the EDTA anticoagulated human plasma matrix. Heparin-treated plasma and serum matrices were also validated. After addition of adefovir as an internal standard, trifluoroacetic acid was used to produce a protein-free extract. Chromatographic separation was achieved with a Polar-RP Synergi, 2.0 mm x 150 mm, reversed-phase analytical column. The mobile phase was 3% acetonitrile/1% acetic acid, aq. Detection of TNF and the internal standard was achieved by ESI MS/MS in the positive ion mode using 288/176 and 274/162 transitions, respectively. The method was linear from 10 to 750 ng/ml with a minimum quantifiable limit of 10 ng/ml when 250 microl aliquots were analyzed. The usefulness of this LC/MS/MS method to routinely monitor plasma concentrations of TNF was demonstrated along with its ability to assist in the performance of pharmacokinetic studies.     

Microdose clinical trial: quantitative determination of fexofenadine in human plasma using liquid chromatography/electrospray ionization tandem mass spectrometry

A sample treatment procedure and high-sensitive liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) method for quantitative determination of fexofenadine in human plasma was developed for a microdose clinical trial with a cold drug, i.e., a non-radioisotope-labeled drug. Fexofenadine and terfenadine, as internal standard, were extracted from plasma samples using a 96-well solid-phase extraction plate (Oasis HLB). Quantitation was performed on an ACQUITY UPLC system and an API 5000 mass spectrometer by multiple reaction monitoring. Chromatographic separation was achieved on an XBridge C18 column (100 mm x 2.1 mm i.d., particle size 3.5 microm) using acetonitrile/2 mM ammonium acetate (91:9, v/v) as the mobile phase at a flow rate of 0.6 ml/min. The analytical method was validated in accordance with the FDA guideline for validation of bioanalytical methods. The calibration curve was linear in the range of 10-1000 pg/ml using 200 microl of plasma. Analytical method validation for the clinical dose, for which the calibration curve was linear in the range of 1-500 ng/ml using 20 microl of plasma, was also conducted. Each method was successfully applied for making determinations in plasma using LC/ESI-MS/MS after administration of a microdose (100 microg solution) and a clinical dose (60 mg dose) in eight healthy volunteers.     

Cherry-picking in an orchard: unattended LC/MS analysis from an autosampler with >32,000 samples online

The 1,536-well microplate format has widely supplanted the 384-well microplate format for high-throughput screening and for IC(50) assays. Previously, liquid chromatography/mass spectrometry (LC/MS) analyses of such samples required manual transfers of the wells of interest from a 1,536-well plate into a 384-well plate. Because this manual transfer introduced a source of potential error, it became clear that a more appropriate solution would be to sample directly from the 1,536-well plates. Currently, commercially available 1,536-well plate auto samplers are not compatible with Waters LC/MS systems. The authors have modified their CTC PAL autosampler to support injection from up to twenty-four 1,536-well plates. This allows them to cherry-pick any sample from up to 36,864 wells on the autosampler. Because of its success at this Institute, sampling from 1,536-well plates has not only become the preferred method for LC/MS analysis from IC(50) plates but also become the standard format used for the handling of and the sampling from large combinatorial libraries.     

Site-specific glycosylation analysis of human apolipoprotein B100 using LC/ESI MS/MS

Human apolipoprotein B100 (apoB100) has 19 potential N-glycosylation sites, and 16 asparagine residues were reported to be occupied by high-mannose type, hybrid type, and monoantennary and biantennary complex type oligosaccharides. In the present study, a site-specific glycosylation analysis of apoB100 was carried out using reversed-phase high-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry (LC/ESI MS/MS). ApoB100 was reduced, carboxymethylated, and then digested by trypsin or chymotrypsin. The complex mixture of peptides and glycopeptides was subjected to LC/ESI MS/MS, where product ion spectra of the molecular ions were acquired data-dependently. The glycopeptide ions were extracted and confirmed by the presence of carbohydrate-specific fragment ions, such as m/z 204 (HexNAc) and 366 (HexHexNAc), in the product ion spectra. The peptide moiety of glycopeptide was determined by the presence of the b- and y-series ions derived from its amino acid sequence in the product ion spectrum, and the oligosaccharide moiety was deduced from the calculated molecular mass of the oligosaccharide. The heterogeneity of carbohydrate structures at 17 glycosylation sites was determined using this methodology. Our data showed that Asn2212, not previously identified as a site of glycosylation, could be glycosylated. It was also revealed that Asn158, 1341, 1350, 3309, and 3331 were occupied by high-mannose type oligosaccharides, and Asn 956, 1496, 2212, 2752, 2955, 3074, 3197, 3438, 3868, 4210, and 4404 were predominantly occupied by mono- or disialylated oligosaccharides. Asn3384, the nearest N-glycosylation site to the LDL-receptor binding site (amino acids 3359-3369), was occupied by a variety of oligosaccharides, including high-mannose, hybrid, and complex types. These results are useful for understanding the structure of LDL particles and oligosaccharide function in LDL-receptor ligand binding.     

Quantitative analysis of Tenecteplase in rat plasma samples using LC-MS/MS as an alternative for ELISA

An LC-MS/MS method has been developed for the quantitative determination of a protein drug (Tenecteplase; M(W) 58,777 Da) in rat plasma. The protein was digested with trypsin without prior clean-up of the plasma sample, without the use of a label nor internal standard. A limited validation was performed to assess the linearity, the sensitivity and the specificity of the method. In addition, the developed method was applied to the quantitative analysis of Tenecteplase in rat plasma samples originating from a single-dose study in rats.     

An automated SPE/LC/MS/MS method for the analysis of cocaine and metabolites in whole blood

As laboratories are called upon to develop novel, fast, and sensitive methods, here we present a completely automated method for the analysis of cocaine and its metabolites (benzoylecgonine, ecgonine methyl ester, ecgonine and cocaethylene) from whole blood. This method utilizes an online solid-phase extraction (SPE) with high performance liquid chromatographic separation and tandem mass spectrometric detection. Pretreatment of samples involve only protein precipitation and ultracentrifugation. An efficient online solid-phase extraction (SPE) procedure was developed using Hysphere MM anion sorbent. A gradient chromatography method with a Gemini C6-Phenyl (50mmx3.00mm i.d., 5microm) column was used for the complete separation of all components. Analysis was by positive ion mode electrospray ionization tandem mass spectrometry, using multiple reaction monitoring (MRM) to enhance the selectivity and sensitivity of the method. For the analysis, two MRM transitions are monitored for each analyte and one transition is monitored for each internal standard. With a 30-microL sample injection, linearity was analyte dependent but generally fell between 8 and 500ng/mL. The limits of detection (LODs) for the method ranged from 3 to 16ng/mL and the limits of quantitation (LOQs) ranged from 8 to 47ng/mL. The bias and precision were determined using a simple analysis of variance (ANOVA: single factor). The results demonstrate bias as <7%, and %precision as <9% for all components at each QC level.