An LC-MS/MS procedure for the quantification of naproxen in human plasma: development, validation, comparison with other methods, and application to a pharmacokinetic study

A sensitive, precise and accurate quantitative LC-MS/MS method for the measurement of naproxen in human plasma was developed and completely validated according to current FDA and EMA guidelines. The new method employs acetonitrile protein precipitation for sample preparation and uses ketoprofen as the internal standard. Suitability of the new assay was assessed in comparison with 36 reported bioanalytical assays and the pharmacokinetic results obtained by the new method were compared to 11 reported studies in humans. The principal advantage of this LC-MS/MS method is the simultaneous achievement of high absolute recovery (90.0±3.6%), acceptable sensitivity (lower limit of quantitation of 0.100 μg/mL), high inter-day precision (CV≤9.4%), high analytical recovery (between 94.4 and 103.1%), and excellent linearity over the concentration range 0.100-50.0 μg/mL (r(2)≥0.998) combined with a short run time of only 2 min.     

LC-MS/MS method for simultaneous determination of valproic acid and major metabolites in human plasma

A rapid and sensitive method using liquid chromatography-tandem mass spectroscopy (LC-MS/MS) was developed and validated for simultaneous quantitative determination of valproic acid and three major metabolites (3-OH-valproic acid, 4-ene-valproic acid and 5-OH-valproic acid) in human plasma. The analytes and internal standard were isolated from 200 μL samples by solid phase extraction using a ZORBAX SB-C? column (3.5 μm, 2.1×100 mm) with an isocratic mobile phase consisting of methanol-10mM ammonium acetate (80:20, v/v) containing 0.1% formic acid at a flow rate of 0.3 mL/min. The method had a chromatographic total run time of 2.0 min. The lower limit of quantification of valproic acid, 3-OH-valproic acid, 4-ene-valproic acid and 5-OH-valproic acid of the method was 2030, 51.5, 50.15 and 51.25 ng/mL, respectively. The method was linear for valproic acid and the three metabolites with correlation coefficients >0.995 for all analytes. The intra-day and inter-day accuracy and precision of the assay were less than 15.0%. This analytical method was successfully used to assay plasma concentrations of valproic acid and the three metabolites in human plasma from epileptic patients.     

Direct cocktail analysis of drug discovery compounds in pooled plasma samples using liquid chromatography-tandem mass spectrometry

Direct plasma injection technology coupled with a LC-MS/MS assay provides fast and straightforward method development and greatly reduces the time for the tedious sample preparation procedures. In this work, a simple and sensitive bioanalytical method based on direct plasma injection using a single column high-performance liquid chromatography (HPLC) and tandem mass spectrometry (MS/MS) was developed for direct cocktail analysis of double-pooled mouse plasma samples for the quantitative determination of small molecules. The overall goal was to improve the throughput of the rapid pharmacokinetic (PK) screening process for early drug discovery candidates. Each pooled plasma sample was diluted with working solution containing internal standard and then directly injected into a polymer-coated mixed-function column for sample clean-up, enrichment and chromatographic separation. The apparent on-column recovery of six drug candidates in mouse plasma samples was greater than 90%. The single HPLC column was linked to either an atmospheric pressure chemical ionization (APCI) or electrospray ionization (ESI) source as a part of MS/MS system. The total run cycle time using single column direct injection methods can be achieved within 4 min per sample. The analytical results obtained by the described direct injection methods were comparable with those obtained by semi-automated protein precipitation methods within +/- 15%. The advantages and challenges of using direct single column LC-MS/MS methods with two ionization sources in combination of sample pooling technique are discussed.     

Simultaneous quantification of cyclophosphamide and its active metabolite 4-hydroxycyclophosphamide in human plasma by high-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry (LC-MS/MS)

Cyclophosphamide is a cytotoxic prodrug with a very narrow therapeutic index. To study the clinical pharmacology of cyclophosphamide in a large cohort of patients a previously published method for the simultaneous quantitative determination of cyclophosphamide and 4-hydroxycyclophosphamide in human plasma using liquid chromatography tandem mass spectrometry (LC-MS/MS) was optimized. Addition of an isotopically labelled internal standard and adaptation of the gradient resulted in a fast, robust and sensitive assay. Because 4-hydroxycyclophosphamide is not stable in plasma, the compound is derivatized with semicarbazide immediately after sample collection. Sample preparation was carried out by protein precipitation with methanol-acetonitrile (1:1, v/v), containing isotopically labelled cyclophosphamide and hexamethylphosphoramide as internal standards. The LC separation was performed on a Zorbax Extend C18 column (150 mm x 2.1 mm ID, particle size 5 microm) with 1 mM ammonium hydroxide in water-acetonitrile (90:10, v/v) as the starting gradient, at a flow-rate of 0.40 mL/min with a total run time of 6 min. The lower limit of quantification (LLQ, using a 100 microL sample volume) was 200 ng/mL and the linear dynamic range extended to 40,000 ng/mL for cyclophosphamide and 50-5000 ng/mL for 4-hydroxycyclophosphamide. Accuracies as well as precisions were lower than 20% at the LLQ concentration and lower than 15% for all other concentrations. This method has been successfully applied in our institute to support ongoing studies into the pharmacokinetics and pharmacogenetics of cyclophosphamide.     

Quantification of isosorbide 5-mononitrate in human plasma by liquid chromatography-tandem mass spectrometry using atmospheric pressure photoionization

Isosorbide 5-mononitrate (5-ISMN) is an organic nitrate widely used for its vasodilating properties in the treatment of angina pectoris. In the present study, an efficient, sensitive, robust method was developed for the determination and quantification of isosorbide 5-mononitrate, in human plasma, by liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS), using photospray ionization. Isosorbide 5-mononitrate was extracted from 0.5 mL human plasma by liquid-liquid extraction (LLE). The method had a chromatographic run of 2.0 min using a C(8) analytical column (100 mm x 2.1 mm i.d.) and the linear calibration curve over the range was linear from 20 to 2000 ng mL(-1) (r(2)>0.995). The between-run precision, based on the relative standard deviation replicate quality controls, was 7.9% (60 ng mL(-1)), 5.2% (300 ng mL(-1)) and 7.0% (1800 ng mL(-1)). The between-run accuracy was 94.9%, 94.1% and 88.8% for the above-mentioned concentrations, respectively. The method herein described was employed in a bioequivalence study of two tablet formulations of isosorbide 5-mononitrate 40 mg.     

Determination of azatadine in human plasma by liquid chromatography/tandem mass spectrometry

A sensitive method using liquid chromatography with tandem mass spectrometric detection (LC-MS/MS) was developed and validated for the analysis of antihistamine drug azatadine in human plasma. Loratadine was used as internal standard (IS). Analytes were extracted from human plasma by liquid/liquid extraction using ethyl acetate. The organic phase was reduced to dryness under a stream of nitrogen at 30 °C and the residue was reconstituted with the mobile phase. 5 μL of the resulting solution was injected onto the LC-MS/MS system. A 4.6 mm × 150 mm, I.D. 5 μm, Agilent TC-C(18) column was used to perform the chromatographic analysis. The mobile phase consisted of ammonium formate buffer 0.010 M (adjusted to pH 4.3 with 1M formic acid)/acetonitrile (20:80, v/v) The chromatographic run time was 5 min per injection and flow rate was 0.6 mL/min. The retention time was 2.4 and 4.4 min for azatadine and IS, respectively. The tandem mass spectrometric detection mode was achieved with electrospray ionization (ESI) iron source and the multiple reaction monitoring (MRM) (291.3 → 248.2m/z for azatadine, 383.3 → 337.3m/z for IS) was operated in positive ion modes. The low limit of quantitation (LLOQ) was 0.05 ng/mL. The intra-day and inter-day precision of the quality control (QC) samples was 8.93-11.57% relative standard deviation (RSD). The inter-day accuracy of the QC samples was 96.83-105.07% of the nominal values.     

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.     

Determination of 5-aminoimidazole-4-carboxamide in human plasma by ion-pair extraction and LC-MS/MS

A liquid chromatography/tandem mass spectrometry (LC-MS/MS) method was established for the determination of 5-aminoimidazole-4-carboxamide (AICA) in human plasma. The method included a solvent extraction of AICA as an ion pair with 1-pentanesulfonate ion and a separation on a Hypersil ODS2 column with the mobile phase of methanol-water (68:32, v/v). Determination was performed using an electrospray ionization source in positive ion mode (ESI(+)). Multiple reaction monitoring (MRM) was utilized for the detection monitoring m/z at 127-->110 for AICA, and 172-->128 for IS. The calibration curve was linear within a range from 20 to 2000 ng/mL and the limit of quantity for AICA in plasma was 20 ng/mL. RSD of intra-assay and inter-assay were no more than 5.90% and 5.65%.     

A high throughput and sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the estimation of bisoprolol in human plasma using multiplexing technique

A high throughput and sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method has been developed and validated for the estimation of bisoprolol in human plasma using multiplexing technique (two HPLC units connected to one MS). Bisoprolol was extracted from human plasma using solid-phase extraction technique using metoprolol as internal standard. A Betabasic 8 column provided chromatographic separation of analytes followed by detection with mass spectrometry. The mass transition ion-pair was followed as m/z 326.2-->116.1 for bisoprolol and m/z 268.2-->191.0 for metoprolol. The method involves a simple multiplexing, rapid solid-phase extraction, simple isocratic chromatography conditions and mass spectrometric detection which enable detection at sub-nanogram levels. The proposed method has been validated for a linear range of 0.5-70.0 ng/mL with correlation coefficient > or =0.9991. The precision and accuracy were within 10% for intra-HPLC runs and inter-HPLC runs. The overall recoveries for bisoprolol and metoprolol were 93.89% and 77.65%, respectively. Total MS run time was 0.90 min only. The developed method was applied for the determination of pharmacokinetic parameters of bisoprolol following a single oral administration of a 10mg bisoprolol tablet in 18 healthy male volunteers.     

Simultaneous determination of a novel KDR kinase inhibitor and its N-oxide metabolite in human plasma using 96-well solid-phase extraction and liquid chromatography/tandem mass spectrometry

To support pharmacokinetic studies, a selective and sensitive liquid chromatography/tandem mass spectrometry (LC-MS/MS) method has been developed and validated for the simultaneous determination of a novel KDR kinase inhibitor (1) and its active metabolite (2) in human plasma. The method is fully automated using a Packard MultiPROBE II system and a TomTec Quadra 96 liquid handling workstation to perform sample preparation and solid-phase extraction (SPE). Following the extraction on a mixed-mode SPE using Oasis MCX 96-well plate, the analytes were separated on a Aquasil C18 column (50 mm x 2.1 mm, i.d., 3 microm) with a mobile phase consisting of acetonitrile/ammonium acetate buffer (5 mM, pH 5.0) (60/40, v/v). The run time for each injection was 4.5 min with the retention times of approximately 2.0 and 2.7 min for 1 and 2 respectively, at a flow rate of 0.25 mL/min. A tandem mass spectrometric detection was conducted using multiple reaction monitoring (MRM) under the positive ion mode with a turbo ion-spray interface. The linear ranges of the calibration curves were 0.05-400 ng/mL for 1 and 0.1-400 ng/mL for 2 on a PE Sciex API 4000 LC-MS/MS system. The lower limits of quantitation (LLOQ) of the assay were 0.05 and 0.1 ng/mL for 1 and 2 respectively, when 0.4 mL of plasma was processed. Intra-day assay precision (using five standard curves prepared by spiking compounds to five lots of plasma) was less than 4.9% for 1 and less than 9.6% for 2 on each concentration. Assay accuracy was found to be 95.1-104.6% of nominal for 1 standards and 93.5-105.6% for 2 standards. QC samples were stable when kept at room temperature for 4 h, at -70 degrees C for 10 days, and after three freeze-thaw cycles. The extraction recoveries were 80%, 83% and 84% for 1 and 2 and I.S. respectively, and no significant matrix effects were observed. The method was successfully applied to plasma samples from clinical studies after oral administration of compound 1.     

Use of online-dual-column extraction in conjunction with chiral liquid chromatography tandem mass spectrometry for determination of terbutaline enantiomers in human plasma

An online sample extraction chiral bioanalytical method was developed and validated for the quantification of terbutaline, a beta2-selective adrenoceptor agonist, spiked into human plasma by using two extraction columns and a chiral stationary phase (CSP) in conjunction with liquid chromatography tandem mass spectrometry (LC-MS/MS). In this method, two Oasis HLB extraction columns were used in parallel for plasma sample purification and a Chirobiotic T CSP was used for enantiomeric separation. Atmospheric pressure chemical ionization MS/MS was employed in multiple reaction monitoring mode for the detection and quantification. Subsequent to the addition of an internal standard solution, the plasma samples were directly injected onto the system for extraction and analysis. This method allowed the use of one of the extraction columns for purification while the other was being equilibrated. Hence, the time required for reconditioning the extraction columns did not contribute to the total analysis time per sample, which resulted in a shorter run time and higher throughput. A lower limit of quantification of 1.0 ng/mL was achieved using only 50 microliter of human plasma. The method was validated with a dynamic range of 1.0-200 ng/mL. The intra- and interday precision was no more than 11% CV and the assay accuracy was between 94-106%.     

Artifact-Free Quantification of Free 3-Chlorotyrosine, 3-Bromotyrosine, and 3-Nitrotyrosine in Human Plasma by Electron Capture–Negative Chemical Ionization Gas Chromatography Mass Spectrometry and Liquid Chromatography–Electrospray Ionization Tandem Mass Spectrometry

Halogenation and nitration of biomolecules have been proposed as key mechanisms of host defense against bacteria, fungi, and viruses. Reactive oxidants also have the potential to damage host tissue, and they have been implicated in disease. In the current studies, we describe specific, sensitive, and quantitative methods for detecting three stable markers of oxidative damage: 3-chlorotyrosine, 3-bromotyrosine, and 3-nitrotyrosine. Our results indicate that electron capture-negative chemical ionization-gas chromatography/mass spectrometry (EC-NCI GC/MS) is 100-fold more sensitive than liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-MS/MS) for analyzing authentic 3-chlorotyrosine, 3-bromotyrosine, and 3-nitrotyrosine. Using an isotopomer of tyrosine to evaluate artifactual production of the analytes during sample preparation and analysis, we found that artifact generation was negligible with either technique. However, LC-MS/MS proved cumbersome for analyzing multiple samples because it required 1.5 h of run and equilibration time per analysis. In contrast, EC-NCI GC/MS required only 5 min of run time per analysis. Using EC-NCI GC/MS, we were able to detect and quantify attomole levels of free 3-chlorotyrosine, 3-bromotyrosine, and 3-nitrotyrosine in human plasma. Our results indicate that EC-NCI GC/MS is a sensitive and specific method for quantifying free 3-chlorotyrosine, 3-bromotyrosine, and 3-nitrotyrosine in biological fluids in a single, rapid analysis and that it avoids generating any of the analytes ex vivo.     

Quantitative determination of MK-0767, a dual alpha/gamma peroxisome proliferator-activated receptor (PPAR) agonist, in human plasma by liquid chromatography-tandem mass spectrometry

5-[2,4-Dioxothiazolidin-5-yl)methyl]-2-methoxy-N-[[(4-trifluoromethyl)-phenyl]methyl]benzamide (I, MK-0767 or KRP-297, Fig. 1), is a dual alpha/gamma peroxisome proliferator-activated receptor (PPAR) agonist. A LC-MS/MS method for the determination of I in human plasma has been successfully developed, validated and applied to clinical programs. The analyte and internal standard (II) are extracted from 0.05 mL plasma via solid phase extraction (SPE). HPLC is used for the separation of I and II from possible co-extracted endogenous and other compounds. Detection is by MS/MS in multiple reaction monitoring (MRM) mode using a TurboIonSpray probe. The whole sample preparation is automated by using a Packard Multiprobe liquid handling system. The linear range is 4-2000 ng/mL in plasma. Recoveries were 71.1% and 69.4% for I and II, respectively. The method exhibited good linearity, reproducibility and sensitivity, selectivity and robustness when used for the analysis of clinical samples.     

Rapid and sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the determination of clonidine in human plasma

A rapid and sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method has been developed and validated for the estimation of clonidine in human plasma. Clonidine was extracted from human plasma by using solid-phase extraction technique. Nizatidine was used as the internal standard. A Hypurity C18 (50 mm x 4.6 mm i.d., 5 microm particle size) column provided chromatographic separation of analyte followed by detection with mass spectrometry. The method involves a rapid solid-phase extraction from plasma, simple isocratic chromatography conditions and mass spectrometric detection that enables detection up to picogram levels with a total run time of 3.0 min only. The method was validated over the range of 50-2500 pg/mL. The absolute recoveries for clonidine (71.86%) and IS (69.44%) achieved from spiked plasma samples were consistent and reproducible.     

Simultaneous determination of glycyrrhizin, a marker component in radix Glycyrrhizae, and its major metabolite glycyrrhetic acid in human plasma by LC-MS/MS

Glycyrrhizin (GLY) which has been widely used in traditional Chinese medicinal preparation possesses various pharmacological effects. In order to investigate the pharmacokinetic behavior of GLY in human after oral administration of GLY or licorice root, a liquid chromatography/tandem mass spectrometry (LC-MS/MS) method was developed and validated for the simultaneous determination of GLY and its major metabolite glycyrrhetic acid (GA) in human plasma. The method involved a solid phase extraction of GLY, GA, and alpha-hederin, the internal standard (IS), from plasma with Waters Oasis MCX solid phase extraction (SPE) cartridges (30 mg) and a detection using a Micromass Quattro LC liquid chromatography/tandem mass spectrometry system with electrospray ionization source in positive ion mode. Separation of the analytes was achieved within 5min on a SepaxHP CN analytical column with a mobile phase of acetonitrile:water (50:50, v:v) containing 0.1% formic acid and 5mM ammonium acetate. Multiple reaction monitoring (MRM) was utilized for the detection monitoring 823--> 453 for GLY, 471--> 177 for GA and 752--> 456 for IS. The LC-MS/MS method was validated for specificity, sensitivity, accuracy, precision, and calibration function. The assay had a calibration range from 10 to 10,000 ng/mL and a lower limit of quantification of 10 ng/mL for both GLY and GA when 0.2 mL plasma was used for extraction. The percent coefficient of variation for accuracy and precision (inter-run and intra-run) for this method was less than 11.0% with a %Nominal ranging from 87.6 to 106.4% for GLY and 93.7 to 107.8% for GA. Stability of the analytes over sample processing (freeze/thaw, bench-top and long-term storage) and in the extracted samples was also tested and established.     

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.     

A semi-automated 96-well plate method for the simultaneous determination of oral contraceptives concentrations in human plasma using ultra performance liquid chromatography coupled with tandem mass spectrometry

Two semi-automated, relatively high throughput methods using ultra performance liquid chromatography coupled with tandem mass spectrometry (UPLC-MS/MS) were developed for the simultaneous determination of ethinyl estradiol (EE) in combination with either 19-norethindrone (NE) or levonorgestrel (LN) in human plasma. Using 300 microL plasma, the methods were validated over the concentration ranges of 0.01-2 ng/mL and 0.1-20 ng/mL for EE and NE (or LN), respectively. The existing methods for the determination of the oral contraceptives in human plasma require large volumes of plasma (> or =500 microL), and sample extraction is labor-intensive. The LC run time is at least 6 min, enabling analysis of only about 100 samples a day. In the present work the throughput was greatly improved by employing a semi-automated sample preparation process involving liquid-liquid extraction and derivatization with dansyl chloride followed by UPLC separation on a small particle size column achieving a run time of 2.7 min. The validation and actual sample analysis results show that both methods are rugged, precise, accurate, and well suitable to support pharmacokinetic studies where approximately 300 samples can be extracted and analyzed in a day.     

Simultaneous determination of norethindrone and ethinyl estradiol in human plasma by high performance liquid chromatography with tandem mass spectrometry--experiences on developing a highly selective method using derivatization reagent for enhancing sensitivity

In the present work, for the first time, a liquid chromatographic method with tandem mass spectrometric detection (LC-MS/MS) for the simultaneous analysis of norethindrone, and ethinyl estradiol, was developed and validated over the concentration range of 50-10000pg/ml and 2.5-500pg/ml, respectively, using 0.5 ml of plasma sample. Norethindrone, ethinyl estradiol, and their internal standards norethindrone-(13)C2, and ethinyl estradiol-d4, were extracted from human plasma matrix with n-butyl chloride. After evaporation of the organic solvent, the extract was derivatized with dansyl chloride and the mixture was injected onto the LC-MS/MS system. The gradient chromatographic elution was achieved on a Genesis RP-18 (50 mm x 4.6 mm, 3 microm) column with mobile phase consisted of acetonitrile, water and formic acid. The flow rate was 1.0 ml/min and the total run time was 5.0 min. Important parameters such as sensitivity, linearity, matrix effect, reproducibility, stability, carry-over and recovery were investigated during the validation. The inter-day precision and accuracy of the quality control samples at low, medium and high concentration levels were <6.8% relative standard deviation (RSD) and 4.4% relative error (RE) for norethindrone, and 4.2% RSD and 5.9% RE for ethinyl estradiol, respectively. Chromatographic conditions were optimized to separate analytes of interest from the potential interference peaks, arising from the derivatization. This method could be used for pharmacokinetic and drug-drug interaction studies in human subjects.     

The validation of a bioanalytical method for the determination of clopidogrel in human plasma

A fast, sensitive and specific LC-MS/MS bioanalytical method for the determination of unchanged clopidogrel in human plasma has been developed and validated over the range of 10-12,000 pg mL(-1) (r2 0.9993) by the Contract Research group at HFL. Samples (0.3 mL) were buffered (pH 6.8), extracted using diethyl ether and 10 microL of the sample extract was injected onto the LC-MS/MS system. Analysis was performed using a C8 column (temperature controlled to 50 degrees C) by gradient elution at a flow rate of 0.9 mL min(-1) over a 3 min run time. Retention times of 1.61 and 1.59 min were observed for clopidogrel and 2H3-clopidogrel (I.S.), respectively. Detection was achieved using a Sciex API 4000, triple quadrupole mass spectrometer, in positive TurboIonspray (electrospray) ionisation mode. Ion transitions were monitored using MRM (multiple reaction monitoring) for clopidogrel (m/z 322-212) and for 2H3-clopidogrel (m/z 327-217). This validated method was used to support a pharmacokinetic study in healthy volunteers.     

A sensitive LC-MS/MS method for determination of levamisole in human plasma: application to pharmacokinetic study

A sensitive and rapid LC-MS/MS method was developed and validated for the determination of levamisole in human plasma. The assay was based on liquid-liquid extraction of analytes from human plasma with ethyl ether. Chromatographic separation was carried on an Agilent HC-C(8) column (150 mm × 4.6 mm, 5 μm) at 40°C, with a mobile phase consisting of acetonitrile-10 mM ammonium acetate (70:30, v/v), a flow rate of 0.5 mL/min and a total run time of 6 min. Detection and quantification were performed by mass spectrometry in the multiple reaction monitoring mode with positive electrospray ionization m/z at 205.1→178.2 for levamisole, and m/z 296.1→264.1 for mebendazole (internal standard). The assay was linear over a concentration range of 0.1-30 ng/mL with a lower limit of quantification of 0.1 ng/mL. The coefficient of variation of the assay precision was less than 8.5%. The assay was successfully used to analyze human plasma samples in a pharmacokinetic study where levamisole was administered as a liniment.