Validation and application of a novel LC/MS/MS method for the determination of isoginkgetin in rat plasma

Isoginkgetin is a biflavonoid compound isolated from the leaf extracts of Ginkgo biloba. In this study, an liquid chromatography–tandem mass spectrometry (LC/MS/MS) with liquid–liquid extraction was developed and validated for the analysis of isoginkgetin in rat plasma. In the process of chromatographic separation, selected reaction monitoring transitions for isoginkgetin and IS were m/z 566.8 → 134.7 and m/z 430.8 → 269.3, respectively. The validation parameters including selectivity, linearity, LLOQ, accuracy, precision, matrix effect, stability and recovery were satisfactory. The intra‐ and inter‐batch precision (RSD) were <12.1% in plasma, while the accuracy (RE) was within ±14.3%. This method was employed in a pharmacokinetic study on rats after the intravenous administration of isoginkgetin.     

Development and validation of a simple,sensitive and accurate LC‐MS/MS method for the determination of guanfacine,a selective α2A‐adrenergicreceptor agonist,in plasma and its application to a pharmacokinetic study

A simple, practical, accurate and sensitive liquid chromatography–tandem mass spectrometry (LC‐MS/MS) method was developed and fully validated for the quantitation of guanfacine in beagle dog plasma. After protein precipitation by acetonitrile, the analytes were separated on a C₁₈ chromatographic column by methanol and water containing 0.1% (v/v) formic acid with a gradient elution. The subsequent detection utilized a mass spectrometry under positive ion mode with multiple reaction monitoring of guanfacine and enalaprilat (internal standard) at m/z 246.2 → 159.0 and m/z 349.2 → 205.9, respectively. Good linearity was obtained over the concentration range of 0.1–20 ng/mL for guanfacine in dog plasma and the lower limit of quantification of this method was 0.1 ng/mL. The intra‐ and inter‐day precisions were <10.8% relative standard deviation with an accuracy of 92.9–108.4%. The matrix effects ranged from 89.4 to 100.7% and extraction recoveries were >90%. Stability studies showed that both analytes were stable during sample preparation and analysis. The established method was successfully applied to an in vivo pharmacokinetic study in beagle dogs after a single oral dose of 4 mg guanfacine extended‐release tablets. Copyright © 2013 John Wiley & Sons, Ltd.     

Development and validation of a bioanalytical method by LC‐MS/MS for the quantification of the LAFIS 10 – an antimalarial candidate – and its pharmacokinetics first evaluation

A rapid and highly sensitive method by LC‐MS/MS was developed and validated for the quantification of an antimalarial candidate (LAFIS10) in rat plasma using dexamethasone as internal standard (IS). The chromatographic separation was performed with a Poroshell 120 EC‐C₁₈ column. The mobile phase consisted of water (A) and acetonitrile (B), both containing 10 m m of ammonium formate and 0.1% formic acid, delivered in the form of elution gradient. The LAFIS10 was monitored using an electrospray ionization interface operating in the positive mode in multiple reaction monitoring mode, monitoring the transitions 681.47 → 538.2 for LAFIS10 and 393.20 → 355.30 for the IS. The flow rate was 500 μL/min. The column temperature was kept at 40 °C and the injection volume was 2 μL. The lower limit of quantification was of 10 ng/mL and linearity between 10 and 1000 ng/mL was observed, with an R² > 0.99. The accuracy of the method was >90%. The relative standard deviations intra‐ and interday were <8.80 and <6.37%, respectively. The method showed sensitivity, linearity, precision, accuracy and selectivity required to quantify LAFIS 10 in preclinical pharmacokinetic studies according to criteria established by the US Food and Drug Administration and European Medicines Agency. Copyright © 2014 John Wiley & Sons, Ltd.     

A sensitive LC–MS/MS method for the determination of triptolide and its application to pharmacokinetic research in rats

Triptolide is one of the main active ingredients of Tripterygium wilfordii Hook. F. In this study, a sensitive LC–MS/MS method was established and validated to determine the concentration of triptolide in rat plasma. Triptolide and an internal standard [(5R)‐5‐hydroxytriptolide] were extracted from 100 μL of rat plasma with acetonitrile, and the dried residue was then reconstituted and reacted with benzylamine to produce benzylamine triptolide and benzylamine (5R)‐5‐hydroxytriptolide. Derivatization increased the sensitivity of triptolide detection by ~100‐fold. Quantification was performed using a QTRAP 5500 tandem mass spectrometer with positive electrospray ionization in multiple reaction monitoring mode with an ion transition m/z 468.5 → 192.0 for benzylamine triptolide and m/z 484.3 → 192.1 for benzylamine (5R)‐5‐hydroxytriptolide. Good linearity was observed in the range of 0.030–100 ng/mL with a lower limit of quantitation of 0.030 ng/mL. The intra‐ and inter‐day precision was <6.5%, and the accuracy ranged from ?11.7 to ?4.4%. The recovery remained consistent and was reproducible at different concentrations. This method was successfully applied to the study of triptolide drug–drug interactions in Sprague–Dawley rats. With the use of itraconazole (40 mg/kg, p.o.) as a CYP3A inhibitor, the plasma exposure of triptolide in rats was increased by 36%.     

Quantification of heteroclitin D in rat plasma: validation of an LC/MS/MS method and its application in a preclinical pharmacokinetic study

A rapid, sensitive and specific liquid chromatography tandem mass spectrometry (LC/MS/MS) method was developed and validated for the quantification of heteroclitin D in rat plasma after using gambogic acid as internal standard (IS). Chromatographic separation was done on a Thermo Hypersil GOLD column (30 × 2.1 mm, 3 µm) using a mobile phase consisting of methanol–water–formic acid (80:20:0.1, v/v/v). The mass spectrometer worked with positive electrospray ionization in multiple reaction monitoring mode, using target ions at [M + H]⁺ m/z 483.3 for heteroclitin D and [M + H]⁺ m/z 629.3 for the IS. The standard curve was linear (R² ≥0.995) over the concentration range 9.98–2080 ng/mL and had good back‐calculated accuracy and precision. The intra‐ and interday precision and accuracy determined on three quality control samples (29.94, 166.4 and 1872 ng/mL) were ≤12.8 and –8.9–3.6%, respectively. The extraction recovery was ≥88.2% and the lower limit of quantification was 9.98 ng/mL. The method was successfully applied to evaluate pharmacokinetics of heteroclitin D in Sprague–Dawley rats following a single intravenous bolus injection of 2.0 mg/kg heteroclitin. Copyright © 2014 John Wiley & Sons, Ltd.     

A validated LC‐MS/MS assay for simultaneous quantification of methotrexate and tofacitinib in rat plasma: application to a pharmacokinetic study

A highly sensitive, specific and rapid LC‐ESI‐MS/MS method has been developed and validated for simultaneous quantification of methotrexate (MTX) and tofacitinib (TFB) in rat plasma (50 μL) using phenacetin as an internal standard (IS), as per the US Food and Drug Administration guidelines. After a solid‐phase extraction procedure, the separation of the analytes and IS was performed on a Chromolith RP_18e column using an isocratic mobile phase of 5 m m ammonium acetate (pH 5.0) and acetonitrile at a ratio of 25:75 (v/v) using flow‐gradient with a total run time of 3.5 min. The detection was performed in multiple reaction monitoring mode, using the transitions of m/z 455.2 → 308.3, m/z 313.2 → 149.2 and m/z 180.3 → 110.2 for MTX, TFB and IS, respectively. The calibration curves were linear over the range of 0.49–91.0 and 0.40–74.4 ng/mL for MTX and TFB, respectively. The intra‐ and interday accuracy and precision values for MTX and TFB were <15% at low quality control (QC), medium QC and high QC and <20% at lower limit of quantification. The validated assay was applied to derive the pharmacokinetic parameters for MTX and TFB post‐dosing of MTX and TFB orally and intravenously to rats. Copyright © 2014 John Wiley & Sons, Ltd.     

Trace quantification of 1‐triacontanol in beagle plasma by GC‐MS/MS and its application to a pharmacokinetic study

1‐Triacontanol (TA), a member of long chain fatty alcohol, has recently been received great attention owing to its antitumor activity. In this study, an accurate, sensitive and selective gas chromatography–tandem mass spectrometry method was developed and validated for the quantification of TA in beagle plasma using 1‐octacosanal as the internal standard (IS) for the first time. With temperature programming, chromatographic separation was carried out on an HP‐5MS column, using helium as carrier gas and argon as collision gas, both at a flow rate of 1 mL/min. TA was analyzed using positive ion electrospray ionization in multiple‐reaction monitoring mode, with the precursor to product ion transitions of m/z 495.6 → 97.0 and m/z 467.5 → 97.0 for TA and the IS, respectively. The lower limit of quantitation, linearity, intra‐ and interday precision, accuracy, stability, extraction recovery and matrix effect of TA were within the acceptable limits. The validated method was successfully applied to a pharmacokinetic study of TA in beagles. Copyright © 2014 John Wiley & Sons, Ltd.     

Comparison of GC–MS and MEKC methods for caffeine determination in preworkout supplements

In this study, GC–MS‐ and MEKC‐based methods for determination of caffeine (CAF) in preworkout supplements were developed and validated. The proposed protocols utilized minimal sample preparation (simple dilution and syringe filtration). The developed methods achieved satisfactory validation parameters, i.e. good linearity (R² > 0.9988 and R² > 0.9985 for GC–MS‐ and MEKC‐based method, respectively), satisfactory intra‐ and interaccuracy (within 92.6–100.7% for method utilizing GC–MS and 92.1–110.3% for protocol based on MEKC) and precision (CV < 15.9% and CV < 6.3% for GC–MS‐ and MEKC‐based method, respectively) and recovery (within 100.1–100.8% for method utilizing GC–MS and 101.5–106.2% for protocol based on MEKC). The LOD was 0.03 and 3 μg/mL for method utilizing GC–MS and MEKC, respectively. The CAF concentrations determined by GC–MS‐ and MEKC‐based methods were found to be in the range of 8.53–11.23 and 8.20–11.61 μg/mL, respectively. Taking into consideration information on the labels, the investigated supplements were found to contain from 110.0 to 167.3% of the declared CAF content, which confirmed the literature reports on incompatibility of the declared product compositions with real ones. Nevertheless, the consumption of examined supplements as recommended by producers did not lead to exceeding the CAF safe limit of 400 mg per day. Additionally, the MEKC‐based method allowed for detection and identification of vitamin B3 and B6 in all of the investigated supplement samples, which demonstrated that MEKC‐based protocols may be an appropriate assays for simultaneous determination of CAF and vitamins.     

Quantification of complanatoside A in rat plasma using LC‐MS/MS and its application to a pharmacokinetic study

Complanatoside A is a flavonol glycoside isolated from Astragalus complanatus, and currently it is used as a quality control index for A. complanatus in the 2010 edition of the Chinese Pharmacopoeia. For the first time, a simple and sensitive LC‐MS/MS method was developed for the determination of complanatoside A in rat plasma over the range of 2.3–575 ng/mL. Complanatoside A was extracted from plasma by a protein precipitation procedure, separated by LC and detected by MS/MS in positive electrospray ionization mode. The method was validated for selectivity, carryover, sensitivity, linearity, extraction recovery, matrix effect, accuracy, precision and stability studies. The lower limit of quantification was established at 2.3 ng/mL. Intra‐ and inter‐day precisions (LLOQ, low‐QC, med‐QC and high‐QC) were <7.9%, and accuracies were between 94.0 and 105.1%. Matrix effect was acceptable (97.9–103.0%) and extraction recovery was reproducible (88.5–94.4%). Complanatoside A was stable in the investigated conditions. The method was applied to the pharmacokinetics of complanatoside A in rats. Copyright © 2015 John Wiley & Sons, Ltd.     

Simultaneous determination of glaucocalyxin A and glaucocalyxin B in rat plasma by LC‐MS/MS and its application to a pharmacokinetic study after oral administration of Rabdosia japonica extract

A specific and sensitive liquid chromatography tandem mass spectrometry (LC‐MS/MS) method was developed and validated for the analysis of glaucocalyxin A and glaucocalyxin B in rat plasma using praeruptorin A as an internal standard. Separation was performed on a Hypurity C₁₈ column (2.1 × 50 mm, 5 μm) with isocratic elution using 0.2% formic acid in water–acetonitrile (20:80, v/v). Mass spectrometric detection was conducted using selected reaction monitoring via an electrospray ionization source. Both analytes exhibited good linearity within their concentration ranges (r² > 0.9932). The lower limit of quantitation of glaucocalyxin A and glaucocalyxin B was 1.10 ng/mL. Intra‐ and inter‐day precision exhibited an RSD within 14.5%, and the accuracy (RE) ranged from –12.1 to 15.0% at the lower limit of quantitation and three quality control levels. The developed assay was successfully applied to a pharmacokinetic study of glaucocalyxin A and glaucocalyxin B in rats after oral administration of Rabdosia japonica extract.     

Rapid and sensitive LC‐MS/MS method for determination of megestrol acetate in human plasma: application to a human pharmacokinetic study

A rapid, simple and fully validated LC‐MS/MS method was developed and validated for the determination of megestrol acetate in human plasma using tolbutamide as an internal standard (IS) after one‐step liquid–liquid extraction with methyl‐tert‐butyl‐ether. Detection was performed using electrospray ionization in positive ion multiple reaction monitoring mode by monitoring the transitions m/z 385.5 → 267.1 for megestrol acetate and m/z 271.4 → 155.1 for IS. Chromatographic separation was performed on a YMC Hydrosphere C₁₈ column with an isocratic mobile phase, which consisted of 10 mm ammonium formate buffer (adjusted to pH 5.0 with formic acid)–methanol (60:40, v/v) at a flow rate of 0.4 mL/min. The achieved lower limit of quantitation (LLOQ) was 1 ng/mL (signal‐to‐noise ratio > 10) and the standard calibration curve for megestrol acetate was linear (r > 0.99) over the studied concentration range (1–2000 ng/mL). The proposed method was fully validated by determining its specificity, linearity, LLOQ, intra‐ and inter‐day precision and accuracy, recovery, matrix effect and stability. The validated LC‐MS/MS method was successfully applied for the evaluation of pharmacokinetic parameters of megestrol acetate after oral administration of a single dose 800 mg of megestrol acetate (Megace?) to five healthy Korean male volunteers under fed conditions. Copyright © 2012 John Wiley & Sons, Ltd.     

Simultaneous quantification of multiple active components from Xiexin decoction in rat plasma by LC‐ESI‐MS/MS: application in pharmacokinetics

A sensitive and specific liquid chromatography–electrospray ionization–tandem mass spectrometric (LC‐ESI‐MS/MS) method was developed and validated to simultaneously quantify 11 active compounds (coptisine, jatrorrhizine, berberine, palmatine, baicalin, baicalein, wogonoside, wogonin, rhein, emodin and aloeemodin) from Xiexin decoction (XXD) in rat plasma. Plasma samples extracted by a single‐step protein precipitation procedure were separated using the gradient mode on a Dikma ODS‐C₁₈ column. Selected reaction monitoring scanning was employed for quantification with switching electrospray ion source polarity between positive and negative modes in a single run. Calibration curves offered satisfactory linearity (r > 0.995) at linear range of 0.47–60 ng/mL for coptisine, jatrorrhizine, berberine and palmatine, 15–1930 ng/mL for baicalin, 20–2560 ng/mL for baicalein, 14–1790 ng/mL for wogonoside, 0.57–72.8 ng/mL for wogonin, 10–1280 ng/mL for rhein, 0.6–76.8 ng/mL for emodin and 3.0–384 ng/mL for aloeemodin. The intra‐ and interday precisions were less than 10.2% in terms of relative standard deviation (RSD), and the accuracies were within ±10.84% in terms of relative error (RE). It was successfully applied to the evaluation of pharmacokinetics after single oral doses of XXD were administered to rats. Copyright © 2010 John Wiley & Sons, Ltd.     

Sensitive and validated LC‐MS/MS methods to evaluate mycophenolic acid pharmacokinetics and pharmacodynamics in hematopoietic stem cell transplant patients

Monitoring of pharmacodynamics in addition to pharmacokinetics is one of strategies to individualize mycophenolate mofetil therapy. The purpose of this study was to develop sensitive liquid chromatography–tandem mass spectrometry (LC‐MS/MS) methods for evaluation of the pharmacokinetics and pharmacodynamics of mycophenolic acid (MPA). Concentrations of mycophenolic acid glucuronide (MPAG), mycophenolic acid acyl‐glucuronide, as well as unbound MPA and MPAG, were determined, and inosine‐5′‐monophosphate dehydrogenase activity was calculated by measuring concentrations of produced xanthosine‐5′‐monophosphate (XMP) and intracellular adenosine‐5′‐monophosphate after incubation of peripheral blood mononuclear cell (PBMC) lysates. A metal‐free Mastro^TM column and two gradient patterns were used to improve the quantification limit of XMP to 0.1 μm . In the clinical MPA concentration range, the linearity of the calibration curve, inter‐ and intra‐day precision and accuracy satisfied the relevant US Food and Drug Administration guidelines. The MPA concentrations in hematopoietic stem cell transplant (HSCT) patients determined by the enzyme assay and the present LC‐MS/MS method showed a good correlation (r² = 0.95, p < 0.001). In this study, we report sensitive and validated LC‐MS/MS methods to evaluate the pharmacokinetics and pharmacodynamics of MPA, which are sufficiently sensitive to assess small quantities of PBMC lysates collected shortly after HSCT. Copyright © 2015 John Wiley & Sons, Ltd.     

Ultra‐fast LC–ESI‐MS/MS method for the simultaneous determination of six highly toxic Aconitum alkaloids from Aconiti kusnezoffii radix in rat plasma and its application to a pharmacokinetic study

A fast, sensitive, and efficient ultra‐fast LC–ESI‐MS/MS method was developed for the simultaneous quantitation of six highly toxic Aconitum alkaloids, that is, aconitine, mesaconitine, hypaconitine, benzoylaconine, benzoylmesaconine, and benzoylhypaconine, in rat plasma after oral administration of crude ethanol extracts from Aconiti kusnezoffii radix by ultrasonic extraction, reflux extraction for 1 h, and reflux extraction for 3 h, respectively. The separation of six Aconitum alkaloids and aminopyrine (internal standard) was performed on an InertSustain® C₁₈ column, and the quantification of the analytes was performed on a 4000Q ultra‐fast LC–MS/MS system with turbo ion spray source in the positive ion and multiple‐reaction monitoring mode. Absolute recoveries ranged within 65.06–85.1% for plasma samples. The intra‐ and interday precision and accuracy of analytes were satisfactory. The methods were validated with sensitivity reaching the lower LOQ for aconitine, mesaconitine, hypaconitine, benzoylaconine, benzoylmesaconine, and benzoylhypaconine, which were 0.025, 0.025, 0.050, 0.025, 0.025, and 0.100 ng/mL, respectively. The method was successfully applied to a pharmacokinetic study of six Aconitum alkaloids in rat plasma after oral administration of crude ethanol extracts from the raw root of Aconitum kusnezoffii Reichb. by three different extraction processes.     

Development and validation of a rapid LC‐MS/MS method to quantify letrozole in human plasma and its application to therapeutic drug monitoring

A selective, rapid, and sensitive liquid chromatography–tandem mass spectrometry(LC‐MS/MS) method was developed and validated for the determination of letrozole (LTZ) in human plasma, using anastrozole as internal standard (IS). Sample preparation was performed by one‐step protein precipitation with methanol. The analyte and IS were chromatographed on a reversed‐phase YMC‐ODS‐C₁₈ column (2.0 × 100 mm i.d., 3 µm) with a flow rate of 0.3 mL/min. The mobile phase consisted of water containing 0.1% formic acid (v/v) and methanol containing 0.1% formic acid (v/v). The mass spectrometer was operated in selected reaction monitoring mode through electrospray ionization ion mode using the transitions of m/z 286.2 → 217.1 for LTZ and m/z 294.1 → 225.1 for IS, respectively. The method was validated for selectivity, linearity, lower limit of quantitation, precision, accuracy, matrix effects and stability in accordance with the US Food and Drug Administration guidelines. Linear calibration curves were 1.0–60.0 ng/mL. Intra‐ and inter‐batch precision (CV) for LTZ were <9.34%, and the accuracy ranged from 97.43 to 105.17%. This method was successfully used for the analysis of samples from patients treated with LTZ in the dose of 2.5 mg/day. It might be suitable for therapeutic drug monitoring of these patients and contribute to predict the risk of adverse reactions. Copyright © 2015 John Wiley & Sons, Ltd.     

An LC–MS/MS assay for the quantitative determination of 2‐pyridyl acetic acid,a major metabolite and key surrogate for betahistine,using low‐volume human K2EDTA plasma

Betahistine is widely used for the treatment of vertigo. Owing to first‐pass metabolism, 2‐pyridyl acetic acid (2PAA, major metabolite of betahistine) was considered as surrogate for quantitation. A specific and sensitive LC–MS/MS method was developed and validated for quantitation of 2PAA using turbo‐ion spray in a positive ion mode. A solid‐phase extraction was employed for the extraction of 2PAA and 2PAA d₆ (IS) from human plasma. Chromatographic separation of analytes was achieved using an ACE CN, 5 μm (50 × 4.6 mm) column with a gradient mobile phase comprising acetonitrile–methanol (90:10% v /v) and 0.7% v/v formic acid in 0.5 mm ammonium trifluoroacetate in purified water (100% v/v). The retention times of 1.15 and 1.17 min for 2PAA and internal standard, respectively, were achieved. Quantitation of 2PAA and internal standard was achieved by monitoring multiple reaction monitoring transition pairs (m /z 138.1 to m /z 92.0 and m /z 142.1 to m /z 96.1, respectively). The developed method was validated for various parameters. The calibration curves of 2PAA showed linearity from 5.0 to 1500 ng/mL, with a lower limit of quantitation of 5.0 ng/mL. The bias and precision for inter‐ and intra‐batch assays were <10%. The developed method was used to support clinical sample analysis.     

Development and validation of a highly sensitive LC‐MS/MS method for quantitation of bivalirudin in human plasma: application to a human pharmacokinetic study

A sensitive, specific and simple LC‐MS/MS method was developed for the identification and quantification of bivalirudin in human plasma using diazepam as an internal standard (IS). The API‐4000 LC‐MS/MS was operated under multiple‐reaction monitoring mode using electrospray ionization. The sample preparation consisted of an easy protein precipitation sample pretreatment with methanol. Chromatographic separation was achieved on a Zorbax Eclipse plus C₁₈ 100 × 2.1 mm column with a mobile phase of water–methanol–0.1% formic acid. The analytes were detected with a triple quadrupole Quantum Access with positive ionization. Ions monitored in the multiple‐reaction monitoring mode were m/z 1091 → 650 for bivalirudin (at 2.70 min) and m/z 285 → 193 for diazepam (at 3.85 min). The developed method was validated in human plasma with a lower limit of quantitation of 20 µg/L for bivalirudin. A linear response function was established for the range of concentrations 20–10,000 µg/L (r > 0.998) for bivalirudin. The intra‐ and inter‐day precision values for bivalirudin met the acceptance criteria as per US Food and Drug Administration guidelines. Bivalirudin was stable in the battery of stability studies, viz. bench‐top, freeze–thaw cycles and long‐term stability. The developed assay method was applied to an intravenous administration study in humans. Copyright © 2013 John Wiley & Sons, Ltd.     

Simultaneous determination of anti‐diabetes/anti‐obesity drugs by LC/PDA,and targeted analysis of sibutramine analog in dietary supplements by LC/MS/MS

The safety of dietary supplements is questionable as there have been occasional reports of products contaminated with illegal adulterants. The present study was carried out to develop trustworthy methodologies to screen for six anti‐diabetic drugs (phenformin, rosiglitazone, glipizide, glimepiride, glybenclamide and gliclazide) and six anti‐obesity drugs (ephedrine, fenfluramine, T3, T4, fluoxetine and sibutramine) in dietary supplements. A simultaneous determination method of the 12 drugs by liquid chromatography coupled with a photodiode array (LC/PDA) was established and was validated for linearity (r² > 0.99), precision (RSD <13.3%), recoveries (88.8–115.9%) and reproducibility. Sibutramine and its analogs, N‐desmethylsibutramine, were subject to further investigation by LC/MS/MS because they were one of the major illegal adulterants. Our proposed method to monitor illegal drug adulterations in dietary supplements using LC/PDA is a simple and reliable, and therefore applicable to routine drug‐adulteration screening. Copyright © 2009 John Wiley & Sons, Ltd.     

LC–MS/MS method with chemical derivatization for quantitation of L‐threonate in human plasma

An LC–MS/MS‐based bioanalytical method has been developed to measure the concentration of L‐threonate at its endogenous level in human plasma. Following isotope dilution and protein precipitation, the samples were acetylated and chromatographed under reversed‐phase conditions for baseline separation of the derivatized L‐threonate and its stereoisomer D‐erythronate. The method was assessed by a fit‐for‐purpose validation with a calibration range from 100 to 10,000 ng/mL. The intra‐run coefficients of variation (CVs) were <3.6% and the inter‐run CV was 3.2% for the QC samples at endogenous level. At the lower limit of quantitation, the intra‐run CV was 6.1% and the average inaccuracy was ?1.4%. This method provides an efficient and reliable quantitation of L‐threonate and could be useful to certain biomarker investigators.     

Novel UHPLC‐MS/MS method for the determination of rotigotine in the plasma of patients with Parkinson's disease

A novel ultra‐high‐pressure liquid chromatography–tandem mass spectrometry method was developed and validated for the determination of the dopamine receptor agonist rotigotine in human plasma. Following liquid–liquid extraction with tert‐ butyl methyl ether from 500 μL plasma, the chromatographic analysis was performed on a Gemini NX3 column using 5 mm pH 5.0 ammonium acetate–5 mm ammonium acetate in methanol as binary gradient mobile phase, at a flow rate of 0.3 mL/min. The MS/MS ion transitions were 316.00 → 147.00 for rotigotine and 256.10 → 211.00 for the internal standard (lamotrigine). The lower limit of quantitation was 50 pg/mL and the linearity was determined from 50 to 2500 pg/mL. The mean recovery was 96.9%. Both intra‐ and interassay imprecision and inaccuracy were ≤15% at all quality control concentrations. The method was successfully applied to measure morning trough plasma rotigotine concentrations in a series of patients with Parkinson's disease on chronic treatment. The present study describes the first fully validated method for rotigotine determination in human plasma.