Simultaneous analysis by Quadrupole‐Orbitrap mass spectrometry and UHPLC‐MS/MS for the determination of sedative‐hypnotics and sleep inducers in adulterated products

Adulterated products are continuously detected in society and cause problems. In this study, we developed and validated a method for determining synthetic sedative‐hypnotics and sleep inducers, including barbital, benzodiazepam, zolpidem, and first‐generation antihistamines, in adulterated products using Quadrupole‐Orbitrap mass spectrometry and ultrahigh performance liquid chromatography with tandem mass spectrometry. In Quadrupole‐Orbitrap mass spectrometry analysis, target compounds were confirmed using a combination of retention time, mass tolerance, mass accuracy, and fragment ions. For quantification, several validation parameters were employed using ultrahigh performance liquid chromatography with tandem mass spectrometry. The limit of detection and limit of quantitation was 0.05–53 and 0.17–177 ng/mL, respectively. The correlation coefficient for linearity was more than 0.995. The intra‐ and interassay accuracies were 86–110 and 84–111%, respectively. Their precision values were evaluated as within 4.0 (intraday) and 10.7% (interday). Mean recoveries of target compounds in adulterated products ranged from 85 to 116%. The relative standard deviation of stability was less than 10.7% at 4°C for 48 h. The 144 adulterated products obtained over 3 years (2014–2016) from online and in‐person vendors were tested using established methods. After rapidly screening with Quadrupole‐Orbitrap mass spectrometry, the detected samples were quantified using ultrahigh performance liquid chromatography with tandem mass spectrometry. Two of them were adulterated with phenobarbital.     

Comparative analysis of main bio‐active components in the herb pair Danshen‐Honghua and its single herbs by ultra‐high performance liquid chromatography coupled to triple quadrupole tandem mass spectrometry

A sensitive, reliable, and powerful ultra‐high performance liquid chromatography coupled to triple quadrupole tandem mass spectrometry method was developed for simultaneous quantification of the 15 main bio‐active components including phenolic acids and flavonoids within 13 min for the first time. The proposed method was first reported and validated by good linearity (r ² > 0.9975), limit of detection (1.12–7.01 ng/mL), limit of quantification (3.73–23.37 ng/mL), intra‐ and inter‐day precisions (RSD ≤ 1.92%, RSD ≤ 2.45%), stability (RSD ≤ 5.63%), repeatability (RSD ≤ 4.34%), recovery (96.84–102.12%), and matrix effects (0.92–1.02). The established analytical methodology was successfully applied to comparative analysis of main bio‐active components in the herb pair Danshen‐Honghua and its single herbs. Compared to the single herb, the content of most flavonoid glycosides was remarkably increased in their herb pair, and main phenolic acids were decreased, conversely. The content changes of the main components in the herb pair supported the synergistic effects on promoting blood circulation and removing blood stasis. The results provide a scientific basis and reference for the quality control of Danshen‐Honghua herb pair and the drug interactions based on variation of bio‐active components in herb pairs.     

A validated HPLC‐MS/MS method for determination of genipin‐1‐o‐glucuronic acid in rat plasma after administration of genipin and its application to a pharmacokinetic study

A sensitive and specific method was developed and validated for the quantitation of one major metabolite of genipin in rats plasma. The major metabolite was isolated from rat bile via semi‐preparative HPLC technology and its chemical structure was identified as genipin‐1‐o‐glucuronic acid (GNP‐GLU), which was for the first time used as a standard compound for quantitative analysis in rat plasma after administration of genipin. The application of high‐performance liquid chromatography–tandem mass spectrometry in negative mode in multiple reaction monitoring mode was investigated. Chromatographic separation was achieved on an Eclipse XDB‐C₁₈ column using a mobile phase consisting of water with 0.1% formic acid (A)–acetonitrile (B). The limit of detecation was 0.214 ng/mL and the lower limit of quantification was 0.706 ng/mL. The calibration curve was linear from 1.27 to 3810 ng/mL for plasma samples, with a correlation coefficient of 0.9924. The intra‐ and inter‐day precisions and accuracy were all within 15%. The recoveries of GNP‐GLU and puerarin were above 90.0 and 76.2%, respectively. The highly sensitive method was successfully applied to estimate pharmacokinetic parameters of GNP‐GLU following oral and intravenous administration of genipin to rats. Copyright © 2013 John Wiley & Sons, Ltd.     

Simultaneous quantification and semi‐quantification of amentoflavone and its metabolites in human intestinal bacteria by liquid chromatography Orbitrap high‐resolution mass spectrometry

A quick, easy, effective method followed by ultra‐high‐pressure liquid chromatography coupled with linear ion trap–Orbitrap tandem mass spectrometry (UHPLC‐LTQ‐Orbitrap MS) was developed for the simultaneous identification and quantification of the metabolites produced by amentoflavone (AMF) in human intestinal bacteria from human feces. The method validated for quantification of AMF concerning precision, accuracy, recovery, matrix effect, stability and limits showed acceptable results. Compared with blank human intestinal bacteria chromatography, three metabolites were identified based on high‐accuracy protonated precursors and multi‐stage mass spectrometry (MSⁿ ) using the proposed strategy. At the same time, a new method was developed for semi‐quantification of three metabolites. We describe the trend over 24 h of concentration–time curves for AMF and its metabolites. Moreover, the main metabolic pathway of AMF was clarified in human intestinal bacteria. The method was validated and successfully applied to the detection and quantification of AMF and its metabolites.     

High‐throughput salting‐out‐assisted liquid–liquid extraction for the simultaneous determination of atorvastatin,ortho‐hydroxyatorvastatin,and para‐hydroxyatorvastatin in human plasma using ultrafast liquid chromatography with tandem mass spectrometry

A high‐throughput, specific, and rapid liquid chromatography with tandem mass spectrometry method was established and validated for the simultaneous determination of atorvastatin and its two major metabolites, ortho‐hydroxyatorvastatin and para‐hydroxyatorvastatin, in human plasma. A simple salting‐out‐assisted liquid–liquid extraction using acetonitrile and a mass‐spectrometry‐friendly salt, ammonium acetate, was employed to extract the analytes from human plasma. A recovery of more than 81% for all analytes was achieved in 1 min extraction time. Chromatographic separation was performed on a Kinetex XB C₁₈ column utilizing a gradient elution starting with a 60% of water solution (1% formic acid), followed by increasing percentages of acetonitrile. Analytes were detected on a tandem mass spectrometer equipped with an electrospray ionization source that was operated in the positive mode, using the transitions of m/z 559.3 → m/z 440.2 for atorvastatin, and m/z 575.3 → m/z 440.2 for both ortho‐ and para‐hydroxyatorvastatin. Deuterium‐labeled compounds were used as the internal standards. The method was validated over the concentration ranges of 0.0200–15.0 ng/mL for atorvastatin and ortho‐hydroxyatorvastatin, and 0.0100–2.00 ng/mL for para‐hydroxyatorvastatin with acceptable accuracy and precision. It was then successfully applied in a bioequivalence study of atorvastatin.     

Simultaneous determination of tandospirone and its active metabolite, 1‐[2‐pyrimidyl]‐piperazine in rat plasma by LC–MS/MS and its application to a pharmacokinetic study

A rapid, sensitive and selective liquid chromatography–tandem mass spectrometry method for the detection of tandospirone (TDS) and its active metabolite 1‐[2‐pyrimidyl]‐piperazine (1‐PP) in Sprague–Dawley rat plasma is described. It was employed in a pharmacokinetic study. These analytes and the internal standards were extracted from plasma using protein precipitation with acetonitrile, then separated on a CAPCELL PAK ADME C₁₈ column using a mobile phase of acetonitrile and 5 mm ammonium formate acidified with formic acid (0.1%, v/v) at a total flow rate of 0.4 mL/min. The detection was performed with a tandem mass spectrometer equipped with an electrospray ionization source. The method was validated to quantify the concentration ranges of 1.000–500.0 ng/mL for TDS and 10.00–500.0 ng/mL for 1‐PP. Total time for each chromatograph was 3.0 min. The intra‐day precision was between 1.42 and 6.69% and the accuracy ranged from 95.74 to 110.18% for all analytes. Inter‐day precision and accuracy ranged from 2.47 to 6.02% and from 98.37 to 105.62%, respectively. The lower limits of quantification were 1.000 ng/mL for TDS and 10.00 ng/mL for 1‐PP. This method provided a fast, sensitive and selective analytical tool for quantification of tandospirone and its metabolite 1‐PP in plasma necessary for the pharmacokinetic investigation.     

Determination of multiple pesticide residues in teas by gas chromatography with accurate time‐of‐flight mass spectrometry

In this work, gas chromatography tandem with electron ionization and full‐scan high‐resolution mass spectrometry with a time‐of‐flight mass analyzer was evaluated for analyzing pesticide residues in teas. The relevant aspects for mass spectrometry analysis, including the resolution and mass accuracy, acquisition rate, temperature of ion source, were investigated. Under acquisition condition in 2‐GHz extended dynamic range mode, accurate mass spectral library including 184 gas chromatography detectable pesticides was established and retrieval parameters were optimized. The mass spectra were consistent over a wide concentration range (three orders) with good match values to those of NIST (EI‐quadrupole). The methodology was verified by the validation of 184 pesticides in four tea matrices. A wide linear range (1–1000 μg/kg) was obtained for most compounds in four matrices. Limit of detection, limit of quantification, and limit of identification values acquired in this study could satisfy the requirements for maximum residue levels prescribed by the European Community. Recovery studies were performed at three concentrations (10, 50, and 100 μg/kg). Most of the analytes were recovered at an acceptable range of 70–120% with relative standard deviations ≤ 20% in four matrices. The potential extension of qualitative screening scope makes gas chromatography tandem with electron ionization and mass spectrometry with a time‐of‐flight mass analyzer a more powerful tool compared with gas chromatography with tandem mass spectrometry.     

Determination of synephrine in feeds by a novel quick,easy, cheap,effective, rugged,and safe solid‐phase extraction method combined with UHPLC–MS/MS

To detect and quantify synephrine in feed, an effective analytical method based on quick, easy, cheap, effective, rugged, and safe solid‐phase extraction coupled to ultra high performance liquid chromatography with tandem mass spectrometry was developed with isotopic internal standards. Pretreatment was performed using quick, easy, cheap, effective, rugged, and safe solid‐phase extraction with primary secondary amine and C18 sorbent as sorbents in combination with Oasis MCX column clean‐up to extract and purify feed samples. Tandem mass spectrometry detection in positive ion mode was conducted in positive multiple reaction monitoring mode in addition to the quantitative internal standard method. Two transitions of synephrine at m/z 168.1/150.0 and 168.1/135.0 were selected, and m/z 168.1/135.0 was determined as the quantification ion pair. D₉‐Terbutaline was selected as an internal standard, for which m/z 235.1/153.0 was selected as the quantification ion pair. Good linearity was shown for synephrine in the range of 0.5–50 μg/L, and the correlation coefficient exceeded 0.999. The recoveries in three different feed samples at three spiked levels were 81.42–112.08%, and the relative standard deviations were not greater than 14.66%. The method proposed in this study was reliable and highly effective, and its sensitivity, accuracy, and precision are suitable for determining synephrine residues in feed samples.     

Determination of a novel paclitaxel derivative (NPD‐103) in human plasma by ultra‐performance liquid chromatography–tandem mass spectrometry

A sensitive and specific ultra‐performance liquid chromatography–tandem mass spectrometry (UPLC‐MS‐MS) method for quantification of a newly developed anticancer agent NPD‐103 has been established. An aliquot of human plasma sample (200 µL) was spiked with ¹³C‐labeled paclitaxel (internal standard) and extracted with 1.3 mL of tert‐butyl methyl ether. NPD‐103 was quantitated on a C₁₈ column with methanol–0.1% formic acid (75:25, v/v) as mobile phase using UPLC‐MS‐MS operating in positive electrospray ionization mode with a total run time of 3.0 min. For NPD‐103 at the concentrations of 1.0, 5.0 and 10.0 µg/mL in human plasma, the absolute extraction recoveries were 95.58, 102.43 and 97.77%, respectively. The linear quantification range of the method was 0.1–20.0 µg/mL in human plasma with linear correlation coefficients greater than 0.999. The intra‐ and inter‐day accuracy for NPD‐103 at 1.0, 5.0 and 10.0 µg/mL levels in human plasma fell into the ranges of 95.29–100.00% and 91.04–94.21%, and the intra‐ and inter‐day precisions were in the ranges of 8.96–11.79% and 7.25–10.63%, respectively. This assay is applied to determination of half‐life of NPD‐103 in human plasma. Copyright © 2008 John Wiley & Sons, Ltd.     

Sensitive and simultaneous quantitation of 6β‐hydroxycortisol and cortisol in human plasma by LC‐MS/MS coupled with stable isotope dilution method

CYP3A phenotyping provides a means for personalized drug therapy. We focused our attention on the plasma 6β‐hydroxycortisol (6β‐OHF) to cortisol ratio as an index for CYP3A phenotyping. In the present study, we developed a sensitive and reliable method for the simultaneous determination of 6β‐OHF and cortisol in human plasma using high‐performance liquid chromatography/tandem mass spectrometry together with picolinylester derivatization or nonderivatization methods and 6β‐[9,11,12,12‐²H₄]hydroxycortisol and [1,2,4,19‐¹³C₄]cortisol as internal standards for in vivo CYP3A phenotyping in humans. The lower limits of quantification were 38.513 pg/mL for 6β‐OHF and 38.100 pg/mL for cortisol. The relative error and relative standard deviation of the lower limits of quantification were <5% for both methods. The intra‐day and inter‐day assay reproducibilities of the determined 6β‐OHF and cortisol concentrations were consistent with the actual amounts added as relative errors and relative standard deviations for both methods, which were <5.4% and <3.9%, respectively. Both methods were applied for the quantification of plasma 6β‐OHF and cortisol concentrations in healthy subjects taking oral contraceptives. The absolute concentrations and time course of 6β‐OHF and cortisol were found to be consistent when measured using the 2 methods. The ratio as an index for in vivo CYP3A activity decreased after 21 days of taking oral contraceptives for both methods. To the best of our knowledge, this is the first study reporting the detailed investigation of accuracy and precision in the simultaneous measurement of 6β‐OHF and cortisol in human plasma using liquid chromatography/tandem mass spectrometry coupled with stable isotope dilution method, which can be applied to CYP3A phenotyping.     

A comparative pharmacokinetic study of three flavonoids and three anthraquinones in normal and gastrointestinal motility disorders rat plasma after the oral administration of Wei‐Chang‐Shu tablet using high‐performance liquid chromatography–tandem mass spectrometry

A simple, fast and reliable high‐performance liquid chromatography–tandem mass spectrometry method was developed and validated for the simultaneous quantification and pharmacokinetic study of three flavonoids (liquiritigenin, isoliquiritigenin and formononetin) and three anthraquinones (emodin, rhein and aloe‐emodin), which are the bioactive ingredients of Wei‐Chang‐Shu tablet found in rat plasma. After extraction by liquid–liquid extraction with ethyl acetate, chromatographic separation was achieved on an Agilent Zorbax SB‐C₁₈ column (4.6 × 150 mm, 5 μm) at a flow rate of 1 mL/min by gradient elution using 0.1% aqueous acetic acid and acetonitrile. The detection was performed using a triple quadrupole mass spectrometer equipped with electrospray ionization source in the negative ionization and selected reaction monitoring mode. Method validation was performed in terms of specificity, carryover, linearity (r > 0.99), intra−/inter‐day precision (1.0–10.1%), accuracy (relative error, <7.6%), stability (0.6–13.2%), extract recovery (74.9–91.9%) and matrix effect (89.1–109%). The lower limits of quantification of the six analytes varied from 0.92 to 10.4 ng/mL. The validated method was successfully applied to compare the pharmacokinetic properties of Wei‐Chang‐Shu tablet in normal rats and in rats with gastrointestinal motility disorders. The results indicated that there were obvious differences in the pharmacokinetic behavior between normal and model rats. This study will be helpful in the clinical application of Wei‐Chang‐Shu tablet.     

Determination of 14 heterocyclic aromatic amines in meat products using solid‐phase extraction and supercritical fluid chromatography coupled to triple quadrupole mass spectrometry

A novel, simple, and sensitive method has been developed for simultaneous determination of 14 heterocyclic aromatic amines in meat product using solid‐phase extraction combined with ultrahigh‐performance supercritical fluid chromatography coupled to tandem quadrupole mass spectrometry. The analytes could be separated within 7 min and identified using their retention times and mass. The developed method was validated based on the linearity, limits of quantification, precision, and accuracy. The recovery ranged from 52.3 to 97.5% with an acceptable standard deviation, which is not higher than 6%. The limits of quantitation ranged from 0.03 to 0.17 µg/kg. The selectivity and sensitivity were satisfactory in multiple reaction monitoring mode. The method was applied to commercial meat products, and the results demonstrated that the novel method has potential for the analysis of the targets in food matrices. This is the first work reporting the simultaneous quantification of 14 heterocyclic aromatic amines by means of ultrahigh‐performance supercritical fluid chromatography coupled to tandem quadrupole mass spectrometry.     

An LC–MS/MS method for quantitation of cyanidin‐3‐O‐glucoside in rat plasma: Application to a comparative pharmacokinetic study in normal and streptozotocin‐induced diabetic rats

A sensitive and reliable liquid chromatography tandem mass spectrometry (LC–MS/MS) method was developed to determine cyanidin‐3‐O‐glucoside (Cy‐3G) in normal and streptozotocin‐induced diabetic rat plasma. Chromatographic separation was carried out on a Zorbax SB‐C₁₈ (50 × 4.6 mm, 5 μm) column and mass spectrometric analysis was performed using a Thermo Finnigan TSQ Quantum Ultra triple‐quadrupole mass spectrometer coupled with an ESI source in the negative ion mode. Selected reaction monitoring mode was applied for quantification using target fragment ions m/z 447.3 → 285.2 for Cy‐3G and m/z 463.0 → 300.1 for quercetin‐3‐O‐glucoside (internal standard). The calibration curve was linear over the range 3.00–2700 ng/mL (r² ≥ 0.99) with the lower limit of quantitation at 3.00 ng/mL. Intra‐ and inter‐day precision was <14.5% and mean accuracy was from −11.5 to 13.6%. Stability testing showed that Cy‐3G remained stable during the whole analytical procedure. After validation, the assay was successfully used to support a preclinical pharmacokinetic comparison of Cy‐3G between normal and diabetic rats. Results indicated that diabetes mellitus significantly altered the in vivo pharmacokinetic characteristics of Cy‐3G after oral administration in rats.     

Solid‐phase extraction and analysis of paroxetine in human plasma by ultra performance liquid chromatography–electrospray ionization mass spectrometry

A rapid, sensitive and rugged solid‐phase extraction ultra performance liquid chromatography tandem mass spectrometry (UPLC‐MS/MS) method was developed for determination of paroxetine in human plasma. The procedure for sample preparation includes simple SPE extraction procedure coupled with Hypersil Gold C₁₈ column (100 mm ? 2.1 mm, i.d., 1.9 μm) with isocratic elution at a flow‐rate of 0.350 mL/min and fluoxetine was used as the internal standard. The analysis was performed on a triple‐quadrupole tandem mass spectrometer by multiple reactions monitoring mode via electrospray ionization. Using 500 μL plasma, the methods were validated over the concentration range 0.050–16.710 ng/mL for paroxetine, with a lower limit of quantification of 0.050 ng/mL. The intra‐ and inter‐day precision and accuracy of the quality control samples were within 10.0%. The recovery was 69.2 and 74.4% for paroxetine and fluoxetine respectively. Total run time was only 1.9 min. The method was highly reproducible and gave peaks with excellent chromatography properties. Copyright © 2009 John Wiley & Sons, Ltd.     

Quantification of midazolam,morphine and metabolites in plasma using 96‐well solid‐phase extraction and ultra‐performance liquid chromatography–tandem mass spectrometry

Currently, pharmacokinetic–pharmacodynamic studies of sedatives and analgesics are performed in neonates and children to find suitable dose regimens. As a result, sensitive assays using only small volumes of blood are necessary to determine drug and metabolite concentrations. We developed an ultra‐performance liquid chromatographic method with tandem mass spectrometry detection for quantification of midazolam, 1‐hydroxymidazolam, hydroxymidazolamglucuronide, morphine, morphine‐3‐glucuronide and morphine‐6‐glucuronide in 100 μL of plasma. Cleanup consisted of 96 wells micro‐solid phase extraction, before reversed‐phase chromatographic separation (ultra‐performance liquid chromatography) and selective detection using electrospray ionization tandem mass spectrometry. Separate solid‐phase extraction methods were necessary to quantify morphine, midazolam and their metabolites because of each group's physicochemical properties. Standard curves were linear over a large dynamic range with adequate limits of quantitation. Intra‐ and interrun accuracy and precision were within 85–115% (of nominal concentration using a fresh calibration curve) and 15% (coefficient of variation, CV) respectively. Recoveries were >80% for all analytes, with interbatch CVs (as a measure of matrix effects) of less than 15% over six batches of plasma. Stability in plasma and extracts was sufficient, allowing large autosampler loads. Runtime was 3.00 min per sample for each method. The combination of 96‐well micro‐SPE and UPLC‐MS/MS allows reliable quantification of morphine, midazolam and their major metabolites in 100 μL of plasma. Copyright © 2010 John Wiley & Sons, Ltd.     

Ultra‐high‐performance liquid chromatography–tandem mass spectrometry for pharmacokinetics of bakuchiol in rats

Psoralea Corylifolia L. is a traditional Chinese medicine with many beneficial effects in medical therapies. Bakuchiol was the main active ingredient of Psoralea Corylifolia L., used for the treatment of various diseases and also as a natural food additive. A specific and reliable ultra‐high performance liquid chromatography–tandem mass spectrometry has been developed and fully validated for the quantification of bakuchiol in rat plasma. Chromatographic separation of bakuchiol and an internal standard, daidzein, was achieved on a Hypersil Gold C₁₈ column with gradient elution that consisted of methanol and water at a flow rate of 0.2 mL/min. The compounds were detected at negative ionization mode using mass transition m/z 255.2 → 172.0 and 252.9 → 132.0 for bakuchiol and daidzein, respectively. Good linearity was obtained over the range of 2–1000 ng/mL and the lower limit of quantification was 2 ng/mL. The intra‐ and inter‐day accuracies ranged from 91.1 to 105.7% and precisions (relative standard deviations) were within 9.3%. Bakuchiol was found to be stable under three freeze–thaw cycles, short‐term temperature, post‐preparative and long‐term temperature conditions. The method was applied to a pharmacokinetic study of bakuchiol intravenously administered to rats at a dose of 5 mg/kg. Copyright © 2013 John Wiley & Sons, Ltd.     

A rapid and sensitive liquid chromatography–tandem mass spectrometric assay for moexipril,an angiotensin‐converting enzyme inhibitor in human plasma

A simple, rapid and sensitive liquid chromatography/tandem mass spectrometry method was developed and validated for the quantification of angiotensin‐converting enzyme inhibitor, moexipril, in human plasma. Benazepril was used as an internal standard (IS). Analyte and IS were extracted from the human plasma by liquid–liquid extraction technique using ethyl acetate. The reconstituted samples were chromatographed on a C₁₈ column by using a mixture of methanol and 0.1% formic acid buffer (85:15, v/v) as the mobile phase at a flow rate of 0.5 mL/min. The calibration curve obtained was linear (r ≥ 0.99) over the concentration range of 0.2–204 ng/mL. The multiple reaction‐monitoring mode was used for quantification of ion transitions at m/z 499.4/234.2 and 425.2/351.1 for moexipril and IS, respectively. The results of the intra‐ and inter‐day precision and accuracy studies were well within the acceptable limits. A run time of 2.0 min for each sample made it possible to analyze more than 400 plasma samples per day. The proposed method was found to be applicable to clinical studies. Copyright © 2012 John Wiley & Sons, Ltd.     

Quantitative determination of duloxetine and its metabolite in rat plasma by HPLC‐MS/MS

The major metabolite of duloxetine is a glucuronide conjugate of 4‐hydroxy duloxetine (4‐HD). However, interestingly, there have been no reports determining concentrations of 4‐HD and no fully validated method has been established for measuring duloxetine and 4‐HD in rat plasma. We developed a method for the simultaneous quantification of duloxetine and its metabolite in rat plasma using high‐performance liquid chromatography tandem mass spectrometry. Duloxetine and 4‐HD were analyzed on a reverse‐phase C₁₈ analytical column after protein precipitation of the plasma sample with methanol, using carbamazepine as an internal standard. The isocratic mobile phase of 5 mm ammonium acetate–methanol (4:6, v/v) was eluted at 0.4 mL/min. Quantification was performed on a triple‐quadrupole mass spectrometer using electrospray ionization, and the ion transition monitored in selective reaction monitoring mode. The coefficient of variation for assay precision was <18.0%, and the accuracy was 84.0–118.0%. This method was successfully used to measure the concentrations of duloxetine and its metabolite in plasma following the oral administration of a single 40 mg/kg dose in rats. Copyright © 2013 John Wiley & Sons, Ltd.     

Pharmacokinetic study of dendrobine in rat plasma by ultra‐performance liquid chromatography tandem mass spectrometry

Dendrobine, considered as the major active alkaloid compound, has been used for the quality control and discrimination of Dendrobium which is documented in the Chinese Pharmacopoeia. In this work, a sensitive and simple ultra‐performance liquid chromatography tandem mass spectrometry (UPLC‐MS/MS) method for determination of dendrobine in rat plasma is developed. After addition of caulophyline as an internal standard (IS), protein precipitation by acetonitrile–methanol (9:1, v/v) was used to prepare samples. Chromatographic separation was achieved on a UPLC BEH C₁₈ (2.1 ×100 mm, 1.7 µm) column with acetonitrile and 0.1% formic acid as the mobile phase with gradient elution. An electrospray ionization source was applied and operated in positive ion mode; multiple reaction monitoring mode was used for quantification using target fragment ions m/z 264.2 → 70.0 for dendrobine and m/z 205.1 → 58.0 for IS. Calibration plots were linear throughout the range 2–1000 ng/mL for dendrobine in rat plasma. The RSDs of intra‐day and inter‐day precision were both <13%. The accuracy of the method was between 95.4 and 103.9%. The method was successfully applied to pharmacokinetic study of dendrobine after intravenous administration. Copyright © 2015 John Wiley & Sons, Ltd.     

A fast and accurate isotope dilution GC‐IT‐MS/MS method for determination of eugenol in different tissues of fish: Application to a depletion study in mandarin fish

An accurate, rapid and effective method was established for determination of eugenol in plasma, muscle, skin, liver, kidney and gill of fish using gas chromatography–ion trap tandem mass spectrometry. Samples of muscle, skin, liver, kidney and gill were prepared using the modified QuEChERS (quick, easy, cheap, effective, rugged and safe) procedure, and a plasma sample was prepared by a liquid–liquid extraction procedure. Eugenol was monitored in <7 min using an electron‐ionization source in MS/MS mode and quantified by an internal standard of eugenol‐d₃. The limit of detection was 5.0 μg/kg, and the limit of quantification was 10.0 μg/kg. The calibration curve was linear in the range of 5–1000 μg/L (R² = 0.9996). Intra‐ and inter‐day precisions of eugenol expressed as relative standard deviation were within 9.74%, and the accuracy exhibited a relative error ranging from −2.20 to 8.89%. The developed method was successfully used to study the elimination regularity of eugenol in mandarin fish.