Simple magnetization of Fe3O4/MIL‐53(Al)‐NH2 for a rapid vortex‐assisted dispersive magnetic solid‐phase extraction of phenol residues in water samples

The present work describes a simple route to magnetize MIL‐53(Al)‐NH₂ sorbent for rapid extraction of phenol residues from environmental samples. To extend the applications and performances of the metal‐organic frameworks in the field of adsorption materials, we combined the properties of metal‐organic frameworks and magnetite to decrease the extraction time and simplify the extraction process as well. In this study, a simple and quick vortex‐assisted dispersive magnetic solid phase extraction method for the extraction of ten United States Environmental Protection Agency's priority phenols from water samples prior to analysis by high‐performance liquid chromatography with photodiode array detection was proposed. The developed method exhibits a rapid enrichment of the target analytes within 10 s for extraction and 10 s for desorption. Low detection limits of 1.8‐41.7 µg/L and quantitation limits of 6.0‐139.0 µg/L with the relative standard deviations for intra‐ and interday analyses less than 12% were achieved. Satisfactory recoveries in the range of 80‐111% with the relative standard deviations less than 11% demonstrated that Fe₃O₄/MIL‐53(Al)‐NH₂ is promising sorbent in the field of magnetic solid‐phase extraction for environmental samples.     

Simultaneous quantitation of polygalaxanthone III and four ginsenosides by ultra‐fast liquid chromatography with tandem mass spectrometry in rat and beagle dog plasma after oral administration of Kai‐Xin‐San: Application to a comparative pharmacokinetic study

A fast, selective, and quantitative ultra‐fast liquid chromatography with tandem mass spectrometry method has been developed and validated for the simultaneous quantitation of polygalaxanthone III, ginsenoside Rb1, ginsenoside Rd, ginsenoside Re, and ginsenoside Rg1 in the plasma of rat and beagle dog after oral administration of Kai‐Xin‐San. After addition of the internal standard, salidroside, the plasma samples were extracted by liquid–liquid extraction and separated on a Venusil MP C₁₈ column with methanol/0.01% acetic acid water as mobile phase. The tandem mass spectrometric detection was performed in the multiple reaction monitoring with turbo ion spray source in a switching ionization mode. The method was examined, and found to be precise and accurate with the linearity range of the compounds. The intra‐ and interday precision and accuracy of the analytes were well within acceptance criteria (±15%). The mean extraction recoveries of analytes and internal standard were all >75.0%. The validated method has been successfully applied to comparing pharmacokinetic profiles of analytes in rat and beagle dog plasma. The results indicated that no significant differences were observed in pharmacokinetic parameters of ginsenoside Rg1, while the others had significant differences, which may due to the different mechanisms of absorption and metabolism.     

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.     

Determination of risperidone and 9‐Hydroxyrisperidone using HPLC,in plasma of children and adolescents with emotional and behavioural disorders

A simple, rapid, selective, accurate and precise method is described for the determination of risperidone and its active metabolite, 9‐hydroxyrisperidone, in plasma using a chemical derivative of risperidone (methyl‐risperidone) as the internal standard. The sample workup involved a single‐step extraction of 1 mL plasma, buffered to pH 10, with heptane–isoamyl alcohol (98:2 v/v), then evaporation of the heptane phase and reconstitution of the residue in mobile phase. HPLC separation was carried out at on C₁₈ column using a mobile phase of 0.05 m dipotassium hydrogen orthophosphate (containing 0.3% v/v triethylamine) adjusted to pH 3.7 with orthophosphoric acid (700 mL), and acetonitrile (300 mL). Flow rate was 0.6 mL/min and the detection wavelength was 280 nm. Retention times were 2.6, 3.7 and 5.8 min for 9‐hydroxy risperidone, risperidone and the internal standard, respectively. Linearity in spiked plasma was demonstrated from 2 to 100 ng/mL for both risperidone and 9‐hydroxyrisperidone (r ≥ 0.999). Total imprecision was less than 13% (determined as co‐efficient of variation) and the inaccuracy was less than 12% at spiked concentrations of 5 and 80 ng/mL. The limit of detection, determined as three times the baseline noise, was 1.5 ng/mL. Clinical application of the assay was demonstrated for analysis of post‐dose (0.55–4.0 mg/day) samples from 28 paediatric patients (aged 6.9–17.9 years) who were taking risperidone orally for behavioural and emotional disorders. Copyright © 2009 John Wiley & Sons, Ltd.     

A high‐throughput screening method for determination of multi‐antibiotics in animal feed

A high‐throughput method based on ultrasonic‐assisted extraction, 96‐well plate thin‐film microextraction was established to determinate 18 antibiotics in animal feed. In this method, the extraction was implemented by ultrasonic‐assisted extraction for 30 min with disodium ethylenediaminetetraacetic acid‐McIlvaine buffer (pH 5) containing 6% sodium chloride w/v, purified by thin‐film microextraction and combined with 96‐well plate system to improve the efficiency. Optimization of thin‐film microextraction conditions was performed by methods of single factor and response surface, and finalized as: condition time: 20 min; adsorption time: 55 min; washing time: 5 s with water; desorption time: 30 min with acetonitrile/water (8:2, v/v) containing 0.1% formic acid v/v. Evaluation of different extractive phases showed that polystyrene‐divinylbenzene‐polyacrylonitrile was the optimum coating. The analysis was performed by ultra‐high performance liquid chromatography with tandem mass spectrometry. Recovery, inter‐ and intraday precision, linearity, limit of detection, and quantitation were evaluated. The average recoveries of 18 antibiotics were 66.6–93.5% at three spiked levels, intraday precision was 1–8.4%, and interday precision was 3.0–16.4%. The linearity was good for r² > 0.99. Limits of detection and quantification were found in the range of 1–14 and 4–48 µg/kg, respectively.     

Rapid determination of nosiheptide in feed based on dispersive SPE coupled with HPLC

A novel, simple, and reliable method based on high‐performance liquid chromatography coupled with fluorescence detection has been developed for the determination of nosiheptide in feed. The feed samples were extracted with acetonitrile 0.1% formic acid aqueous solution and then purified via a dispersive solid‐phase extraction procedure using silica gel powder as the sorbent. Using a mixture of acetonitrile and 5 mM ammonium acetate solution (containing 0.1% formic acid) as the mobile phase, good separation and peak shape were obtained for nosiheptide on a Poroshell C₈ column (250 × 4.6 mm id, 4 μm) via the isocratic elution program. The resulting calibration curve shows high levels of linearity (r² > 0.999) for nosiheptide concentrations of 50–1000 μg/L. At three spiked levels, i.e., 0.500, 2.50 and 5.00 mg/kg, the intra‐ and interday recoveries of nosiheptide in five types of feed ranged from 78.5–96.8 and 84.9–94.2%, respectively. The intra‐ and interday relative standard deviations were less than 10.8%. The limits of quantification for nosiheptide in complete feed and premixes were measured as 50 and 100 μg/kg, respectively. Compared with other common adsorbents, silica gel presents stronger recovery and purification results for feed samples during the dispersive solid‐phase extraction process.     

GC–MS/MS method for the determination and pharmacokinetic analysis of borneol and muscone in rat after the intravenous administration of Xingnaojing injection

A simple and sensitive gas chromatography with tandem mass spectrometry method was developed and validated for the simultaneous determination of borneol and muscone in rat plasma. The analytes and internal standard, naphthalene, were extracted using a convenient one‐step liquid–liquid extraction method with ethyl acetate. The chromatographic separation was realized on a HP‐5MS capillary column and detected in multiple reaction monitoring mode. Excellent linearity (R ² ≥ 0.996) was shown over 10.0–5000 ng/mL for borneol and 2.5–250 ng/mL for muscone. The lower limit of quantitation was 10 and 2.5 ng/mL for borneol and muscone, respectively. The intra‐ and interday precisions were less than 7.52%, and the accuracy values were between  −8.03 and 14.52%. The extraction recovery, matrix effect, and stability were sufficient to meet the Food and Drug Administration criteria. Meanwhile, the assay was successfully applied to the preclinical pharmacokinetic study of borneol and muscone following intravenous administration of Xingnaojing injection, a modern Chinese herbal medicine preparation.     

Concurrent determination of olanzapine,risperidone and 9‐hydroxyrisperidone in human plasma by ultra performance liquid chromatography with diode array detection method: application to pharmacokinetic study

A simple and sensitive ultra‐performance liquid chromatography (UPLC) method has been developed and validated for simultaneous estimation of olanzapine (OLZ), risperidone (RIS) and 9‐hydroxyrisperidone (9‐OHRIS) in human plasma in vitro. The sample preparation was performed by simple liquid–liquid extraction technique. The analytes were chromatographed on a Waters Acquity H class UPLC system using isocratic mobile phase conditions at a flow rate of 0.3 mL/min and Acquity UPLC BEH shield RP₁₈ column maintained at 40°C. Quantification was performed on a photodiode array detector set at 277 nm and clozapine was used as internal standard (IS). OLZ, RIS, 9‐OHRIS and IS retention times were found to be 0.9, 1.4, .1.8 and 3.1 min, respectively, and the total run time was 4 min. The method was validated for selectivity, specificity, recovery, linearity, accuracy, precision and sample stability. The calibration curve was linear over the concentration range 1–100 ng/mL for OLZ, RIS and 9‐OHRIS. Intra‐ and inter‐day precisions for OLZ, RIS and 9‐OHRIS were found to be good with the coefficient of variation <6.96%, and the accuracy ranging from 97.55 to 105.41%, in human plasma. The validated UPLC method was successfully applied to the pharmacokinetic study of RIS and 9‐OHRIS in human plasma. Copyright © 2015 John Wiley & Sons, Ltd.     

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.     

Simultaneous derivatization and lighter‐than‐water air‐assisted liquid–liquid microextraction using a homemade device for the extraction and preconcentration of some parabens in different samples

Simultaneous derivatization and air‐assisted liquid–liquid microextraction using an organic that is solvent lighter than water has been developed for the extraction of some parabens in different samples with the aid of a newly designed device for collecting the extractant. For this purpose, the sample solution is transferred into a glass test tube and a few microliters of acetic anhydride (as a derivatization agent) and p‐xylene (as an extraction solvent) are added to the solution. After performing the procedure, the homemade device consists of an inverse funnel with a capillary tube placed into the tube. In this step, the collected extraction solvent and a part of the aqueous solution are transferred into the device and the organic phase indwells in the capillary tube of the device. Under the optimal conditions, limits of detection and quantification for the analytes were obtained in the ranges of 0.90–2.7 and 3.0–6.1 ng/mL, respectively. The enrichment and enhancement factors were in the ranges of 370–430 and 489–660, respectively. The method precision, expressed as the relative standard deviation, was within the range of 4–6% (n = 6) and 4–9% (n = 4) for intra‐ and interday precisions, respectively. The proposed method was successfully used for the determination of methyl‐, ethyl‐, and propyl parabens in cosmetic, hygiene and food samples, and personal care products.     

Simultaneous determination of short‐chain fatty acids in human feces by HPLC with ultraviolet detection following chemical derivatization and solid‐phase extraction segmental elution

Short‐chain fatty acids are currently the most studied metabolites of gut microbiota, but the analysis of them, simultaneously, is still challenging due to their unique property and wide concentration range. Here, we developed a sensitive and versatile high‐performance liquid chromatography with ultraviolet detection method, using pre‐column derivatization and solid‐phase extraction segmental elution, for the quantification of both major and trace amounts of short‐chain fatty acids in human feces. Short‐chain fatty acids were converted to 3‐nitrophenylhydrazine‐derived analytes, and then solid‐phase extraction segmental elution was used for extraction of major analytes and enrichment of trace analytes. The method validation showed limits of quantitation ?0.04 mM, and coefficient of determination > 0.998 at a wide range of 0.04–8.0 mM. The intra‐ and interday precision of analytes were all within accepted criteria, and the recoveries were 96.12 to 100.75% for targeted analytes in fecal samples. This method was successfully applied in quantification of eight analytes in human feces, which therefore could provide a sensitive and versatile high‐performance liquid chromatography with ultraviolet detection method for precise and accurate quantitation of short‐chain fatty acids in human feces.     

Quantitative determination of seven chemical constituents and chemo‐type differentiation of chamomiles using high‐performance thin‐layer chromatography

A simple and rapid high‐performance thin‐layer chromatographic method was developed for the separation and determination of six flavonoids (rutin, luteolin‐7‐O‐β‐glucoside, chamaemeloside, apigenin‐7‐O‐β‐glucoside, luteolin, apigenin) and one coumarin, umbelliferone from chamomile plant samples and dietary supplements. The separation was achieved on amino silica stationary phase using dichloromethane/acetonitrile/ethyl formate/glacial acetic acid/formic acid (11:2.5:3:1.25:1.25 v/v/v/v/v) as the mobile phase. The quantitation of each compound was carried out using densitometric reflection/absorption mode at their respective absorbance maxima after postchromatographic derivatization using natural products reagent (1% w/v methanolic solution of diphenylboric acid‐β‐ethylamino ester). The method was validated for specificity, limits of detection and quantification, precision (intra‐ and interday) and accuracy. The limits of detection and quantification were found to be in the range from 6–18 and 16–55 ng/band for six flavonoids and one coumarin, respectively. The intra‐ and interday precision was found to be <5% RSD and recovery of all the compounds was >90%. The data acquired from high‐performance thin‐layer chromatography was processed by principal component analysis using XLSTAT statistical software. Application of principal component analysis and agglomerative hierarchial clustering was successfully able to differentiate two chamomiles (German and Roman) and Chrysanthemum.     

Dispersive admicelle solid‐phase extraction based on sodium dodecyl sulfate coated Fe3O4 nanoparticles for the selective adsorption of three alkaloids in Gegen‐Qinlian oral liquid before high‐performance liquid chromatography

A novel dispersive admicelle solid‐phase extraction method based on sodium dodecyl sulfate‐coated Fe₃O₄ nanoparticles was developed for the selective adsorption of berberine, coptisine, and palmatine in Gegen‐Qinlian oral liquid before high‐performance liquid chromatography. Fe₃O₄ nanoparticles were synthesized by a chemical coprecipitation method and characterized by using transmission electron microscopy. Under acidic conditions, the surface of Fe₃O₄ nanoparticles was coated with sodium dodecyl sulfate to form a nano‐sized admicelle magnetic sorbent. Owing to electrostatic interaction, the alkaloids were adsorbed onto the oppositely charged admicelle magnetic nanoparticles. The quick separation of the analyte‐adsorbed nanoparticles from the sample solution was performed by using Nd‐Fe‐B magnet. Best extraction efficiency was achieved under the following conditions: 800 μL Fe₃O₄ nanoparticles suspension (20 mg/mL), 150 μL sodium dodecyl sulfate solution (10 mg/mL), pH 2, and vortexing time 2 min for the extraction of alkaloids from 10 mL of diluted sample. Four hundred microliters of methanol was used to desorb the alkaloids by vortexing for 1 min. Satisfactory extraction recoveries were obtained in the range of 85.9–120.3%, relative standard deviations for intra‐ and interday precisions were less than 6.3 and 10.0%, respectively. Finally, the established method was successfully applied to analyze the alkaloids in two batches of Gegen‐Qinlian oral liquids.     

Developing a novel packed in‐tube solid‐phase extraction method for determination ∆9‐tetrahydrocannabinol in biological samples and cannabis leaves

A novel plate‐like nano‐sorbent based on copper/cobalt/chromium layered double hydroxide was synthesized by a simple coprecipitation method. The synthesized nanoparticels were introduced into a stainless steel cartridge using a dry packing method. Then, the packed cartridge was introduced as a novel on‐line “packed in‐tube” configuration and followed by high performance liquid chromatography for the determination of trace amounts of ^?9‐tetrahydrocannabinol from biological samples and cannabis leaves. The as‐prepared sorbent exhibited long lifetime, good chemical stability, and high anion‐exchange capacity. Several important factors affecting the extraction efficiency, such as extraction and desorption times, pH of the sample solution and flow rates of the sample and eluent solutions, were investigated and optimized. Under optimized conditions, this method showed good linearity for ^?9‐tetrahydrocannabinol in the ranges of 0.09–500, 0.3–500, and 0.4–500 µg/L with coefficients of determination of 0.9999, 0.9991, and 0.9994 in water, serum and plasma samples, respectively. The inter‐ and intra‐assay precisions (n = 3) were respectively in the ranges of 1.8–4.6% and 1.9–4.0% at three concentration levels of 10, 50, and 100 µg/L. The limits of detection were also in the range of 0.02–0.1 µg/L.     

Simple HPLC‐UV for the quantification of a new leishmanicidal candidate (E)‐1‐4(trifluoromethyl) benzylidene)‐5‐(2‐4‐dichlorozoyl) carbonylhydrazine (LASSBio‐1736) in rat plasma for pharmacokinetics assessment

In this study, a sensitive HPLC‐UV assay was developed and validated for the determination of LASSBio‐1736 in rat plasma with sodium diclofenac as internal standard (IS). Liquid–liquid extraction using acetonitrile was employed to extract LASSBio‐1736 and IS from 100 μL of plasma previously basified with NaOH 0.1 M. Chromatographic separation was carried on Waters Spherisorb^®S5 ODS2 C₁₈ column (150 × 4.6 mm, 5 μm) using an isocratic mobile phase composed by water with triethylamine 0.3% (pH 4), methanol and acetonitrile grade (45:15:40, v/v/v) at a flow rate of 1 mL/min. Both LASSBio‐1736 and IS were eluted at 4.2 and 5 min, respectively, with a total run time of 8 min only. The lower limit of quantification was 0.2 μg/mL and linearity between 0.2 and 4 μg/mL was obtained, with an R² > 0.99. The accuracy of the method was >90.5%. The relative standard deviations intra and interday were <6.19 and <7.83%, respectively. The method showed the sensitivity, linearity, precision, accuracy and selectivity required to quantify LASSBio‐1736 in preclinical pharmacokinetic studies according to the criteria established by the US Food and Drug Administration and European Medicines Agency. Copyright © 2016 John Wiley & Sons, Ltd.     

Determination of eight illegal drugs in human urine by combination of magnetic solid‐phase extraction with capillary zone electrophoresis

Using magnetite/silica/poly(methacrylic acid‐co‐ethylene glycol dimethacrylate) (Fe₃O₄/SiO₂/poly(MAA‐co‐EDMA)) magnetic microspheres, a rapid and high‐throughput magnetic solid‐phase extraction coupled with capillary zone electrophoresis (MSPE‐CZE) method was developed for the determination of illegal drugs (ketamine, amphetamines, opiates, and metabolites). The MSPE of target analytes could be completed within 2 min, and the eight target analytes could be baseline separated within 15 min by CZE with 30 mM phosphate buffer solution (PBS, pH 2.0) containing 15% v/v ACN as background electrolyte. Furthermore, hydrodynamic injection with field‐amplified sample stacking (FASS) was employed to enhance the sensitivity of this MSPE‐CZE method. Under such optimal conditions, the limits of detection for the eight target analytes ranged from 0.015 to 0.105 μg/mL. The application feasibility of MSPE‐CZE in illegal drugs monitoring was demonstrated by analyzing urine samples, and the recoveries of target drugs for the spiked sample ranging from 85.4 to 110.1%. The method reproducibility was tested by evaluating the intra‐ and interday precisions, and relative standard deviations of <10.3 and 12.4%, respectively, were obtained. To increase throughput of the analysis, a home‐made MSPE array that has potential application to the treatment of 96 samples simultaneously was used.     

Determination of total retronecine esters‐type hepatotoxic pyrrolizidine alkaloids in plant materials by pre‐column derivatization high‐performance liquid chromatography

A pre‐column derivatization high‐performance liquid chromatography method with diode array detection was developed and validated to determine the total retronecine esters‐type hepatotoxic pyrrolizidine alkaloids (RET‐HPAs) in herbs. The RET‐HPAs reacted with o‐chloranil in methanolic solution heated for 3 h, and an oxidative derivative was produced that could be detected at a maximal absorption of 223 nm. The analysis was performed using a C₁₈ column with an isocratic elution of methanol and aqueous 0.01% triethylamine (adjusted to pH 4 with formic acid), and the detection was carried out with DAD at 223 nm. The validation of the method included linearity, sensitivity, recovery and stability. It showed a good linear regression (r² > 0.9900) in the range of 2.5–250 µm with a limit of detection (S/N = 3) of 0.5 µm . The method provided desirable repeatability with overall intra‐ and inter‐day variations of less than 4.6%. The obtained recoveries for both of the extraction and derivatization process were between 94.6 and 100.7% (n = 3). Copyright © 2009 John Wiley & Sons, Ltd.     

Reversed‐phase liquid chromatography method for the determination of total plasma thiols after derivatization with 1‐benzyl‐2‐chloropyridinium bromide

A high‐performance liquid chromatography method was developed for simultaneous detection and quantitation of total cysteine, glutathione, homocysteine and cysteinylglycine in human plasma. The two key steps in the analysis are reduction of disulfides and treatment with 1‐benzyl‐2‐chloropyridinium bromide, which rapidly and quantitatively reacts with thiol groups to form stable S‐pyridinium derivatives with intense UV absorption. The derivatives are well separated on a Zorbax SB C₁₈ column using reversed‐phase high‐performance liquid chromatography and monitored at 315 nm. The calibration graphs were linear over concentration ranges covering most experimental and clinical cases with a regression coefficients better than 0.999. The detection and quantitation limits for all analytes were 0.2 and 0.5 µmol/L, respectively. The recoveries were 99.25–101.68%. The intra‐ and interassay imprecisions were 0.88–4.24 and 1.68–5.14%, respectively. The method was applied for plasma samples donated by apparently healthy volunteers. Copyright © 2009 John Wiley & Sons, Ltd.     

Development and optimization of a supercritical fluid chromatography tandem mass spectrometry method for the high‐throughput determination of nimodipine in beagle plasma

A simple, sensitive, and efficient supercritical fluid chromatography with tandem mass spectrometry method was established for the determination of nimodipine in beagle plasma. One‐step protein precipitation with acetone was used to extract the analytes from the plasma. Nitrendipine was used as the internal standard. The chromatographic separation was achieved on an ACQUITY UPC²? BEH 2‐EP column, and a gradient elution program was applied at a flow rate of 1.5 mL/min. The detection was carried out on a triple quadrupole tandem mass spectrometer with an electrospray ionization source operating in positive ion mode. Quantification was performed using multiple reaction monitoring of the transitions of m/z 419.3→301.3 for nimodipine and m/z 361.4→315.2 for nitrendipine. A satisfactory linearity was obtained over the concentration range of 0.5–800 ng/mL (r > 0.996). The intra‐ and interday precision and accuracy results were <9.1% across the quality control levels. The peak concentration and area under concentration‐time curve (0–720 min) values of the test and reference formulations were 279.28 ± 211.46 and 265.13 ± 149.26 ng/mL, 25608.00 ± 17553.65 and 28553.67 ± 20207.92 ng·min/mL, respectively. The validated method was successfully applied to reveal the pharmacokinetic profiles of nimodipine in beagle dogs after oral administration. Moreover, the analytical method could be used for further bioequivalence studies.     

Simultaneous analysis of multiple urinary biomarkers for the evaluation of oxidative stress by automated online in‐tube solid‐phase microextraction coupled with negative/positive ion‐switching mode liquid chromatography–tandem mass spectrometry

This study described an automated online method for the simultaneous determination of 8‐isoprostane, 8‐hydroxy‐2′‐deoxyguanosine, and 3‐nitro‐l ‐tyrosine in human urine. The method involves in‐tube solid‐phase microextraction using a Carboxen 1006 PLOT capillary column as an extraction device, followed by liquid chromatography with tandem mass spectrometry using a CX column and detection in the negative/positive switching ion‐mode by multiple reaction monitoring. Using their stable isotope‐labeled internal standards, each of these oxidative stress biomarkers showed good linearity from 0.02 to 2.0 ng/mL. Their detection limits (S/N = 3) were 3.4–21.5 pg/mL, and their intra‐ and inter‐day precisions (relative standard deviations) were >3.9 and 6.5% (n = 5), respectively. This method was applied successfully to the analysis of urine samples, without any other pretreatment and interference peaks.