Simultaneous determination of fifteen multiclass organic pollutants in human saliva and serum by liquid chromatography–tandem ultraviolet/fluorescence detection: A validated method

A quick and inexpensive validated method, based on sample treatment by liquid–liquid microextraction followed by liquid chromatography (LC) coupled with ultraviolet tandem fluorescence detection is proposed for the determination of 15 multiclass pollutants both in serum and in saliva, as a simple and easy to draw matrix. The method was set up and validated according to European guidelines. The compounds of interest include some endocrine‐disrupting chemicals (i.e. bisphenol A, bisphenol B, bisphenol E, bisphenol F, bisphenol AF, bisphenol A diglycidyl ether, bisphenol M, diethylhexyl phthalate, monoethylhexyl phthalate, triclosan and 4‐nonylphenol), as well as other pollutants belonging to the class of volatile organic compounds (2‐chlorophenol, 1,2 dichlorobenzene, 1,2,4,5‐tetrachlorobenzene). The limits of quantifications ranged from 2.28 × 10^?3 μg mL^?1 (bisphenol A diglycidyl ether) to 6.29 μg mL^?1 (diethylhexyl phthalate), while those of detection ranged from 0.068 × 10^?3 μg mL^?1 (bisphenol A diglycidyl ether) to 1.031 μg mL^?1 (diethylhexyl phthalate). To test method suitability, it was applied to real saliva and serum samples of healthy human volunteers and was found to meet the demands of the laboratories handling simple and relatively inexpensive equipment for screening oriented at rapid and reliable contamination assessment of a population.     

Determination of Palmatine in Rabbit Plasma by RP-HPLC with Solid-Phase Extraction

A rapid and specific reversed-phase high performance liquid chromatography (RP-HPLC) method for the determination of palmatine in rabbit plasma has been developed and validated. The chromatographic separation was performed on a C₁₈ column at 40 °C. The mobile phase, delivered at 1.0 mL min^?1, consisted of acetonitrile/phosphate buffer (pH 3.0) 40:60 (v/v). The detection wavelength was set at 345 nm. Palmatine and internal standard (IS) berberine were extracted from plasma by solid-phase extraction using C18 cartridges. Linearity was confirmed in the concentration range of 0.01 to 5 μg mL^?1, the inter-day and intra-day RSDs were within 10.0, the recoveries of palmatine ranged from 93.1 to 110.3, and the limit of detection (LOD, S/N > 3) was 0.002 μg mL^?1. The method is applicable to the determination of palmatine in rabbit plasma after intravenous administration of palmatine.     

Development of High Performance Liquid Chromatography Method for Costunolide and Dehydrocostuslactone in Mice Plasma and Tissues:Application to Pharmacokinetic Study

A simple and sensitive high performance liquid chromatographic (HPLC) method for simultaneous determination of costunolide and dehydrocostuslactone in mice plasma and tissues was developed and validated. Costunolide and dehydrocostuslactone were extracted into acetonitrile and separated using an isocratic mobile phase, on a Hypersil ODS C18 column. The effluent was monitored by UV detector at 210 nm and at a flow rate of 1.0 mL· min^?1 and 25°C. The linearity ranges of proposed method were 0.223–8.920 µg·mL^?1 for costunolide and 0.227–9.080 µg·mL^?1 for dehydrocostuslactone. The intra‐day and inter‐day RSD of the assay method for the two components were less than 5%, and mean recovery was within the 86.5% to 101.8% range. The method was found to be precise, accurate, and specific during the study. The method was successfully applied for pharmacokinetic study of costunolide and dehydrocostuslactone after application of ethanol extraction of Muxiang (EEM) in mice.     

Optimization of modified dispersive liquid–liquid microextraction coupled with high‐performance liquid chromatography for the simultaneous preconcentration and determination of nitrazepam and midazolam drugs: An experimental design

A simple, sensitive, and rapid microextraction method, namely, ultrasound‐assisted surfactant‐enhanced emulsification microextraction based on the solidification of floating organic droplet method coupled with high‐performance liquid chromatography was developed for the simultaneous preconcentration and determination of nitrazepam and midazolam. The significant parameters affecting the extraction efficiency were considered using Plackett–Burman design as a screening method. To obtain the optimum conditions with consideration of the selected significant variables, a Box–Behnken design was used. The microextraction procedure was performed using 29.1 μL of 1‐undecanol, 1.36% (w/v) of NaCl, 10.0 μL of sodium dodecyl sulfate (25.0 μg mL^?1), and 1.0 μL of Tween80 (25.0 μg mL^?1) as an emulsifier in an extraction time of 20.0 min at pH 7.88. In order to investigate the validation of the developed method, some validation parameters including the linear dynamic range, repeatability, limit of detection, and recoveries were studied under the optimum conditions. The detection limits of the method were 0.017 and 0.086 ng mL^?1 for nitrazepam and midazolam, respectively. The extraction recovery percentages for the drugs studied were above 91.0 with acceptable relative standard deviation. The proposed methodology was successfully applied for the determination of these drugs in a number of human serum samples.     

Development and validation of a generic RP‐HPLC PDA method for the simultaneous separation and quantification of active ingredients in cold and cough medicines

A novel generic reverse phase high performance liquid chromatography (RP‐HPLC) method is developed and validated for simultaneous determination of seven pharmaceutically active ingredients, namely, acetaminophen, dextromethorphan, doxylamine, phenylephrine, guaifenesin, caffeine and aspirin. All seven ingredients were quantified in soft gel, syrup and tablet formulations of the over‐the‐counter US‐marketed products, as per the guidelines of the International Conference on Harmonization. The separation was achieved in a 16 min run time on an Agilent Zorbax Phenyl column using a gradient method with two mobile phases. Mobile phase A was 0.15% trifluoro acetic acid in purified water and while mobile phase B was a mixture of acetonitrile and methanol (750:250 v/v) with 0.02% trifluoro acetic acid. The flow rate was 1.0 mL min^?1 and injection volume was 10 μL. Detection was performed at 280 nm using a photodiode array detector. As part of the method validation, specificity, linearity, precision and recovery parameters were verified. The concentration and area relationships were linear (R² > 0.999), over the concentration ranges 20–120 μg mL^?1 for acetaminophen, 75–450 μg mL^?1 for dextromethorphan, 31.25–187.5 μg mL^?1 for doxylamine, 25–150 μg mL^?1 for phenylephrine, 25–150 μg mL^?1 for aspirin, 6.5–39 μg mL^?1 for caffeine and 12–72 μg mL^?1 for guaifenesin. The relative standard deviations for precision and intermediate precision were <1.5%. The proposed RP‐HPLC generic method is applicable for routine analysis of cold and cough over‐the‐counter products.     

Porous carbon derived from a metal–organic framework as an efficient adsorbent for the solid‐phase extraction of phthalate esters

A porous carbon designated as MOF‐5‐C was prepared by directly carbonizing a metal–organic framework (MOF‐5). The morphology and microstructure of MOF‐5‐C were characterized by scanning electron microscopy, N₂ adsorption, and powder X‐ray diffraction. The MOF‐5‐C retained the original porous structures of MOF‐5, and showed a high Brunauer–Emmett–Teller surface area (1808 m² g^?1) and large pore volume (3.05 cm³ g^?1). To evaluate its adsorption performance, the MOF‐5‐C was used as an adsorbent for the solid‐phase extraction of four phthalate esters from bottled water, peach juice, and soft drink samples followed by high‐performance liquid chromatographic analysis. Several parameters that could affect the extraction efficiencies were investigated. Under the optimum conditions, a good linearity was achieved in the concentration range of 0.1–50.0 ng mL^?1 for bottled water sample and 0.2–50.0 ng mL^?1 for peach juice and soft drink samples. The limits of detection of the method (S/N = 3) were 0.02 ng mL^?1 for bottled water sample, and 0.04–0.05 ng mL^?1 for peach juice and soft drink samples. The results indicated that the MOF‐5‐C exhibited an excellent adsorption capability for trace levels of phthalate esters, and it could be a promising adsorbent for the preconcentration of other organic compounds.     

An LC–MS–MS Method for the Simultaneous Quantitation of Acyclovir and Valacyclovir in Human Plasma

A simple, sensitive and selective LC–MS–MS method has been developed for the simultaneous determination of acyclovir and valacyclovir in human plasma. Acyclovir and valacyclovir in plasma were concentrated by solid phase extraction and chromatographed on a C18 column using a mobile phase of 0.1% formic acid: methanol (30:70% v/v). The method was validated over a linear range of 47–10,255 and 5–1,075 ng mL^?1 for acyclovir and valacyclovir respectively. The LOQs were 47.6 and 5.0 ng mL^?1. The validated method was applied for the quantitation of acyclovir and valacyclovir from plasma samples in a pharmacokinetic study.     

Simple determination of betaine,l‐carnitine and choline in human urine using self‐packed column and column‐switching ion chromatography with nonsuppressed conductivity detection

A sequential online extraction, clean‐up and separation system for the determination of betaine, l ‐carnitine and choline in human urine using column‐switching ion chromatography with nonsuppressed conductivity detection was developed in this work. A self‐packed pretreatment column (50 × 4.6 mm, i.d.) was used for the extraction and clean‐up of betaine, l ‐carnitine and choline. The separation was achieved using self‐packed cationic exchange column (150 × 4.6 mm, i.d.), followed by nonsuppressed conductivity detection. Under optimized experimental conditions, the developed method presented good analytical performance, with excellent linearity in the range of 0.60–100 μg mL⁻¹ for betaine, 0.75–100 μg mL⁻¹ for l ‐carnitine and 0.50–100 μg mL⁻¹ for choline, with all correlation coefficients (R²) >0.99 in urine. The limits of detection were 0.15 μg mL⁻¹ for betaine, 0.20 μg mL⁻¹ for l ‐carnitine and 0.09 μg mL⁻¹ for choline. The intra‐ and inter‐day accuracy and precision for all quality controls were within ±10.32 and ±9.05%, respectively. Satisfactory recovery was observed between 92.8 and 102.0%. The validated method was successfully applied to the detection of urinary samples from 10 healthy people. The values detected in human urine using the proposed method showed good agreement with the measurement reported previously.     

Simultaneous Determination of Three Flavonoids in Rat Plasma by RP-LC After Oral Administration of the Total Flavonoids of Scutellaria barbata

A liquid chromatographic method for the simultaneous determination of three flavonoids, scutellarin (SCU), isoscutellarein-8-O-glucuronide (ISO) and luteolin (LUT) in rat plasma was developed and validated. Following a single-step liquid–liquid extraction with ethyl acetate, the analytes and internal standard (IS) (rutin) were successfully separated on a Diamonsil C₁₈ column using a mobile phase composed of acetonitrile (A)–0.2% phosphoric acid aqueous solution (B) (0–5 min, 20% A–29% A; 5–25 min, 29% A, v/v) at a flow rate of 1.0 mL min^?1. The linear range was 0.044–2.20 μg mL^?1 for SCU, 0.042–2.08 μg mL^?1 for ISO, and 0.056–2.80 μg mL^?1 for LUT, with the correlation coefficients of 0.9995, 0.9989 and 0.9963, respectively. The limit of quantification of SCU, ISO and LUT were 44, 41.6 and 56 ng mL^?1, respectively. The accuracy of assay was between 88.4 and 103.0%. The inter-day and intra-day precisions (RSD) were less than 10.5%. The developed method was simple, rapid and applied successfully to study the pharmacokinetics of SCU, ISO and LUT after oral administration of the total flavonoids of Scutellaria barbata.     

Microwave-assisted extraction followed by headspace solid-phase microextraction and gas chromatography with mass spectrometry detection (MAE-HSSPME-GC-MS/MS) for determination of polybrominated compounds in aquaculture samples

This paper describes the first validated method for the extraction, purification and determination of trace levels of a number of pollutants of growing concern, including polybrominated biphenyls (PBBs) and polybrominated diphenyl ethers (PBDEs), in aquaculture feeds and products. The new procedure comprises microwave-assisted extraction (MAE; optimized, using a central composite experimental design, to 15 min at 85 °C in 14 mL of 1:1 hexane/dichloromethane), and concentration by headspace solid-phase microextraction (HSSPME), and separation/quantification by gas chromatography with mass spectrometry detection (GC-MS/MS). The method was validated on the reference materials IAEA-406 and WMF-01. Limits of detection for fourteen of the fifteen analytes considered range from 10 to 600 pg g⁻¹, and limits of quantification from 50 pg g⁻¹ to 1.9 ng g⁻¹. Linear ranges, accuracies and precisions are reported.     

Development and validation of an LC‐MS/MS method for the determination of a novel thienoquinolin urea transporter inhibitor PU‐48 in rat plasma and its application to a pharmacokinetic study

A specific, sensitive and stable high‐performance liquid chromatographic–tandem mass spectrometry (LC‐MS/MS) method was developed and validated for the quantitative determination of methyl 3‐amino‐6‐methoxythieno [2,3‐b]quinoline‐2‐carboxylate (PU‐48), a novel diuretic thienoquinolin urea transporter inhibitor in rat plasma. In this method, the chromatographic separation of PU‐48 was achieved with a reversed‐phase C₁₈ column (100 × 2.1 mm, 3 μm) at 35°C. The mobile phase consisted of acetonitrile and water with 0.05% formic acid added with a gradient elution at flow rate of 0.3 mL/min. Samples were detected with the triple‐quadrupole tandem mass spectrometer with multiple reaction monitoring mode via electrospray ionization source in positive mode. The retention time were 6.2 min for PU‐48 and 7.2 min for megestrol acetate (internal standard, IS). The monitored ion transitions were mass‐to‐charge ratio (m/z) 289.1 → 229.2 for PU‐48 and m/z 385.3 → 267.1 for the internal standard. The calibration curve for PU‐48 was linear over the concentration range of 0.1–1000 ng/mL (r² > 0.99), and the lower limit of quantitation was 0.1 ng/mL. The precision, accuracy and stability of the method were validated adequately. The developed and validated method was successfully applied to the pharmacokinetic study of PU‐48 in rats.     

Optimisation of an in-tube solid phase microextraction method coupled with HPLC for determination of some oestrogens in environmental liquid samples using different capillary columns

A simple on-line method for simultaneous determination of some oestrogens including oestriol (E3), norethisterone (NORE), ethynylestradiol (EE2), D-norgestrel (NORG) and bisphenol A (BPA), in environmental liquid samples was developed by coupling in-tube solid phase microextraction (in-tube SPME) to high-performance liquid chromatography with diode array (DAD) and fluorescence (FLD) detectors. Two capillary chromatographic columns (Supel-Q? and Carboxen? 1006 porous layer open tubular) were selected to develop this method. To achieve optimum extraction performance, several parameters were investigated including number of draw/eject cycles and the sample volume for each of the columns. Reproducibility was satisfactory for inter- and intra-day precision, yielding % RSDs of less than 10% and 7.6%, respectively. Limits of detection (LODs) and quantification (LOQs) for the proposed method using a DAD detector were achieved in the ranges of 0.04–0.63?ng?mL^?1 and 0.12–1.9?ng?mL^?1, depending of the capillary column used. Fluorescence detection improved these parameters for E3, BPA and EE2, obtaining LODs of 0.005–0.03?ng?mL^?1 and LOQs of 0.015–0.08?ng?mL^?1 using Supel-Q and LODs of 0.01–0.015?ng?mL^?1 and LOQs of 0.025–0.04?ng?mL^?1 using Carboxen. The proposed method was successfully applied to spiked environmental waters obtaining recoveries greater than 80%.     

Simultaneous Determination of Free Cortisol,Cortisone and their Tetrahydrometabolites in Urine by Single Solvent Extraction and Liquid Chromatography–Tandem Mass Spectrometry

Abstract

A fast, efficient and low-cost high performance liquid chromatography–tandem mass spectrometry methodology was developed and validated for the simultaneous determination of free urinary cortisone, cortisol and their tetrahydro-metabolites. The developed method comprises a simple liquid-liquid extraction with CH₂Cl_2, followed by reversed-phase liquid chromatography–tandem mass spectrometry (LC–MS/MS) with electrospray ionization (ESI) in positive mode. The baseline chromatographic separation of the analytes, including the stereoisomers tetrahydrocortisol (THF) and allo-THF, was achieved on a Hypersil Gold C₁₈ column with a mobile phase consisting of 0.05%v/v formic acid in water—acetonitrile, using a gradient elution program. The influence of the mobile phase composition and the ESI parameters on the sensitivity of the method was extensively studied. Sample preparation was also optimized, testing two techniques: solid phase extraction (SPE) and liquid-liquid extraction (LLE). Recoveries ranged from 74.7% (a-THF) to 93.5% (cortisol) and the method limits of detection (MLD) ranged from 0.34?ng mL^?1 (cortisol) to 1.37?ng mL^?1 (THF). Intra- and inter-day coefficient of variation of the assay varied from1.5% (allo-THF) to 13% (tetrahydrocortisone) and from 3.6% (allo-THF) to 14.9% (tetrahydrocortisone), respectively. The method was applied for the analysis of urine samples from 53 healthy individuals with a mean age of 13.96?years in order to estimate the concentration of the five corticosteroids and the ratio of the metabolites. Associations between urinary cortisol/cortisone and serum cortisol/cortisone values were also characterized.     

Analysis of Cembranoids in Flue‐cured Tobacco by Accelerated Solvent Extraction and Gas Chromatography‐Mass Spectrometry‐Selected Ion Monitoring

An efficient and sensitive analytical method based on accelerated solvent extraction (ASE) and gas chromatography‐mass spectrometry‐selected ion monitoring (GC‐MS‐SIM) was developed and validated for analysis of cembranoids in flue‐cured tobacco leaves. Extraction efficiency of different pretreatment methods including liquid‐solid extraction (LSE), ultrasound‐assisted extraction (UAE), Soxlet extraction and accelerated solvent extraction (ASE) was compared and ASE was chosen as the optimal extraction method. During ASE procedure, effect of four parameters on extraction efficiency was considered and the experimental conditions were selected as follows: extraction solvent: dichloromethane; oven temperature: 50 °C; static time: 5 min and number of cycles: 2. Working standards of cembranoids were isolated by silica gel column chromatography and the identification was performed by mass spectrometry. Performance characteristics such as linearity, limit of detection (LOD), limit of quantitation (LOQ), precision and recovery were studied. The LOD and LOQ values were ranging from 5.0 × 10^?3 to 6.9 × 10^?3 μg/mL and 1.7 × 10^?2 to 2.3 × 10^?2 μg/mL for all analytes. At three different spiked levels, recoveries for CBT‐ol, α‐CBT‐diol and β‐CBT‐diol were 94.6%‐105.1%, 93.0%‐97.2% and 88.7%‐107.5% while the relative standard deviations (RSDs) were in the ranges of 3.9%‐6.2%, 1.8%‐8.7% and 1.7%‐6.0%, respectively. The proposed analytical methodology was successfully applied in the analysis of cembranoids in tobacco samples.     

Multi-determination of organic pollutants in water by gas chromatography coupled to triple quadrupole mass spectrometry

A multi-determination method has been developed for the determination and confirmation of 68 organic pollutants in water samples by gas chromatography coupled to triple quadrupole mass spectrometry (GC-MS/MS). The following chemical families were determined in a chromatographic run of less than 26?min: polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), polybrominated diphenylethers (PBDEs), and pesticides (organochlorine, organophosphorus, triazine and others). The sample preparation involved a liquid-liquid extraction (LLE) procedure, obtaining recoveries ranging from 70 to 130% when dichloromethane was used as the extracting solvent. The detection limits of the proposed method were between 0.75 and 19.8?ng?L^?1. Samples from the Maipo River in central Chile were taken from 29 different points. Seven pesticides and two PAHs were detected in field collected samples with concentrations ranging from 10 to 95?ngL^?1. Concentrations of benzo[a]pyrene in environmental samples ranged from 25 to 33?ngL^?1 and were near the maximum levels established by the European Union Directives (50?ng?L^?1).     

Simultaneous Determination of Atenolol and Chlorthalidone by LC–MS–MS in Human Plasma

A simple, sensitive, selective and rapid liquid chromatography–tandem mass spectrometry method was developed and validated for the simultaneous separation and quantitation of atenolol and chlorthalidone in human plasma using metoprolol and hydrochlorothiazide as internal standard. Following solid phase extraction, the analytes were separated by an isocratic mobile phase on a reversed-phase C₁₈ column and analyzed by MS in the multiple reaction-monitoring mode (atenolol in positive and chlorthalidone in the negative ion mode). The limit of quantitation for this method was 10 and 15 ng mL^?1 and the linear dynamic range was generally 10–2,050 ng mL^?1 and 15–3,035 ng mL^?1 for atenolol and chlorthalidone, respectively.     

Determination of polychlorinated biphenyls by liquid chromatography–atmospheric pressure photoionization–mass spectrometry

This study presents the atmospheric pressure photoionization (APPI) of high‐chlorinated (five or more chlorine atoms) polychlorinated biphenyls (PCBs) using toluene as dopant, after liquid chromatographic separation. Mass spectra of PCB 101, 118, 138, 153, 180, 199, 206 and 209 were recorded by using liquid chromatography‐APPI‐tandem mass spectrometry (LC‐APPI‐MS/MS) in negative ion full scan mode. Intense peaks appeared at m/z that correspond to [M ? Cl + O]^? ions, where M is the analyte molecule. Furthermore, a detailed strategy, which includes designs of experiments, for the development and optimization of LC‐APPI‐MS/MS methods is described. Following this strategy, a sensitive and accurate method with low instrumental limits of detection, ranging from 0.29 pg for PCB 209 to 8.3 pg for PCB 101 on column, was developed. For the separation of the analytes, a Waters XSELECT HSS T3 (100 mm × 2.1 mm, 2.5 µm) column was used with methanol/water as elution system. This method was applied for the determination of the above PCBs in water samples (surface water, tap water and treated wastewater). For the extraction of PCBs from water samples, a simple liquid–liquid extraction with dichloromethane was used. Method limits of quantification, ranged from 4.8 ng l^?1, for PCB 199, to 9.4 ng l^?1, for PCB 180, and the recoveries ranged from 73%, for PCB 101, to 96%, for PCB 199. The estimated analytical figures were appropriate for trace analysis of high‐chlorinated PCBs in real samples. Copyright © 2014 John Wiley & Sons, Ltd.     

Cloud point extraction of disulfiram for its HPLC-MS/MS determination in synthetic urine

A new simple cloud point extraction/preconcentration method was developed for the HPLCMS/MS determination of disulfiram in synthetic urine. Some parameters with an effect on the extraction, such as the concentration of Triton X-114, pH influence, incubation time, equilibration temperature and centrifuging parameters, were studied and optimised. The method proposed for the HPLC-MS/MS determination of disulfiram in synthetic urine with preliminary cloud point extraction was validated. The calibration curve was linear in the range of 0.025–15.4 ng mL?1. The limits of detection (3σ) and quantification (10σ) were 0.008 ng mL^?1 and 0.025 ng mL^?1, respectively. The matrix effect (96 %), recovery of the extraction procedure (95 %) and overall “process efficiency” (91 %) were also estimated. The results show that the sensitivity, metrological characteristics, ecological safety, simplicity and convenience of the suggested procedure exceed its analogues based on extraction using organic solvents.     

Simultaneous LC–MS–MS Analysis of Danshensu, Salvianolic Acid B, and Hydroxysafflor Yellow A in Beagle Dog Plasma, and Application of the Method to a Pharmacokinetic Study of Danhong Lyophilized Powder for Injection

A reliable and sensitive liquid chromatographic–tandem mass spectrometric method, with rutin as internal standard, has been developed and validated for simultaneous determination of danshensu, salvianolic acid B (SAB), and hydroxysafflor yellow A (HSYA) in beagle dog plasma. Plasma samples spiked with the analytes were extracted by solid-phase extraction and the analytes were separated on a 250 × 4.6 mm i.d., 5-μm particle, C₁₈ column with methanol–acetonitrile–0.5% formic acid 20:25:55 (v/v) as mobile phase at a flow rate of 1 mL min^?1. LC–MS–MS analysis was performed with a Finnigan TSQ triple-quadrupole tandem mass spectrometer operated in negative-ion selected-reaction-monitoring mode, using electrospray ionization. The accuracy and precision of the method were acceptable and linearity was good over the range 20–4,000 ng mL^?1 for danshensu, 50–10,000 ng mL^?1 for SAB, and 10–2,000 ng mL^?1 for HSYA. The method was successfully applied to a pharmacokinetic study of a traditional Chinese medicinal preparation, Danhong lyophilized powder for injection.     

LC–MS–MS Method to Simultaneously Determine Six Probe Drugs for CYP450 Isozymes in Human Liver Microsomes

Here, we report a rapid and specific method based on high-performance liquid chromatography coupled with tandem mass spectrometry (LC–MS–MS) capable of quantifying six CYP450-specific probe substrates in human liver microsomal incubation mixtures simultaneously. These analytes were prepared by single-step extraction and detected in one run by switching polarity of electrospray ionization mode three times. Following optimization of the chromatographic conditions, the peaks were well separated, and retention times ranged between 2.0 and 8.4 min. The total run time for a single injection was within 9 min. This method was fully validated over linear range of 18.8–3,000.0 ng mL^?1 for diclofenac, 0.8–3,000.0 ng mL^?1 for dapson, 1.5–3,000.0 ng mL^?1 for dextromethorphan, 2.0–4,000.0 ng mL^?1 for omeprazole, 75.0–3,000.0 ng mL^?1 for chlorzoxazone and 0.8–3,000.0 ng mL^?1 for phenacetin using diazepam as internal standard. Samples were prepared by protein precipitation and analyzed on the LC–MS–MS equipped with ESI interface. For each analyte, inter- and intra-day precision (RSD%) were <15 % and accuracy was within 85–115 %. The specificity, precision, accuracy, stabilities and matrix effect were evaluated.