Simultaneous Determination of Fluoroquinolones, Tetracyclines and Sulfonamides in Chicken Muscle by UPLC–MS–MS

A rapid and sensitive analytical method for the simultaneous determination of four fluoroquinolones, four tetracyclines and six sulfonamides in chicken muscle using ultra-performance liquid chromatography coupled to tandem mass spectrometry (UPLC–MS–MS) has been developed and validated. Samples were extracted with McIlvaine buffer-acetonitrile, defatted with n-hexane, and analyzed by UPLC–MS–MS. Solvent delay technique was applied in the analysis to remove the non-volatile phosphate and carry out farther on-line SPE clean-up. Satisfactory recoveries (55–110%) of all the veterinary drugs were demonstrated in 1, 10 and 20 μg kg^?1 spiked levels with the overall RSD for intra- and inter-day of 14 analytes less than 18%. The LOD and LOQ were 0.3 and 1.0 μg kg^?1, respectively. Quantitative results of 103 real samples indicated that the present method was suitable for the quantitative analysis of real samples.     

Validation of a hydrophilic interaction ultra‐performance liquid chromatography–tandem mass spectrometry method for the determination of gemcitabine in human plasma with tetrahydrouridine

A simple and reproducible bioanalytical method for the determination of gemcitabine in human plasma treated with tetrahydrouridine (THU) was developed and validated using a hydrophilic interaction ultra‐performance liquid chromatography with tandem mass spectrometry (UPLC‐MS/MS). To prevent deamination of gemcitabine, blood was treated with THU, and the plasma samples obtained after centrifugation were used in this study. Gemcitabine and gemcitabine‐¹³C, ¹⁵N₂ used as an internal standard, were extracted from human plasma treated with THU using a 96‐well Hybrid SPE‐Precipitation plate. Extracts were chromatographed on a hydrophilic interaction chromatography column with isocratic elution. Detection was performed using Quattro Premier with positive electrospray ionization multiple reaction monitoring mode. The standard curve ranged from 10 to 10,000 ng/mL without carryover. No significant interferences were detected in blank plasma and no interferences by 2′‐2′‐difluoro‐2′‐deoxyuridine, a metabolite of gemcitabine. Accuracy and precision in the intra‐batch reproducibility study using quality control samples with three THU levels did not exceed ±5.4 and 7.3%, respectively, and the inter‐batch reproducibility results also met the criteria. Stability of gemcitabine was ensured in whole blood and plasma as well as stability of THU in solutions. The UPLC‐MS/MS method developed was successfully validated and can be applied for gemcitabine bioanalysis in clinical studies. Copyright © 2015 John Wiley & Sons, Ltd.     

Solid-Phase Extraction Combined with UHPLC-MS/MS Method for Determination of Remifentanil in Human Whole Blood

A sensitive and reliable method have been developed and validated using solid phase extraction (SPE) combined with ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) to determine remifentanil in human blood. Quantification was performed by external standard calibration (r = 0.9991, n = 5). Remifentanil was separated on an ACQUITY UPLC BEH C18 column (50 mm × 2.1 mm, 1.7 µm) and analyzed in positive-ion electrospray-ionization (ESI +) mode. The mobile phase was methanol and water with a gradient elution program. The total run time was 4.5 min and injection volume was 5 μL. Limit of detection (LOD) and limit of quantitation (LOQ) were 0.20 ng/mL and 0.60 ng/mL, respectively. Remifentanil was eluted at 1.89 min. Recoveries of remifentanil ranged between 91.88%–93.79%. The intra-day and the inter-day precision (RSD) for remifentanil were 2.51%–3.48% and 2.76%–3.78%, respectively. The performance of the method was successfully verified for the determination of remifentanil in human blood.     

Simultaneous Determination of Paracetamol and Caffeine in Human Plasma by LC–ESI–MS

A rapid, selective and convenient liquid chromatography–mass spectrometric method for the simultaneous determination of paracetamol and caffeine in human plasma was developed and validated. Analytes and theophylline [internal standard (I.S.)] were extracted from plasma samples with diethyl ether-dichloromethane (3:2, v/v) and separated on a C₁₈ column (150 × 4.6 mm ID, 5 μm particle size, 100 Å pore size). The mobile phase consisted of 0.2% formic acid–methanol (60:40, v/v). The assay was linear in the concentration range between 0.05 and 25 μg mL^?1 for paracetamol and 10–5,000 ng mL^?1 for caffeine, with the lower limit of quantification of 0.05 μg mL^?1 and 10 ng mL^?1, respectively. The intra- and inter-day precision for both drugs was less than 8.1%, and the accuracy was within ±6.5%. The single chromatographic analysis of plasma samples was achieved within 4.5 min. This validated method was successfully applied to study the pharmacokinetics of paracetamol and caffeine in human plasma.     

Synthesis and Application of Histidine-Modified Poly(Glycidyl Methacrylate/Ethylene Glycol Dimethacrylate) Sorbent for Isolation of Caffeine from Black and Green Tea Samples

This work presents the synthesis of a polymeric mixed-mode solid-phase extraction (SPE) sorbent for clean-up and isolation of caffeine from black and green tea samples. The material was synthesized by a simple thermally initiated copolymerization of glycidyl methacrylate and ethylene glycol dimethacrylate. Further functionalization was executed with histidine (HIS). Functional groups were investigated by attenuated total-reflection infrared spectroscopy. Furthermore, nitrogen sorption porosimetry was executed and revealed surface areas of 90 m² g^??1. Adsorption capacities for caffeine were compared between functionalized and non-modified polymers and showed maximum capacities of 3.01 and 4.82 mg g^??1 polymer, respectively. Time adsorption profiles revealed an equilibrium adsorption after 15 min. The proposed polymer was used for SPE of black and green tea extracts and showed excellent clean-up efficiency for isolation of caffeine with recoveries ranging from 89 to 93%. When compared to commercially available Oasis HLB, the HIS-functionalized polymer demonstrated a distinctly better performance for clean-up. Finally, the proposed method was validated regarding international (ICH) guidelines and regulations.     

A highly sensitive caffeine immunoassay based on a monoclonal antibody

A new immunoassay has been developed based on a commercially available anti-caffeine monoclonal antibody and a de novo synthesized tracer, using horseradish peroxidase and UV–visible detection. Caffeine, which is frequently found in surface waters, can be quantified with a relative error lower than 20% for concentrations above 0.025 μg L^?1 (limit of quantitation, direct analysis). The limit of detection is 0.001 μg L^?1 and can be reduced by solid-phase extraction (SPE). Moreover, with minor adaptations, the assay can be used to quantify caffeine in several beverages, shampoo, and caffeine tablets. The results obtained by ELISA correlate well with those from liquid chromatography–tandem mass spectrometry (LC–MS–MS) for the tested matrices. Several surface waters from Berlin were analysed and all tested positive for caffeine, with concentrations higher than 0.030 μg L^?1. In one run 66 samples can be analysed within 2 h.

Applications of a Novel Sample Preparation Method for the Determination of Sulfonamides in Edible Meat by CZE

A simple, rapid and reliable method based on SPE clean-up and CZE separation was validated for the trace determination of sulfonamides (SAs) in meat. Acetonitrile was used for the extraction of SAs (sulfamethoxazole, sulfamethazine, sulfamerazine, and sulfadimethoxine) from the samples and 1-propanol was used for the denaturing of the proteins present in the sample matrix. SPE procedure was employed for the clean-up and pre-concentration of SAs prior to CZE analysis. Complete separation was achieved by using 45 mmol L^?1 phosphate buffer (pH = 6.3) at an applied voltage of 20 kV. Overall obtained recoveries were from 83.3 to 94.5% for the SAs. The detection limit of each sulfonamide ranges from 4 to 6 μg kg^?1. The presented one step SPE clean-up method is highly applicable for the determination of the SAs at a residue level below the maximum residue limit.     

Development of a Flow Injection Manifold for Napropamide Determination by Photo-Induced Chemiluminescence

A new, rapid, and simple method is proposed for the determination of the pesticide napropamide by photo-induced chemiluminescence detection coupled with a flow injection analysis (FIA) system. The emission was obtained by oxidation with periodate in basic medium, of the photoproducts generated on-line by UV irradiation (254 nm) of napropamide in acidic SDS (sodium dodecyl sulfate) medium. The flow method, in combination with the solid phase extraction (SPE) performed off-line with C₁₈ cartridges, allowed the determination of this pesticide over the 0.8–14.0 µ gL^?1 range, with a limit of detection of 0.3 µ gL^?1. The relative standard deviation (n = 9) at 2.5 µ gL^?1 level was 4.3% for the combined FIA-SPE system. After testing the influence of several potential interfering compounds, including ions and other pesticides, the method was successfully applied to the determination of napropamide in spiked water samples with recoveries between 96–103%.     

Validated UPLC‐MS/MS method for determination of moclobemide in human brain cell supernatant and its application to bidirectional transport study

A simple and sensitive analytical method based on ultraperformance liquid chromatography–tandem mass spectrometry (UPLC‐MS/MS) has been developed for determination of moclobemide in human brain cell monolayer as an in vitro model of blood–brain barrier. Brucine was employed as the internal standard. Moclobemide and internal standard were extracted from cell supernatant by ethyl acetate after alkalinizing with sodium hydroxide. The UPLC separation was performed on an Acquity UPLC^TM BEH C₁₈ column (50 × 2.1 mm, 1.7 µm, Waters, USA) with a mobile phase consisting of methanol–water (29.5:70.5, v/v); the water in the mobile phase contained 0.05% ammonium acetate and 0.1% formic acid. Detection of the analytes was achieved using positive ion electrospray via multiple reaction monitoring mode. The mass transitions were m/z 269.16 → 182.01 for moclobemide and m/z 395.24 → 324.15 for brucine. The extraction recovery was 83.0–83.4% and the lower limit of quantitation (LLOQ) was 1.0 ng/mL for moclobemide. The method was validated from LLOQ to 1980 ng/mL with a coefficient of determination greater than 0.999. Intra‐ and inter‐day accuracies of the method at three concentrations ranged from 89.1 to 100.9% for moclobemide with precision of 1.1–9.6%. This validated method was successfully applied to bidirectional transport study of moclobemide blood–brain barrier permeability. Copyright © 2013 John Wiley & Sons, Ltd.     

Development of a mesoporous silica based solid-phase extraction and ultra-performance liquid chromatography–MS/MS method for quantifying lignans in Justicia procumbens

Justicia procumbens is a food and medicine homologous variety, popularly used for making vegetable soups. In this study, a novel mesoporous silica was synthesized and used as the sorbent of SPE for the purification of lignans from J. procumbens. A laboratory-made SPE cartridge was packed with 100 mg of mesoporous silica, which was washed with 10% methanol and eluted using 0.8 mL acetonitrile after sample loading. Afterward, the extract was analyzed by ultra-performance liquid chromatography (UPLC) and MS/MS. All the lignans were efficiently separated in 6 min with the noise level in the range of 50–150 cps. 6′-Hydroxy justicidin B, 6′-hydroxy justicidin A, justicidin B, chinensinaphthol methyl ether, justicidin C, and neojusticdin A were identified to be the dominant molecular species in J. procumbens with contents of 0.065−0.37 mg/g in three tested sample batches from different geographic origins. In conclusion, the proposed mesoporous silica based SPE UPLC–MS/MS method is efficient in linearity (R² = 0.9989−0.9996), sensitivity (LOD ≤0.13 μg/kg and LOQ ≤0.42 μg/kg), precision (RSD_intra-day ≤3.12 and RSD_inter-day ≤4.56), and recovery (83.42−96.11%, RSD ≤2.88%).     

Flow injection determination of cyromazine in natural water samples using diperiodatoargentate(III)–H2SO4–chemiluminescence system

A simple and sensitive chemiluminescence (CL) procedure is proposed for the determination of cyromazine (CYR) using flow injection technique. CYR has strong enhancing effect on the CL reaction of diperiodatoargentate-(III) complex (DPA) in H₂SO₄ medium. The CL intensity with solid phase extraction (SPE) technique and with and without using online ion exchange resin column (IERC; OH-form) was proportional to the concentration of CYR over the range 0.1–200, 10–1000 and 2–2500 µg L^–1 (R² = 0.9974, 0.9980 and 0.9990, n = 7 each), respectively. Under the conditions, the limits of detection (S/N = 3) 0.029, 2.5 and 0.5 µg L^–1, relative standard deviations (n = 3) 1.9–3.6%, 1.4–2.7% and 1.0–3.0% and sample throughputs were 120, 80 and 120 h^–1. The effect of reagents concentration, flow rate, sample loop volume, photomultiplier voltage and IERC length was optimised. The mean results for natural water samples analysed by the proposed method were not significantly different at 95% confidence limit with the previously reported HPLC method. Interference from chloride ions could be eliminated by using SPE procedure or incorporating an in-line IERC. The CL mechanism of DPA–H₂SO₄–CYR system was also discussed briefly.     

Simultaneous Determination of Carbamazepine and its Active Metabolite Carbamazepine-10,11-epoxide in Human Plasma by UPLC

A simple method for the determination of carbamazepine and its active metabolite carbamazepine-10,11-epoxide by ultra performance liquid chromatography (UPLC) with ultraviolet absorbance detection (TUV) was developed. The method involves a two-step protein precipitation by liquid–liquid extraction. Phenytoin sodium was used as the internal standard. The separation was carried out on Acquity C18 column with acetonitrile:methanol:KH₂PO₄ buffer (adjusting pH to 4.6 with 85% o-phosphoric acid) (180/180/170, v/v/v) as the mobile phase at a flow rate of 0.4 mL min⁻¹. Linear detection response was obtained for concentrations ranging from 50 to 5,000 ng mL⁻¹. The limit of quantification (LOQ) was 50 ng mL⁻¹. The method was validated successfully for the determination of carbamazepine and its active metabolite carbamazepine-10,11-epoxide, which can be applied through pharmacokinetics and bioequivalence studies.

     

Quantitative Determination of Allicin in Allium sativum L. Bulbs by UPLC

An UPLC method for determination of allicin in garlic bulb powder has been developed and validated. Chromatographic separation and determination were performed on an Acquity UPLC BEH C₁₈ column using a mobile phase of methanol/water (50:50, v/v). Linearity between the allicin concentration and the peak area was good within the concentration ranges 2.04–510 mg L⁻¹. The method was validated over this range for both accuracy and precision. The method was successfully used for the quantitative analysis of allicin in ten garlic varieties.

     

A molecular imprint-coated stirrer bar for selective extraction of caffeine, theobromine and theophylline

We have prepared a novel caffeine imprinted polymer on a stir bar that can be used for selective extraction of caffeine, theobromine and theophylline from beverages. The polymerization time and quantities of reagents (template, cross-linker, porogenic solvent) were optimized. The morphology of the molecularly imprinted polymer-coating was studied by scanning electron microscopy and Fourier transform IR spectroscopy. A rapid and sensitive method was worked out for the extraction of caffeine, theobromine and theophylline from beverages by using the molecularly imprinted stir bar followed by HPLC analysis. The effects of extraction solvent, stirring speed, desorption solvent, adsorption and desorption time were optimized. The method displays a linear response in the 5–150 μg L^?1 caffein concentration range, with a correlation coefficient of >0.9904. The recoveries for three analytes in tea, carbonated and functional beverages were 91–108 %, 90–110 % and 93–109 %, with relative standard deviations ranging from 3.6–5.7 %, 3.5–7.9 % and 3.2–7.9 %, respectively.

Trace Determination of Manganese in Urine by Graphite Furnace Atomic Absorption Spectrometry and Inductively Coupled Plasma–Mass Spectrometry

This paper describes a simple and sensitive method for the determination of manganese in human urine by graphite furnace atomic absorption spectroscopy (GFAAS), which includes sample preparation by microwave digestion. Matrix modifier combinations, the digestion power, pyrolysis, and atomization temperatures were optimized. A mixture of 5.0 µg Pd(NO₃)₂ and 3.2 µg Mg(NO₃)₂ modifier presented the best performance. The optimal temperatures for pyrolysis and atomization were 1500°C and 1950°C, respectively. The GFAAS method was compared to inductively coupled plasma–mass spectrometry (ICP–MS) for the determination of manganese in urine. Analytical figures of merit for GFAAS and ICP–MS were: accuracy (3.46%, 2.19%), precision (3.61%, 5.84%), LOD (0.109 µg · L^?1, 0.015 µg · L^?1), LOQ (0.327 µg · L^?1, 0.045 µg · L^?1), and recovery (80–100%, 74–89%). Both methods were employed for the determination of Mn in urine and the results were compared statistically.     

High-performance liquid chromatography with fluorescence detection and ultra-performance liquid chromatography with electrospray tandem mass spectrometry method for the determination of indoleamine neurotransmitters and their metabolites in sea lamprey plasma

We present a comparison of two sensitive methods, HPLC with fluorescence detector (HPLC/FLD) and UPLC with electrospray tandem mass spectrometry (UPLC/MS/MS), for the determination of indoleamine neurotransmitters (NTs) and their metabolites in sea lamprey plasma samples. Liquid–liquid extraction (LLE) and solid-phase extraction (SPE) were also tested for recovery and matrix effect. The recoveries of SPE determined by HPLC/FLD and UPLC/MS/MS ranged from 75 to 123% and 78 to 105%, respectively, while the recoveries of LLE ranged from 45 to 73% and 48 to 75%, respectively. SPE combined with HPLC/FLD and UPLC/MS/MS to determine the target analytes in plasma samples were validated of the sensitivity, reproducibility, accuracy and precision. Both methods exhibited excellent linearity in the range of 0.2–50 ng mL⁻¹ for all analytes. The limits of detection (LOD) varied from 0.04 ng mL⁻¹ to 0.13 ng mL⁻¹ for HPLC/FLD method and 0.003 ng mL⁻¹ to 0.02 ng mL⁻¹ for UPLC/MS/MS method. The inter-day accuracy ranged from 82.5 to 127.0% for HPLC/FLD and 93.0 to 113.0% for UPLC/MS/MS. The inter-day precision ranged from 9.9 to 32.3% for HPLC/FLD and 5.4 to 13.2% for UPLC/MS/MS. These results demonstrated that the values obtained by both methods were within the satisfactory range and the UPLC/MS/MS method provided more accurate and precise measurements than HPLC/FLD method. The comparison is of great importance to determine the available detectors, considering the complexity and expensiveness versus quality parameters. These two methods were applied to the analysis of four important indoleamine neurotransmitter analytes (5-hydroxytryptamine, 5-hydroxyindole-3-acetic acid, tryptamine and melatonin) in sea lamprey plasma samples.     

Validation of an ultra‐performance liquid chromatography–tandem mass spectrometry method for the determination of flecainide in human plasma and its clinical application

A simple and reproducible bioanalytical method for the determination of flecainide in human plasma was developed and validated using an ultra‐performance liquid chromatography with tandem mass spectrometry (UPLC‐MS/MS) to obtain higher sensitivity than the current available methods. After simple protein precipitation, flecainide and a stable isotope‐labeled internal standard (IS) were chromatographed on an Acquity UPLC BEH C₁₈ column (2.1 × 100 mm, 1.7 µm) with isocratic elution of mobile phase consisting of 45% methanol containing 0.1% formic acid at a flow rate 0.25 mL/min. Detection was performed in positive electrospray ionization by monitoring the selected ion transitions at m/z 415.4/301.1 for flecainide and m/z 419.4/305.1 for the IS. The method was validated according to current bioanalytical method validation guidelines. The calibration standard curve was linear from 2.5 to 1000 ng/mL using 0.1 mL of plasma. No significant interferences were detected in blank human plasma. Accuracy and precision in the intra‐ and inter‐batch reproducibility study were within acceptance criteria. Neither hemolysis effects nor matrix effects were observed. The UPLC‐MS/MS method developed was successfully applied to determine plasma flecainide concentrations to support clinical studies and incurred sample reanalysis also ensured the reproducibility of the method. Copyright © 2015 John Wiley & Sons, Ltd.     

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.     

Determination of Chloramphenicol in Milk Using a QuEChERS-Based on Liquid Chromatography Tandem Mass Spectrometry Method

A quantitative method for the determination of chloramphenicol in milk samples was developed based on the QuEChERS (quick, easy, cheap, effective, rugged, and safe) approach for liquid chromatography–tandem mass spectrometry (LC–MS/MS). Homogenized milk samples were extracted with acetonitrile. The partitioning step was performed after the addition of magnesium sulfate and sodium chloride. Chloramphenicol was determined using the electrospray negative ionization mode with tandem mass spectrometry. The procedure was validated according to the requirements of Commission Decision 2002/657/EC. The apparent recovery ranged from 90% to 110% and within-laboratory reproducibility was lower than 12%. The calculated limit of decision was 0.10 μg kg^?1 and the detection capability was 0.15 μg kg^?1. Validation results demonstrated that this method fulfills criteria for the determination of chloramphenicol in milk.     

Total Sulfur Dioxide Determination in Red Wine by Suppressed Ion Chromatography with In-Sample Oxidation and SPE

Suppressed ion chromatography (IC) based on in-sample oxidation and SPE is described for total sulfur dioxide determination in red wines. In this method, sulfur dioxide was converted to stable sulfate ion through a simple H₂O₂ oxidation step and then the impurities were removed with C-18 micro-column SPE pretreatment. Finally, the sulfate was determined by suppressed ion chromatography coupled with conductivity detection and the content of total sulfur dioxide could be obtained through sulfate content by blank deduction method. By using a mixture of NaHCO₃ and Na₂CO₃ as mobile phase, the analysis of one sample with nine anions could be completed within 25 min. For sulfate detection, a linear calibration curve with correlation coefficient of 0.9993 was obtained from the peak area with low detection limit (0.45 mg L^?1, 3σ) and excellent repeatability (RSD?=?1.12%, n?=?6). This method was applied to sulfur dioxide determination in real wine samples and compared with conventional iodometry.