N-(1-Naphthyl)ethylenediamine, a New UV Labeling Reagent Used for LC Determination of Valproic Acid in Human Plasma

A high performance liquid chromatography method is presented for the determination of valproic acid levels in human plasma. The method was based on pre-column derivatization using N-(1-naphthyl)ethylenediamine as a new labeling agent. The calibration curve was linear in the investigated concentration range between 0.1 and 100 μg mL^?1 and showed good accuracy and reproducibility. The assay provided a limit of quantification of 0.1 μg mL^?1 for valproic acid and a limit of detection of 10 ng mL^?1, respectively. The presented method was successfully applied to the determination of valproic acid levels in plasma after oral administration of 600 or 800 mg of sodium valproate.     

Simultaneous derivatization and extraction of iodine from milk samples by hollow fiber liquid-phase microextraction followed by gas chromatography-electron capture detection

A simple, low-cost and sensitive method is demonstrated for derivatization and extraction of iodine from milk samples using hollow fiber liquid-phase microextraction (HF-LPME) and gas chromatography-electron capture detection. Iodide ions are converted to iodine under acidic medium and in the presence of an oxidant. The generated iodine reacted with 3-pentanone in extraction vial to give 2-iodo-3-pentanone and was extracted into 4 μL of 1-octanol located in the lumen of a hollow fiber. Organic solvent was selected using one variable at a time optimization method and the other main factors affecting derivatization and HF-LPME procedures were evaluated using a Taguchi’s L₁₆ (4⁵) orthogonal array. Under optimal conditions, the method showed low limit of detection (0.5 ng mL^?1), wide linear range (1–2,000 ng mL^?1) with good correlation coefficient (0.9997) and acceptable relative standard deviation (4.6 %, n = 5). Finally, the developed method was successfully applied for determination of iodide in real samples including infant milk formulas and cow milk with reasonable relative recoveries (99.8–110.5 %).     

Determination of Pantoprazole, Rabeprazole, Esomeprazole, Domperidone and Itopride in Pharmaceutical Products by Reversed Phase Liquid Chromatography Using Single Mobile Phase

A simple, sensitive, and precise high performance liquid chromatographic method for the analysis of pantoprazole, rabeprazole, esomeprazole, domperidone and itopride, with ultraviolet detection at 210 nm, has been developed, validated, and used for the determination of compounds in commercial pharmaceutical products. The compounds were well separated on a Hypersil BDS C18 reversed-phase column by use of a mobile phase consisting of 0.05 M, 4.70 pH, potassium dihydrogen phosphate buffer - acetonitrile (720:280 v/v) at a flow rate of 1.0 mL min^?1. The linearity ranges were 400–4,000 ng mL^?1 for pantoprazole, 200–2,000 ng mL^?1 for rabeprazole, 400–4,000 ng mL^?1 for esomeprazole, 300–3,000 ng mL^?1 for domperidone and 500–5,000 ng mL^?1 for itopride. Limits of detection (LOD) obtained were: pantoprazole 147.51 ng mL^?1, rabeprazole 65.65 ng mL^?1, esomeprazole 131.27 ng mL^?1, domperidone 98.33 ng mL^?1 and itopride 162.35 ng mL^?1. The study showed that reversed-phase liquid chromatography is sensitive and selective for the determination of pantoprazole, rabeprazole, esomeprazole, domperidone and itopride using single mobile phase.     

Development and Validation of an RP–LC–UV Method for the Determination of Ondansetron: Application to Pharmaceutical Dosage Forms

A new, simple, rapid, sensitive and specific isocratic RP–LC–UV method was developed and validated for the determination of ondansetron in pharmaceutical dosage forms of orally disintegrating tablets, oral solution and injection. The LC separation was achieved on a Hypersil C4 column (250 × 4.6 mm, 5 μm) using a mobile phase of 50 mM potassium dihydrogen phosphate anhydrous adjusted to pH 3.5 with orthophosphoric acid and acetonitrile (30:70, v/v) at a flow rate of 1.0 mL min^?1 and UV detection at 310 nm. The method was validated for specificity, linearity, precision, accuracy, limit of quantification, limit of detection, robustness and solution stability. The calibration curve was linear over a concentration range of 100–1,000 ng mL^?1 (r ²  = 0.9996) with limit of detection and limit of quantification 50 and 100 ng mL^?1, respectively. The intra-day and inter-day precision and accuracy were between 0.79 and 2.37% and ?0.64 and 1.65%, respectively. The method was successfully applied for analysis of ondansetron in the presence of excipients in commercially available pharmaceutical dosage forms.     

Highly Sensitive LC Method with Automated Co-Sense System and Fluorescence Detection for Determination of Sertraline in Human Plasma

A highly sensitive LC method with column-switching “Co-sense” system and fluorescence detection has been proposed for trace determination of sertraline in human plasma. A simple pre-column derivatization procedure with 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole reagent was employed. Fluxetine was used as an internal standard. Under the optimum chromatographic conditions, a linear relationship with good correlation coefficient (r = 0.9997) was found between the peak area ratio and sertraline concentration in the range of 5–5,000 ng mL^?1. The limit of detection and limit of quantitation were 1.41 and 4.28 ng mL^?1, respectively. The intra- and inter-assay precisions were satisfactory; the relative standard deviations did not exceed 5.63%. The accuracy of the method was proved; the recovery of sertraline from the spiked human plasma was 99.76–102.62 ± 2.19–5.63%. The proposed method had high throughput as the analysis involved simple sample pre-treatment procedure and short run-time (~12 min). The results demonstrated that the method would have a great value if applied in bioavailability and pharmacokinetic studies for sertraline.     

Development and Validation of an Stability Indicating RP-LC Method for Determination of Imatinib Mesylate

A new, sensitive and stability indicating liquid chromatographic method has been developed for the determination of imatinib mesylate (IM). Efficient chromatographic separation was achieved using a C₁₈ column with simple mobile phase combination delivered in an isocratic mode and quantitation was carried out using ultraviolet detection. For the first time, a novel microwave assisted degradation procedure was employed for stress testing studies. In addition, orthogonal separation technique was applied to demonstrate selectivity of the proposed method. The method has demonstrated excellent linearity over the range of 25–1,600 ng mL^?1. Moreover, the method was found to be sensitive with a low limit of detection (3.35 ng mL^?1) and limit of quantitation (10.16 ng mL^?1). The method has shown good and consistent recoveries (99.35–100.69%) with low intra- and inter-day relative standard deviation (RSD) (<2.5%). Experimental design confirmed that peak area was unaffected by small changes in critical factors, in robustness study. The validated method was successfully applied for determination of IM in pharmaceutical formulations.     

A novel chemiluminescence reaction system for the determination of lincomycin with diperiodatonickelate(IV)

A sensitive and high selective chemiluminescence (CL) method was developed for the determination of lincomycin in acid medium using diperiodatonickelate as a reagent. The mechanism leading to luminescence is discussed by comparing the spectra of fluorescence and CL. Relative CL intensity is linear in the range from 8.0 ng mL^?1 to 1.0 µg mL^?1, the limit of detection is 2.5 ng mL^?1 (3σ), and the relative standard deviation is 4.0% at 0.1 µg mL^?1 of lincomycin (n?=?7). The method was successfully applied to the determination of lincomycin in injections, human urine, and in serum samples.     

Simultaneous Quantitation of Paracetamol, Pseudoephedrine and Chlorpheniramine in Dog Plasma by LC-MS-MS

A simple, rapid and sensitive liquid chromatography/electrospray tandem mass spectrometry quantitative detection method, using amantadine as internal standard, was developed for the simultaneous analysis of paracetamol, pseudoephedrine and chlorpheniramine concentrations. Analytes were extracted from plasma samples by liquid–liquid extraction with n-hexane–dichloromethane–2-propanol (2:1:0.1, v/v), separated on a C18 reversed-phase column with 0.1% formic acid–methanol (40:60, v/v) and detected by electrospray ionization mass spectrometry in positive multiple reaction monitoring mode. Calibration curves for plasma were linear over the concentration range 10–10,000 ng mL^?1 of paracetamol, 2–2,000 ng mL^?1 of pseudoephedrine and 0.2–200 ng mL^?1 of chlorpheniramine. The method has a lower limit of quantitation of 10 ng mL^?1 for paracetamol, 2.0 ng mL^?1 for pseudoephedrine and 0.2 ng mL^?1 for chlorpheniramine. Recoveries, precision and accuracy results indicate that the method was reliable within the analytical range, and the use of the internal standard was very effective for reproducibility by LC-MS-MS. This method is feasible for the evaluation of pharmacokinetic profiles of a novel multicomponent sustained release formulation containing 325 mg of paracetamol, 30 mg of pseudoephedrine hydrochloride and 2 mg of chlorpheniramine maleate. It is the first time the pharmacokinetic evaluation of a novel sustained-action formulation containing paracetamol, pseudoephedrine and chlorpheniramine has been elucidated in vivo using LC-MS-MS.     

LC–MS/MS Determination of Catecholamines in Urine Using FMOC-Cl Derivatization on Solid-Phase Extraction Cartridge

A method for the determination of catecholamine derivatives in human urine is proposed that includes the derivatization of target compounds on a solid-phase extraction cartridge and determination of the analytes by a UHPLC method with tandem mass-spectrometric detection. 9-Fluorenyl-methoxycarbonyl chloride was used as the derivatization agent. The limits of detection for the analytes were 2.5 ng mL^?1 for 9-fluorenyl-methoxycarbonyl-adrenaline, 5 ng mL^?1 for 9-fluorenyl-methoxycarbonyl-octopamine, and 25 ng mL^?1 for 9-fluorenyl-methoxycarbonyl-dopamine. The proposed procedure was tested on real samples obtained from volunteers.     

Development and Validation of Atorvastatin by LC–ESI–MS and Application in Bioequivalence Research in Healthy Chinese Volunteers

The aim of this research was to develop a sensitive liquid chromatographic–electrospray ionization–mass spectrometric (LC–MS) method for direct measurement of the concentration of Atorvastatin in human plasma. Plasma samples (1 mL) were extracted with 3 mL ethyl acetate, and by a simple reversed-phase chromatography. Pitavastatin was used as internal standard (IS). The LOQ was 0.25 ng mL^?1 (RSD 4.24%). The assay was linear from 0.25–20 ng mL^?1. And the correlation coefficient for the calibration regression line was 0.9996 or better. Intra-day and inter-day accuracy were better than 15%. The method has been successfully used for a pharmacokinetic study with human subjects. A two-period crossover designed bioequivalence research was also progressed in healthy Chinese volunteers. Among the pharmacokinetic data obtained, T _max was 1.36 ± 0.68 h for reference formulation and 0.81 ± 0.54 h for test formulation. C _max was 8.54 ± 5.06 ng mL^?1 for reference formulation and 9.54 ± 3.68 ng mL^?1 for test formulation. t _1/2 was 8.50 ± 2.74 h for reference formulation and 9.24 ± 3.17 h for test formulation. AUC _0?48h was 54.77 ± 21.82 h ng mL^?1 for reference formulation and 55.66 ± 20.91 h ng mL^?1 for test formulation. The method was successfully applied to the study of pharmacokinetics of Atorvastatin in healthy Chinese volunteers.     

Determination of 5-Hydroxytryptamine, Norepinephrine, Dopamine and Their Metabolites in Rat Brain Tissue by LC–ESI–MS–MS

A liquid chromatography–electrospray ionization tandem mass spectrometry method has been developed to perform the determination of 5-hydroxytryptamine (5-HT), norepinephrine (NE), dopamine (DA) and their metabolites, i.e., 5-hydroxyindole-3-acetic acid (5-HIAA), 4-hydroxy-3-methoxyphenylglycol (MHPG) sulfate, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in rat brain tissue. Analytes were separated on a Thermo C₁₈ column (4.6 mm × 250 mm, 5 μm, SN: 1245575T, Thermo electron corporation, USA) with a mobile phase of 0.05% formic acid/acetonitrile (92:8 for ESI⁺, 82:18 for ESI^?, v/v) at the flow-rate of 0.8 mL min^?1. The LC system was coupled to a Waters Micromass Quattro Premier XE tandem quadruple mass spectrometer. MS acquisition of 5-HT, NE and DA was performed in positive electrospray ionization multiple reaction monitoring (MRM) mode, while negative electrospray ionization MRM mode was used to monitor their metabolites. The calibration curves were linear within the concentration range of 4–4,450 ng mL^?1 for 5-HT, 4–4,110 ng mL^?1 for NE and 4–4,100 ng mL^?1 for DA (r ≥ 0.999). The limit of quantitation was 4 ng mL^?1. 5-HIAA, MHPG, DOPAC and HVA have good linearity within the range of 12–1,000 ng mL^?1(r ≥ 0.998) and the limit of quantitation was 12 ng mL^?1. The intra- and inter-day RSD were lower than 8.45%. The method is sensitive, fast, accurate and usable for quantity determination of monoamine neurotransmitters and their metabolites in neuropsychiatric diseases.     

An Experimental Design Approach to Selecting the Optimum LC Conditions for the Determination of Local Anaesthetics

A sensitive high performance liquid chromatographic (HPLC) method has been developed and validated for the simultaneous determination of four local anaesthetics: lidocaine, proparacaine, bupivacaine and oxybuprocaine. A full factorial design was used. The chromatographic separation was achieved using a Bondesil C₈ (4.6 × 2.5 mm i.d., particle size 5 μm) analytical column. An optimised mobile phase consisted of acetonitrile and sodium dihydrogen phosphate (pH = 3.0, 20 mM) (30:70, v/v) at a flow rate of 1.2 mL min^?1. Local anaesthetics detection was performed by UV-Vis detector at 220 nm. The retention times for lidocaine, proparacaine, bupivacaine and oxybuprocaine were 5.74, 9.28, 16.84 and 26.26 min, respectively. HPLC-UV-Vis method was linear in the range of 50–5,000 ng mL^?1 for lidocaine and proparacaine and 100–5,000 ng mL^?1 for bupivacaine and oxybuprocaine. The limit of detection (LOD) was 25 ng mL^?1 for lidocaine, proparacaine and 30 ng mL^?1 for bupivacaine and oxybuprocaine. The limit of quantification (LOQ) was found to be 50 ng mL^?1 for lidocaine, proparacaine and 100 ng mL^?1 for bupivacaine, oxybuprocaine. In intra-day and inter-day precision and accuracy analysis, the relative standard deviation was found to be less than 8%.     

Simultaneous Determination of Ebastine and Its Active Metabolite (Carebastine) in Human Plasma Using LC–MS–MS

A sensitive and rapid LC–MS–MS method was developed for the simultaneous determination of ebastine and carebastine in human plasma. Solid-phase extraction was used to isolate the compounds from the biological matrix followed by separation on a Symmetry C18 column under isocratic conditions. The mobile phase was 10 mM ammonium formate in water/acetonitrile (40:60, v/v). Detection was carried out using a triple-quadrupole mass spectrometer in positive electrospray ionization and multiple reaction monitoring mode. The method was fully validated over the concentration range of 0.1–10 ng mL^?1 for ebastine and 0.2–200 ng mL^?1 for carebastine in human plasma, respectively. The lower limit of quantification (LLOQ) was 0.1 ng mL^?1 for ebastine and 0.2 ng mL^?1 for carebastine. For ebastine and carebastine inter- and intra-day precision (CV%) and accuracy values were all within ±15% and 85–115%, respectively. The extraction recovery was on average 60.0% for ebastine and 60.3% for carebastine.     

An Accurate Assay for Simultaneous Determination of Irinotecan and Its Active Metabolite SN-38 in Rat Plasma by LC with Fluorescence Detection

An accurate LC method was developed and validated for simultaneous determination of irinotecan (CPT-11) and its active metabolite SN-38 in rat plasma. Plasma samples were pretreated with 0.4 g mL^?1 sodium dodecyl sulfate to inactive the carboxylesterase and avoid the conversion of CPT-11 to SN-38. Chromatographic separation was achieved on a Diamaonsil C₁₈ column using acetonitrile–50 mM phosphate buffered solution (30:70, v/v) at pH 4.0 as the mobile phase with the flow rate of 1 mL min^?1. The linear quantitation ranges for CPT-11 and SN-38 were 5.05–3,030 and 3.15–315 ng mL^?1 with r ² > 0.99, respectively. The lower limit of quantification (LLOQ) was 2.33 ng mL^?1 for CPT-11 and 0.26 ng mL^?1 for SN-38 with intra- and inter-day relative standard deviation of <12% and the accuracy values of >90%. The method was proved to be accurate and sensitive enough and was successfully applied to a pharmacokinetic study of CPT-11 in rats.     

Magnetic Nanoparticle-Based Micro-Solid Phase Extraction and GC�CMS Determination of Oxadiargyl in Aqueous Samples

A new facile, rapid, inexpensive, and sensitive method based on magnetic micro-solid phase extraction (M-??-SPE) coupled to gas chromatography?Cmass spectrometry (GC?CMS) was developed for determination of the herbicide oxadiargyl in environmental water samples. The feasibility of employing non-modified magnetic nanoparticles (MNPs) as sorbent was examined and applied to perform the extraction process. Influential parameters affecting the extraction efficiency along with desorption conditions were investigated and optimized. The limit of detection (LOD, S/N = 3) and limit of quantification (LOQ, S/N = 10) of the method under optimized conditions were 0.005 and 0.030 ng mL^?1, respectively. The relative standard deviations (RSD) (n = 3) at a concentration of 0.10 ng mL^?1 was 11%. The calibration curve of oxadiargyl showed linearity in the range of 0.050?C0.50 ng mL^?1. The developed method was successfully applied to the extraction of oxadiargyl from spiked tap water and Zayande-Rood River water samples and the relative recoveries of 98 and 94% were obtained, respectively.     

Development and Validation of an Stability Indicating RP-LC Method for Determination of Imatinib Mesylate

A new, sensitive and stability indicating liquid chromatographic method has been developed for the determination of imatinib mesylate (IM). Efficient chromatographic separation was achieved using a C₁₈ column with simple mobile phase combination delivered in an isocratic mode and quantitation was carried out using ultraviolet detection. For the first time, a novel microwave assisted degradation procedure was employed for stress testing studies. In addition, orthogonal separation technique was applied to demonstrate selectivity of the proposed method. The method has demonstrated excellent linearity over the range of 25–1,600 ng mL⁻¹. Moreover, the method was found to be sensitive with a low limit of detection (3.35 ng mL⁻¹) and limit of quantitation (10.16 ng mL⁻¹). The method has shown good and consistent recoveries (99.35–100.69%) with low intra- and inter-day relative standard deviation (RSD) (<2.5%). Experimental design confirmed that peak area was unaffected by small changes in critical factors, in robustness study. The validated method was successfully applied for determination of IM in pharmaceutical formulations.

     

GC Determination of Famotidine,Ranitidine, Cimetidine,and Metformin in Pharmaceutical Preparations and Serum Using Methylglyoxal as Derivatizing Reagent

A capillary gas chromatography (GC) procedure has been developed for the determination of four pharmaceutical preparations (famotidine, ranitidine, cimetidine, and metformin) after precolumn derivatization with methylglyoxal (MGo). GC was carried out using an HP-5 column (30 m × 0.32 mm id) at an initial column temperature of 90 °C for 2 min, followed by heating rate of 25 °C min⁻¹ up to 265 °C. Nitrogen flow rate was 2.5 mL min⁻¹ with split ratio 10:1. A linear calibration curve was obtained within 50–1,000 ng mL⁻¹ and the limit of detection (LOD) was within 17–25 ng mL⁻¹. The derivatization, GC elution, and separation were repeatable in terms of retention time and peak height/peak area with relative standard deviation within ±4.6 %. The procedure was applied to the determination of the drugs in pharmaceutical preparations and the sera of volunteers who were given oral doses of the drugs. The results of the analysis agreed with the labeled values of the pharmaceutical preparations and were 147–4,903 ng mL⁻¹ in serum with an RSD within 1.0–4.2 %, after ingestion of a single dose of 40–500 mg of active ingredient in a tablet.

     

Enantioselective Separation and Determination of Carnosine in Rat Plasma by Fluorescence LC for Stereoselective Pharmacokinetic Studies

A sensitive fluorescence liquid chromatographic analytical method was developed for the simultaneous determination of carnosine enantiomers in rat plasma. The method was applied to pharmacokinetic studies. Chiral separation of carnosine enantiomers was achieved by pre-column derivatization with o-phthaldialdehyde and the thiol N-acety-l-cysteine as derivating reagents. They were separated on an ODS column and detected by fluorescence detection (λ_ex = 350 nm, λ_em = 450 nm). γ-Aminobutyric acid was used as internal standard. The method was linear up to 6,000 ng mL^?1 for l-carnosine, 4,000 ng mL^?1 for d-carnosine. Low limit of quantitation (LLOQ) was 40 ng mL^?1 for each isomer. The relative standard deviations obtained for intra- and inter-day precision were lower than 12% and the recoveries were higher than 75% for both enantiomers. The method was applied to a stereoselective study on the pharmacokinetics of carnosine after oral administration with a single dose (carnosine, 75 mg kg^?1 for each isomer) to a rat. The initial data indicated that l-carnosine had a larger value of the highest plasma concentration than d-carnosine (C _max 5,344 vs. 1,914 ng mL^?1), and that of l-carnosine had a lower value of AUC_(0?∞) and t _1/2(h) (AUC_(0?∞) 5,306 vs. 6,321 ng h mL^?1, t _1/2 1.43 vs. 3.37 h). Our results indicated that the pharmacokinetic of l-carnosine and d-carnosine revealed enantioselective properties significantly.     

Quantitative Analysis of Sertraline in Human Serum by LC with Fluorescence Detection After Pre-Column Derivatization with 4-Chloro-7-nitrobenzofurazan

An accurate and sensitive reversed-phase high-performance liquid chromatographic method for analysis of sertraline in human serum, using 4-chloro-7-nitrobenzofurazan as pre-column derivatization agent, is described. The drug and an internal standard (azithromycin) were extracted from serum by use of a mixture of diethyl ether and chloroform, and subjected to pre-column derivatization with the reagent. Analysis of the resulting derivatives was performed on a 250 mm × 4.0 mm cyano column with 63:37 (v/v) methanol–sodium phosphate buffer (0.05 M, pH 3.7) containing 2 mL L^?1 triethylamine as mobile phase. Detector response was monitored at excitation and emission wavelengths of 470 and 537 nm, respectively. The calibration plot was linear over the concentration range 2–640 ng mL^?1. The lower limits of detection and quantification were 0.5 and 2 ng mL^?1, respectively. The method was validated for specificity, sensitivity, linearity, precision, accuracy, and stability and shown to be accurate (intra-day and inter-day accuracy from 0.3 to 4.2%) and precise (intra-day and inter-day precision from 2.4 to 15.5%). The drug was detected at concentrations as low as 2 ng mL^?1 in 0.5 mL serum and the method described can be easily applied to human single-dose pharmacokinetic studies of sertraline.     

Development of a Sensitive LC Assay with Fluorescence Detection for the Determination of Zearalenone in Rat Serum

A simple and sensitive liquid chromatographic assay with fluorescence detection assay was developed for the determination of zearalenone levels in rat serum. The assay utilized a single liquid–liquid extraction with t-butyl methyl ether and isocratic elution using a mobile phase consisting of acetonitrile and 0.1% triethylamine in distilled water (pH = 6) (50:50, v/v). Linearity was observed over a concentration range from 10 to 1,000 ng mL^?1 (r = 0.9995), with the limit of quantification at 10 ng mL^?1 with 100 μL of rat serum. The validated assay was applied to a pharmacokinetic study in rats.