Simple, sensitive and rapid liquid chromatographic/electrospray ionization tandem mass spectrometric method for the quantification of lacidipine in human plasma

A simple, sensitive and rapid liquid chromatographic/electrospray ionization tandem mass spectrometric method was developed and validated for the quantification of lacidipine in human plasma using its structural analogue, amlodipine, as internal standard (IS). The method involves a simple single-step liquid-liquid extraction with tert-butyl methyl ether. The analyte was chromatographed on an Xterra MS C(18) reversed-phase chromatographic column by isocratic elution with 20 mM ammonium acetate buffer-acetonitrile (10:90, v/v; pH 6) and analyzed by mass spectrometry in the multiple reaction monitoring mode. The precursor to product ion transitions of m/z 456.4 --> 354.4 and m/z 409.3 --> 238.3 were used to measure the analyte and the I.S., respectively. The chromatographic run time was 1.5 min and the weighted (1/x(2)) calibration curves were linear over the range 0.1-25 ng ml(-1). Lacidipine was sensitive to temperature in addition to light. The method was validated in terms of accuracy, precision, absolute recovery, freeze-thaw stability, bench-top stability and re-injection reproducibility. The limit of detection and lower limit of quantification in human plasma were 50 and 100 pg ml(-1), respectively. The within- and between-batch accuracy and precision were found to be well within acceptable limits (<15%). The analyte was stable after three freeze-thaw cycles (deviation <15%). The average absolute recoveries of lacidipine and amlodipine (IS) from spiked plasma samples were 51.1 +/- 1.3 and 50.3 +/- 4.9%, respectively. The assay method described here could be applied to study the pharmacokinetics of lacidipine.     

Simple,rapid and sensitive method for the determination of mefenamic acid in pharmaceutical preparations

Two simple and fast automated methods for the direct determination of mefenamic acid (MEF) in pharmaceutical samples are described. Continuous flow and stopped-flow systems with spectrophotometric detection of mefenamic acid with sodium nitroprusside and hydroxylamine hydrochloride were developed. Both methods show a good reproducibility (RSD < 1.5 and 1.8%, respectively) and a wide range of linearity (between 10–500 and 3–300 μg/mL). The stopped-flow protocol has a lower detection limit (1.2 μg/mL) with a sensitivity of about two times greater than the continuous flow technique. The proposed procedures are rapid, reliable and can be applied successfully to the estimation of mefenamic acid in different commercial forms.     

Simple and sensitive liquid chromatographic method with fluorimetric detection for the analysis of gamma-amino-n-butyric acid in human urine

A simple and sensitive liquid chromatographic method is described for the analysis of γ-amino-n-butyric acid (GABA) in human urine. GABA is increased in the urine of cancer patients and could be used as a biomarker in the diagnosis and treatment of related patients. The method is based on derivatizing GABA with a fluorescent reagent (naproxen acyl chloride) for transforming the non-chromophoric GABA to a derivative with chromophoric and fluorophoric properties. The resulting derivative is highly responsive to a fluorimetric detector (λ_ex = 230 nm, λ_em = 350 nm). The lower quantitation of the method is attainable at 100 nM GABA with a detection limit about 10 nM (S/N = 3 with 20 μL injected). Application of the method to the analysis of GABA in the urine of patients with ovarian and uterine cancer was demonstrated.     

Simple, sensitive and rapid liquid chromatography/atmospheric pressure chemical ionization mass spectrometric method for the quantitation of Ranolazine in rat plasma

A sensitive and specific method using liquid chromatography with atmospheric pressure chemical ionization mass spectrometry (LC/APCI-MS) has been developed and validated for the identification and quantification of Ranolazine in rat plasma. A simple liquid-liquid extraction procedure was followed by injection of the extracts onto a C18 column with isocratic elution and detection using a single quadrupole mass spectrometer in selected ion monitoring (SIM) mode. The method was tested using six different batches of blank plasma. Linearity was established for the concentration range 0.02-10.0 microg/mL, with a coefficient of determination (r) of 0.9998 and good back-calculated accuracy and precision. The intra- and inter-day precision (relative standard deviation (RSD) %) was lower than 10%, and accuracy ranged from 85 to 115%. The lower limit of quantification was reproducible at 0.01 microg/mL with 20 microL plasma. The proposed method enables the unambiguous identification and quantification of Ranolazine for pre-clinical and clinical studies.     

A rapid and sensitive method for the quantification of ganciclovir in plasma using liquid chromatography/selected reaction monitoring/mass spectrometry

A method using reversed-phase liquid chromatography coupled with electrospray ionization and selected reaction monitoring mass spectrometry has been developed for the quantitative analysis of ganciclovir in rat plasma. Acyclovir, a structurally related analog of ganciclovir, was used as the internal standard. A small volume of plasma (50 microL) was spiked with the internal standard and plasma proteins were precipitated by methanol. The supernatant was dried under nitrogen, and then reconstituted in water. The use of liquid chromatography/selected reaction monitoring/mass spectrometry effectively eliminated potential interference from endogenous constituents in the plasma. This highly selective and sensitive method made it possible to analyze plasma ganciclovir with a lower limit of quantitation of 10 ng/mL. The assay was reproducible and linear in the range 10-10,000 ng/mL. The precision and accuracy values were in the range 2.0-6.9% and 89.0-109.6%, respectively. The analyte recovery was greater than 88%. This method was successfully used to monitor the pharmacokinetic profile of ganciclovir in normal rats following intraperitoneal administration of the drug.     

Simple and sensitive catalytic method for determination of copper in blood serum

Summary A new catalytic method is proposed for determination of copper in blood serum, based on the oxidation of sulphanilic acid with H₂O₂, catalysed by copper(II). Because of its high sensitivity the method requires a serum sample of only 0.10 ml. Using the fixed-time method reduces the procedure to that of an ordinary photometric determination. The method shows reasonable precision and accuracy and is suitable for routine serial analyses in clinical practice.

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Zusammenfassung Eine neue katalytische Methode wurde für die Bestimmung des Kupfers in Blutserum vorgeschlagen. Sie beruht auf der durch Cu(II) katalysierten Oxydation der Sulfanilsäure mit H₂O₂. Infolge ihrer großen Sensitivität genügt für diese Methode eine Serumprobe von nur 0,10 ml. Infolge Ablesung nach Ablauf einer bestimmten Zeit verlangt das Verfahren nicht mehr Zeit als eine gewöhnliche photometrische Methode. Es zeigt gute Genauigkeit und eignet sich für Serienanalysen in der klinischen Praxis.

     

Development and validation of a rapid high-performance liquid chromatography method for the quantification of exenatide

The objective was to develop a simple HPLC method to quantify exenatide—a 39 amino acid residue incretin mimetic used in diabetes therapy. To date, only non‐validated, sometimes incomplete, gradient methods have been reported in the literature. Isocratic separation was achieved using a C₄ column and a mixed solvent system, A–B–C (48:45:7, v/v/v; pH* 5.2), where A represents KH₂PO₄ (pH 4.5; 0.1 m ) and MeCN (60:40, v/v), B corresponds to NaClO₄·H₂O (pH 6.0; 0.2 m ) and MeCN (60:40, v/v), and C is water. Exenatide eluted at 3.64 min and the total run time was 6 min. The method was specific and the response was accurate, precise and linear from 0.75 to 25 µg/mL. It was used to quantify exenatide transport across intact and laser‐porated porcine skin in vitro as a function of laser fluence [0 (i.e. intact skin), 9 and 15 J/cm², respectively]. Although no permeation was observed using intact skin, cumulative exenatide permeation after 8 h through laser porated skin was 9.6 ± 6.5 and 12.4 ± 6.4 µg/cm² at fluences of 9 and 15 J/cm², respectively. This is the first validated isocratic method for exenatide quantification and it may be of use in quality control analysis and with other biological matrices. Copyright © 2010 John Wiley & Sons, Ltd.     

Simple, rapid and selective method using high-performance liquid chromatography for the determination of bretylium in plasma.

A high-performance liquid chromatographic method with ultraviolet detection has been developed for the determination of bretylium in plasma. Following a single-step solid-phase extraction procedure, bretylium is selectively isolated and well recovered from plasma. The assay sensitivity is 0.156 micrograms/ml from 250-microliters plasma samples and its linearity was assessed up to 40 micrograms/ml. The method is accurate (101.0 +/- 5.4%) and precise (maximum coefficient of variation of 8%). It provides a simple and time-saving alternative to existing methods and is particularly suitable for pharmacokinetic studies.     

Rapid and sensitive liquid chromatography tandem mass spectrometry method for the quantification of ambroxol in human plasma

A sensitive, specific and rapid high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was described and validated for the quantification of ambroxol in human plasma using enalaprilat as the internal standard (IS). Chromatographic separation was performed on a Lichrospher CN column with a mobile phase of methanol and water (containing 0.1% formic acid) (70:30, v/v). The total run time was 5.0 min for each sample. The analytes was detected by mass spectrometry with electrospray ionization source in positive selected reaction monitoring mode. The precursor-fragment ion reaction for ambroxol was m/z 378.9 --> 263.8, and for IS was m/z 349.0 --> 205.9. The linearity was established over the concentration range of 1.56-400.00 ng/mL. The inter-day and the intra-day precisions were all within 10%. A simple protein precipitation with methanol was adopted for sample preparation. The extraction recoveries of ambroxol and IS were higher than 90.80%. The validated method was successfully applied in pharmacokinetic study after oral administration of 90 mg ambroxol to 24 healthy volunteers.     

A novel liquid chromatography-fluorescence method for the determination of delafloxacin in human plasma

Delafloxacin is a novel fluoroquinolone antibiotic that was approved by the European Medicine Agency to treat bacterial infections of the skin and underlying tissues, and community-acquired pneumonia. Despite being in the market since 2019 in the European Union, there is no published liquid chromatography-fluorescence method for delafloxacin quantification in biological samples. A novel, rapid, and sensitive high-performance liquid chromatographic method was developed to determine delafloxacin in human plasma using its native fluorescence. Plasma delafloxacin concentrations were determined by reverse-phase chromatography with fluorescence detection at 405/450 nm of excitation/emission wavelengths. Delafloxacin was separated on a Kromasil C18 column 250 × 4.6 mm id, 5 µm using isocratic elution. The mobile phase was a mixture of 0.05% trifluoroacetic acid/acetonitrile (52/48). Retention times were 5.4 and 11.6 min for delafloxacin and valsartan (internal standard), respectively. Regression calibration curves were linear over the range of 0.1–2.5 µg/mL. The lower limit of detection was 0.05 µg/mL, and the lower limit of quantification was 0.1 µg/mL. Accuracy and precision were always <11%, and the limit of quantification was <16%. Mean recovery was 98.3%. This method can be applied to determine delafloxacin in human plasma and could be useful to perform pharmacokinetic studies.     

Simple and rapid high-performance liquid chromatographic method for endogenous alpha-tocopherol determination in human plasma

A simple and rapid reversed-phase high-performance liquid chromatographic method was developed and validated for the determination of endogenous alpha-tocopherol in human plasma. Following addition of alpha-tocopheryl acetate as the internal standard, the plasma was deproteinized using acetonitrile and isopropanol mixture prior to HPLC analysis. Methanol was used as the mobile phase and the effluent was quantitated at 292 nm. By this developed method, the concentrations of alpha-tocopherol were linearly related to their responses in the range of 0.8-30 microg/mL. The relative standard deviations intra-day and inter-day for alpha-tocopherol in plasma were less than 10%. The percentage of bias was within +/-4%, which confirmed the accuracy of the method. The method has been successfully applied for determining endogenous alpha-tocopherol in healthy Thai male volunteers.     

A simple, sensitive liquid chromatographic method for quantitation of D-galactose and D-glucose in blood plasma

The concentrations of D-glucose and D-galactose in plasma of galactosemic rats were quantitatively measured by a liquid chromatographic method, based on retention of the weakly ionized monosaccharides by an anion exchange column under alkaline conditions, elution with 9 mmol/L NaOH, and electrochemical detection. This method is both simple and sensitive, since very dilute plasma samples can be directly analysed.