Determination of L‐Vesamicol in Serum Samples Using Enantioselective,Potentiometric Membrane Electrodes Based on Antibiotics

Abstract

Enantioselective, potentiometric membrane electrodes (EPMEs) based on antibiotics are proposed for the enantioanalysis of L‐vesamicol. A carbon paste was modified with antibiotics (vancomycin, teicoplanin, and teicoplanin modified with acetonitrile), as chiral selectors. The EPMEs based on antibiotics were reliably used for enantiopurity tests of L‐vesamicol using the direct potentiometric technique. The following linear concentration ranges: 1.0×10^?6–1.0×10^?4, 1.0×10^?6–1×10^?3 and 1×10^?7?1×10^?2 mol/L; and detection limits: 1.1×10^?7, 9.6×10^?8, and 3.6×10^?8 mol/L were determine for vancomycin, teicoplanin, and teicoplanin modified with acetonitrile–based EPMEs, respectively. The proposed EPMEs were applied for the enantioanalysis of L‐vesamicol in urine samples.     

Electrochemical Determination of Citalopram by Adsorptive Stripping Voltammetry–Determination in Pharmaceutical Products

Abstract

The electrochemical behavior of citalopram was studied by square‐wave and square‐wave adsorptive‐stripping voltammetry (SWAdSV). Citalopram can be reduced and accumulated at a mercury drop electrode, with a maximum peak current intensity being obtained at a potential of approximately ?1.25 V vs. AgCl/Ag, in an aqueous electrolyte solution of pH 12. A SWAdSV method has been developed for the determination of citalopram in pharmaceutical preparations. The method shows a linear range between 1.0×10^?7 and 2.0×10^?6 mol L^?1 with a limit of detection of 5×10^?8 mol L^?1 for an accumulation time of 30 s. The precision of the method was evaluated by assessing the repeatability and intermediate precision, achieving good relative standard deviations in all cases (≤2.3%). The proposed method was applied to the determination of citalopram in five pharmaceutical products and the results obtained are in good agreement with the labeled values.     

Flexible Potentiometric Minisensor Based on Manganese Dioxide‐Composite for the Determination of Hydrogen Peroxide in Bleach and Pharmaceutical Products

Abstract

A new flexible minisensor based on MnO₂/graphite/epoxy resin composite for the potentiometric determination of hydrogen peroxide was developed in this work. Under optimum experimental conditions, such as 25°C, 4 h of conditioning time in 0.1 mol L^?1 NH₃‐NH₄ ⁺ buffer solution (pH 8.5) and a composition of 10/60/30% w/w MnO₂/graphite/epoxy resin, respectively, the minisensor presented a Nernstian response for H₂O₂ in the concentration range from 6.0×10^?7 to 1.0×10^?3 mol L^?1, with a slope of ?58.5±0.2 mV/pH₂O₂ with a detection limit of 1.6×10^?8 mol L^?1 H₂O₂. The useful lifetime of the proposed minisensor was at least 6 months (over 670 determinations for each composite), the response time was smaller than 1.5 min, and it was successfully applied in the determination of hydrogen peroxide in bleach and pharmaceutical products.     

Spectrophotometric Determination of Some Fluoroquinolone Derivatives in Dosage Forms and Biological Fluids Using Ion‐Pair Complex Formation

Abstract

A simple, rapid, sensitive, and reproducible procedure for assaying norfloxacin (NOR), ciprofloxacin (CIP), and ofloxacin (OFL) was investigated. The procedure is based on the reaction of selected drugs with Sudan II (I), Congo red (II), and Gentian violet (III) in universal buffer to give soluble ion‐pair complexes. The effects of various parameters have been studied. Beer's law plots were obeyed in the concentration ranges 0.5–11 µg ml^?1, whereas Ringbom optimum ranges were 0.7–9.5 µg ml^?1. The apparent molar absorptivity (6.4×10⁴ L mol^?1 cm^?1), Sandell sensitivity (4.99 ng cm^?2), detection (0.13 µg ml^?1), and quantification (0.44 µg ml^?1) limits were calculated. The relative standard deviation for ten determinations, for samples containing 4.0 µg ml^?1, was found to be 1.40%. The influence of commonly employed excipients in the determination of the studied drugs was examined. There was no interference from degradate product results from thermal and hydrolytic treatments. The results obtained by the proposed procedure were statistically validated. The developed procedure was successfully applied to the determination of the studied drugs in dosage forms and biological fluids.     

Electrochemical Acetylcholinesterase Biosensor Based on Polylactide–Nanosilver Composite for the Determination of Anti-dementia Drugs

A new acetylcholinesterase biosensor has been developed for the determination of anticholinesterase drugs applied for neurodegenerative disease treatment. For this purpose, silver nanosendrites were deposited by potentiostatic electrolysis on a glassy carbon electrode covered with oligolactides cross-linked with p-tert-butylthiacliax[4]arene core in the cone, partial cone, and 1,3-alternate configurations. The roles of macrocycle configuration and electrolysis conditions on the silver depostion were characterized and optimal conditions selected for the subsequent immobilization of acetylcholinesterase. Silver nanoparticles provide higher response at low working potential (0.05?V) due to the electrostatic accumulation of silver ions and prevention of their leaching after reoxidation. The biosensor allows the determination of 10^?12 – 10^?7 M donepezil, berberine, and huperzine A within 20-30?s by the relative decay of the current related to the oxidation of thiocholine formed in enzymatic reaction. The reversible inhibition of immobilized acetylcholinesterase with huperzine A was quantified for the first time. The developed biosensor was employed for the analysis of spiked urine samples.     

Determination of Octanol–Water Partition Coefficients by MEEKC Based on Peak-Shift Assay

A novel microemulsion electrokinetic chromatography method based on peak-shift assay (p-s MEEKC) has been developed for the determination of octanol–water partition coefficients (log P _o/w) of compounds. The log P _o/w values of 12 compounds were determined. The RSD of obtained values were less than 5.0% except 4-tert-butylphenol (RSD = 5.9%). All log P _o/w values of the investigated compounds measured by p-s MEEKC were within 0.51 logarithm unit variation as compared to the literature values, with mean difference of 0.27. Compared to the conventional MEEKC method, the novel method does not suffer from the deficiencies related to the reference compounds and migration time of microemulsion phase, and showed the potential of being an alternative method for the determination of log P _o/w values of compounds without reference compounds.     

Determination of Amine-Containing Drugs in Micellar Matrices by Spectrophotometry Using Box–Behnken Plans

Journal of Analytical Chemistry - The results of using the “response surface” methodology and the Box–Behnken design in the spectrophotometric determination of medicinal...     

Quantitative Determination of Lobeline Hydrochloride in Rabbit Plasma by LC–MS–MS and Its Application

A sensitive and selective liquid chromatography tandem mass spectrometry method for quantitative determination of lobeline hydrochloride in rabbit plasma was developed and validated. After addition of triazolam as internal standard, protein precipitation by acetonitrile was used as sample preparation. Chromatographic separation was achieved on a Zorbax SB-C18 column with acetonitrile-0.1% formic acid as mobile phase with gradient elution. Electrospray ionization source was applied and operated in positive ion mode; multiple reaction monitoring mode was used for quantification using target fragment ions m/z 338.1 → 315.8 for lobeline hydrochloride and m/z 342.9 → 308.0 for the IS. Calibration plots were linear over the range of 2–500 ng mL^?1 for lobeline hydrochloride in plasma. Lower limit of quantitation for lobeline hydrochloride was 2 ng mL^?1. Mean recovery of lobeline hydrochloride from plasma was in the range 97.5–102.3%. RSD of intra-day and inter-day precision were both <9%. This developed method is successfully used in pharmacokinetic study of lobeline hydrochloride in rabbit.     

Determination of Gastrodin and Ligustrazine Hydrochloride in Plasma and Brain Dialysate by LC–Tandem MS

A gradient liquid chromatography-tandem mass spectrometry method has been developed and validated for the determination of gastrodin and ligustrazine hydrochloride in rat plasma and brain dialysates. Zolpidem was used as internal standard. For plasma samples, solid-phase extraction was used and the brain dialysates were collected from freely moving rats using brain microdialysis. Both were followed by HPLC separation and positive electrospray ionization tandem mass spectrometry detection (ESI–MS–MS). Chromatographic separation was achieved on a Symmetry RP-18 column using gradient elution with methanol and water containing 0.5% formic acid and 2 mM ammonium formate. Selected reaction monitoring (SRM) mode was used for quantitation. Good linearities were obtained in the range of 0.05–100 and 0.01–50 μg mL^?1 for gastrodin and ligustrazine hydrochloride in rat plasma, and 0.05–1,000 ng mL^?1 for both in dialysate. The lower limit of quantitation was 0.01 ng mL^?1 for gastrodin and 0.05 ng mL^?1 for ligustrazine. The method is precise and reliable and can be applied to pharmacokinetic studies.     

Post‐chemiluminescence Method of the Determination of Loperamide Hydrochloride in Human Plasma and Pharmaceutical by Using Dichlorofluorescein as Chemiluminescence Reagent

Abstract

A post‐chemiluminescence (PCL) was observed when loperamide hydrochloride solution was injected into the reaction mixture after the finish of CL reaction of alkaline N‐Chlorosuccinimide (NCS) and dichlorofluorescein. Based on this phenomenon, a simple, sensitive and fast flow injection PCL method was established for the determination of loperamide hydrochloride. The possible mechanism for the PCL reaction was discussed via the investigation of the CL kinetic characteristics, the CL spectra, the fluorescence spectra. The PCL intensity responded linearly to the concentration of loperamide hydrochloride in the range 8.0×10^?10 to 6.0×10^?7 g · ml^?1 with a linear correlation of 0.9995. The detection limit was 4×10^?10 g · ml^?1. The relative standard deviation was 2.4% for 4.0×10^?8 g · ml^?1 loperamide hydrochloride (n=11). This method has been applied to the determination of loperamide hydrochloride in human plasma and pharmaceutical samples with satisfactory results.     

Development of a Liquid–Liquid Microextraction Method Based on a Switchable Hydrophilicity Solvent for the Simultaneous Determination of 11 Drugs in Urine by GC–MS

A new and green liquid–liquid microextraction method based on a switchable hydrophilicity solvent for the determination of 11 drugs in urine is presented for the first time. The protonated N,N-dimethylcyclohexylamine was used as an extraction solvent and sodium hydroxide was injected as a trigger for organic-phase separation. The extraction procedure has been optimized and investigated in this study. The intraday and interday recovery ranged from 73.8 to 103.0% and the relative standard deviations were in the range from 2.2 to 13.5% (n?=?5). The linear range was from 5.0 to 2000.0 µg L^?1, and R² was greater than 0.99, and the limit of detection was in the range from 0.36 to 12.50 µg L^?1. The proposed method may be a useful procedure for the determination of 11 drugs in urine, and easily incorporated into routine testing for a laboratory.

Graphical Abstract

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Determination of Alkylphenols in Water by Dispersive Liquid–Liquid Microextraction Based on Solid Formation without a Disperser

Dispersive liquid–liquid microextraction based on solid formation without a disperser combined with high-performance liquid chromatography has been developed for the determination of 4-tert-butylphenol, 4-n-nonylphenol, and 4-tert-octylphenol. This method is rapid, easy, and uses only 10 µL of a low toxicity organic solvent (1-hexadecanethiol) for the extraction solvent and no disperser solvent. The extraction time and centrifugation time require less than 10 min. The linear range was 1–500 ng mL^?1 for 4-tert-butylphenol, 2–1000 ng mL^?1 for 4-tert-octylphenol, and 5–500 ng mL^?1 for 4-n-nonylphenol with r² ≥ 0.9986. The detection limits were between 0.2 and 1.5 ng mL^?1. The recoveries of lake and river water samples were in the range of 79% to 108%, and the relative standard deviations were 5% to 10%.     

Determination of Ketotifen Fumarate in Raw Material and Pharmaceutical Products Using Ion‐pair Formation

Abstract

A simple and sensitive extractive spectrophotometric method has been described for the determination of Ketotifen. The developed method is based on the formation of a colored ion‐pair complex (1∶1 drug/dye) of Ketotifen and bromocresol green in buffer pH 3 and extraction in chloroform. The extracted complex shows absorbance maxima at 423 nm. Beer's law is obeyed in the concentration range of 5.15–61.91 µg/ml. The proposed method has been applied successfully for the determination of drug in commercial tablets and syrup dosage form. No significant interference was observed from the excipients commonly used as pharmaceutical aids with the assay procedure.     

An Acetylcholinesterase Sensor Based on a Pillar[6]arene–Silver Nanoparticle Composite for the Determination of Drugs for the Treatment of Alzheimer’s Disease

Journal of Analytical Chemistry - We developed a voltammetric sensor based on a glassy carbon electrode modified with carbon black, pillar[6]arene, and silver nanoparticles for the determination of...     

Retention Time Locking in the Determination of Narcotic Drugs by Chromatography and Chromatography–Mass Spectrometry

The use of retention time locking (RTL) in the development of unified procedures for the detection and quantitative determination of drugs in biological fluids was considered. With consideration for the use of RTL, a chromatographic procedure with flame-ionization and mass-selective detection was developed for the detection and quantitative determination of opiates and their synthetic analogs; phenylalkylamine derivatives; cocaine; ketamine; and other narcotic drugs, their derivatives, and metabolites in urine. The analytical ranges for chromatography–mass spectrometry were 0.05–1000 and 0.005–1000 g/mL under the conditions of total ion current (TIC) scanning and selected ion monitoring (SIM), respectively. With flame-ionization detection (GC–FID), the analytical range was 0.5–1000 g/mL.     

Simultaneous Determination of Mepyramine Maleate,Lidocaine Hydrochloride,and Dexpanthenol in Pharmaceutical Preparations by Partial Least‐Squares Multivariate Calibration

Abstract

A partial least‐squares calibration (PLS) method has been developed for simultaneous quantitative determination of mepyramine maleate (MAM), lidocaine hydrochloride (LIH), and dexpanthenol (DPA) in pharmaceutical preparations. The resolution of these mixtures has been accomplished by using partial least‐squares (PLS‐2) regression analysis of electronic absorption spectral data without prior separation or derivatization. The experimental calibration matrix was constructed with 27 samples. The concentration ranges considered were 2, 3, 4 µg mL^?1 for MAM, 2, 3, 4 µg mL^?1 for LIH, and 8, 10, 12 µg mL^?1 for DPA. The absorbances were recorded between 190 and 340 nm every 5 nm. The results show that PLS‐2 is a simple, rapid, and accurate method applied to the determination of these compounds in pharmaceuticals.     

LC–MS Simultaneous Determination of Itopride Hydrochloride and Domperidone in Human Plasma

A rapid, simple, sensitive and specific liquid chromatography–tandem mass spectrometry method was developed and validated for simultaneous quantification of itopride hydrochloride and domperidone in human plasma. Both drugs were extracted by liquid–liquid extraction with ethyl acetate and saturated borax solution. The chromatographic separation was performed on a reversed-phase C18 column with a mobile phase of water–methanol (2:98, v/v) containing 0.5% formic acid. The protonated analyte was quantitated in positive ionization by multiple reaction monitoring with a mass spectrometer. The assay exhibited linearity over the concentration range of 3.33–500 ng mL^?1 for itopride hydrochloride and 3.33–100 ng mL^?1 for domperidone in human plasma. The precursor to product ion transitions of m/z 359.1–72.3 and 426.0–147.2 were used to measure itopride hydrochloride and domperidone respectively. The method was found suitable for the analysis of plasma samples collected during phase 1 pharmacokinetics study of itopride HCl 50 mg and domperidone 20 mg in 12 healthy volunteers after single oral doses of the combination drug.     

Study on Determination of Chemical Oxygen Demand in Water with Ion Chromatography

A new method for determining chemical oxygen demand （COD） value in water using ion chromatography coupled with nano TiO2-K2S2O8 co-existing system was described. The photocatalytic oxidation system and nano TiO2-K2S2O8 co-existing system could degrade the organic compounds in water. All sulfur-containing species in the reactive solution were eventually transformed to sulfate which could be determined by conductivity detector in ion chromatography. The change of conductivity of sulfate was proportional to COD value. The optimal experimental conditions and the mechanism of the detection were discussed. The application range was 10.0-300.0 mg·L^-1 and the lowest limit of detection was 3.5 mg·L^-1. It was considered that the value obtained could be reliably correlated with the COD value obtained using the conventional methods.     

Sensitive Determination of 17β-Estradiol using a Magneto Sensor Based on Magnetic Molecularly Imprinted Polymer

The analysis of 17β-estradiol with high sensitivity and selectivity is extremely relevant to control the impacts that this compound can cause on health and the environment. Thus, we describe the development and application of a magneto carbon paste electrode based on magnetic molecularly imprinted polymer (MCPE-MMIP) for determination of 17β-estradiol. The analyte adsorbed on the MMIP was immobilized on the electrode surface by magnetic capture. The morphological and structural characterization of the obtained MMIP suggests that the material was effectively synthesized. MCPE-MMIP showed an improvement in the sensitivity for 17β-estradiol detection when compared to electrode configurations in the absence of this material. The optimum conditions (0.10 mol L⁻¹ phosphate buffer pH 7.0) were reached by differential pulse adsorptive stripping voltammetry (DPAdSV), in which the method presented linearity ranged from 0.06 to 175 μmol L⁻¹ with limits of detection and quantification of 0.02 and 0.06 μmol L⁻¹, respectively. The proposed sensor was applied effectively in the analysis of 17β-estradiol in river water and raw milk samples, exhibiting excellent recovery values (between 96.20 and 104 %), which were confirmed by HPLC analysis.