Simultaneous Determination of Valsartan and Hydrochlorothiazide in Tablets by High-Performance Liquid Chromatography

ABSTRACT

A method for the simultaneous determination of valsartan and hydrochlorothiazide in tablets is described. The procedure, based on the use of reversed-phase high-performance liquid chromatography, is linear in the concentration range 5.0-10.0 μg ml^?1 for valsartan and 0.5-2.0 μg ml^?1 for hydrochlorothiazide, is simple and rapid and allows accurate and precise results. The limit of detection was 1.0 μg ml^?1 for valsartan and 0.05 μg ml^?1 for hydrochlorothiazide.     

Sensitivity enhancement by palladium addition in the electrothermal atomic absorption spectrometry of mercury

In graphite-furnace atomic absorption spectrometry of mercury, addition of 50 μg ml^?1 palladium improves the peak height for 5 μg Hg ml^?1 50 times. Further addition of 20 μg ml^?1 platinum doubles the enhanced peak height. The effect is due to amalgam formation. The best sensitivity is 0.3 ng (1% absorption) and the detection limit is 0.1 ng. The method allows higher ashing temperatures than for solutions without noble metal addition and can be applied to solutions containing substantial amount of organic matter.     

Colorimetric Determination of Propofol in Bulk form,Dosage Form and Biological Fluids

ABSTRACT

Propofol is coupled with 2, 6-dichloroquinone-4-chlorimide (DCQ) in a reaction buffered at pH 9.6 to give a colored product having an analytically useful maximum at 635 nm. The factors affecting the color generation were optimized and incorporated in the procedure. The reacted propofol has a molar absorptivity of 3.9 × 10^?4 L mol^?1 cm^?1, and Beer's law is obeyed for concentrations 1-5 μg ml^?1 with detection limit 0.25 μg ml^?1. The method was found applicable to biological fluids (plasma and urine) spiked with propofol at concentration levels 1-5 μg ml^?1 for plasma and 1-5 μg 0.5 ml^?1 urine (less sensitivity is obtained with urine volumes above 0.5 ml) with detection limits 0.28 μg ml^?1 for plasma and 0.4 μg 0.5 ml^?1 urine. The average recovery for the commercial preparation (1% w/v propofol emulsion intravenous injection for infusion) was 99.54% with an RSD of 1.05%. The method was validated by an adopted HPLC method. The results obtained by the HPLC method for the commercial preparation were statistically compared with the proposed method and evaluated at the 95% confidence limits.     

Radical scavenging activity and antioxidant capacity of bay leaf extracts

Bay leaves (BL) (Laurus nobilis L., Family: Lauraceae) are traditionally used orally to treat the symptoms of gastrointestinal problems, such as epigastric bloating, impaired digestion, eructation, and flatulence. In this study, lyophilized extracts (both water and ethanol) of BL were studied for their antioxidant properties. The antioxidant activity, reducing power, free radical scavenging, superoxide anion radical scavenging, hydrogen peroxide scavenging and metal chelating activities were evaluated to determine the total antioxidant capacity of both BL extracts. Both extracts exhibited strong total antioxidant activity in linoleic acid emulsion. Concentrations of 20, 40, and 60 μg ml^?1 showed 84.9, 95.7, 96.8, and 94.2, 97.7, and 98.6% inhibition of lipid peroxidation of linoleic acid emulsion, for water and ethanol extracts, respectively. On the other hand, 60 μg ml^?1 of the standard antioxidants butylated hydroxyianisole (BHA), butylated hydroxytoluene (BHT), and α-tocopherol exhibited 96.6, 99.1, and 76.9% inhibition of lipid peroxidation in linoleic acid emulsion, respectively. In addition, the both BL extracts had effective reducing power, DPPH? free radical scavenging, superoxide anion radical scavenging, hydrogen peroxide scavenging and metal chelating activities at 20, 40, and 60 μg ml^?1. The total amount of phenolic compounds in each BL extract was determined as gallic acid equivalents.     

Simultaneous determination of ammonia and urea with an asymmetric merging zones/flow-injection configuration

A method is proposed for the simultaneous determination of urea and ammonia using a reagent-injection configuration that includes a dual injection valve (for insertion of Nessler's reagent and for accommodating the enzyme reactor). The resolution of the two peaks obtained on each injection allows the determination of both analytes in mixtures. The determination range is 1–5 μg ml^?1 for ammonia and 1–6 μg ml^?1 for urea, with relative standard deviations of 1.13% and 2.31% for ammonia (first and second peaks) and 1.86% for urea.     

A Fluorosensor with Immobilized Cyclodextrin As A Substrate

Abstract

A flow-through optosensor for phenylalanine and tyrosine is described in this paper. The sensor is developed in conjunction with a flow-injection analysis system and uses immobilized β-cyclodextrin as the sensing agent. The analytical performance characteristics of the proposed sensor for analysis of very low levels of phenylalanine and tyrosine were as follows: the detection limits for phenylalanine and tyrosine were 0.20 μg ml^?1 and 8.9 ng ml^?1, respectively. The observed relative standard deviations were 1.03% for 50 μg ml^?1 of phenylalanine (n = 7) and 3.6% for 0.1 μg ml^?1 of tyrosine (n = 7), respectively.     

Modular stopped-flow/diode-array detection system for simultaneous kinetic analysis

The coupling of a stopped-flow module to a diode-array spectrophotometric detector has been exploited for the simultaneous kinetic resolution of mixtures. The analytical possibilities are shown with the resolution of a mixture of two analytes (hydrazine and phenylhydrazine), yielding products with different spectral features (after reaction with p-dimethylaminobenzaldehyde), so that only the simultaneous measurement of their respective initial rates at their corresponding maximum absorption wavelengths is possible. The method allows 0.02–30 μg ml^?1 hydrazine and 8–2200 μg ml^?1 phenylhydrazine to be determined simultaneously.     

Phosphorescence detection in flowing systems: selective determination of aluminium by flow-injection liquid room-temperature phosphorimetry

The concept of the micelle stabilized liquid room-temperature phosphorescence (MS-LRTP) was applied to the determination of a metal (aluminium) in a flowing system. A three-line flow-injection manifold was developed and various parameters were optimized. A linear calibration graph was obtained for 0–4 μg ml^?1 aluminium. The limit of detection was 50 ng ml^?1 and the relative standard deviations for 0.1 and 1.0 μg ml^?1 aluminium were 2.7 and 1.3% respectively. The proposed procedure is fairly selective. More than 20 common ions studied did not interfere with the determination of aluminium or could be masked by appropriate reagents. The flow-injection method proposed was applied without any preliminary separation to the determination of aluminium in simulated synthetic samples in water and in clinical samples of particular importance in the control of aluminium toxicity in renal failure patients.     

Spectrophotometric determination of iron(III) with EDTA tetrahydrazide

The tetrahydrazide of ethylenediamine tetraacetic acid (NH₂NH)₄-EDTA was synthesized from the EDTA ester and hydrazine hydrate in ethanolic solution, the resulting (NH₂NH)₄-EDTA being recrystallized in 60% ethanol. When the spectrophotometric study of the iron(III) (NH₂NH)₄-EDTA complex in aqueous solution was made two absorption maxima at 530 and 450 nm at pH 4.5 and 11.0, respectively, were found. Beer's law is obeyed in the range 1.0–20.0 μg Fe(III) ml^?1 at 530 nm and pH 4.5 and 0.5–12.0 μg Fe(III) ml^?1 at 450 nm and pH 11.0, the molar absorptivities being 1.95 × 10³ 1 mol^?1 cm^?1 at 530 nm and 3.35 × 10³ 1 mol^?1 cm^?1 at 450 nm, respectively. The Ringbom optimal interval falls between about 3 and 18 μg Fe(III) ml^?1 at 530 nm and about 2–14 μg Fe(III) ml^?1 at 450 nm. The reaction between the metal and the ligand was also investigated. The method has been successfully applied to the determination of iron in talcs.     

Integrated Retention/Spectrophotometric Detection Method for the Determination of Formaldehyde

Abstract

An integrated-sensor method for the determination of formaldehyde based on retention of the reaction product of the analyte with p-rosaniline and sulfite in a flow-cell packed with Dowex 1-X-8 anion exchange resin was developed. The method has a good selectivity with a detection limit of 0.3 μg ml^?1 (1 ml sample) or 75 ng ml^?1 (2 ml sample), and a linear range between 1–30 μg ml^?1. The relative standard deviations (n = 11) were 2.8 and 1.3% for 2 and 20 μg ml^?1 formaldehyde, respectively. Depending on the working conditions, the sampling frenquency ranged between 10 and 18 h^?1. The method was applied to the determination of formaldehyde in well water.     

Simultaneous flow-injection determination of aluminium and zinc using LED photometric detection

A flow photometer with a multi-LED detector was applied to the simultaneous determination of aluminium and zinc with microcomputer control of photometric measurements and data processing. Xylenol Orange is the photometric reagent and the reaction is carried out in acetate buffer. Calibration graphs are linear for both metals in the concentration ranges 0.2–25 μg ml^?1 (Al) and 0.2–30 μg ml^?1 (Zn). Both elements can be determined for Al to Zn ratios varying from 0.01 to 100 with r.s.d. 1.1 and 1.4%, respectively. The method developed was applied to the determination of Al and Zn in alloys.     

Kinetic-Spectrophotometric Determination of Molybdenum(VI) Based on Its Catalytic Effect on the Thionine-Hydrazine Reaction

Abstract

A kinetic method for the determination of trace amounts of Mo(VI) (0.05-4 μg ml^?1) based on its catalytic effect on the reduction of thionine by hydrazine monochloride in strongly acidic media is reported. The reaction is monitored spectrophotometrically by measuring the decrease in absorbance of thionine at 605 nm after a fixed time (5 min.). The detection limit of the method is 23 ng ml^?1 and the relative standard deviation (RSD) for 0.05 μg ml^?1 of Mo(VI) is 1.2% (n=7). The method is almost free from interferences, especially from large amounts of tungsten. The procedure was successfully applied to the determination of trace amounts of molybdenum in steel.     

LC–QToF–MS method for quantification of ethambutol,isoniazid, pyrazinamide and rifampicin in human plasma and its application

In this research, we developed and validated a liquid chromatography coupled to mass spectrometry (LC–QToF–MS) method for simultaneous quantification of the anti-tuberculosis drugs ethambutol, isoniazid, pyrazinamide and rifampicin in human plasma. Plasma samples spiked with cimetidine (internal standard) were extracted using protein precipitation with acetonitrile containing 1% formic acid. Separation was performed using a C₁₈ column under flow gradient conditions with water and acetonitrile, both containing 5 mm ammonium formate and 0.1% formic acid. The method was validated according to the ANVISA and US Food and Drug Administration guidelines for bioanalytical method validation. The calibration curve was linear over a concentration range of 0.2–5 μg ml⁻¹ for ethambutol, 0.2–7.5 μg ml⁻¹ for isoniazid, 1–40 μg ml⁻¹ for pyrazinamide and 0.25–2 μg ml⁻¹ for rifampicin, all with adequate precision and accuracy. The method was reproducible, selective and free of carryover and matrix effects. The validated LC–QToF–MS method was successfully applied to real samples and shown to be applicable to future therapeutic and pharmacokinetic monitoring studies.     

Determination of phosphorus in biological tissues by aluminium block digestion and flow-injection spectrophotometry

Biological tissues are digested with nitric and perchloric acids in a heated aluminium block. Flow-injection spectrophotometry is then used to measure phosphate via the phosphovanadomolybdate complex at 413 nm. The detection limit is 0.3 μg ml^?1 phosphorus; relative standard deviations are 0.7% and 0.4% at 1 μg ml^?1 and 25 μg ml^?1 phosphorus, respectively. Interferences are discussed. The decomposition procedure is evaluated for model compounds and standard reference materials.     

Flow-injection spectrophotometric determination of ascorbic acid by reduction of vanadotungstophosphoric acid

Ascorbic acid may be determined spectrophotometrically at 360 nm based on reduction of vanadotungstophosphoric acid using flow-injection analysis. The carrier stream was distilled water and the reagent streams were buffer solution (pH 3.0), 1.735 × 10^?3 M dodecatungstophosphoric acid and 1.735 × 10^?3 M sodium vanadate. The injection rate was 80 h^?1. The calibration graph was linear up to 80 μg ml^?1 ascorbic acid and the relative standard deviation for the determination of 20 μg ml^?1 ascorbic acid was 1.5% (n=10). The detection limit was 1.0 μg ml^?1 ascorbic acid, based on an injection volume of 250 μl. The system was applied to the determination of ascorbic acid in vitamin C tablets.     

Fluorescent Complexes of Nucleic Acids/8-Hydroxyquinoline/Lanthanum(III) and the Fluorometry of Nucleic Acids

Abstract

The ternary fluorescent complexes of nucleic acids/8-hydroxyquinoline/ lanthanum (III) were studied. Nucleic acids in the study involve natured and thermally denatured calf thymus DNA, fish sperm DNA and yeast RNA. In the range of pH 8.0–8.4 (controlled by NH₃-NH₄Cl buffer) ternary fluorescent complexes are formed which emit at 485.0 nm for calf thymus DNA and at 480.0 nm for yeast RNA (when excited at 267.0 nm) and emits at 483.0 nm for fish sperm DNA when excited at 265.0 nm. Based on the fluorescence reactions sensitive fluorometric methods for nucleic acids were proposed. Using optimal conditions, the calibration curves were linear in the range of 0.4–3.6 μg˙ml^?1 for calf thymus DNA, 0.4–4.0 μg-ml^?1 for fish sperm DNA and 0.4–4.0 μg˙ml^?1 for yeast RNA, respectively. The limits of determination (3σ) were 0.076 μg˙ml^?1 for calf thymus DNA, 0.068 μg˙ml^?1 for fish sperm DNA and 0.329 μg˙ml^?1 for yeast RNA, respectively. Five synthetic samples were determined with satisfaction.

     

High performance liquid chromatographic determination of sodium benzoate, methylparaben and propylparaben as preservative components in nystatin suspensions

A simple and sensitive method was developed for the analysis of preservatives sodium benzoate, methylparaben and propylparaben in nystatin suspensions by reversed-phase high performance liquid chromatography (HPLC), equipped with a C18 column and PDA detector. The mobile phase was a mixture of acetonitrile and acetate buffer of pH 4.4 (35:65 v/v). Under the optimized experimental conditions, separation of the preservatives was achieved in less than 20 min. The limits of quantifications (LOQs) and the linear dynamic ranges (LDRs) of sodium benzoate, methylparaben and propylparaben were 0.3 and 50–1000 μg Ml^?1, 0.5 and 50–600 μg ml^?1 and 0.3 and 50–900 μg ml^?1, respectively; the respective precisions (%RSD) at 500 μg ml^?1 level were 0.72%, 0.73% and 0.51% (n = 6). The average recoveries of sodium benzoate, methylparaben and propylparaben for spiked nystatin samples were obtained as 98%, 97% and 98%, respectively.     

Sensitive spectrofluorimetric determination of zinc at ultra-trace levels

An ultra-trace method based on the reaction of zinc with salicylthiocarbohydrazone (SATCH) and Triton X-100 as a non-ionic surfactant was developed for the fluorimetric determination of zinc at the picogram level. The reaction is carried out in the pH range 4.4–4.7 in an aqueous ethanolic medium [52% (v/v) ethanol]. The influence of the reaction variables is discussed. The detection limit is 10 pg ml^?1 and the range of application is 0.01–500 μg l^?1, with an optimum range of 0.04–400 μg l^?1. The relative standard deviations are 0.68% (0.01–0.1 μg l^?1 of zinc), 0.41% (0.1–1.0 μg l^?1 of zinc), 0.64% (1–10 μg l^?1 of zinc), 0.82% (10–100 μg l^?1 of zinc) and 0.15% (100–500 μg l^?1 of zinc). The method is highly sensitive and selective in the presence of Cd^II and Hg^II. The effect of interferences from other metal ions and anions was studied; the masking action is discussed. The advantages of the proposed method include its high sensitivity, simplicity and selectivity.     

Use of diode-array detectors for the simultaneous spectrophotometric determination of calcium and magnesium by flow injection

A method for the simultaneous flow injection spectrophotometric determination of calcium and magnesium with Arsenazo III based on the use of diode-array detector and merging zones is described. The method is applicable to the resolution of mixtures in which the chromogenic reagent has a high absorbance and its spectrum strongly overlaps those of its complexes. In resolving the mixtures, the excess reagent is considered as another component. Quantitation is based on the normal absorbance and first-derivative absorbance spectra. The method is applied to 0.2–1.5 μg ml^?1 Ca and 0.1–1.0 μg ml^?1 Mg. The analysis rate is 50 h^?1.     

Flow-Injection Chemiluminescence Determination of Fluoroquinolones

ABSTRACT

A new flow-injection CL method was developed for the determination of fluoroquinolones including ofloxacin, norfloxacin, ciprofloxacin and lomefloxacin in pharmaceutical preparations, based on the chemiluminescence reaction of sulphite with cerium(IV) sensitized by these compounds. The linear ranges are 0.04 to 4.0 μg ml^?1 for ofloxacin and 0.4 to 40.0 μg ml^?1 for norfloxacin, ciprofloxacin and lomefloxacin, respectively. The detection limits are 0.016 μg ml^?1 for ofloxacin and 0.16 μg ml ^?1 for norfloxacin, ciprofloxacin and lomefloxacin, respectively. The relative standard deviations (RSD) are 2.1 to 2.6% (n=10) for these fluoroquinolones. The analytical procedure has been applied to the determination of the fluoroquinolones in pharmaceutical commercial formulations. The results are in agreement with those obtained by the official methods.