Spectrophotometric Determination of Risedronate and Etidronate in Pharmaceutical Formulations via the Molybdovanadate Method

Abstract

An accurate and sensitive spectrophotometric method was developed for the determination of risedronate and etidronate in pharmaceuticals. The method was based on oxidation of the studied drugs with potassium persulfate and reaction of the generated orthophosphate ions with molybdovanadate reagent. The produced yellow phosphovanadomolybdate complex was measured at 313 nm. The method was rectilinear in the ranges 0.5–10 and 0.5–8 µg/mL with detection limits of 0.087 and 0.122 µg/mL for risedronate and etidronate, respectively. The method was applied for the determination of the studied drugs in their tablets, and the results agreed with those obtained by the comparison methods.     

基于纳米TiO2的化学发光法检测核黄素

纳米TiO2与NaOH溶液作用能产生化学发光辐射,在表面活性剂十六烷基三甲基溴化铵(CTAB)的存在下,核黄素的加入能增强纳米TiO2-NaOH溶液的化学发光强度。基于此,构建了纳米TiO2-NaOH溶液化学发光新体系,建立了纳米TiO2-NaOH-核黄素体系检测核黄素的化学发光新方法。在优化实验条件下,核黄素质量浓度在5.0×10-6～3.5×10-4g/mL范围内与化学发光强度呈良好的线性关系,检出限为3.0×10-6g/mL,对2.5×10-5g/mL的核黄素进行11次平行测定,相对标准偏差为2.9%。该方法用于维生素B2片剂的测定,其结果与药典方法测得一致。该文同时对化学发光反应的机理进行了初步探讨。     

Utility of Certain π‐Acceptors for the Spectrophotometric Determination of Tranexamic Acid in Commercial Dosage Forms

Abstract

In this study, two simple, fast, accurate, and sensitive spectrophotometric methods have been developed for the determination of tranexamic acid in commercial dosage forms. These methods (A and B) are based on the reaction of tranexamic acid as n‐electron donor with 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ) and 7,7,8,8‐tetracyanoquinodimethane (TCNQ) as π‐acceptors to give highly colored complex species that absorb maximally at 470 and 750 nm, respectively. Beer's law was obeyed in the concentration limit of 0.5–10 µg/mL for tranexamic acid. The limit of detection (LOD) and limit of quantification (LOQ) were calculated and found to be 0.18 µg/mL and 0.60 µg/mL for method A and 0.12 µg/mL and 0.39 µg/mL for method B, respectively. A Job's plot of the absorbance versus the molar ratio of tranexamic acid to each of the acceptors under consideration indicated 1∶1. The proposed methods were found to be rapid, accurate, precise, and sensitive for the determination of tranexamic acid in commercial dosage forms without interferences from common additives encountered.     

A Rapid,Simple, and Sensitive Spectrophotometric Determination of Traces of Vanadium (V) in Foodstuffs,Alloy Steels,and Pharmaceutical,Water, Soil,and Urine Samples

Abstract

A rapid, simple, sensitive, and selective spectrophotometric method is investigated for the determination of traces of vanadium (V) in foodstuffs, alloy steels, and pharmaceutical, water, soil, and urine samples in aqueous DMF medium. The metal ion forms a green colored complex with 2-hydroxy-3-methoxy benzaldehyde thiosemicarbazone (HMBATSC) in an acidic buffer of pH 6.0. The green colored solution, having an absorbance maximum at 380 nm, is stable for more than 72 hours. Beer's law is obeyed in the range of 0.051–2.037 µg ml^?1. The molar absorptivity and Sandell's sensitivity of the method are found as 2.75 × 10⁴ l mol^?1 cm^?1 and 0.0018 µg cm^?2, respectively. The green colored complex has 1:2 [V(V)-HMBATSC] stoichiometry. The stability constant of the complex is determined as 3.267 × 10¹¹ by Job's method. The optimum reaction conditions and other analytical parameters are studied. A sensitive and selective second-order derivative spectrophotometry has also been proposed for the determination of V(V). The interference of various cations and anions are studied. The present method is successfully applied to the determination of vanadium (V) in foodstuffs, alloy steels, and pharmaceutical, water, soil, and urine samples.     

Liquid Chromatographic Analysis of Cephalexin in Human Plasma by Fluorescence Detection of the 9-Fluorenylmethyl Chloroformate Derivative

Abstract

A simple and sensitive precolumn derivatization method for the determination of cephalexin in human plasma has been developed. Cephalexin was derived with 9-fluorenylmethyl chloroformate (FMOC-Cl) in borate buffer (5 mM, pH 8.5) for 15 min at 25°C. Optimal conditions for the derivatization were described. The derivative was chromatographed on an XDB-C₁₈ column with water–acetonitrile (10:90, v/v) as mobile phase at a flow rate of 1.0 mL/min. The fluorescence excitation and emission wavelengths were 268 nm and 314 nm, respectively. The standard curve in spiked plasma was linear over the range of 0.0234–58.5 µg/mL; the detection limit (signal-to-noise ratio = 3; injection volume, 10 µL) was about 0.014 µg/mL. The performance of analysis was studied, and the validated method showed excellent performance in terms of selectivity, sensitivity, precision, and accuracy.     

Liquid Chromatographic Determination of Glyoxal and Methylglyoxal from Serum of Diabetic Patients using Meso‐Stilbenediamine as Derivatizing Reagent

Abstract

Meso‐stilbenediamine has been used as derivatizing reagent for liquid chromatographic (LC) determination of glyoxal (Go), methylglyoxal (MGo), and dimethylglyoxal (DMGo) at pH 3. Liquid chromatographic elution and separation was carried out from the column Kromasil 100 C‐18, 5 µm (15×0.46 mm i.d.) with methanol: water:acetonitrile (59:40:1, v/v/v) with a flow rate of 1 mL/min and ultraviolet detection at 254 nm. The linear calibration curves were obtained for Go, MGo, and DMGo within 0.97–4.86 µg/mL, 1.52–7.6 µg/mL, and 1.41–7.08 µg/mL with detection limits of 48 ng/mL, 76 ng/mL, and 70.8 ng/mL, respectively. The method was applied for the determination of Go and MGo from serum of patients suffering from diabetes and ketosis. The amounts of Go and MGo found were 0.150–0.260 µg/mL and 0.160–0.270 µg/mL with coefficient of variation (C.V.) 2.6–4.7% and 2.5–4.6%, respectively. The results obtained were compared with normal subjects with Go and MGo contents of 0.025–0.065 µg/mL and 0.030–0.070 µg/mL with C.V 1.5–4.9% and 1.6–4.8% in the serum.     

Square Wave Adsorptive Stripping Voltammetric Determination of Cyromazine Insecticide with Multi-Walled Carbon Nanotube Paste Electrode

The electrochemical behavior of cyromazine (N-cyclopropyl-1,3,5-triazine-2,4,6 triamine) insecticide has been studied at newly prepared multi-wall carbon nanotubes paste electrodes using square wave stripping voltammetry. The cyromazine was accumulated at 0.0 mV [vs. Ag/AgCl (3 M NaCl)] and a well-defined anodic peak obtained at +1110 mV in 0.1 M H₂SO₄. The cyclic voltammetric measurements showed an irreversible nature of oxidation wave in the range of scan rates comprised between 500 and 4000 mV s^?1. The calibration curve obtained from square wave stripping voltammetry was linear in the range 0.41 to 83.30 µg/mL with a detection limit of 0.12 µg/mL. The method was applied to the direct determination of cyromazine in natural water samples. Recoveries calculated for river and tap water samples spiked with 10.0 µg/mL level were 101.5 ± 1.9% and 100.6 ± 2.3% at 95% confidence level, respectively. The method was extended to the determination of cyromazine in agrochemical formulation Trigard® with a recovery of 100.49% and accuracy was in agreement with that obtained by HPLC comparison method. Influences of some interfering ions and pesticides were also investigated.     

Electrochemical Behavior of Dopamine at a Mercury Electrode in the Presence of Citrate: Analytical Applications

Abstract

Dopamine can be determined by voltammetric methods using a mercury electrode, previously oxidized at +0.30 V. The oxidation product formed is stabilized in the presence of citrate and undergoes reduction at ?0.31 V. This work describes the electrochemical behavior of dopamine at a mercury electrode in the presence of citrate and its application in the development of a square‐wave voltammetric method for the dopamine determination in pharmaceutical formulations. The method was in‐house validated for determination of dopamine in injectable formulations. The detectability of the method was 0.02 µg ml^?1.     

Cathodic Stripping Voltammetric Determination of Tellurium(IV) with in situ Plated Bismuth-Film Electrode

Abstract

A very sensitive and reliable method is proposed for the determination of tellurium(IV) [Te(IV)] by Osteryoung square-wave cathodic stripping voltammetry. This method is based on the reduction of Te(IV) with bismuth(III) onto an edge-plane pyrolytic graphite electrode, followed by a cathodic potential scan. The reduced Te gave a well-defined catalytic hydrogen wave at ?1200 mV vs. Ag/AgCl. The peak height of the catalytic wave was directly proportional to the initial Te(IV) concentration in the concentration ranges of 0.01–0.10 and 0.1–1.0 µg L^?1 with 30 s deposition time. A 3σ detection limit of 1.0 ng L^?1 Te(IV) was obtained with the same deposition time. The relative standard deviation was 3% on replicate runs (n = 5) for the determination of 0.1 µg L^?1 Te(IV). Analytical results of natural water samples demonstrate that the proposed method is applicable to the determination of traces of Te(IV).     

Voltammetric Determination of Dye-Uptake for C. I. Acid Blue 120 Dyeing Silk

Abstract

The electrochemical behavior of Colour Index Acid Blue 120 at carbon paste electrode is studied with cyclic voltammetry and square wave voltammetry for the first time. Two irreversible oxidative peaks at 0.61 V (P_a,1) and 0.90 V(P_a,2) (both vs. SCE) are found at a scan rate of 0.1 V/s. Their electrode processes are both adsorption-controlled with two electrons and two protons participating. The peak currents of the P_a,1 are proportional to the concentration of Colour Index Acid Blue 120 in the range of 2.08–20.80 µM and 62.4–520.0 µM. The coexisting substances such as inorganic ions and fatty alcohol polyoxyethylene ether do not interfere with the determination. The method is applied to the determination of dye-uptake for Colour Index Acid Blue 120 dyeing silk. The results are in good agreement with the spectrophotometric method.     

Photophysical and photochemical processes of riboflavin (vitamin B2) by means of the transient absorption spectra in aqueous solution

Using time-resolved techniques of 337 and 248 nm laser flash photolysis, the photo physical and photochemical processes of riboflavin (RF, vitamin B₂) were studied in detail in aqueous solution. The excited triplet state of riboflavin (³RF^*) was produced with 337 nm laser, while under 248 nm irradiation, both³RF^* and hydrated electron (e_aq) formed from photoionization could be detected. Photobiological implications have been inferred on the basis of reactivity of³RF^* including energy transfer, electron transfer and hydrogen abstraction. The RF^·+ was generated by oxidation of SO₄ ^·-radical with the aim of confirming the results of photolysis.     

Flow-Injection Analysis Based on Extraction and Spectrophotometric Determination of Penicillins with Thiazine Dyes

Abstract

A new method for flow-injection analysis (FIA) for the determination of penicillins based on the extraction and spectrophotometric determination of ion associates with selected thiazine dyes (methylene blue, azure A, and azure B) is proposed. The reaction conditions (c_dye = 2 × 10^?4 mol l^?1, c_KCl = 1 mol l^?1, pH ? 6, λ = 635 nm) were found. The factorial design has been carried out to determine the optimum flow conditions. A wide linear dynamic range of calibration curves (5.1–700 µg ml^?1 for penicillin V with all dyes, R = 0.9985) and good repeatability (e.g., relative standard deviation [RSD] = 4.6–0.6% in this concentration range for the reaction with azure B) were found. The detection limit for penicillin V is 1.5 µg ml^?1, and the determination limit is 5.1 µg ml^?1. The maximum analysis rate is 35 samples per h. The practical samples of pharmaceutics were tested. There are no interferences from the additives in pharmaceutics.     

Spectrophotometric Determination of Hydrazine

Abstract

A simple sensitive and selective method is described for the determination of trace amounts of hydrazine. The method is based on the reduction of nitrate to nitrite. Hydrazine in ammoniacal condition is used as reducing agent with copper(II) as catalyst. The nitrite prepared is determined based on the diazo coupling reaction between p‐nitroaniline and N‐(1‐naphthyl)ethylenediammine dihydrochloride(NEDA). The method obeys Beer's law in the concentration range of 0–15 µg of hydrazine in a sample volume of 10 ml at 545 nm and the colour is stable for 3 h. The molar absorptivity is calculated to be 3.83×10⁴ l/mol/cm with a correlation coefficient of 0.999. The relative standard deviation is 1.8% (n=10) at 12 µg of hydrazine. Interferences due to foreign ions have been studied and the method has been applied for the determination of hydrazine in boiler feed water.     

Voltammetric Ultra Trace Determination of Tellurium

Abstract

A simple and convenient method is described for the determination of low concentration tellurium based on differential pulse polarographic reduction of Te(IV) in alkaline medium. Linearity of the calibration curve was achieved up to 25.5 ppm with a limit of determination of 0.02 µg/mL. The possible interference of coexisting metal ions was examined and ruled out. The method has been successfully applied for the analysis of tellurium in industrial waste samples.     

Rapid Flow-Injection Method for the Determination of Colistin by Sensitized Chemiluminescence Using the Acidic Permanganate–Sulfite System

Abstract

A simple, rapid, and sensitive chemiluminescence method for the determination of colistin (Polymyxin E), a cyclic polypeptide with antibiotic effect produced by certain strains of Bacillus polymyxa, has been developed by combining a flow-injection technique and the bacteria's sensitizing effect on the chemiluminescence reaction between sulfite and acidic permanganate. The optimum conditions for chemiluminescence emission were established. The chemiluminescence was proportional to the log of concentration of colistin over the range 4–100 µg mL^?1 (3.5–87 µM). The detection limit was 1.2 µg mL^?1 (1.0 µM) of colistin. The method has been satisfactorily used for the determination of colistin in pharmaceuticals.     

Cloud Point Extraction of Serum Albumin and Its Spectrophotometric Determination in Serum Samples

Abstract

A new method based on the cloud point extraction (CPE) separation and ultraviolet spectrometry determination was proposed for the determination of albumin. When the system temperature is higher than the cloud point extraction temperature (CPT) of the mixed surfactant of p‐octyl polyethyleneglycolphenyether (Triton X‐100) and sodium dodecyl sulfate (SDS), serum albumin could be extracted into surfactant‐rich phase. The main factors affecting the cloud point extraction were investigated systematically. Under the optimized conditions, the determination limit for serum albumin as low as 0.18 µg/mL was obtained by preconcentrating a 10 mL sample solution, and the relative standard deviation (n=10, c=40.0 µg/mL) was 3.77%. The proposed method was applied to the determination of albumin in serum samples. The results obtained by this method were in good agreement with coomassie brilliant blue (CBB).     

Synchronized stability indicating RP-LC methods for determination of metolazone with losartan potassium or spironolactone in presence of their degradation products

Abstract

Two precise and selective stability-indicating RP-LC methods have been developed and validated for simultaneous determination of metolazone in its binary mixture with losartan potassium (method 1) and spironolactone (method 2) in the presence of their degradation products. For method 1, the chromatographic separation was achieved on Kromasil C₁₈ column, the mobile phase consisted of a mixture of 0.1% ortho-phosphoric acid in acetonitrile and 0.1% ortho-phosphoric acid in water (28:72, v/v) pumped at flow rate 2?mL/min and UV detection at 235?nm. Linearity was determined over the concentration range of 2–16µg/mL for metolazone and 40–320µg/mL for losartan potassium. For method 2, chromatographic separation of metolazone and spironolactone was achieved on a Symmetry C₈ column using a mobile phase that consisted of acetonitrile, methanol, and 0.1% ortho-phosphoric in water in gradient mode pumped at a flow rate 1.5?mL/min with programed wavelength detection. Linearity was determined over the concentration range of 2–16µg/mL for metolazone and 20–160µg/mL for spironolactone. The suggested methods were proved to be highly selective, precise and accurate for simultaneous determination of the cited drugs in their combined pharmaceutical dosage form in the presence of their degradation products. The proposed methods were validated in compliance with ICH guidelines.

1. Highlights

2. Synchronized determination of metolazone and co-formulated drugs in presence of their degradation products.

3. Act as a method for screening of metolazone and co-formulated drugs in quality control laboratories.

4. Validation of suggested methods according to ICH guidelines.

5. The pathway of degradation of metolazone under different stress conditions was proposed.

     

A new rapid and economic liquid chromatographic method for simultaneous determination of meglitinides with metformin: application in the presence of metformin and repaglinide impurities and related compounds

A new liquid chromatographic method was developed for simultaneous determination of the widely used oral antidiabetic, metformin hydrochloride with antidiabetics comprising the meglitinides class in bulk, laboratory-prepared mixtures and pharmaceutical products. It was applied in the presence of metformin-reported impurity (1-cyanoguanidine). It was also applied for the determination of repaglinide in the presence of its related compounds. Chromatographic separation was achieved with isocratic elution mode using a mobile phase of acetonitrile: 0.01 M sodium dihydrogen phosphate (pH: 2.8) (67:33; v/v) flowing through a LiChrospher NH₂ (amino) Agilent^® column (250 × 4.6 mm—5 µm) at a rate of 0.8 mL/min at ambient temperature in a run time of 4 min. UV detection was carried out at 220 nm. The method was validated according to International Conference on Harmonization guidelines. Linearity, accuracy and precision were satisfactory over concentration ranges (µg/mL): 3.5–350 for metformin hydrochloride, 14–140 for nateglinide, 1–100 for mitiglinide calcium and 0.1–100 for repaglinide. Coefficients of determination were ?0.99 for all analytes. Limits of quantification were found (in µg/mL): 0.06, 0.08, 0.198 and 0.029 for metformin hydrochloride, nateglinide, mitiglinide calcium and repaglinide, respectively. The present method was found to be rapid, selective, economic and simple in operation satisfying the chromatographers’ needs for quality assessment of pharmaceutical products.     

Kinetic Method for the Determination of α‐Methyldopa in Pharmaceutical Preparations: Analytical Procedure and Reaction Mechanism Considerations

Abstract

A reliable and very simple kinetic method is proposed for the determination of α‐methyldopa in pharmaceutical preparations. It is based of the oxidation of α‐methyldopa, a catechol derivative, to quinone, by the ferric ion in the presence of salicylic acid and HCl. The deep blue complex formed between iron(III) and salicylate (λ_max 525 nm) allows the reaction to be watched as absorbance decreases with the reduction of the ferric ions to ferrous with the consequent dissociation of the complex. Four pharmaceutical preparations were analyzed and the results were compared with those obtained with the spectrophotometric United States Pharmacopeia method. The statistical t‐Student and the F‐tests were applied to compare the results obtained with the two independent methods. In all cases complete agreement, in terms of accuracy and precision, was observed with a confidence level of 95% (α=0.05). Considering the four samples analyzed, using the proposed method, and five determinations for each sample, the observed mean relative standard deviation (RSD) is about 0.8%. The concentration range studied was from about 2×10^?4 mol L^?1 to 18×10^?4 mol L^?1 (about 40 µg/mL to 360 µg/mL) in the final solution and it is quite adequate for the analytical procedure at 25.0±0.1°C. A typical coefficient of determination, r², of the calibration curve, is 0.9994. For the kinetic pseudo first order curves a typical observed r² is 0.99998. The Arrhenius activation energy was found to be 84.2±3.4 kJ mol^?1. A schematic mechanism of the reaction is proposed.     

Flow Injection Post-Chemiluminescence Reaction of Astemizole in N-Bromosuccinimide-Calcein System and Its Application

A flow injection post chemiluminescence (FI-PCL) reaction was found when astemizole was mixed with the CL reaction mixture of N-bromosuccinimide and calcein under alkaline conditions. Based on this observation, a simple and sensitive post chemiluminescence (PCL) technique for the assay of astemizole was described. Under the optimized conditions, the PCL values responded linearly to the concentration of astemizole in the range 1.0 × 10^?3–3.0 µg/mL, with a detection limit of 7.0 × 10^?4 µg/mL. The relative standard deviation was 1.7% for 1.0 × 10^?2 µg/mL astemizole solution (n = 13). It was applied to the determination of astemizole in pharmaceutical preparations with satisfactory results.