Extraction-spectrophotometric determination of amprolium hydrochloride using bromocresol green, bromophenol blue and bromothymol blue

A new procedure for the determination of amprolium hydrochloride by reaction with bromocresol green (BCG), bromophenol blue (BPB) and bromothymol blue (BTB) has been developed. The method consists of extracting the yellow ion-pair formed into chloroform from aqueous medium. The ion-pairs have absorption maxima at 420, 410 and 415 nm with molar absorptivities of 3.64 × 10⁴, 3.12 × 10⁴ and 2.31 × 10⁴1 mol^–1 cm^–1 for BCG, BPB and BTB, respectively. The method obeys Beer's law over the concentration ranges 0.6–12.0, 0.12–8.8 and 1.2–11.3 ag/ml amprolium hydrochloride for BCG, BPB and BTB, respectively. The method is simple, precise (relative standard deviation 0.665–2.210%), accurate (recovery 97.8–100.8%) and easily applied for pharmaceutical quality assurance for amprolium hydrochloride in raw materials and in formulated veterinary soluble powder.     

Spectrophotometric assay of cephalosporins in pharmaceutical products,using chromotrope 2B and chromotrope 2R

A simple, rapid and sensitive Spectrophotometric method is proposed for the determination of cephadroxil (I), cephalexin (II) and cephradine (III). The method is based on ion-pair complex formation between these derivatives and Chromotrope 2B (C2B) or Chromotrope 2R (C2R), to give a highly coloured radical anion. The coloured products are quantified spectrophotometrically at 542 and 564 nm for C2B and C2R, respectively. The optimization of the experimental conditions is described. The method has been used for the determination of 0.4–15, 0.4–14 and 0.4–18 g/ml of drugs I, II and III, respectively. The accuracy of the method is indicated by the excellent recovery (100.0±1.7%) and the precision is supported by the low relative standard deviations 1.5%. The sensitivity of the method is discussed and the results are compared with the official method. The interference from common degradation products and excipients was also studied. The proposed method was applied successfully to the determination of the different cephalosporins in dosage forms, with good precision and accuracy. The results were compared with those given by the official B.P. 1993 method.     

Indirect Spectrofluorimetric Determination of Piroxicam and Propranolol Hydrochloride in Bulk and Pharmaceutical Preparations

A simple and sensitive indirect spectrofluorimetric method for the assay of piroxicam (PX) and propranolol hydrochloride (PPH) in the pure form and in pharmaceutical formulations is proposed. This method is based on the oxidation of PX and PPH by a known excess of N-bromosuccinimide (NBS) followed by the reaction of the excess NBS with methdilazine hydrochloride (MDH) to yield fluorescent species. The fluorescence intensities were measured at 377 nm after excitation at 343 nm. The fluorescence intensities decrease linearly with an increase in concentration of PX and PPH over the ranges of 0.2–8.0 and 0.4–18.0 g/mL respectively. The common excipients and additives did not interfere in the determination. The proposed method has been successfully applied for the determination of PX and PPH in pharmaceutical formulations. The results have been validated by statistical data.     

RP-HPLC Determination of Famotidine and its Potential Impurities in Pharmaceuticals

A simple, sensitive, and rapid reversed-phase high-performance liquid chromatographic method has been developed for determination of famotidine (FMT) and its impurities in pharmaceutical formulations. Separations were performed on a Supelcosil LC18 column with an isocratic mobile phase—13:87 (v/v) acetonitrile–0.1 M dihydrogen phosphate buffer containing 0.2% triethylamine (pH 3.0). The mobile phase flow rate was 1 mL min^–1 and the detection wavelength was 265 nm. Response was linearly dependent on concentration between 1 and 80 g mL^–1 (regression coefficient, R², from 0.9981 to 0.9999). RSD from determination of method repeatability (intraday) and reproducibility (interday) were <2% (n=6). Lowest detectable concentrations ranged from 0.08 to 0.14 g mL^–1. The proposed liquid chromatographic method can be satisfactorily used for routine quality control of famotidine in pharmaceutical formulations.     

Spectrophotometric procedures for the determination of roxithromycin in pharmaceutical formulations

Four simple and sensitive visible spectrophotometric procedures for the assay of roxithromycin (RXT) have been developed. Procedures A and B are based on the formation of ion-pairs of roxithromycin with the dyes supracen violet 3B and tropaeolin 000, which are extracted into chloroform and have absorption maxima at 590 nm (SV 3B) and 490 nm (TP 000). Procedures C and D are based on condensation between the hydrolysis product of RXT in the presence of 3.6M hydrochloric acid in acetic acid medium and vanillin orp-dimethylaminobenzaldehyde (PDAB) to form coloured products with _max at 500 nm. Regression analysis of the Beer's plot showed good correlation in the concentration ranges 5–60 (A), 5–40 (B) and 5–50 (C & D) g/ml. No interference was observed from excipients and the validity of the procedures was tested by analysing pharmaceutical formulations. Recoveries were 99.0–102.0%. The concentration measurements are reproducible within a relative standard deviation of 1.0%.     

Analysis of various very slightly water soluble drugs in micellar medium

A potentiometric and/or visual method for the determination of sulphamethoxazole (SULF) in pure form in the range of 5.3 × 10^–5 to 5.0 × 10^–4 mol/L is proposed. To enhance the solubility, the determination has been carried out in a micellar medium formed by an aqueous 5.0 × 10^–2 mol/L N-hexadecyl-N,N,N-trimethyl ammonium bromide (CTAB) solution which increases the dissociation constant K of SULF about tenfold. The titration is performed with NaOH (2.5 × 10^–3 or 5.0 × 10^–2 mol/L) and the end-point is determined by the second derivative graph. The results agree with those obtained by the official method of the USP XXIII. The method is simple, accurate, economical and can successfully replace the more complicated, more expensive and time-consuming existent procedures which are carried out in a non-aqueous medium.     

Spectrophotometric Determination of Certain Vicinal Dihydroxybenzene Derivatives with Sodium Bismuthate

A simple and accurate spectrophotometric method is developed for the determination of certain vicinal dihydroxybenzene derivatives, namely, dopamine (DPH), levodopa (LD), methyldopa (MD) and pyrocatechol (PC) using sodium bismuthate in an acid medium. The method is based on the formation of a yellow colored product by the oxidation of vicinal dihydroxybenzene derivatives using sodium bismuthate. Beer's law was obeyed over the concentration range of 8–130 g/mL with the maximum absorption at 422–429 nm. The molar absorptivity and Sandell's sensitivity as evaluated from Beer's law data were found to be in the range of 1.02–1.34 × 10^–3L mol^–1cm^–2and 108–185 ng/cm²respectively. The proposed method has been successfully applied for the determination of DPH, LD and MD in injections and tablets of pharmaceutical preparations. The reliability of the methods was established by replicate determinations with the reported and official method.     

Ion-pair adsorption film colorimetry of iron (III) in water samples and human serum

The anionic chelate of iron(III)-2,2-dihydroxyazobenzene (H₂L), [FeL₂]^–, formed 1 1 ion-pair with crystal violet cation (CV⁺), CV⁺ [FeL₂]^–, and was adsorbed on a surface of transparent polyvinyl chloride (PVC) film plasticized with di-n-octyl phthalate. Enrichment of the blue violet species of the ion-pair onto the transparent PVC film has enabled a highly sensitive and simple method for the determination of iron(III). The detection limits are 1 × 10^–8 mol dm^–3 (0.6 ppb) by spectrophotometry at 592 nm, and 4 × 10^–8 mol dm^–3 (2 ppb) by visual colorimetry. The method has been successfully applied to the determination of iron in water samples and human serum. No preparatory procedures for the separation of serum protein and other coexisting substances are required, since ion-pair adsorption process provides a new method to prevent interference of serum matrix.     

Determination of 1,4-benzodiazepines in drug dosage forms by difference spectrophotometry

A spectrophotometric method has been developed for the determination of seven 1,4-benzodiazepines, namely: chlordiazepoxide, diazepam, nitrazepam, oxazepam, lorazepam, temazepam and cinolazepam. The method involves reduction of the target compounds using Zn/HCl and measuring the difference in the absorbance before and after reduction. The quantities of zinc and acid required for efficient reduction were carefully studied. 1–20 g ml^–1 of the compounds could be determined with < 1% error. The method was applied successfully to the determination of these compounds in pharmaceutical dosage forms. The results were sufficiently accurate and precise and comparable to those from the official methods.     

HPLC Determination of Ritodrine Hydrochloride in Pharmaceutical Formulations

A simple, rapid, and accurate HPLC method is described for the determination of ritodrine hydrochloride (RTH) in both pure form and pharmaceutical formulations. A Hypersil Shendon ODS column with a mobile phase of dibasic phosphate buffer and acetonitrile (75 : 25) and isoxsuprine hydrochloride were used as an internal standard. The flow rate was 1 mL min^–1 and the effluent was monitored at 270 nm pH 4.0. The calibration graph is linear in the range 2–30 g mL^–1. The proposed HPLC method has been successfully employed for the determination of RTH in Yutopar tablets and injection solutions.     

Spectrophotometric estimation of ketotifen fumarate in pharmaceutical formulations

Four simple and sensitive spectrophotometric methods (A–D) for the determination of Ketotifen fumarate in bulk samples and pharmaceutical formulations are described. They are based on the formation of coloured species by the coupling of the diazotised sulphanilamide with the drug (method A, _max 520 nm) or by oxidizing it with excessN-bromo-succinimide and determining the consumed NBS with decrease in colour intensity of celestine blue (method B: _max 540 nm) or by the reduction of Folin-Ciocalteau reagent (method C: _max 720 nm) or by the formation of a chloroform-soluble, coloured ionassociation complex between the drug and Azocarmine G at pH 1.5 (method D: _max 540 nm). Regression analysis of Beer-Lambert plots showed good correlations in the concentration ranges 1–10, 2–12, 4–28 and 2.5–25 g/ml for methods A–D, respectively. The validity of the proposed methods was tested by analysing pharmaceutical formulations containing KTF: the relative standard deviations were within ±1.0%. Recoveries were 98.9–100.2%.     

Electrochemical studies and square-wave voltammetric determination of fenofibrate in pharmaceutical formulations

The electrochemical reduction of fenofibrate at a hanging mercury drop electrode (HMDE) was investigated by cyclic voltammetry, square-wave voltammetry, and chronoamperometry. Different buffer solutions were used over a wide pH range (3.0–10.0). The best definition of the analytical signals was found in borate buffer (pH 9.0)–tetrabutylammonium iodide mixture containing 12.5% (v/v) methanol at –1.2 V (versus Ag/AgCl). According to cyclic voltammetric studies, the reduction was irreversible and diffusion controlled. The diffusion coefficient was 2.38×10^–6 cm² s^–1 as determined by chronoamperometry. Under optimized conditions of square-wave voltammetry, a linear relationship was obtained between 0.146–4.96 g mL^–1 of fenofibrate with a limit of detection of 0.025 g mL^–1. Validation parameters such as sensitivity, accuracy, precision, and recovery were evaluated. The proposed method was applied to the determination of fenofibrate in pharmaceutical formulations. The results were compared with those obtained by a published high-performance liquid chromatography method. No difference was found statistically.     

Spectrophotometric determination of some phenolic sympathomimetic drugs through reaction with 2,6-dihaloquinone chlorimides

A spectrophotometric procedure is described for the determination of three phenolic sympathomimetic drugs: etilefrine hydrochloride, prenalterol hydrochloride and ritodrine hydrochloride. The method involves the use of 2,6-dichloro- and 2,6-dibromoquinone chlorimides as chromogenic reagents. The phenolic drugs produce a blue color, peaking from 610 to 630 nm. The colors produced obey Beer's law and are suitable for the quantitative determination of the named compounds. The molar ratios of the reactions were established and a proposal for the reaction pathway is given. The procedures described were applied successfully to the determination of the compounds in their dosage forms. The results showed that the proposed procedures compared favourably with the reference methods and satisfactory sensitivity, accuracy and precision (SD < 0.1 g ml^–1) were noted. Detection limits are typically 0.2–0.4 g ml^–1. Other advantages of the procedures are their simplicity and speed.     

High-Performance Liquid Chromatographic Method for the Determination of Nimesulide in Pharmaceutical Preparations

A simple, rapid, and precise high-performance liquid chromatographic method for the determination of nimesulide in pharmaceutical preparations was proposed using Ibuprofen as an internal standard. The separation was performed on a CLC C₁₈ (5 m, 25 cm × 4.6 mm i.d.) column with a mobile phase consisting of an acetonitrile–0.05 M KH₂PO₄ buffer mixture of pH 7.00 (55 : 45, v/v). The detection was carried out at 230 nm and the linearity range was found to be 0.5–100 g/mL. The method has been applied successfully to the determination of nimesulide in pharmaceutical formulations. The recovery values were found to be in the range of 99.23–100.13% with RSD values of less than 0.97%.     

Spectrophotometric determination of some pharmaceutically-important aminoquinoline antimalarials

A simple and rapid spectrophotometric method for the assay of amodiaquine hydrochloride, chloroquine phosphate and primequine phosphate is described. The method is based on the interaction of the drug with tetracyanoethylene to give a stable charge transfer complex. The spectra of the complex show maxima at 413, 415 and 415nm, respectively, with high apparent molar absorptivities. Beer's law is obeyed in the concentration ranges 2–12, 1–8 and 2–12 g ml^–1 of the three drugs studied. The proposed method is applied to the determination of these drugs in certain formulations and the results are favourably comparable to the official methods.     

Rapid spectrofluorimetric determination of lisinopril in pharmaceutical tablets using sequential injection analysis

The present work reports for the first time a simple and rapid method for the spectrofluorimetric determination of lisinopril (LSP) in pharmaceutical formulations using sequential injection analysis (SIA). The method is based on reaction of LSP with o-phthalaldehyde (OPA) in the presence of 2-mercaptoethanol (borate buffer medium, pH=10.6). The emission of the derivative is monitored at 455 nm upon excitation at 346 nm. The various chemical and physical conditions that affected the reaction were studied. The calibration curve was linear in the range 0.3–10.0 mg L^–1 LSP, at a sampling rate of 60 injections h^–1. Consumption of OPA reagent was significantly reduced compared with conventional flow injection (FI) systems, because only 50 L of OPA was consumed per run. The method was found to be adequately precise (s_r=2% at 5 mg L^–1 LSP, n=10) and the 3 detection limit was 0.1 mg L^–1. The method was successfully applied to the analysis of two pharmaceutical formulations containing LSP. The results obtained were in good agreement with those obtained by use of high-performance liquid chromatography (HPLC), because the mean relative error, e_r, was <1.8%.     

Use of alizarin red S as a chromogenic agent for the colorimetric determination of dothiepin hydrochloride in pharmaceutical formulations

The present study describes two simple, rapid, selective and cost-effective spectrophotometric methods for the determination of dothiepin hydrochloride (DOTH), an antidepressant drug, in bulk drug and pharmaceutical formulations. The first method (method A) is based on the formation of yellow colored ion-pair complex between DOTH and alizarin red S (ARS) in acid medium which was extracted into dichloromethane and the absorbance was measured at 445 nm. The second method (method B) is based on the breaking of the yellow DOTH–ARS ion-pair complex in alkaline medium followed by the measurement of the violet color free dye at 570 nm. Under the optimized conditions, Beer’s law is obeyed over the concentration ranges of 2.50–55.0 and 1.00–35.0 μg ml⁻¹ DOTH for method A and method B, respectively. The molar absorptivity, Sandell’s sensitivity, detection and quantification limits are also calculated. The methods were validated for intra-day and inter-day accuracy and precision; selectivity and robustness and ruggedness. The proposed methods were applied successfully to the determination of DOTH in pure drug and commercial formulations. The accuracy and reliability of the proposed methods were further established by parallel determination by the official method and also by recovery studies via standard addition technique.     

Spectrophotometric Determination of Antiallergic Drug in Bulk Powder and in Its Pharmaceutical Formulations

Two simple, rapid and selective spectrophotometric methods have been described for the determination of promethazine hydrochloride (PMH) either in pure or pharmaceutical formulations. The methods are based on the formation of a green colored product with sulphanilic acid (SPA) in presence of N-bromosuccinimide (NBS) or a red colored, chloroform soluble product with p-nitroaniline (PNA) in presence of ceric ammonium sulphate (CAS). The chromogen formed has maximum absorption at 600 nm and at 510 nm with SPA and PNA, respectively. The optimum reaction conditions and other analytical parameters are evaluated. Beer's law is valid in the concentration range of 0.5–25 g/mL (R= 0.9983) with SPA and 2–75 g/mL (R = 0.9981) with PNA. Molar absorptivity values as calculated from the Beer's law data are 5.54 × 10³ L/mol/cm and 3.05 × 10³ L/mol/cm for SPA and PNA, respectively. The results are in good agreement with those of the official method. No interference was observed from common pharmaceutical excipients.     

Sequential Determination of Hydrocortisone and Epinephrine in Pharmaceutical Formulations via Photochemically Enhanced Fluorescence

The study describes a simple and sensitive method for the sequential determination of hydrocortisone (HDC) and epinephrine (EP) in pharmaceutical formulations. The intrinsic fluorescence of epinephrine was measured before submitting the sample to a photochemical reaction to form a fluorescent product from HDC or HDC esters (succinate and acetate). The sample treatment eliminated the fluorescence from EP, thus minimizing spectral interference on the HDC fluorescence. Limits of detection (3S_b/m) were estimated to be 40ngmL^–1 for HDC or HDC salts and 0.2ngmL^–1 for EP. Recovery experiments, made with commercial and laboratory simulated formulations, gave values between 96 and 103% for both HDC and EP. This method can be easily automated, e.g. via flow-injection techniques.     

Spectrophotometeric determination of someN-substituted phenothiazine derivatives usingN-bromophthalimide

A simple, rapid and sensitive spectrophotometric method is described for the quantitative determination ofN-substituted phenothiazines. The method depends on the formation of a stable phenothiazine free radical cation by the use ofN-bromophthalimide as oxidising agent in a strong acid medium (methanol/ sulphuric acid 1 1 v/v). The produced red or violet color possesses absorption maximum range from 500 to 530 nm. A linear relationship exists between the absorbance at (_max) and concentration in the range 5 to 40 g ml^–1 with apparent molar absorptivities range from 6 × 10³ to 12 × 10³1 mol^–1 cm^–1. The color is developed instantaneously for all the studied phenothiazines except for thioproperazine mesylate, trifluoperazine dihydrochloride and prochlorperazine mesylate that require 25, 15 and 25 min, respectively, for complete reaction. The developed colors are stable over 24 h. The average % recovery is 99.85±0.61 to 100.28±0.95. The method was applied successfully to the microdetermination of chlorpromazine HCl, promethazine HCl, pericyazine, thioproperazine mesylate, perphenazine, prochlorperazine mesylate, trimeprazine tartrate and trifluoperazine 2HCl either in pure form or incorporated in their pharmaceutical preparations. The results of analysis are in good agreement with those of the official B.P. 1988 and USP XXII.