Sensitive spectrophotometric determination of ascorbic acid in fruit juices and pharmaceutical formulations using 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (Br-PADAP)

A simple and very sensitive method has been developed for the determination of ascorbic acid based on the oxidation of ascorbic acid to dehydroascorbic acid by iron(III), followed by a complexation of iron(II) with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol(Br-PADAP). The iron(II) complex is formed immediately, with absorption maxima at 560 and 748 nm and a molar absorptivity of 1.31 × 10⁵ l mole^–1cm^–1 and 5.69 × 10⁴ l mole^–1cm^–1, respectively. The ascorbic acid determination is possible with a linear range up to 2.4 μg ml^–1, a calibration sensitivity of 0.744 ml μg^–1 at 560 nm and 0.323 ml μg^–1 at 748 nm, and a detection limit of 15 ng ml^–1 and 44 ng ml^–1, respectively. The procedure was used for the ascorbic acid determination in several fruit juices and pharmaceutical formulations. The results demonstrated a good precision (R.S.D. < 1%) and are in agreement with those obtained with others methods. The Br-PADAP method proposed is six times more sensitive than the method using the iron(II)-1,10-phenanthroline system. Received: 7 May 1996 / Revised: 1 July 1996 / Accepted: 8 August 1996     

Sensitive spectrophotometric determination of ascorbic acid in fruit juices and pharmaceutical formulations using 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (Br-PADAP)

A simple and very sensitive method has been developed for the determination of ascorbic acid based on the oxidation of ascorbic acid to dehydroascorbic acid by iron(III), followed by a complexation of iron(II) with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol(Br-PADAP). The iron(II) complex is formed immediately, with absorption maxima at 560 and 748 nm and a molar absorptivity of 1.31 × 10⁵ l mole^–1cm^–1 and 5.69 × 10⁴ l mole^–1cm^–1, respectively. The ascorbic acid determination is possible with a linear range up to 2.4 μg ml^–1, a calibration sensitivity of 0.744 ml μg^–1 at 560 nm and 0.323 ml μg^–1 at 748 nm, and a detection limit of 15 ng ml^–1 and 44 ng ml^–1, respectively. The procedure was used for the ascorbic acid determination in several fruit juices and pharmaceutical formulations. The results demonstrated a good precision (R.S.D. < 1%) and are in agreement with those obtained with others methods. The Br-PADAP method proposed is six times more sensitive than the method using the iron(II)-1,10-phenanthroline system. Received: 7 May 1996 / Revised: 1 July 1996 / Accepted: 8 August 1996     

Titrimetric and Spectrophotometric Determination of Some Phenothiazine Psychotropics in Pure Form and in Pharmaceutical Formulations with Metavanadate

 Two simple, fast, accurate and precise methods for the determination of six phenothiazines and a number of their pharmaceutical formulations are described. The titrimetric method involves the oxidation of the drugs by metavanadate in sulphuric acid medium and titration of vanadium(IV) formed, with cerium(IV) using ferroin indicator and acetone as catalyst. In spectrophotometry, vanadium(IV) formed was reacted with ferriin and the resulting ferroin measured at 510 nm. Phenothiazines in the ranges 5–100 mg and 2.5–25.0 μg mL⁻¹ can be determined by titrimetry and spectrophotometry, respectively, with detection limits of 0.96–2.05 mg and 0.0359–0.0565 μg mL⁻¹, respectively. Both methods were applied successfully to the determination of the studied drugs in pharmaceutical preparations. The reliability of the assays was established by parallel determination by the official methods of British Pharmacopoeia and the results being statistically evaluated. Received September 26, 2000. Revision March 25, 2001.     

Development and validation of spectrophotometric methods for determination of some cephalosporin group antibiotic drugs

A simple and direct spectrophotometric method is developed for the determination of some cephalosporin group antibiotic drugs such as Loracarbef (Lora), Ceftazidime (Ceft), and Cefaclor (Cefa) in bulk and pharmaceutical formulations. The optimum conditions for the analysis of aqueous solutions of drugs are studied. Under the optimum conditions, the three drugs could be assayed in the concentration range 2–9 × 10⁻⁵, 2–6 × 10⁻⁵, and 3–9 × 10⁻⁵ M for Lora, Ceft and Cefa, respectively. Detection and quantification limits are calculated. The obtained results showed good recoveries of 100.4, 107.4, and 100.7% for Lora, Ceft, and Cefa, respectively. The results obtained are compared favorably with those given by literature methods.     

Indirect spectrophotometric determination of diltiazem hydrochloride in pure form and pharmaceutical formulations

Three simple, accurate, and sensitive spectrophotometric methods (A, B and C) have been described for the indirect assay of diltiazem hydrochloride (DIL.HCl), either in pure form or in pharmaceutical formulations. The first method (A) is based on the oxidation of DIL.HCl by N-bromosuccinimide (NBS) and determination of unconsumed NBS by measuring the decrease in absorbance of amaranth dye (AM) at a suitable λ _max =521 nm. Other methods (B) and (C) involve the addition of excess cerric ammonium sulfate (CAS) and subsequent determination of the unconsumed oxidant by a decrease in the red color of chromotrope 2R (C2R) at a suitable λ _max =528 nm or a decrease in the orange-pink color of rhodamine 6G (Rh6G) at λ _max =525 nm, respectively. Regression analysis of Beer-Lambert plots showed good correlation in the concentration ranges 3.0–9.0, 3.5–7.0 and 3.5–6.3 μg ml⁻¹ for methods A, B and C, respectively. The apparent molar absorptivity, Sandell's sensitivity, detection and quantification limits were calculated. The proposed methods have been applied successfully for the analysis of the drug in its pure form and its dosage form. No interference was observed from a common pharmaceutical adjuvant. Statistical comparison of the results with the reference method shows excellent agreement and indicates no significant difference in accuracy and precision.     

Vanadophosphoric Acid as a Modified Reagent for the Spectrophotometric Determination of Certain Cephalosporins and their Dosage Forms

Summary.  Vanadophosphoric acid in acidic medium is proposed as a modified reagent for the spectrophotometric determination of cephalexin, cephaprine sodium, cefazolin sodium, and cefotaxime in pure samples and in pharmaceutical preparations. The method is based on acid hydrolysis of cephalosporins and subsequent oxidation with vanadophosphoric acid. The resulting solution exhibits maximum absorption at about 516 nm. The effects of reaction conditions were investigated. Lambert-Beer’s law was obeyed over a concentration range of about 0.4–45 μg · cm⁻³. For more accurate results, Ringbom optimum concentration ranges were obtained, and the molar absorptivities and Sandell sensitivities were derived. The proposed method was applied to the determination of the drugs in pharmaceutical formulations; the results demonstrated that the proposed method is as accurate, pecise, and reproducible as the official methods. Received August 13, 1999. Accepted (revised) December 7, 1999     

Use of a diazocoupling reaction for sensitive and selective spectrophotometeric determination of furosemide in spiked human urine and pharmaceuticals

Two simple, sensitive, and selective spectrophotometric methods for the determination of 5-(aminosulfonyl)-4-chloro-2-((2-furanylmethyl)amino)benzoic acid (furosemide, FUR) are described. The methods are based on acid hydrolysis of FUR to free primary aromatic amine and diazotization followed by coupling with N-1-napthylethylene diamine (NEDA) (method A) or 4,5-dihydroxynaphthalene-2,7-disulfonic acid (chromotropic acid, CTA) (method B). The colored reaction product can be measured spectrophotometrically at 520 nm (method A) or 500 nm (method B). Beer’s law is obeyed over the ranges of 1.75–21.0 μg mL⁻¹ and 2.5–30.0 μg mL⁻¹, for method A and method B, respectively. Apparent molar absorptivities and Sandell’s sensitivities (in L mol⁻¹ cm⁻¹ and μg cm⁻² per 0.001 absorbance unit, respectively) were 1.34 × 10⁴ and 0.0253 using NEDA as the coupling agent, and 8.5 × 10³ and 0.0389 using CTA for the same purpose. Analysis of solutions containing seven different concentrations of FUR gave a correlation coefficient of 0.9979 using NEDA and 0.9984 using CTA, while the slope and the correlation coefficient of the regression equation were calculated. The reaction stoichiometry in both methods was evaluated by the limiting logarithmic method and was found to be 1: 1 (diazotized FUR: NEDA or diazotized FUR: CTA). The methods were successfully applied to the determination of FUR in spiked human urine and in pharmaceutical formulations. The recovery of FUR from spiked urine was satisfactory resulting in the values of (109.4 ± 4.37) % using NEDA and (113.0 ± 4.74) % using CTA. Results of the analysis of pharmaceuticals demonstrated that the proposed procedures are at least as accurate and precise as the official method while a statistical analysis indicated that there was no significant difference between the results obtained by the proposed methods and those of the official method.     

Adsorptive stripping voltammetric determination of netilmicin in the presence of formaldehyde

A linear sweep adsorptive stripping voltammetric method for the determination of netilmicin in the presence of formaldehyde has been proposed for the first time. In the presence of 3.0×10⁻³ g ml⁻¹ formaldehyde, netilmicin exhibits a sensitive cathodic peak at −1.30 V (vs. the saturated calomel electrode, SCE) in a medium of Britton–Robinson buffer (pH 8.7) with a scan rate of 100 mV s⁻¹ after a preconcentration period of 120 s at −1.10 V (vs. SCE). The peak current showed a linear dependence on the netilmicin concentration over the range 4.2×10⁻⁹–1.0×10⁻⁷ g ml⁻¹. The achieved limits of detection and quantitation were 1.0×10⁻¹⁰ and 3.3×10⁻¹⁰ g ml⁻¹ netilmicin, respectively. It was deduced from the experiments that the amine–aldehyde condensation product formed between netilmicin and formaldehyde is mainly responsible for the appearance of the peak. The electrochemical behavior of netilmicin in the presence of formaldehyde has been studied. The method was applied to the direct determination of netilmicin in injectable formulations and spiked human urine and serum samples.      

High sensitive determination of trace amount of cobalt by catalytic adsorptive stripping voltammetry

A very sensitive and selective catalytic adsorptive cathodic stripping procedure for trace measurements of cobalt is presented. The method is based on adsorptive accumulation of cobalt-CCA (calcon carboxylic acid) complex onto a hanging mercury drop electrode followed by reduction of the adsorbed species by voltammetric scan using differential pulse modulation. The reduction current is enhanced catalytically by nitrite. The effect of various parameters such as pH, concentration of CCA, concentration of nitrite, accumulation potential and accumulation time on the selectivity and sensitivity were studied. The optimum condition for the analysis of cobalt, include pH 5.2 (Acetate buffer), 2.1 μM clacon carboxylic acid, 0.032 M sodium nitrite and an accumulation potential of 0.05 V (versus Ag/AgCl). Under these optimum conditions and for an accumulation time of 60 s, the measured peak current at −0.480 V is proportional to the concentration of cobalt over the entire concentration range tested 0.003–2.0 ng ml⁻¹ with a detection limit of 1 pg ml⁻¹ for an accumulation time of 60 s and 2.0–10.0 ng ml⁻¹ for an accumulation time of 40 s. The relative standard deviations for ten replicate measurement of 0.5 ng ml⁻¹ of cobalt were 3.1%. The main advantage of this new system is the microtrace Co(II) determination by ASV. The method was applied to determination of cobalt in a water sample and some analytical grade salts with satisfactory results. Published in Elektrokhimiya in Russian, 2009, Vol. 45, No. 2, pp. 221–228. The article is published in the original.     

Comparison of analytical methods for quality control of pharmaceutical formulations containing glutathione

Summary The aim of this investigation was the study and development of analytical procedures suitable for the assay of glutathione (GSH) in pharmaceutical formulations. Two are based on isocratic HPLC with a 250 mm×4.6 mm i.d., 5 μm C₁₈ column and UV detection. In the first procedure sample solutions were injected without pretreatment whereas in the second the samples were injected after derivatization with Ellman’s reagent which forms an easily detectable adduct with GSH. Good linearity was obtained over the range 0.12–6.00×10⁻⁴M for the direct procedure and 0.25–3.00×10⁻⁴M for the derivatization procedure. The precision and rapidity of analysis were also good for both methods. The third method is based on capillary zone electrophoresis (CZE) in a 27 cm×75 μm i.d untreated fused silica capillary containing pH 7 phosphate buffer. All results are in good agreement with a spectrophotometric procedure used as reference method.     

Development of membrane electrodes for selective determination of some antiepileptic drugs in pharmaceuticals,plasma and urine

Newly developed, simple, low-cost and sensitive ion-selective electrodes have been proposed for determination of some antiepileptic drugs such as lamotrigine, felbamate, and primidone in their pharmaceutical preparations as well as in biological fluids. The electrodes are based on poly(vinyl chloride) membranes doped with drug–tetraphenyl borate (TPB) or drug–phosphotungstic acid (PT) ion-pair complexes as molecular recognition materials. The novel electrodes displayed rapid Nernstian responses with detection limits of approximately 10⁻⁷ M. Calibration graphs were linear over the ranges 5.2 × 10⁻⁷–1.0 × 10⁻³, 1.5 × 10⁻⁶–1.0 × 10⁻³, and 2.6 × 10⁻⁷–1.0 × 10⁻³ M for drug–TPB and 5.8 × 10⁻⁷–1.0 × 10⁻³, 1.8 × 10⁻⁷–1.0 × 10⁻³, and 6.6 × 10⁻⁷–1.0 × 10⁻³ M for drug–PT electrodes, respectively, with slopes ranging from 52.3 to 62.3 mV/decade. The membranes developed have potential stability for up to 1 month and proved to be highly selective for the drugs investigated over other ions and excipients. The results show that the selectivity of the ion-selective electrodes is influenced significantly by the plasticizer. The proposed electrodes were successfully applied in the determination of these drugs in pharmaceutical preparations in four batches of different expiry dates. Statistical Student’s t test and F test showed insignificant systematic error between the ion-selective electrode methods developed and a standard method. Comparison of the results obtained using the proposed electrodes with those found using a reference method showed that the ion-selective electrode technique is sensitive, reliable, and can be used with very good accuracy and high percentage recovery without pretreatment procedures of the samples to minimize interfering matrix effects. Figure Structure of lamotrigine, felbanate and primidone     

Development and validation of a new high-performance liquid chromatographic method for the loperamid hydrochloride determination in drugs

A selective, precise and new high-performance liquid chromatographic method for the analysis of loperamid hydrochloride in pharmaceutical formulations was developed and validated. The mobile phase consisting buffer (sodium-octansulphonate, triethylamine and ammonium hydroxide) in water: acetonitriie (45: 55, v/v) (pH 3.2). The absorbance was monitored with a DAD detector at 226 nm. The flow rate was 1.5 cm³ min⁻¹. The linearity (r = 0.9947) and the recovery (98.58–100.42%) were found to be satisfactory. The detection and quantitation limits were found to be 0.95 and 3.12 μg cm⁻³. The results demonstrated that the procedure was accurate, precise and reproducible. It can be suitably applied for the estimation of lopera-mid hydrochloride in pharmaceutical formulations. The article is published in the original.     

Simultaneous determination of chromium (III) and copper (II) by using derivative spectrophotometry with MEDTA

The application of derivative spectrophotometry to the simultaneous determination of chromium (III) and copper (II) with MEDTA is described. The procedure is suitable for concentrations of 0.40–2.60 mg ml⁻¹ of chromium (III) and 0.15–0.60 mg ml⁻¹ of copper (II). The main interferences, both anionic and cationic, are easily eliminated. The method was applied to different aqueous matrices. It was compared with an atomic absorption method and good results were obtained.     

Application of Internal Standard for Micro Extraction– Spectrophotometric Determination of Bismuth in Pharmaceutical Formulations

 A micro extraction – spectrophotometric procedure is developed for the determination of bismuth in pharmaceutical formulations. The procedure is based on the extraction of tetraiodobismuthate(III) ion paired with benzyltributylammonium cation into chloroform. The application of Nile Blue as internal standard (IS) enabled good analytical performance for micro-scale analysis. The ratio between the absorbances measured at 491 nm (bismuth complex) and at 632 nm (IS) was taken as the analytical signal. The procedure was carried out in Eppendorf tubes, lowering significantly the use of reagents and the volume of organic solvent. In the calibration range up to 60 mgċl⁻¹, the linear regression coefficient was 0.9999, the CV for 15 mgċl⁻¹ and for 50 mgċl⁻¹ Bi were 1.6% and 0.7% respectively. The results obtained in the analysis of pharmaceutical formulations were in good agreement with the results of EDTA titration method. Received November 25, 1999. Revision February 14, 2000.     

Spectrofluorometric determination of nicardipine,nifedipine and isradipine in pharmaceutical preparations and biological fluids

A simple and highly sensitive spectrofluorometric method was developed for the determination of some 1,4-dihydropyridine compounds namely, nicardipine, nifedipine and isradipine in pharmaceutical preparations and biological fluids. The method is based on the reduction of nicardipine, nifedipine and isradipine with Zn/HCl and measuring the fluorescence intensity obtained (λ_em/λ_ex) at 460/364, 450/393 and 446/360 nm, respectively. The factors affecting the development of the fluorophore and its stability were studied and optimized. The effect of some surfactants such as β-cyclodextrin (βCD), carboxymethylcelullose (CMC), sodium dodecyl sulphate (SDS) and triton X-100, on the fluorescence intensity was studied. The fluorescence intensity-concentration plots of nicardipine, nifedipine and isradipine were rectilinear over the ranges 0.4–6.0, 0.2–4.0 and 0.1–9.0 μg ml⁻¹ with detection limits of 0.0028, 0.017 and 0.016 μg ml⁻¹, respectively. The proposed method was successfully applied to commercial tablets containing the compounds; the percentage recovery agreed well with those obtained using the official methods. The method was further extended to the in vitro determination of the compounds in spiked human plasma and urine samples. A proposal of the reduction reaction pathway was postulated.      

A validated HPLC method for assay of morphine hydrochloride and hydromorphone hydrochloride in pharmaceutical injections

Summary A sensitive and rapid routine HPLC method is proposed for quantitative estimation of morphine hydrochloride and hydromorphone hydrochloride in pharmaceutical dosage forms. The drugs were chromatographed on a C₁₈ reversed-phase column; the mobile phase was acetonitrile-water, 35:65 (v/v), containing sodium dodecyl sulphate (0.5%, w/v), as ion pairing reagent, and acetic acid (0.4% v/v). Detection was at 230 nm. The optimized method was validated and linearity (r>0.999), precision, and accuracy were found to be acceptable within the concentration ranges 86–124 μg mL⁻¹ for morphine hydroloride and 60–180 μg mL⁻¹ for hydromorphone hydrochloride. The method is being used to investigate the stability of morphine hydrochloride and hydromorphone hydrochloride in solution used for intramuscular injection.     

Determination of mono and disaccharide content of enteral formulations by gas chromatography

Summary A quantitative GC method has been developed which allows determination of mono and disaccharides in enteral formulations. The method is based on the isolation of the mono and disaccharide fraction on a charcoal-celite column and conversion to trimethylsilylated oximes (TMS-oximes). The repeatability of the complete method and recovery were acceptable. In the five commercial samples assayed, maltose was the main sugar (5.24–8.85 gL⁻¹) followed by glucose (1.06–2.41 gL⁻¹) and lactose (0–1.17 gL⁻¹) Low levels of fructose (0–0.18 gL⁻¹) and sucrose (0–0.07 gL⁻¹) were observed and galactose was detected in two of the samples. The presence of maltulose is reported in enteral formulations for the first time. Maltulose formed from maltose during processing, was present in variable amounts (0.12–1.07 gL⁻¹) and could be a useful indicator for enteral formulation classification.     

PLS and first derivative of ratio spectra methods for determination of hydrochlorothiazide and propranolol hydrochloride in tablets

Two new analytical methods have been developed as convenient and useful alternatives for simultaneous determination of hydrochlorothiazide (HCT) and propranolol hydrochloride (PRO) in pharmaceutical formulations. The methods are based on the first derivative of ratio spectra (DRS) and on partial least squares (PLS) analysis of the ultraviolet absorption spectra of the samples in the 250–350-nm region. The methods were calibrated between 8.7 and 16.0 mg L⁻¹ for HCT and between 14.0 and 51.5 mg L⁻¹ for PRO. An asymmetric full-factorial design and wavelength selection (277–294 nm for HCT and 297–319 for PRO) were used for the PLS method and signal intensities at 276 and 322 nm were used in the DRS method for HCT and PRO, respectively. Performance characteristics of the analytical methods were evaluated by use of validation samples and both methods showed to be accurate and precise, furnishing near quantitative analyte recoveries (100.4 and 99.3% for HCT and PRO by use of PLS) and relative standard deviations below 2%. For PLS the lower limits of quantification were 0.37 and 0.66 mg L⁻¹ for HCT and PRO, respectively, whereas for DRS they were 1.15 and 3.05 mg L⁻¹ for HCT and PRO, respectively. The methods were used for quantification of HCT and PRO in synthetic mixtures and in two commercial tablet preparations containing different proportions of the analytes. The results of the drug content assay and the tablet dissolution test were in statistical agreement (p < 0.05) with those furnished by the official procedures of the USP 29. Preparation of dissolution profiles of the combined tablet formulations was also performed with the aid of the proposed methods. The methods are easy to apply, use relatively simple equipment, require minimum sample pre-treatment, enable high sample throughput, and generate less solvent waste than other procedures. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

Electroreduction and Quantification of Furazolidone and Furaltadone in Different Media

 Adsorptive cathodic stripping voltammetry was used for the determination of furazolidone (FZ) and furaltadone (FD) in borax and phosphate buffers, respectively, using HMDE as working electrode. The influence of different factors upon the peak current response such as accumulation potential, scan rate, preconcentration time, pH and other variables was studied. Furazolidone and furaltadone showed an adsorption character on HMDE in presence of borax and phosphate buffers, respectively. A single cathodic peak at −0.36 V in borax (pH = 9.5) was observed for FZ, while FD gave a cathodic peak at −0.32 V in phosphate buffer (pH = 8.5). The calibration graph showed a linear behavior over the range 3×10⁻⁹–9×10⁻⁸ mol dm⁻³ for furazolidone. In the case of FD, concentrations from 3×10⁻⁹ to 2×10⁻⁷ mol dm⁻³ gave a linear relationship with the peak current. A detection limit of 2×10⁻⁹ mol dm⁻³ and 1×10⁻⁹ mol dm⁻³ was obtained for furazolidone and furaltadone, respectively. This method was applied to determine these drugs in pharmaceutical formulations, urine and serum samples. Received December 15, 1998. Revision February 4, 2000.     

Flow-injection chemiluminescence determination of aminomethylbenzoic acid and aminophylline based on N-bromosuccinimide-luminol reaction

A novel and sensitive chemiluminescence (CL) method for the determination of aminomethylbenzoic acid and aminophylline coupled with flow-injection analysis (FIA) technique is developed in this paper. It is based on the inhibition effect of the studied drugs on the chemiluminescence emission of N-bromosuccinimide-luminol (NBS-luminol) system. Under the optimum conditions, the decreased CL intensity is linear with the concentration of aminomethylbenzoic acid in the range of 2×10⁻⁸ to 1.0×10⁻⁶ g ml⁻¹ and with the concentration of aminophylline in the range of 1×10⁻⁷ to 7.0×10⁻⁶ g ml⁻¹, respectively. The detection limit is 7.0×10⁻⁹ g ml⁻¹ for aminomethylbenzoic acid (3σ) and 3.4×10⁻⁸ g ml⁻¹ for aminophylline (3σ). The relative standard deviations (R.S.D.) for 11 parallel measurements of 2.0×10⁻⁷ g ml⁻¹ aminomethylbenzoic acid and 1.0×10⁻⁶ g ml⁻¹ aminophylline are 2.6 and 3.0%, respectively. The proposed methods have been applied for the determination of the studied drugs in their pharmaceutical formulations with satisfactory results. The possible use of the proposed system for the determination of aminomethylbenzoic acid in plasma sample was also tested. The possible inhibition mechanism of aminomethylbenzoic acid and aminophylline on luminol-NBS system was discussed briefly.