Μg mL-1 For Method Research Articles

Development and Validation of an HPLC Method for the Quantification of Morin Flavonoid Encapsulated within PLGA Nanoparticles

Background: Morin flavonoid exerts neuroprotective effects with potential interest in neurodegenerative disorders. For this, the use of surface-modified polymeric nanoparticles loaded with morin is an interesting approach. Objective: To develop and validate an HPLC method for the quantification of morin released from a new delivery system consisting of poly lactic-co-glycolic (PLGA) nanoparticles functionalized with the dipeptide phe-phe (phenylalanine-phenylalanine) used to facilitate their access to the CNS. Method: The HPLC procedure was developed and validated with morin hydrate dissolved either in methanol (method A) or in methanol: 0.1N HCl (50:50, v/v, method B). Two new nanoparticle formulations were developed and characterized: morin-loaded PLGA nanoparticles (formulation F1), and morin-loaded PLGA phe-phe nanoparticles (formulation F2). Results: Method A was linear within the concentration range of 5-30 μg.mL-1 and, 1-30 μg mL-1 for method B. LOD and LOQ with method A were 1.23 μg.mL-1 and 3.90 μg.mL-1, respectively, and 0.481 μg.mL-1 and 1.458 μg.mL-1, respectively for method B. The average amount of phe-phe bound to formulation F2 (50 mg of NPs) was 431.33 μg. The encapsulation efficiency of morin within PLGA nanoparticles was around 80%. After functionalization, this value decreased significantly. Conclusion: Method B showed better sensitivity, accuracy and precision for the quantification of morin. The procedure used to functionalize the nanoparticles was adequate for linking the dipeptide to their surfaces, but this procedure is not adequate when encapsulating water-soluble compounds.

Determination and Evaluation of Doses of Metronidazole in Different Quantities and Formulations with Multiple Spectroscopic Methods

Three quick and sensitive spectrum methods have been suggested to determine Metronidazole. All spectral methods that were used included reducing Metronidazole by mixing zinc powder with hydrochloric acid. The first method (A) included the process of the conjugation of resorcinol reagent with metronidazole and the production of red chromophores, which was then estimated spectrally at a maximum wavelength of 520 nm. Method–B including the reaction p-chloro benzaldihyde in acidic medium to product yellow color Schiff base has an absorbance at 305 nm. The method C employing a charge transfer reaction with hydroquinone accepter in basic medium to product orange to yellow product absorbed at 335 nm. The best experimental conditions were used by applying the beer's Law for a range of concentrations 2.0-50 μg ml-1, 1.0-35 μg ml-1 and 1.5-30 μg ml-1for methods A, B and C respectively, and the corresponding molar absorptivity values are 1.375×104, 8.672×104, 1.995×104 L mol-1cm-1 with a Correlation coefficient of 0.9996, 0.9998, and 0.9988 and Limits Of Detection (LOD) 0.145 μg ml-1, 0.0776 μg ml-1and 0.110 μg ml-1 and Limits of Quantitation (LOQ) 0.4412 μg ml-1, 0.2352 μg ml-1and 0.3333 μg ml-1 for methods A, B and C Sequentially. The methods were successfully applied to the determination of Metronidazole in pharmaceutical preparation.

Application of redox reactions for the determination of valganciclovir hydrochloride in pharmaceuticals

Two simple, selective and sensitive spectrophotometric methods were developed and validated for the determination of valganciclovir hydrochloride (VLGH) in pure drug and tablets. The first method was based on the reduction of iron(III) to iron(II) by VLGH and subsequent formation of iron(III)-ferricyanide complex (Prussian blue) in acid medium which was measured at 730 nm (method A). In the second method (method B), permanganate was reduced by VLGH to bluish green manganate in alkaline medium and the absorbance was measured at 610 nm. The absorbance measured in each case was related to VLGH concentration. The experimental conditions were carefully studied and optimized. Beer’s law was obeyed over the concentration ranges of 2.5-20.0 and 2.0-40.0 µg mL-1 for method A and method B, respectively, with corresponding molar absorptivity values of 1.28×104 and 6.88×103 L mol-1 cm-1. The limits of detection (LOD) and quantification (LOQ) were 0.11 and 0.33 µg mL-1 (method A) and 0.21 and 0.64 µg mL-1 (method B). Within-day and between-day relative standard deviations (%RSD) at three different concentrations levels were < 2.4%, and the respective relative errors (%RE) were ≤ 3%. The proposed methods were successfully applied to the determination of VLGH in tablets, and the results confirmed that the proposed methods were equally precise and accurate as the official method.

Application of Oxidizing Properties of Permanganate to the Determination of Famotidine in Pharmaceutical Formulations

One titrimetric and two spectrophotometric methods are described for the determination of famotidine (FMT) in either pure form or in its pharmaceutical formulations. The methods are based on redox reaction between FMT and KMnO4 in acid and alkaline media. In titrimetry, an acidified solution of FMT is titrated directly with permanganate. Direct spectrophotometry (method A) involves treating the alkaline solution of the drug with permanganate and measuring the bluish green product at 610 nm. In indirect spectrophotometry (method B), the drug solution is treated with a fixed concentration of permanganate in H2SO4 medium, and after a specified time, the unreacted permanganate is measured at 545 nm. The molar combining ratio in titrimetry and the optimum assay conditions are studied. Titrimetry is applicable over 1-10 mg range and the calculations are based on a 1:3 (FMT: KMnO4) molar-ratio. In spectrophotometry, Beer’s law is obeyed over 0.75-7.5 and 2.5-20 μg mL-1 for method A and method B, respectively. The molar absorptivity values are calculated to be 2.79 Å~ 104 and 1.62 Å~ 104 L mol-1 cm-1 for method A and method B, respectively, and the corresponding Sandell sensitivity values are 0.012 and 0.021 μg cm-2. The limits of detection (LOD) and quantification (LOQ) are also reported for the spectrophotometric methods. The applicability of the developed methods was demonstrated by the determination of FMT in pure drug as well as in commercial dosage forms

Circular Dichroism Spectroscopy: A Facile Approach for Quantitative Analysis of Captopril and Study of Its Degradation.

Simple and selective zero- and second-order derivative circular dichroism (CD) spectroscopic methods have been designed for the assay of captopril in commercially available dosage forms. A normal CD spectroscopic scan (zero order) exhibits a negative band at 208 nm (method A) in distilled water. The calibration curve shows a linear response over the concentration range of 10–80 μg mL–1. The second-order derivative (D2) CD spectrum shows one positive band at 208 nm (method B) and one negative band at 225 nm (method C). Linear calibration curves were obtained in the concentration range of 10–70 μg mL–1 for both the methods (B and C). The detection limits were found to be 1.26, 1.48, and 2.38 μg mL–1 for methods A, B, and C, respectively. The study under stressed acidic, basic, and oxidative conditions showed the degradation of captopril. The proposed methods were validated as per ICH guidelines. All the proposed methods were compared with the reference method to demonstrate its suitability for quality control of captopril in its dosage forms.

Simple and Selective Titrimetric and Spectrophotometric Methods for the Determination of Loratadine Using Bromate-Bromide, Methyl Orange and Methylene Blue

One indirect titrimetric and two indirect visible spectrophotometric methods were described for the determination of loratadine in bulk drug and in its formulations. The methods used bromate-bromide, methyl orange and methylene blue as reagents. In titrimetry (method A), loratadine was treated with a known excess of bromate-bromide mixture in acidic medium and the residual bromine was back titrated iodometrically after the reaction between loratadine and in situ bromine was ensured to be complete. In spectrophotometric methods, the excess of bromine was estimated by treating with a fixed amount of either methyl orange (method B) and measuring the absorbance at 520 nm or methylene blue (method C) and measuring the absorbance at 680 nm. In all the methods, the amount of reacted bromine corresponded to the loratadine content. Titrimetric method was applicable over 1-8 mg range and the calculations were based on a 1:0.666 (loratadine:bromate) stoichiometric ratio. In spectrophotometry, the calibration graphs were found to be linear over 150- 350 and 1.75-3.5 μg mL-1 for method B and method C, respectively, with corresponding molar absorptivity values of 9.15 × 102 and 1.10 × 105 L mol-1 cm-1. Accuracy and precision of the assays were determined by computing the intra-day and inter-day variations at three different levels of loratadine. The methods were successfully applied to the assay of loratadine in tablet preparations and the results were compared with those of a reference method by applying Student’s t and F-tests. No interference was observed from common pharmaceutical excipients. The reliability of the methods was further ascertained by performing recovery tests by standard addition method

Simple and rapid spectrophotometric assay of albendazole in pharmaceuticals using iodine and picric acid as CT complexing agents

Two simple, rapid and inexpensive spectrophotometric methods are described for the determination of albendazole (ALB) in bulk drug and in tablets. The methods are based on charge-transfer (CT) complexation reaction involving ALB as n-donor and iodine as σ-acceptor (method A) in dichloromethane or picric acid (PA) as π-acceptor (method B) in chloroform. The absorbance of CT complexes was measured at 380 nm for method A, and 415 nm for method B. The optimization of the experimental conditions is described. Under optimum conditions, Beer's law obeyed over the concentration ranges 8.0-240 and 2.4-42 μg mL-1 for method A and method B, respectively. The apparent molar absorptivity of CT complexes at the respective λmax are calculated to be 1.17×103 and 5.22×103 L mol-1cm-1 respectively, and the corresponding Sandell sensitivity values are 0.2273 and 0.0509 ng cm-2. The limits of detection (LOD) and quantification (LOQ) are calculated to be (0.69 and 2.08), and (0.10 and 0.30) μg mL-1 with method A, and method B, respectively. The intra-day and inter-day accuracy expressed as % RE and precision expressed as % RSD were less than 3%. The methods were applied to the determination of ALB in tablets.

Utility of certain nucleophilic aromatic substitution reactions for the assay of pregabalin in capsules.

BackgroundPregabalin (PG) is an anticonvulsant, analgesic and anxiolytic drug. A survey of the literature reveals that all the reported spectrophotometric methods are either don't offer high sensitivity, need tedious extraction procedures, recommend the measurement of absorbance in the near UV region where interference most probably occurs and/or use non specific reagent that don't offer suitable linearity range.ResultsTwo new sensitive and simple spectrophotometric methods were developed for determination of pregabalin (PG) in capsules. Method (I) is based on the reaction of PG with 1,2-naphthoquinone-4-sulphonate sodium (NQS), yielding an orange colored product that was measured at 473 nm. Method (II) is based on the reaction of the drug with 2,4-dinitrofluorobenzene (DNFB) producing a yellow product measured at 373 nm. The different experimental parameters affecting the development and stability of the reaction product in methods (I) and (II) were carefully studied and optimized. The absorbance-concentration plots were rectilinear over the concentration ranges of 2-25 and 0.5-8 μg mL-1 for methods (I) and (II) respectively. The lower detection limits (LOD) were 0.15 and 0.13 μg mL-1 and the lower quantitation limits (LOQ) were 0.46 and 0.4 μg mL-1 for methods (I) and (II) respectively.ConclusionThe developed methods were successfully applied to the analysis of the drug in its commercial capsules. The mean percentage recoveries of PG in its capsule were 99.11 ± 0.98 and 100.11 ± 1.2 (n = 3). Statistical analysis of the results revealed good agreement with those given by the comparison method. Proposals of the reaction pathways were postulated.

Spectrscopic and Conductometric Analysis of Gabapentin

Four simple, sensitive and reproducible methods were developed for the determination of gabapentin (GPT) in pure form and in pharmaceutical preparations. Methods A and B are based on the reaction of cupric chloride with gabapentin to form stable complex, which could be measured spectrophotometrically at λmax 246 nm (method A) or by using conductometric technique (method B). While method C and D depends on the formation of ion pair complex between the studied drug and bromothymol blue, bromocresol green respectively this was extractable with methylene chloride. The concentration ranges were 40‐95 μg mL-1, 1‐15 mg, 100‐800 and 10‐150 μg mL-1 for methods A, B, C and D respectively .The optimization of various experimental conditions were described .The results obtained showed good recoveries, Ringbom optimum concentration ranges were calculated, in addition to molar absorptivity and sandell’s sensitivity, detection and quantification limits. The methods were successfully applied to the determination of GPT in bulk and pharmaceutical preparations. The results were favorably comparable with the official method. The molar combining ratio for methods (A‐B) was found to be (2:1) (drug: reagent) while for method (C‐D) it was found to be (1:1).

Sensitive Bromatometric Methods for the Determination of Sumatriptan Succinate in Pharmaceutical Formulations

Two simple and sensitive spectrophotometric methods are described for the determination of sumatriptan succinate (STS) in pure and tablets using bromate‐bromide as the bromination reagent in acid medium and two dyes as subsidiary reagents. The two methods are based on the bromination of STS by a known excess of in situ generated bromine followed by determination of unreacted bromine by reacting with a fixed amount of methyl orange (Method A) or indigo carmine (Method B) and measuring the absorbance at 508 or 610 nm. In both methods, the amount of bromine reacted corresponds to the amount of STS. The experimental conditions for the assay have been optimized. In two methods, the absorbance was found to increase linearly with the concentration of STS at the respective wavelengths. Beer’s law was obeyed over the ranges 0.2‐1.6 and 2.0‐12.0 μg mL-1 for method A and method B respectively and the respective molar absorptivity values were 1.898×105 and 2.71×104 L mol-1 cm-1. The statistical analysis of the methods was validated according to the present ICH guidelines. The proposed methods were applied to the analysis of tablet form of STS and the results tallied well with the label claim.

Sensitive spectrophotometric determination of lamotrigine in bulk drug and pharmaceutical formulations using bromocresol green

Two new, simple, rapid and reproducible spectrophotometric methods have been developed for the determination of lamotrigine (LMT) both in pure form and in its tablets. The first method (method A) is based on the formation of a colored ion-pair complex (1:1 drug/dye) of LMT with bromocresol green (BCG) at pH 5.02±0.01 and extraction of the complex into dichloromethane followed by the measurement of the yellow ion-pair complex at 410 nm. In the second (method B), the drug-dye ion-pair complex was dissolved in ethanolic potassium hydroxide and the resulting base form of the dye was measured at 620 nm. Beer’s law was obeyed in the concentration range of 1.5-15 μg mL-1 and 0.5-5.0 μg mL-1 for method A and method B, respectively, and the = corresponding molar absorptivity values are 1.6932 x 104 and 3.748 x 104 L mol-1cm-1. The Sandell sensitivity values are 0.0151 and 0.0068 μg cm-2 for method A and method B, respectively. The stoichiometry of the ion-pair complex formed between the dug and dye (1:1) was determined by Job’s continuous variations method and the stability constant of the complex was also calculated. The proposed methods were applied successfully for the determination of drug in commercial tablets.

Sensitive spectrophotometric determination of lamotrigine in bulk drug and pharmaceutical formulations using bromocresol green

Two new, simple, rapid and reproducible spectrophotometric methods have been developed for the determination of lamotrigine (LMT) both in pure form and in its tablets. The first method (method A) is based on the formation of a colored ion-pair complex (1:1 drug/dye) of LMT with bromocresol green (BCG) at pH 5.02±0.01 and extraction of the complex into dichloromethane followed by the measurement of the yellow ion-pair complex at 410 nm. In the second (method B), the drug-dye ion-pair complex was dissolved in ethanolic potassium hydroxide and the resulting base form of the dye was measured at 620 nm. Beer’s law was obeyed in the concentration range of 1.5-15 μg mL-1 and 0.5-5.0 μg mL-1 for method A and method B, respectively, and the = corresponding molar absorptivity values are 1.6932 x 104 and 3.748 x 104L mol-1cm-1. The Sandell sensitivity values are 0.0151 and 0.0068 μg cm-2 for method A and method B, respectively. The stoichiometry of the ion-pair complex formed between the dug and dye (1:1) was determined by Job’s continuous variations method and the stability constant of the complex was also calculated. The proposed methods were applied successfully for the determination of drug in commercial tablets.

Cerimetric determination of simvastatin in pharmaceuticals based on redox and complex formation reactions

Two sensitive spectrophotometric methods are described for the determination of simvastatin (SMT) in bulk drug and in tablets. The methods are based on the oxidation of SMT by a measured excess of cerium (IV) in acid medium followed by determination of unreacted oxidant by two different reaction schemes. In one procedure (method A), the residual cerium (IV) is reacted with a fixed concentration of ferroin and the increase in absorbance is measured at 510 nm. The second approach (method B) involves the reduction of the unreacted cerium (IV) with a fixed quantity of iron (II), and the resulting iron (III) is complexed with thiocyanate and the absorbance measured at 470 nm. In both methods, the amount of cerium (IV) reacted corresponds to SMT concentration. The experimental conditions for both methods were optimized. In method A, the absorbance is found to increase linearly with SMT concentration (r = 0.9995) whereas in method B, the same decreased (r = -0.9943). The systems obey Beer’s law for 0.6-7.5 and 0.5-5.0 μg mL-1 for method A and method B, respectively.

Sensitive and validated spectrophotometric methods for the determination of pantoprazole sodium in pharmaceuticals using N-bromosuccinimide based on redox and complexation reactions

Two simple, sensitive and rapid methods are described for the determination pantoprazole sodium sesqui hydrate (PNT) in bulk drug and in formulations using N-bromosuccinimide (NBS) as the oxidimetric reagent. The methods involve the addition of a known excess of NBS to PNT in HCl medium followed by estimation of the unreacted oxidant by two reaction schemes involving the use of iron(II) and thiocyanate (method A) or tiron (method B). In both methods, the absorbance is found to decrease linearly with PNT concentration. Beer’s law is obeyed over the ranges 0.25-3.5 and 1-15 µg mL-1 for method A and method B, respectively. The calculated molar absorptivity values are 1.4 × 105 and 2.5 × 104 L mol-1cm-1 for method A and method B, respectively. The limit of detection (LOD) and quantification (LOQ) are also reported for both methods. The RSD values for intra-day and inter-day precision studies were less than 2.5 and 3.0 %, respectively. Both the methods were applied to the determination of PNT in dosage forms and the results were satisfactory, and were comparable with those obtained by the reference method. The accuracy and reliability of the proposed methods were further ascertained by recoveries studies, and the recoveries of the spiked drug ranged between 98.5 and 102.5 %. KEY WORDS: Pantoprazole sodium, Determination, N-bromosuccinimide, Complexation reactions, Pharmaceuticals Bull. Chem. Soc. Ethiop. 2008, 22(1), 135-141.

Cerimetric determination of simvastatin in pharmaceuticals based on redox and complex formation reactions

Two sensitive spectrophotometric methods are described for the determination of simvastatin (SMT) in bulk drug and in tablets. The methods are based on the oxidation of SMT by a measured excess of cerium (IV) in acid medium followed by determination of unreacted oxidant by two different reaction schemes. In one procedure (method A), the residual cerium (IV) is reacted with a fixed concentration of fer- roin and the increase in absorbance is measured at 510 nm. The second approach (method B) involves the reduction of the unreacted cerium (IV) with a fixed quantity of iron (II), and the resulting iron (III) is com- plexed with thiocyanate and the absorbance measured at 470 nm. In both methods, the amount of cerium (IV) reacted corresponds to SMT concentration. The experimental conditions for both methods were opti- mized. In method A, the absorbance is found to increase linearly with SMT concentration (r = 0.9995) whereas in method B, the same decreased (r = -0.9943). The systems obey Beer's law for 0.6-7.5 and 0.5- 5.0 µg mL-1 for method A and method B, respectively. The calculated molar absorptivity values are 2.7 X 104 and 1.06 X 105 Lmol-1 cm-1, respectively; and the corresponding sandel sensitivity values are 0.0153 and 0.0039µg cm-2, respectively. The limit of detection (LOD) and quantification (LOQ) are reported for both methods. Intra-day and inter-day precision, and accuracy of the methods were established as per the current ICH guidelines. The methods were successfully applied to the determination of SMT in tablets and the results were statistically compared with those of the reference method by applying the Student's t-test and F-test. No interference was observed from the common excipients added to tablets. The accuracy and validity of the methods were further ascertained by performing recovery experiments via standard addition procedure.

Use of ceric ammonium sulphate and two dyes, methyl orange and indigo carmine, in the determination of lansoprazole in pharmaceuticals

Two spectrophotometric methods are proposed for the assay of lansoprazole (LPZ) in bulk drug and in dosage forms using ceric ammonium sulphate (CAS) and two dyes, methyl orange and indigo carmine, as reagents. The methods involve addition of a known excess of CAS to LPZ in acid medium, followed by determination of residual CAS by reacting with a fixed amount of either methyl orange, measuring the absorbance at 520 nm (method A), or indigo carmine, measuring the absorbance at 610 nm (method B). In both methods, the amount of CAS reacted corresponds to the amount of LPZ and the measured absorbance was found to increase linearly with the concentration of LPZ, which is corroborated by the correlation coefficients of 0.9979 and 0.9954 for methods A and B, respectively. The systems obey Beer's law for 0.5-7.0 microg mL(-1) and 0.25-3.0 microg mL(-1) for methods A and B, respectively. The apparent molar absorptivities were calculated to be 3.0 x 10(4) and 4.4 x 10(4) L mol(-1) cm(-1) for methods A and B, respectively. The limits of detection (LOD) and quantification (LOQ) were calculated to be 0.08 and 0.25 microg mL(-1) for method A, and 0.09 and 0.27 microg mLs(-1) for method B, respectively. The intra-day and inter-day precision and accuracy of the methods were evaluated according to the current ICH guidelines. Both methods were of comparable accuracy (er < or = 2 %). Also, both methods are equally precise as shown by the relative standard deviation values < 1.5%. No interference was observed from common pharmaceutical adjuvants. The accuracy of the methods was further ascertained by performing recovery studies using the standard addition method. The methods were successfully applied to the assay of LPZ in capsule preparations and the results were statistically compared with those of the literature UV-spectrophotometric method by applying Student's t-test and F-test.

Spectrophotometric determination of lansoprazole in pharmaceuticals using bromate-bromide mixture based on redox and complexation reactions

Two sensitive spectrophotometric methods are described for the determination of lansoprazole (LPZ) in bulk drug and in capsule formulation. The methods are based on the oxidation of lansoprazole by insitu generated bromine followed by determination of unreacted bromine by two different reaction schemes. In one procedure (method A), the residual bromine is treated with excess of iron (II), and the resulting iron (III) is complexed with thiocyanate and measured at 470 nm. The second approach (method B) involves treating the unreacted bromine with a measured excess of iron (II) and remaining iron (II) is complexed with orthophenanthroline at a raised pH, and measured at 510 nm. In both methods, the amount of bromine reacted corresponds to the amount of LPZ. The experimental conditions were optimized. In method A, the absorbance is found to decrease linearly with the concentration of LPZ (r = -0.9986) where as in the method B a linear increase in absorbance occurs (r = 0.9986) The systems obey Beer's law for 0.5-4.0 and 0.5-6.0 µg mL-1 for method A and method B, respectively. The calculated molar absorptivity values are 3.97µ10(4) and 3.07µ10(4) L mol-1cm-1 for method A and method B, respectively, and the corresponding Sandell sensitivity values are 0.0039 and 0.0013 µg cm-2. The limit of detection (LOD) and quantification (LOQ) are also reported for both methods. Intra-day and inter-day precision, and accuracy of the methods were established as per the current ICH guidelines. The methods were successfully applied to the determination of LPZ in capsules and the results tallied well with the label claim and the results were statistically compared with those of a reference method by applying the Student's t-test and F-test. No interference was observed from the concomitant substances normally added to capsules. The accuracy and validity of the methods were further ascertained by performing recovery experiments via standard-addition method.

Adaptation of Color Reactions for Spectrophotometric Determination of Pitavastatin Calcium in Bulk Drugs and in Pharmaceutical Formulations

Three simple, sensitive and cost effective Spectrophotometric methods are described for the determination of pitavastatin calcium (PST) in bulk drugs and in pharmaceutical formulations. These methods are based on the oxidation of PST by ferric chloride in presence of o‐phenanthroline (Method A) or 2, 2’ bipyridyl (Method B) or potassium ferricyanide (Method C). The colored complex formed was measured at 510, 530 and 755 nm for method A, B and C respectively against the reagent blank prepared in the same manner. The optimum experimental parameters for the color production are selected. Beer’s law is valid with in a concentration range of 4‐20 μg mL-1 for method A, 7.5‐37.5 μg mL-1 for method B and 5 ‐25 μg mL-1 for method C. For more accurate results, ringbom optimum concentration ranges are 5‐18 μg mL-1 for method A , 8.5‐35.5 μg mL-1 for method B and 6.0‐23.0 μg mL-1 for method C. The molar absorptivities are 3.55x104, 2.10x104 and 3.10x104 L mol-1 cm-1. Where as sandell sensitivities are 0.024, 0.041 and 0.028 μg cm-22 for method A, B and C respectively. The mean percentage recoveries are 99.95 for method A, 101.35 for method B and 100.33 for method C. The developed methods were applied for the determination of PST in bulk powder and in the pharmaceutical formulations without any interference from tablet excipients.

Sensitive Spectrophotometric Methods for the Determination of Gatifloxacin in Pharmaceuticals Using Bromate‐Bromide, Methylene Blue and Rhodamine‐B as Reagents

Two new simple, precise, rapid and extraction‐free spectrophotometric methods are proposed for the determination of gatifloxacin(GTF) using bromate‐bromide mixture and two dyes, methylene blue and rhodamine B, as reagents. Spectrophotometric methods entail the addition of a known excess of bromate‐bromide mixture to GTF in hydrochloric acid medium followed by determination of residual bromine by reacting with a fixed amount of either methylene blue and measuring the absorbance at 665 nm (Method A) or rhodamine B and measuring the absorbance at 555 nm (Method B). Beer᾽s law is obeyed in the ranges, 0.5‐5.0 and 0.2‐1.5 μg mL-1 for method A and method B, respectively. The apparent molar absorptivities are calculated to be 5.6×104 and 9.6×104 L mol-1cm-1 for method A and method B, respectively, and the corresponding Sandell sensitivity values are 0.0071 and 0.0042 μg cm-2. The methods were successfully applied to the assay of GTF in pharmaceutical formulations with satisfactory results.

Titrimetric and Spectrophotometric Determination of Metaprolol tartrate in Pharmaceuticals Using N‐Bromosuccinimide

One titrimetric and two spectrophotometric methods are presented for the assay of metaprolol tartrate (MPT) in bulk drug and in tablets. The methods employ N‐bromosuccinimide (NBS) as the oxidimetric reagent and two dyes, methyl orange and indigo carmine as spectrophotometric reagents. In titrimetry, an acidified solution of MPT is treated with a known excess amount of NBS and after a definite time, the unreacted oxidant is determined by iodometric back titration. Spectrophotometry involves adding a measured excess of NBS to MPT in acid medium followed by determination of residual NBS by reacting with a fixed amount of either methyl orange and measuring the absorbance at 520 nm (Method A) or indigo carmine and measuring the absorbance at 610 nm (Method B). In all the methods, the amount of NBS reacted corresponds to the amount of MPT. Reaction conditions have been optimized. Titrimetry allows the determination of 1 ‐ 12 mg of MPT and the calculations are based on a 1: 4 (MPT: NBS) reaction stoichiometry. In spectrophotometry, the measured absorbance is found to increase linearly with the concentration of MPT serving as basis for quantitation. The systems obey Beer’s law for 0.5 ‐ 4.0 μg mL-1 and 1.25 ‐ 10.0 μg mL-1 for method A and method B, respectively. The apparent absorptivities are calculated to 1.07 × 105 be and 4.22 × 104 L mol cm-1 for method A and method B, respectively. The methods developed were applied to the assay of MPT in commercial tablet formulations, and the results were compared statistically with those of a reference method. The accuracy and reliability of the methods were further ascertained by performing recovery tests via standard‐addition method.