Validation of a simple and rapid UV spectrophotometric method for dexamethasone assay in tablets

This work reports the validation of an analytical UV spectrophotometric method to assay dexamethasone in tablets (assay and dissolution studies). The method was linear in the range between 1 and 30 µg mL-1 presenting a good correlation coefficient (r = 0.9998, n = 7). Precision and accuracy analysis showed low relative standard deviation (< 2.00%) and good percentual recoveries (95-105%). The procedure was linear, accurate, precise, and robust. The method is simple, and it has low cost. It does not use polluting reagents and can be applied in dissolution studies, being an adequate alternative to assay dexamethasone in tablets.

Reaction mixtures formed by nitrite and selected sulfa-drugs showed mutagenicity in acidic medium

Nitrite, which is present in preserved meat and can be produced in the oral cavity by reduction of nitrate taken from vegetables, could react in stomach with nitrosatable drugs, giving genotoxic-carcinogenic N-nitroso compounds (NOC). The mutagenicity of reaction mixtures formed by sodium nitrite and selected sulfa-drugs (sulfathiazole, HST; phtalylsulfathiazole, PhST; complex Co(II)-sulfathiazole, Co(II)-ST) in acidic medium was evaluated using the Salmonella typhimurium reverse mutation assay (Ames test), with TA98 and TA 100 strains. The reactions were carried out at room temperature, with a mole ratio [nitrite]/[sulfa-drug] > 1. The three reaction mixtures showed mutagenic effects in the considered range.

Development and validation of a GC-FID assay for determination of fluvastatin in pharmaceutical preparations

A gas chromatographic method has been developed for the assay of fluvastatin sodium (FLU). FLU was silylated with N,O-bis(trimethylsilyl)trifluoroacetamide-1% trimethylchlorosilane at 90 ºC for 30 min and analysed in a DB-1 column by capillary gas chromatograph with a flame ionization detector. The method was validated. The assay was linear over the concentration range at 10.0 to 50.0 µg mL-1. The limit of detection and the limit of quantitation were 1.0 and 3.0 µg mL-1, respectively. The recoveries of FLU derivatives were in the range of 99.25-99.80%. In inter-day and intra-day analysis, the values of relative standard deviation (%) and the relative mean error (%) were found between 0.20-0.80% and -0.20-0.75%, respectively. The developed method was succesfully applied to analyze the FLU content in tablet formulation. The results were statistically compared with those obtained by the official method, and no significant difference was found between the two methods. Therefore, it can be recommended for the quality control assay of FLU in pharmaceutical industry.

Development and validation of RP-LC and uv spectrophotometric methods to assay bromopride in oral and injectable solutions

A reversed-phase liquid chromatographic (LC) and ultraviolet (UV) spectrophotometric methods were developed and validated for the assay of bromopride in oral and injectable solutions. The methods were validated according to ICH guideline. Both methods were linear in the range between 5-25 μg mL-1 (y = 41837x - 5103.4, r = 0.9996 and y = 0.0284x - 0.0351, r = 1, respectively). The statistical analysis showed no significant difference between the results obtained by the two methods. The proposed methods were found to be simple, rapid, precise, accurate, and sensitive. The LC and UV methods can be used in the routine quantitative analysis of bromopride in oral and injectable solutions.

Set-up of a method using LC-UV to assay mometasone furoate in pharmaceutical dosage forms

A reliable method using LC-UV to assay mometasone furoate (MF) in creams or nasal sprays using the same chromatographic conditions was set up. Methanol:water 80:20 (v/v) (1.0 mL min-1) was used as mobile phase. MF was detected at 248 nm and analyzed in a concentration range from 1.0 to 20.0 µg mL-1. The method provided acceptable theoretical plates, peak simmetry, peak tailing factor and peak resolution a short run (5 min). The method showed specificity, good linearity (r = 0.9999) and the quantification limit was 0.379 µg mL-1. Furthermore, the method was precise (RSD < 2.0%), accurate (recovery > 97%) and robust.

A fluorescence-based assay for octreotide in kinetic release from depot formulations

Here we report the validation of a derivatization method that makes use of fluorescamine as a selective reactant for the quantitative analysis of peptide and protein drugs in the dissolution profile from depot formulations. Typical current methods require separation of the nano/microparticles and time-consuming chromatographic runs. In this study we report a method which can be conducted without the need for complete physical separation of the particles or removal of the unreacted probe. This method was used here for the analysis of the release profile of octreotide in a depot formulation, with results in excellent agreement with reported chromatographic assays.

Simvastatin assay and dissolution studies by feasible RP-HPLC in tablets

Commonly used HPLC acetonitrile solvent has been through a worldwide shortage with a cost increase in 2008 and 2009. In order to get around this situation, a method by RP-HPLC employing methanol and aqueous acid mobile phase was developed and validated to evaluate simvastatin. The quality control assay and dissolution studies of this lipid-lowering drug were performed in diluents methanol and 0.01 M phosphate buffer with 0.5% SDS, pH 7, respectively. Dissolution test aliquots did not go through sample treatment, as described in USP SIM tablets monograph by ultraviolet spectrophotometry. The proposed method is fast, simple, feasible and robust.

Selective detection of fluoride based on a pyridinium n-phenolate-calix[4]pyrrole displacement assay: an undergraduate laboratory experiment

A two-step experiment is proposed for a third year class in experimental organic chemistry. Over a period of five weeks, the students synthesized calix[4]pyrrole, a receptor that is highly selective for fluoride, and a pyridinium N-phenolate dye. Subsequently, the students used the synthesized compounds to investigate a displacement assay on the basis of the competition in acetonitrile between fluoride and the dye for calix[4]pyrrole. The experiment increased the students' skills in organic synthesis and in the characterization of organic compounds, provided a very attractive and accessible illustration of important supramolecular phenomena, and allowed the study of a chromogenic chemosensor.

Sensitive bromatometric assay methods for finasteride in pharmaceuticals

Three sensitive spectrophotometric methods are presented for the determination of finasteride in bulk and in tablets. The methods rely on the use of bromate-bromide reagent and three dyes namely, methyl orange, indigocarmine and thymol blue as reagents. They involve the addition of a measured excess of bromate-bromide reagent to finasteride in acid medium, and after the bromination reaction is judged to be complete, the unreacted bromine is determined by reacting with a fixed amount of either methylorange and measuring the absorbance at 520 nm (method A) or indigocarmine and measuring the absorbance at 610 nm (method B) or thymol blue and measuring the absorbance at 550 nm (method C). In all the methods, the amount of insitu generated bromine reacted corresponds to the amount of finasteride. The absorbance measured at the respective wavelength is found increase linearly with the concentration of finasteride. Beer's law is obeyed in the ranges 0.25- 2.0, 0.5-6.0 and 1-12 µg mL-1 for method A, method B and method C, respectively. The calculated molar absorptivity values are 5.7x10(4), 3.12x10(4) and 1.77x10(4) L mol-1 cm-1 respectively, for method A, method B and method C, and the corresponding Sandell sensitivity values are 0.0065, 0.012 and 0.021 µg cm-2. The limits of detection (LOD) and quantification (LOQ) are also reported for all the methods. Accuracy and, intra-day and inter-day precisions of the methods were established according to the current ICH guidelines. The methods were successfully applied to the determination of finasteride in commercially available tablets and the results were found to closely agree with the label claim. The results of the methods were statistically compared with those of a reference method by applying Student's t-test and F-test. The accuracy and reliability of the methods were further confirmed by performing recovery tests via standard addition procedure.

Argentimetric assay of ranitidine in bulk drug and in dosage forms

Two simple, rapid and cost-effective methods based on titrimetric and spectrophotometric techniques are described for the assay of RNH in bulk drug and in dosage forms using silver nitrate, mercury(II)thiocyanate and iron(III)nitrate as reagents. In titrimetry, an aqueous solution of RNH is treated with measured excess of silver nitrate in HNO3 medium, followed by determination of unreacted silver nitrate by Volhard method using iron(III) alum indicator. Spectrophotometric method involve the addition a known excess of mercury(II)thiocyanate and iron(III)nitrate to RNH, followed by the measurement of the absorbance of iron(III)thiocyante complex at 470 nm. Titrimetric method is applicable over 4-30 mg range and the reaction stoichiometry is found to be 1:1 (RNH: AgNO3). In the spectrophotometric method, the absorbance is found to increase linearly with concentration of RNH which is corroborated by the correlation coefficient of 0.9959. The system obey Beer's law for 5-70 µg mL-1. The calculated apparent molar absorptivity and sandell sensitivity values are found to be 3.27 ´ 10³ L mol-1 cm-1, 0.107 µg cm-2 respectively. The limits of detection and quantification are also reported for the spectrophotometric method. Intra-day and inter-day precision and accuracy of the methods were evaluated as per ICH guidelines. The methods were successfully applied to the assay of RNH in formulations 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 accuracy of the methods was further ascertained by performing recovery tests by standard addition method.

Titrimetric assay of lisinopril in aqueous and non-aqueous media

Four simple titrimetric procedures are described for the determination of lisinopril (LNP) in bulk and in pharmaceuticals based on the neutralization of basic-amino and acidic carboxylic acid groups present in LNP. Method A is based on the neutralization of basic amino groups using perchloric acid as titrant in anhydrous acetic acid medium. Method B, method C and method D are based on neutralization of carboxylic acid group using NaOH, sodium methoxide and methanolic KOH, as titrants, respectively. Method A is applicable over 2.0-20.0 mg range and the calculations are based in the molar ratio of 1:2 (LNP:HClO4). Method B, method C and method D are applicable over 2.0-20.0 mg, 1.0-10.0 mg and 5.0-15.0 mg range, respectively, and their respective molar ratios are 1:1 (LNP:NaOH), 1:2 (LNP:CH3ONa) and 1:1 (LNP:KOH). Intraday and inter day accuracy and precision of the methods were evaluated and the results showed intra- and inter-day precision less than 2.7% (RSD), and accuracy of < 2.5 % (RE). The developed methods were applied to determine LNP in tablets and the results were validated statistically by comparing the results with those of the reference method by applying the Student's t-test and F-test. The accuracy was further ascertained by recovery studies via standard addition technique. No interferences from common tablet exipients was observed.

Titrimetric and spectrophotometric assay of bupropion hydrochloride in pharmaceuticals using mercury(II) nitrate

Two simple, rapid and accurate methods for the determination of bupropion hydrochloride (BUP) in pure and in pharmaceutical preparations are described. Both methods are based on the measurement of the chloride of its hydrochloride. In the titrimetric method, the chloride content of bupropion hydrochloride is determined by titrating with mercury(II)nitrate using diphenylcarbazone-bromophenol blue as indicator. Titrimetric method is applicable over a range 2-20 mg of BUP and the reaction stoichiometry is found to be 2:1 (BUP: Hg(NO3)2). The spectrophotometric method involves the addition of a measured excess of mercury(II) nitrate reagent in formate buffer to the drug, and after ensuring the reaction had gone to completion, the unreacted mercury(II) is treated with a fixed amount of diphenylcarbazone, and absorbance measured at 515 nm. The absorbance is found to decrease linearly with increasing concentration of BUP and the calibration curve is linear over 1.0-15.0 µg mL-1 BUP. The proposed methods were successfully applied to the determination of BUP in commercially available dosage forms with good accuracy and precision, and without detectable interference by excipients. The accuracy was further ascertained by placebo blank and synthetic mixture analyses and also by recovery experiments via standard-addition procedure.

Optimization of invertase assay conditions in rubber tree plants (Hevea brasiliensis Muell. Arg.)

The objective of this work was to define the optimal conditions for invertase assay, seeking to determine the ideal parameters for the different isoenzymes of leaf and bark tissues in adult rubber trees. Assays of varying pH, sucrose concentration and temperature of the reaction medium were conducted for the two investigated isoenzymes. The results pointed out the existence of two different pH related isoforms for the two analyzed tissues, with an isoenzyme being more active at pH 5,5 and the other at neutral/alkaline pH. Leaf blade isoenzymes presented similar values for substrate concentration, whereas the bark isoenzyme presented maximum values below those previously reported. The assays at different temperatures presented similar values for leaf isoenzymes, though they have differed significantly among the obtained values.

Evaluation of an enzyme-linked immunosorbent assay to detect antibodies against Anaplasma marginale

A rapid indirect enzyme-linked immunosorbent assay (ELISA) was developed for measuring antibodies against Anaplasma marginale using a partially soluble antigen prepared from semi-purified initial bodies from erythrocytes with 80.0% of rickettsiaemia. This technique utilized alkaline phosphatase and p-nitrophenyl phosphate as reaction indicators. The high sensitivity (100.0%) was confirmed with sera from 100 calves experimentally-infected with A. marginale. All of these animals showed seroconversion before or at the same time of the first rickettsiaemia or even when it was not detected. Also the elevated specificity (94.0%) was confirmed by the low percentage of cross-reactions with sera from animals experimentally-infected with Babesia bigemina and Babesia bovis (1.4 and 6.6%, respectively). Performances of ELISA and indirect fluorescent antibody test (IFAT) with 324 sera from enzootically stable area did not show statistical difference (P>0.05), since the former showed 96.9% and the latter 97.2% of positive reactions. The advantage of this ELISA is a shorter execution time than others developed until now, allowing more samples to be analyzed.