Showing papers on "NQS published in 2011"
TL;DR: In this article, two simple spectrophotometric methods for the determination of the antibiotic gemifloxacin mesylate (GFX) in pharmaceutical formulations were described.
29 citations
TL;DR: Two new sensitive and simple spectrophotometric methods were developed for determination of pregabalin (PG) in capsules and successfully applied to the analysis of the drug in its commercial capsules.
Abstract: Pregabalin (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. Two 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. The 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.
19 citations
TL;DR: The proposed method was successfully applied to the determination of gabapentin in capsules with good accuracy and precision and without detectable interference from common excipients.
Abstract: A simple, sensitive, and selective spectrophotometric method has been developed for the determination of gabapentin (GBP) in capsules. The method is based on the reaction of GBP and sodium 1,2-naphthoquinone-4-sulfonate (NQS) in the presence of Clark and Lubs buffer of pH 11 to form an orange-coloured product which was measured at 495 nm. The parameters that affect the reaction were carefully optimized and under the optimized conditions, linear relationship was obtained in the concentration range of 7.5-75 µg ml(-1) GBP. The molar absorptivity, limits of detection (LOD) and quantification (LOQ) and Sandell sensitivity are also reported. The proposed method was successfully applied to the determination of GBP in capsules with good accuracy and precision and without detectable interference from common excipients. The reliability of the proposed method was further established by parallel determination by the reference method and also by recovery studies. The reaction mechanism is proposed and discussed.
9 citations
01 Jan 2011
TL;DR: Two simple, extraction free spectrophotometric methods (Method-1 and 2) for the quantitative estimation of pregabalin (PGB) in bulk drugs and pharmaceutical formulations (Capsules) have been developed as mentioned in this paper.
Abstract: Two simple, extraction free spectrophotometric methods (Method-1 and 2) for the quantitative estimation of pregabalin (PGB) in bulk drugs and pharmaceutical formulations (Capsules) have been developed. The first method is based on the condensation of pregabalin with 1, 2- napthaquinone-4- sulfonic acid sodium (NQS) in alkaline media to yield orange colored products. Pregabalin at its λmax 485 nm shows linearity in the concentration range of 5- 45μg/ml. The first method is based on the oxidation of 2, 4- dinitrophenylhydrazine (2, 4-DNP) and coupling of the oxidized product with drugs to give intensely colored chromogen. Condensed product of pregabalin at its λmax 461 nm shows linearity in the concentration range of 50-450 μg/ml. The relative standard deviations were 0.487% and 0.25% respectively for 2 methods. Linear relationships with good correlation coefficients (0.993-0.998) were found between absorbance and the corresponding concentrations of the drug. The reliability and performance of the proposed methods was validated statistically. Percentage recovery ranged from 100.5 and 99.867 respectively.
7 citations
TL;DR: The developed method was successfully applied for selective determination of CFP in pure form and in pharmaceutical dosage forms as well as CFA in human urine after single dose of C FP without prior need for separation.
5 citations
01 Jan 2011
TL;DR: In this article, two simple, sensitive and accurate spectrophotometric methods have been developed for the determination of stavudine in pure and dosage forms, one is based on the reaction of stavaine(STD) with 1,2-napthaquinone4-sulphonic acid (NQS) to form N-alkylamono naphthionone by replacement of the sulphonate group of the naphtha-quinone sulphonic acid by an amino group.
Abstract: Two simple, sensitive and accurate spectrophotometric methods have been developed for the determination of stavudine in pure and dosage forms. Method-A is based on the reaction of stavudine(STD) with 1,2-napthaquinone4-sulphonic acid (NQS) to form N-alkylamono naphthaquinone by replacement of the sulphonate group of the naphthaquinone sulphonic acid by an amino group. The colored chromogen shows absorption maximum at 464 nm and linear within the limits 2.0-12.0 µg/mL. Method-B is based on oxidation of the drug with 1, 10-phenanthroline producing red colored chromogen which is measured at 480nm. Beer’s law is obeyed in the concentration range of 5.0-30.0 µg/mL for the developed method. Different experimental parameters affecting the color development and stability of colored product are carefully studied and optimized. The developed methods could be successfully applied to pharmaceutical formulations. The results obtained are in good agreement with those obtained using official methods.
5 citations
01 Dec 2011
TL;DR: In this article, a spectrophotometric method was developed for the quantitative determination of aminophenol isomers, based on their reaction with 1,2-Naphthoquinone-4-sulphonate (NQS) reagent in aqueous basic medium forming colored products with maximum absorption at wavelengths 488, 480 and 535 nm for o-, m- and p-aminophenol respectively.
Abstract: A spectrophotometric method was developed for the quantitative determination of aminophenol isomers. The method is based on their reaction with 1,2-Naphthoquinone-4-sulphonate (NQS) reagent in aqueous basic medium forming colored products with maximum absorption at wavelengths 488, 480 and 535 nm for o-, m- and p-aminophenol respectively. Beer' s law is obeyed over the concentration range of 0.2-10, 0.08-7.2 and 0.08-18 µg ml -1 with molar absorptivity values of 5166.6 ,6613.6 and 7673.6 L mol -1 cm -1 for the above isomers, respectively. The average recovery was ranged between 99.14 % to 102.5 % and the precision was better than 4.0 %. The limit of detection was in between 0.0348 and 0.05188 µg ml -1 . The products are formed in ratio of 1:1 and the stability constants are 3.97×10 7 , 8.58×10 5 , 2.95×10 5 L mol -1 for the above isomers, respectively. The method was applied successfully for the determination of o- aminophenol in river, tap, spring and sea waters.
2 citations
TL;DR: The ant-pathogenic fungus Ophiocordyceps unilateralis BCC1869 produces six naphthoquinone derivatives which have antibacterial, anticancer, and antimalarial activities and are red pigments with potential for use as natural colorants.
Abstract: The ant-pathogenic fungus Ophiocordyceps unilateralis BCC1869 produces six naphthoquinone (NQ) derivatives. These NQs can be found in fungal-infected ants or produced in culture. Also, the NQs have antibacterial, anticancer, and antimalarial activities and are red pigments with potential for use as natural colorants. Suppressive subtractive hybridization identified genes that were expressed under NQ–producing conditions but not under nonproducing conditions. On potato dextrose agar, the mycelia produced red pigments and secreted them into the medium and as droplets on top of the colony. High-performance liquid chromatography analysis indicated that the red pigment was predominantly erythrostominone with small amounts of its derivatives. For suppressive subtractive hybridization, the cDNA from O. unilateralis cultures on complete medium agar cultures (lacking NQs) were subtracted from those on potato dextrose agar (which produce and secrete NQs). Sixty-six unique expressed sequence tags (ESTs) were identif...
2 citations
Proceedings Article•
16 Jun 2011
TL;DR: In this article, an enhancement of a PN diode standard model towards including substrate PN junction, and reverse recovery effect models is presented, which leads to improvement in power management, EMC and switching application design.
Abstract: This paper deals with enhancement of a PN diode standard model towards including substrate PN junction, and reverse recovery effect models. This leads to improvement in power management, EMC and switching application design.
1 citations
TL;DR: A simple and sensitive spectrophotometric method has been developed for the assay of lercanidipine hydrochloride in bulk and in formulations and obeyed the Beer's law in the range 20-100 μg mL-1.
Abstract: A simple and sensitive spectrophotometric method has been developed for the assay of lercanidipine hydrochlo- ride (LER) in bulk and in formulations. The method is based on the formation of coloured species between the drug and 1,2-naphthaquinone-4-sulphonic acid sodium salt (NQS) by means of nucleophilic substitution reaction. Absorbance was measured at lmax = 460 nm. The method was analyzed statistically. The system obeyed the Beer's law in the range 20-100 m gm L -1 . Molar absorptivity value was found to be 4.79 × 10 3 L mol -1 cm -1 . Limits of detec- tion and quantification were found to be as low as 0.04 and 0.13 m gm L -1 . Precision (RSD, 0.4 %) and accuracy (reco- very 99.2 ± 0.6 to 101.1 ± 0.8 %) of the developed method were evaluated.
1 citations