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NQS

About: NQS is a research topic. Over the lifetime, 337 publications have been published within this topic receiving 4226 citations.


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Journal ArticleDOI
TL;DR: An extractive-spectrophotometric study based on the reaction of furosemide with 1,2-naphthoquinone-4-sulphonate (NQS) is described in this article.
Abstract: An extractive-spectrophotometric study based on the reaction of furosemide with 1,2-naphthoquinone-4-sulphonate (NQS) is described. Optimal conditions are: NaH2PO4-Na2HPO4 pH 7.5, NQS 7.7×...

27 citations

Journal ArticleDOI
TL;DR: In this paper, the photochemistry of 1,4-naphthoquinone (NQ), the 2-methyl, 2,3-dichloro and 2-bromo derivatives, and vitamin K1 was studied in nonaqueous solvents by time-resolved UV-vis spectroscopy after ns laser pulses at 248 and 308 nm.
Abstract: The photochemistry of 1,4-naphthoquinone (NQ), the 2-methyl, 2,3-dichloro and 2-bromo derivatives, and vitamin K1 was studied in non-aqueous solvents by time-resolved UV-vis spectroscopy after ns laser pulses at 248 and 308 nm. The triplet state of the NQs reacts with alcohols and amines, e.g. triethylamine (TEA) and DABCO, yielding semiquinone radicals (HQ˙/Q˙−). They are the major intermediates and their second-order decay kinetics depend on the properties of the additives and the medium. Transient conductivity measurements suggest the occurrence of photoinduced electron transfer from amines to the triplet state of NQs in acetonitrile. The photoconversion (λirr = 254 nm) of NQs to the 1,4-dihydroxynaphthalenes (H2Q) was measured in the absence and presence of varying concentrations of electron and H-atom donors, and the quantum yield was found to increase with increasing electron- or proton-donor concentration. The mechanisms of photoreduction of NQs by propan-2-ol and TEA in acetonitrile exhibit a number of similarities. Oxygen quenches the triplet state, thereby forming singlet molecular oxygen. Oxygen also reacts with the semiquinone radical, thereby forming HO2˙/O2˙− radicals, and reacts with H2Q, thereby re-forming the quinone. A different pattern, involving intramolecular H-atom transfer, holds for vitamin K1, where 1,3-quinone methide (1,3-QM) diradicals were observed in acetonitrile prior to formation of two 1,2-QM tautomers, but a triplet was not. The decay of the 1,3-QM intermediates becomes faster in the presence of alcohols and amines due to proton-transfer reactions.

27 citations

Journal ArticleDOI
TL;DR: The HPLC-UV method is simple, rapid, quite sensitive, and specific for convenient confirmation of preliminary positive results obtained with immunoassays, as well as general characterization of the derivatives obtained by mass spectrometry.
Abstract: An HPLC-UV method for the simultaneous identification of amphetamine, methamphetamine, 3,4-methylenedioxyamphetamine (MDA) and 3,4-methylenedioxymethamphetamine (MDMA) in urine is described. It includes a rapid extraction procedure of the 4 analogs from urine using Extrelut 3 columns, derivatization with sodium 1,2-naphthoquinone-4-sulphonate (NQS) to obtain highly chromophoric UV-VIS derivatives, and a final HPLC analysis using an ion-pair reversed-phase technique with eluent monitoring at 480 nm. Structural characterization of the derivatives obtained by mass spectrometry is reported. Recoveries of the amphetamines were in the range 80–85% at concentrations of 300 ng/ml. Practical detection limits were 40–60 ng/ml (S/N ratio = 10) for all derivatives. The chromatographic peaks of the NQS derivatized amphetamines are fairly narrow and well resolved. The method is simple, rapid, quite sensitive, and specific for convenient confirmation of preliminary positive results obtained with immunoassays.

26 citations

Journal ArticleDOI
TL;DR: In this paper, a simple scalable non-quasi-static (NQS) small signal equivalent circuit (SSEC) model of Si MOSFET and corresponding direct extraction methodology are developed.
Abstract: A simple scalable non-quasi-static (NQS) small signal equivalent circuit (SSEC) model of Si MOSFET and corresponding direct extraction methodology are developed in this paper. Compared with the conventional SSEC, a parallel gate drain branch is supplemented to describe parasitic gate-drain coupling under high frequency up to 40 GHz together with the impact of substrate loss, terminal resistances and inductances. The new extraction methodology is developed that all extrinsic parasitic components are extracted from zero bias Z-parameters and intrinsic components are extracted from ON state Y-parameters. The proposed model and extraction methodology are verified to achieve good agreement between simulated and measured S-parameters from 0.1 to 40 GHz for devices fabricated with 0.13 μm CMOS technology. The extracted bias dependent model could be further used to construct a nonlinear model in large signal applications.

25 citations

Journal ArticleDOI
TL;DR: New simple and sensitive spectrophotometric and fluorimetric methods have been developed and validated for the determination of fluoxetine hydrochloride (FLX) in its pharmaceutical formulations and both methods were successfully applied.
Abstract: New simple and sensitive spectrophotometric and fluorimetric methods have been developed and validated for the determination of fluoxetine hydrochloride (FLX) in its pharmaceutical formulations. The spectrophotometric method was based on the reaction of FLX with 1,2-naphthoquinone-4-sulphonate (NQS) in an alkaline medium (pH 11) to form an orange-colored product that was measured at 490 nm. The fluorimetric method was based on the reaction of FLX with 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl) in an alkaline medium (pH 8) to form a highly fluorescent product that was measured at 545 nm after excitation at 490 nm. The variables affecting the reactions of FLX with both NQS and NBD-Cl were carefully studied and optimized. The kinetics of the reactions were investigated, and the reaction mechanisms were presented. Under the optimum reaction conditions, good linear relationships were found between the readings and the concentrations of FLX in the ranges of 0.3-6 and 0.035-0.5 mug mL(-1) for the spectrophotometric and fluorimetric methods, respectively. The limits of detection were 0.1 and 0.01 mug mL(-1) for the spectrophotometric and fluorimetric methods, respectively. Both methods were successfully applied to the determination of FLX in its pharmaceutical formulations.

25 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
20221
202114
20208
201912
20185
201715