Polarographic reduction of some potential antidiabetic compounds

The polarographic reduction of 4-arylhydrazone-N′-benzysulphonyl-3-methyl-2-pyrazoline-5-ones gave two, two-electron transfer, well defined, well separated, diffusion controlled, irreversible waves in B.R. buffers of pH range 7.0–11.0. In acidic medium the E_1/2 values of the two waves are so close that only one 4-electron transfer, well defined, diffusion controlled, irreversible waves is obtained. The reduction in these compounds takes place at the-NH-N=C-bond. The effect of substituents and its correlation with the Hammett substituent constant (σ) have also been studied.     

Voltammetric determination of adenosine and guanosine using fullerene-C60-modified glassy carbon electrode

A fullerene-C₆₀-modified glassy carbon electrode (GCE) is used for the simultaneous determination of adenosine and guanosine by differential pulse voltammetry. Compared to a bare glassy carbon electrode, the modified electrode exhibits an apparent shift of the oxidation potentials in the cathodic direction and a marked enhancement in the voltammetric peak current response for both the biomolecules. Linear calibration curves are obtained over the concentration range 0.5 μM-1.0 mM in 0.1 M phosphate buffer solution at pH 7.2 with a detection limit of 3.02 × 10⁻⁷ M and 1.45 × 10⁻⁷ M for individual determination of adenosine and guanosine, respectively. The interference studies showed that the fullerene-C₆₀-modified glassy carbon electrode exhibited excellent selectivity in the presence of hypoxanthine, xanthine, uric acid and ascorbic acid. The proposed procedure was successfully applied to detect adenosine and guanosine in human blood plasma and urine, without any preliminary pre-treatment.     

Simultaneous determination of guanosine and guanosine-5'-triphosphate in biological sample using gold nanoparticles modified indium tin oxide electrode

A nanogold modified indium tin oxide (ITO) electrode was used for the simultaneous determination of guanosine and GTP at pH 7.2. The electrode exhibited an effective catalytic response towards their oxidation and lowered the oxidation potential of guanosine by ∼120 mV and GTP by ∼183 mV. Linear concentration curves were obtained for guanosine with a detection limit of 9.8 × 10⁻⁸ M and 5.5 × 10⁻⁸ M for GTP. The concentration of guanosine and GTP were also estimated in the human blood plasma samples using gold nanoparticles modified ITO electrode with good reproducibility.     

Electrochemical investigations of corticosteroid isomers—testosterone and epitestosterone and their simultaneous determination in human urine

Voltammetric investigation of two corticoid isomers—testosterone and epitestosterone has been carried out at bare and single-wall carbon nanotubes (SWNT)-modified edge plane pyrolytic graphite electrode (EPPGE). Square wave voltammetry (OSWV) has been used for the simultaneous determination of isomeric steroids. The reduction of the two isomers occurred in a pH dependent, 2e, 2H⁺ process and well-defined voltammetric peaks were observed. Under the optimum experimental conditions, linear calibration curves are obtained within the concentration range 5-1000 nM for both the steroids with the limit of detection 2.8 × 10⁻⁹ and 4.1 × 10⁻⁹ M for testosterone and epitestosterone respectively. The developed protocol is successfully implemented for the analysis of both the compounds in the urine samples of normal subjects as well as in patients undergoing treatment with testosterone. The results obtained from the proposed voltammetric method were also compared with HPLC analysis and found to be similar.     

Development and validation of rapid HPLC method for determination of doxofylline in bulk drug and pharmaceutical dosage forms

A simple, selective, rapid, and economical reversed phase high performance liquid chromatography(RP-HPLC) method for the determination of doxofylline in the commercial dosage form has been developed and validated. The separation and quantification were achieved on an HiQ Sil C 18 W column using a mobile phase of acetonitrile: buffer (50: 50), pH 3, at a flow rate of 1 mL/min with detection of analyte at 272 nm. The separation was achieved within 3.1 ± 0.3 min for doxofylline sample. The method showed good linearity in the range of 10–80 μg/mL. The intra and inter day RSD ranged from 0.37–0.53%. The recovery (mean ± S.D.) of low, middle and high concentrations were 100.04 ± 0.80, 100.01 ± 0.20, 100.07 ± 0.30 respectively. Limit of detection and limit of quantification were 0.03 and 0.1 μg/mL, respectively.     

A microfluidic platform for pharmaceutical salt screening

We describe a microfluidic platform comprised of 48 wells to screen for pharmaceutical salts. Solutions of pharmaceutical parent compounds (PCs) and salt formers (SFs) are mixed on-chip in a combinatorial fashion in arrays of 87.5-nanolitre wells, which constitutes a drastic reduction of the volume of PC solution needed per condition screened compared to typical high throughput pharmaceutical screening approaches. Nucleation and growth of salt crystals is induced by diffusive and/or convective mixing of solutions containing, respectively, PCs and SFs in a variety of solvents. To enable long term experiments, solvent loss was minimized by reducing the thickness of the absorptive polymeric material, polydimethylsiloxane (PDMS), and by using solvent impermeable top and bottom layers. Additionally, well isolation was enhanced via the incorporation of pneumatic valves that are closed at rest. Brightfield and polarized light microscopy and Raman spectroscopy were used for on-chip analysis and crystal identification. Using a gold-coated glass substrate and minimizing the thickness of the PDMS control layer drastically improved the signal-to-noise ratio for Raman spectra. Two drugs, naproxen (acid) and ephedrine (base), were used for validation of the platform's ability to screen for salts. Each PC was mixed combinatorially with potential SFs in a variety of solvents. Crystals were visualized using brightfield polarized light microscopy. Subsequent on-chip analyses of the crystals with Raman spectroscopy identified four different naproxen salts and five different ephedrine salts.     

Effect of surface modification of indium tin oxide by nanoparticles on the electrochemical determination of tryptophan

The effect of surface modification of indium tin oxide (ITO) by multi wall carbon nanotube (MWNT) and gold nanoparticles attached multi wall carbon nanotube (AuNP-MWNT) has been studied to determine tryptophan, an important and essential amino acid for humans and herbivores. A detailed comparison has been made among the voltammetric response of bare ITO, MWNT/ITO and AuNP-MWNT/ITO in respects of several essential analytical parameters viz. sensitivity, detection limit, peak current and peak potential of tryptophan. The AuNP-MWNT/ITO exhibited a well defined anodic peak at pH 7.2 at a potential of ∼669 mV for the oxidation of tryptophan as compared to 760 mV at MWNT/ITO electrode. Under optimum conditions linear calibration curve was obtained over tryptophan concentration range 0.5-90.0 μM in phosphate buffer solution of pH 7.2 with detection limit and sensitivity of 0.025 μM and 0.12 μA μM⁻¹, respectively. The oxidation of tryptophan occurred in a pH dependent, 2e⁻ and 2H⁺ process and the electrode reaction followed adsorption controlled pathway. The method has been found selective and successfully implemented for the determination of tryptophan in human urine and plasma samples using standard addition method. The electrode exhibited an efficient catalytic response with good reproducibility and stability.     

A multi-criteria decision making approach for location planning for urban distribution centers under uncertainty

Location planning for urban distribution centers is vital in saving distribution costs and minimizing traffic congestion arising from goods movement in urban areas. In this paper, we present a multi-criteria decision making approach for location planning for urban distribution centers under uncertainty. The proposed approach involves identification of potential locations, selection of evaluation criteria, use of fuzzy theory to quantify criteria values under uncertainty and application of fuzzy TOPSIS to evaluate and select the best location for implementing an urban distribution center. Sensitivity analysis is performed to determine the influence of criteria weights on location planning decisions for urban distribution centers.The strength of the proposed work is the ability to deal with uncertainty arising due to a lack of real data in location planning for new urban distribution centers. The proposed approach can be practically applied by logistics operators in deciding on the location of new distribution centers considering the sustainable freight regulations proposed by municipal administrations. A numerical application is provided to illustrate the approach.