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Sensing mechanism illustrating the proton hopping between the heptazine units of 3D cubic mesostructured carbon nitride.

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The present studies describe the systematic quality by design (QbD)-oriented development and validation of a simple, rapid, sensitive and cost-effective reversed-phase HPLC bioanalytical method for nevirapine in rat plasma. Chromatographic separation was carried out on a C18 column using isocratic 68:9:23% v/v elution of methanol, acetonitrile and water (pH 3, adjusted by orthophosphoric acid) at a flow rate of 1.0 mL/min using UV detection at 230 nm. A Box-Behnken design was applied for chromatographic method optimization taking mobile phase ratio, pH and flow rate as the critical method parameters (CMPs) from screening studies. Peak area, retention time, theoretical plates and peak tailing were measured as the critical analytical attributes (CAAs). Further, the bioanalytical liquid-liquid extraction process was optimized using an optimal design by selecting extraction time, centrifugation speed and temperature as the CMPs for percentage recovery of nevirapine as the CAA. The search for an optimum chromatographic solution was conducted through numerical desirability function. Validation studies performed as per the US Food and Drug Administration requirements revealed results within the acceptance limit. In a nutshell, the studies successfully demonstrate the utility of analytical QbD approach for the rational development of a bioanalytical method with enhanced chromatographic separation and recovery of nevirapine in rat plasma. Copyright © 2015 John Wiley & Sons, Ltd.

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In this study we explain the conductivity changes involved in the sensing mechanism of surface ruthenated tin oxide toward butane. The adsorption free energy is found to be higher for surface ruthenated tin oxide (∆G ) -64.85 kJ/mol) as compared to pure tin oxide (∆G ) -50.2 kJ/mol) implying that the gas adsorbs faster on the ruthenated sample. The ESR studies indicate that butane preferentially adsorbs on the Ru sites, while the IR studies explain the nature of the adsorbed species. A scheme based on these studies is proposed, where surface acetate species is formed on the surface ruthenated tin oxide upon adsorption of butane at 300 °C, while the electronic conduction in these sensors is attributed to the formation of surface states.

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