Potentiometric Determination of Sibutramine Using Batch and Flow Injection Analysis

A simple cost-effective paper-based electrochemical device for detection of adulterated sibutramine in slimming products

This work presents the first paper-based electrochemical device, or ePAD, for direct detection of adulterated sibutramine in slimming products. The ePAD was fabricated using a screen-printing technique for defining the hydrophilic area for sample loading and for the working, reference and counter electrodes. The ePAD gave reproducible responses comparable to both conventional rod electrodes and commercial screen-printed electrodes (SPEs). Use of paper to fabricate the ePAD device provides advantages over the conventional SPE platforms (e.g. glass, ceramics and polymers) in terms of biocompatibility, strong capillary action and environmental friendliness. To detect sibutramine, square wave voltammetry was employed after sample loading on the circular hydrophilic area. The linear range is 2.51 to 83.7 mg L^-1 sibutramine, with a precision of 6 %RSD (n = 3) and an instrumental limit of detection (3SD of intercept/slope) of 2.46 mg L^-1 sibutramine. Recovery of spiked samples ranged from 83 to 116%. The samples were capsules, slimming coffee powders and nutraceutical beverages. The samples were appropriately diluted to give concentrations within the linear calibration range. Filtration of undissolved solids found with the capsules and coffee powder samples was not required, demonstrating that the method is not susceptible to solid particles. The ePAD is cost-effective (<US$1 per device) and suitable for on-site analysis.

USB multiplex analyzer employing screen-printed silver electrodes on paper substrate; A developed design for dissolution testing

Multiplex ion analyzers have been introduced recently for the assay of several inorganic ions, whilst electrochemists have extensively employed screen printed sensors for pharmaceutical analyses. This work aims to develop a USB pluggable sensor with a user-friendly design for multiplex analysis of oppositely charged co-formulated organic ions. The miniaturized screen-printed electrode was developed using silver ink on paper substrate. A compact sensor design was attained by including three electrodes, a single reference electrode along with an indicator electrode for each of the determined ions. Optimized PVC membranes were drop-casted over each of the indicator electrodes for the determination of phenylephrine HCl (PHE) and ibuprofen (IBU). The proposed multiplex potentiometric sensors exhibit Nernstian slopes of 59.2 ± 0.26 and -56.8 ± 0.16 mV/decade for PHE and IBU, respectively, with respective detection limits of 1.6 × 10^-7 and 6.53 × 10^-8 mol L^-1. The fast and stable response of the developed sensor enabled the real-time monitoring of the combined dosage form dissolution. The dissolution profiles obtained by this potentiometric analyzer and an off-line separation technique were compared favourably, albeit our proposed in-line sensor reduced waste and time of analysis. The developed method successfully complies with the most demanding stipulations of green analytical chemistry.

Adsorption and determination of sibutramine in illegal slimming product using porous graphene ink-modified electrode

This work presents a new material, i.e., a porous graphene ink to modify on the GCE surface (PGr-ink/GCE) to improve sensitivity by increasing the surface area of the electrode for the electrochemical determination of sibutramine. The surface characterization and electrochemical adsorption behavior of the PGr-ink/GCE toward sibutramine were investigated using scanning electron microscopy (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), ATR-FTIR spectroscopy and square wave adsorptive stripping voltammetry (SWAdSV). The PGr-ink/GCE exhibited a distinctive anodic response towards sibutramine using SWAdSV in BR buffer (pH 8.00) with a sensitivity 4 times higher than the bare GCE. Under the optimum conditions, the modified electrode showed good electrochemical adsorption and detection of sibutramine by the SWAdSV method with two ranges of linear concentration from 0.015 to 10.0 μg mL^-1 and 10-50 μg mL^-1. The limit of detection and quantitation were 5 ng mL^-1 and 15 ng mL^-1, respectively. Over a short analysis time (180 s), the sensor exhibited high sensitivity (10.9 μAμg^-1mLcm^-2), good reproducibility (RSD <3.4% n = 6), repeatability (RSD between 1.8 and 9.8% (n = 15)), excellent anti-interference properties and was successfully applied for the quantification of sibutramine in different brands of illegal slimming products with good recoveries (93 ± 4-104 ± 1%). The developed electrochemical sibutramine sensor is suitable for application in detecting illegal components in slimming products.

Dissolution testing and potentiometric determination of famciclovir in pure, dosage forms and biological fluids

The performance characteristics of two new plastic membrane ion selective electrodes (ISEs) used for the determination of famciclovir (Fcv) based on the ion associate of Fcv with phosphotungstic acid (PTA) or phosphomolybdic acid (PMA) are described. Different experimental conditions as type of plasticizer to be incorporated in the membrane, life span, effect of soaking, pH, temperature, and interferences were studied. Both electrodes showed similar performance under these conditions, exhibiting Nernstian slopes of S (Fcv-PTA)=58.60±0.84 mV/decade and S (Fcv-PMA)=58.77±0.68 mV/decade within a usable concentration range of 10⁻⁵-10⁻² [Fcv/M] at 298/K. Famciclovir was assayed potentiometrically in its pure solution, pharmaceutical preparations and biological fluids (urine and plasma) using proposed electrodes under batch and flow injection analysis (FIA) conditions with a recovery % ranging between 96.76% and 102.83% having RSD of 0.66%-1.81%. The electrodes were also successfully applied in the determination of the dissolution profile of Fcv tablets and the results came in agreement with the validated results of the HPLC method obtained from the quality control unit of the company producing the tablets.