Spectrofluorimetric determination of butylated hydroxytoluene and butylated hydroxyanisole in their combined formulation: application to butylated hydroxyanisole residual analysis in milk and butter.

Butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA) are two antioxidants that have been extensively used in many applications. Both are well known for their debatable health risks due to their multiple intake sources. Therefore, conservative limits are set for them in different regulations adapted to the matrices in which they exist. Here we present a simple spectrofluorimetric method for the determination of BHT and BHA based on their native fluorescence and synchronous scanning mode. The type of solvent and the interval between emission and excitation wavelengths were carefully optimized. Under the optimized conditions, good linearities were obtained between the emission intensity and the corresponding concentrations of BHT and BHA over the range of 3-18 µg/mL and 0.1-7 µg/mL, respectively with a good correlation coefficient (r > 0.99). The limits of detection were 0.9 and 0.02 µg/mL, and the quantification limits were 3 and 0.05 µg/mL for BHT and BHA, respectively. The suggested procedure was validated according to ICH guidelines Q2 (R1). Furthermore, the method's greenness was assessed by three different methods, and it proved to be eco-reasonable. The method was successfully applied to the determination of BHT and BHA in pharmaceutical formulations. We also applied the suggested method for monitoring the residual BHA in conventional, powdered milk and butter, with good recovery in spiked samples.

Development of chromatographic methods to determine multivitamins formulation depending on their solubility and polarity: comparative study using three greenness assessment tools.

High performance liquid chromatography is one of the techniques of choice for the separation and quantitative determination of drugs in mixture form. Ipriflavone, ascorbic acid, pyridoxine, vitamin D3, and lysine are formulated together as an adjuvant combination in osteoporosis. In this work, we developed and validated two complementary high performance liquid chromatographic methods to determine the five compounds in their pharmaceutical dosage form. The first method (method A) was capable of determining ipriflavone, ascorbic acid, pyridoxine, and vitamin D3 in their bulk and combined pharmaceutical formulation. The method is based on Liquid Chromatographic separation with UV detection at 254 nm using Agilent Eclipse XDB-C18 column with a mobile phase consisting of 25 mM ammonium acetate buffer (pH 4.2): methanol in gradient mode. Due to the high polarity of lysine, it was difficult to achieve satisfactory retention on reversed phase columns. So, we separated it on a strong cation exchange column (Exsil 100 SCX) without derivatization with a mobile phase consisting of 10 mM sodium dihydrogen phosphate and 200 mM sodium chloride (pH 6) with UV detection at 210 nm (method B). Validation of the proposed methods was performed according to ICH guidelines Q2(R1). The proposed methods proved to be valid for selective analysis of the stated drugs in their bulk and combined pharmaceutical formulation. Greenness assessment of the developed methods was evaluated using three assessment tools: ESA, GAPI and the most recently developed tool AGREE, showing a satisfactory comprehensive guide of the greenness of the developed methods.

A new strategy for the determination of the antidiabetics alogliptin, saxagliptin and vildagliptin using all-solid state potentiometric sensors.

Herein, we report on the development of disposable screen printed carbon, nanostructure thin film Au/Pt and Pt/Pt all-solid state potentiometric sensors for some antidiabetic compounds called glibtins. The electrodes showed excellent calibration curves (1 × 10-5-1 × 10-2 M) for alogliptin, saxagliptin and vildagliptin. The electrodes were fully characterized with respect to potential stability, dynamic response time, detection limit, effect of pH and interference according to the IUPAC recommendation. The proposed method is rapid and can be applied for the determination of gliptins at low cost with satisfactory precision (RSD ≤ 1%) and accuracy.

Development of green differential pulse voltammetric strategy for the determination of alfuzosin hydrochloride at pencil graphite and modified carbon paste electrodes.

A sensitive and inexpensive differential pulse voltammetric technique was applied to investigate the electrochemical behavior of alfuzosin hydrochloride at two different working electrodes: silica gel modified carbon paste and pencil graphite electrodes (PGE). The voltammetric conditions were optimized using cyclic voltammetry, showing an irreversible anodic peak in Britton-Robinson buffered medium (pH 6) at 0.86-0.90 V. The electrochemical responses were linearly correlated with alfuzosin concentrations (R2> 0.999) in the ranges of 0.6-20 and 0.3-20 µM, exhibiting higher electrocatalytic activity at PGE with a low detection limit/ detectability of 0.099 µM. In addition, this study was a successful attempt for the drug determination in tablets and spiked urine samples with green profile evaluation, employing the National Environmental Methods Index, analytical Eco-Scale score, and Green Analytical Procedure Index.

Voltammetric Determination of Sulfaclozine Sodium at Sephadex-modified Carbon Paste Electrode.

The electrochemical behavior of Sulfaclozine Sodium (SLC) was studied at a bare and sephadex-modified carbon paste electrodes by cyclic voltammetry and square wave voltammetry. The cyclic voltammetry (CV) showed a well-defined irreversible oxidation peak at 0.94 V in Britton- Robinson buffer pH 7.0. The strong affinity of SLC to sephadex allowed accumulation of SLC at the surface of electrode and thus higher electrochemical sensitivity to SLC. The influence of sephadex loading, the pH of the solution and the scan rate on the peak current was studied. A linear calibration curve covering the concentration range from 0.005 to 1 mM was obtained using SWV. The method was successfully applied for the determination of SLC in the veterinary pharmaceutical formulations with satisfactory accuracy and precision.

Detection of hydrogen peroxide produced during the oxygen reduction reaction at self-assembled thiol-porphyrin monolayers on gold using SECM and nanoelectrodes.

Porphyrin molecules were immobilized on polycrystalline gold and glassy carbon by coordinating cobalt(II) 5,10,15,20-tetraphenyl-21H,23H-porphine to a 4-aminothiophenol self-assembled monolayer. The resulting electrocatalytic activity of the metalloporphyrin-modified substrates with regard to the oxygen reduction reaction was characterized by means of cyclic voltammetry and scanning electrochemical microscopy (SECM) using nanoelectrodes of well-defined geometry. From substrate generation tip collection (SG-TC) mode SECM measurements performed under steady-state conditions and at different applied substrate potentials, it is possible to extract kinetic information relevant to electrocatalyst substrates such as metalloporphyrin-modified gold and glassy-carbon electrodes. Such an approach allows for the isolation of the unique contribution of the electrocatalyst to the oxygen reduction reaction and peroxide formation.

Shearforce-based constant-distance scanning electrochemical microscopy as fabrication tool for needle-type carbon-fiber nanoelectrodes.

Carbon fiber nanoelectrodes with nanometer radii tip curvatures were fabricated using a shearforce-based constant-distance scanning electrochemical microscope and electrochemically induced polymer deposition. A simple DC etching procedure in alkaline solution provided conically sharpened single carbon fibers with well-formed nanocones at their bottom. Coating the stems but not the end of the tips of the tapered structures with anodic electrodeposition paint was the strategy for limiting the bare carbon to the foremost end and restricting a feasible voltammetry current response to exactly this section. The electrodeposition of the polymer was prevented at the foremost end of the tip using a shearforce-based tip-to-sample distance control that allowed approaching the etched tips carefully in just touching distance to a film of a silicone elastomer. Analysis of the steady-state cyclic voltammograms in presence of a reversible redox compound revealed effective radii for the obtained needle-type carbon-fiber nanoelectrodes down to as small as 46 nm. The method offers an alternative pathway toward the fabrication of highly miniaturized carbon electrodes.

SECM visualization of the spatial variability of enzyme-polymer spots. 3. Enzymatic feedback mode.

The responses of a PQQ-GDH entrapped in a polymer structure to mixtures of glucose and maltose were evaluated. Each compound was considered in the concentration range of 0-0.2 mM. Imaging was performed at constant height in the enzymatic feedback mode of scanning electrochemical microscopy (SECM). The enzyme-polymer spot was discretized into 15 x 15 mum(2) substructures which were treated as independent individual microsensors. The response surfaces of the individual microsensors were approximated with a linear regression model. The coefficients in the derived equations represent contributions from topography, glucose concentration, maltose concentration, and the competition of glucose and maltose for the same active site of PQQ-GDH to the measured signal. The ratio of glucose and maltose contributions to the current at the SECM tip was constant for all microsensors and it was predominantly determined by the ratio of the turnover rates of both analytes in the PQQ-GDH catalyzed reaction. Using the difference between these coefficients, it was possible to select the microsensors within the overall enzyme-polymer spot that provided the best data for quantifying glucose and maltose by the artificial neural network used. The quantification of glucose and maltose was successful, except when the contributions from the components of the mixture were n (g)=k n units of glucose and simultaneously n (m)= 1.86(1-k)n units of maltose, for each constant n > 0 and k E <0,1>.