Multivariate analysis of tioconazole - TCNQ charge transfer interaction: Kinetics, thermodynamics and twofold response optimization.

Charge-transfer complex (CTC) formation between tioconazole (TCZ) as an n-electron donor and 7, 7, 8, 8-tetracyanoquinodimethane (TCNQ) as a π-acceptor was studied spectrophotometrically with an accompanying kinetic and thermodynamic investigation. Multivariate data analysis via a set of experimental designs was executed for this purpose. A 23 - two-level full factorial design (FFD) was used for inspecting the proposed variables while a face-centered central composite design (FCCCD) was used to adjust the levels of variables proved to be significant. Two responses were quantified as a result of this interaction; complex I (Y1, measured at 743 nm) and complex II (Y2, measured at 842 nm). Derringer's function and overlaid contour plots were used to concurrently optimize both responses. Benesi-Hildebrand equation was applied to determine of formation constant (K), and the molar absorptivity (Ɛ) of the formed complex. Different thermodynamic parameters; the standard Gibbs free energy change (∆G°), the standard enthalpy of formation (∆H°) and the standard entropy change (∆S°) were determined for the reaction product. The proposed method was validated regarding the linearity, intra-, and inter-day precision and accuracy, limit of detection, limit of quantification and following the ICH standards. The proposed method was also applied for the determination of TCZ in its pharmaceutical preparations. Having a higher molar absorptivity and higher formation constant, complex II was of choice for all subsequent measurements. Application of Benesi-Hildebrand equation supported the formation of 1: 1 CTC. Thermodynamic study revealed the endothermic characters and the spontaneity of formation of the CTC at high temperature.

Plackett-Burman and Box-Behnken designs as chemometric tools for micro-determination of l-Ornithine.

Plackett-Burman (PB) and Box-Behnken (BB) screening and response surface factorial designs were used to evaluate spectrophotometric and spectrofluorimetric approaches for the determination of l-Ornithine (ORN) as per se and in dietary supplements. Both approaches were based on the derivatization of the primary amino group of ORN via Hantzsch condensation reaction producing yellow coloured adducts (dihydrolutidine derivative). The reaction product was determined spectrophotometrically (method A) at λmax=327nm and spectrofluorimetrically (method B) at 480nm (λem) after excitation at 325nm (λex). A multivariate scheme was tailored to investigate the process numerical variables; reaction temperature, heating time, reagent volume, and pH implementing PB as a screening design followed by BB as an optimization strategy. Categorical factors including diluting solvent and sequence of addition were kept invariable. Responses of the reaction systems were the maximum absorbance (Y1) and maximum fluorescence intensity (Y2), correspondingly. Quality tools as well as ANOVA testing, before and after response transformation were used to decide upon the substantial variables. Following the optimization of reaction variables using desirability plots, calibration graphs were found to be rectilinear in the range of 6-14µg/mL and 0.4-1.2µg/mL for methods A and B, respectively. Both methods proved to be sensitive with detection limits (DL) of 337 and 85ng/mL, and quantitation limits (QL) of 1086 and 283ng/mL, for methods A and B, respectively. An interference study was performed using potential foreign species. No significant interference effect was observed on any of the proposed procedures. System performance was addressed following ICH guidelines and considering parameters such as linearity, detection and quantification limits, accuracy and precision, robustness and specificity.

Label-free detection of heparin, streptavidin, and other probes by pulsed streaming potentials in plastic microfluidic channels.

In this paper, pulsed streaming potentials generated in plastic microfluidic channels are used for the label-free detection of some model analytes. The microchannels are fabricated with the commodity plastic cyclic olefin copolymer (COC), and the detection signal arises from a change in the surface charge upon analyte adsorption on the modified microchannel surface. The role of the surface modification is to confer the microchannel with a predetermined charge and a particular specificity toward the adsorption of the target analyte. In this work, several target probes displaying different levels of specificity were investigated. Heparin and streptavidin were detected by adsorption on microchannel surfaces modified with protamine and biotin, respectively, whereas bovine serum albumin (BSA) and methylene blue (MB) showed nonspecific adsorption on almost any modified or unmodified COC microchannel surface. The magnitude of the streaming potential was found to be proportional to the liquid pressure and the surface charge of the microchannel in accord with the Smoluchowski equation. Because the relative polarity of the streaming potential is determined by the surface charge, the most straightforward detection with this method occurs when the charge is reversed upon analyte adsorption. This strategy was used for the species described in this work, and the lowest concentrations detected were approximately 0.01 units/mL for heparin (below clinical relevance), approximately 10 (-9) M for BSA, and approximately 10 (-6) M for MB. Unlike the conventional method of steady flow, in this work, the streaming potentials were measured under pulsed conditions of flow and using nonreference electrodes. This approach removes the need of special electrolytes as it is usually required when using reference electrodes, and at the same time, it mitigates the interference of electrochemical drift from the electrodes. Relative standard deviations of approximately 1-2% and measuring times of approximately 10 s are readily attained with this experimental setup. The on-channel modification of the surface was carried out by UV-photografting methods given the significant UV transparency of COC.