UV–VIS investigation of methyl red in presence of sodium dodecyl sulfate/methanol/ethanol/water system

Ammonia/pH super-sensitive colorimetric labels based on gellan gum, sodium carboxymethyl cellulose, and dyes for monitoring freshness of lamb meat

This study aimed to develop an ammonia and pH super-sensitive label by incorporating methyl red and bromothymol blue (MR-BTB, MB) into gellan gum/sodium carboxymethyl cellulose (GG/CMC-Na, GC). Furthermore, E-nose as an auxiliary tool combined with the labels to monitor meat freshness. Results showed that MB had more color change than pure MR or BTB, and the detection limit of ammonia about the MR-BTB (1:2) group was only 2.82 ppm. The addition of MB significantly increased tensile strength, moisture content, and water solubility, but decreased elongation at break and transmittance of the GC label (p < 0.05). The result of FTIR and SEM indicated the formation of hydrogen bonds and well compatibility between MB and GC. Furthermore, the color of the GC-10.0MB label was constantly obviously changing during meat storage, indicating that the GC-10.0MB label had great potential for monitoring the freshness of the lamb meat. A high correlation was found between ΔE of GC-10.0MB label and TVB-N (R2 = 0.9092) and pH (R2 = 0.9114) of meat. Interestingly, the high correlation between ΔE of GC-10.0 MB label and the response value of S2 (R2 = 0.7531), S6 (R2 = 0.9921), and S7 sensor (R2 = 0.8325) of E-nose was also found.

An evaluation of spectral and statistical parameters of ion pair complexation of Zafirlukast using chromogenic dyes in solid dispersion-based formulations

The purpose of present work was to develop a novel analytical method for orally given leukotriene antagonist Zafirlukast (ZST), present in Meglumine and Eudragit EEPO based solid dispersion formulation. Four simple, extraction-free, fast, and economical methods based on charge transfer complexation among nitrogen of ZST with sulfonyl group comprising chromogenic mediator bromophenol blue (BPB-Method B), bromothymol blue (BTB-Method C) and bromocresol green (BCG-Method D). The first method (A) is based on the analysis using 0.1 M HCl as a solvent at λmax 242 nm while chromogenic methods yield color complex at λmax 415 nm (BPB-Method B), λmax 420 nm (BTB-Method C) and λmax 435 nm (BCG-Method D). The Beer's Law stayed linear in the concentration ranges of 1-10, 10-75, 5-40 and 15-100 μg/ml for methods A, B, C and D, respectively. The spectral and thermodynamic characterization of each method was carried out by the application of Molar Absorptivity, LOD, LOQ, Association Constant and Gibbs free energy (ΔGo). The methods were statistically optimized and evaluated by F-Distribution Value, P-Value, Shapiro-Wilk P-Value, regression analysis, Q-Q plot, prediction interval, residual histogram and plots. Various experimental conditions affecting the complexation and stability of chromogenic complexes are cautiously studied including optimal temperature, chromogenic agent volume, color stability, recovery, precision and accuracy. All the measurements were executed under ICH guidelines. It can be established that proposed would be an appropriate prospective analytical approach for estimation of ZST in pure bulk, solid dispersions and dosage forms.

Application of Plackett–Burman Design for Spectrochemical Determination of the Last-Resort Antibiotic, Tigecycline, in Pure Form and in Pharmaceuticals: Investigation of Thermodynamics and Kinetics

Tigecycline (TIGC) reacts with 7,7,8,8-tetracyanoquinodimethane (TCNQ) to form a bright green charge transfer complex (CTC). The spectrum of the CTC showed multiple charge transfer bands with a major peak at 843 nm. The Plackett–Burman design (PBD) was used to investigate the process variables with the objective being set to obtaining the maximum absorbance and thus sensitivity. Four variables, three of which were numerical (temperature—Temp; reagent volume—RV; reaction time—RT) and one non-numerical (diluting solvent—DS), were studied. The maximum absorbance was achieved using a factorial blend of Temp: 25 °C, RV: 0.50 mL, RT: 60 min, and acetonitrile (ACN) as a DS. The molecular composition that was investigated using Job’s method showed a 1:1 CTC. The method’s validation was performed following the International Conference of Harmonization (ICH) guidelines. The linearity was achieved over a range of 0.5–10 µg mL−1 with the limits of detection (LOD) and quantification (LOQ) of 166 and 504 ng mL−1, respectively. The method was applicable to TIGC per se and in formulations without interferences from common additives. The application of the Benesi–Hildebrand equation revealed the formation of a stable complex with a standard Gibbs free energy change (∆G°) value of −26.42 to −27.95 kJ/mol. A study of the reaction kinetics revealed that the CTC formation could be best described using a pseudo-first-order reaction.