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The latter neutral form is represented by an equilibrium mixture of the colored and fluorescent zwitterions RB ± and the colorless lactones RB , which exist in some solvents, but not in water, where the fraction of RB species is too small to be registered experimentally. In this work, the RB dye was used as a probe to understand the properties of the reversed micellar interface; also, the change in the location of RB in the CTAC reversed micellar media was investigated 2010 © The Japan Society for Analytical Chemistry † To whom correspondence should be addressed. E-mail: tfuji@sci.hiroshima-u.ac.jp The acid-base behavior of rhodamine B (RB) in reversed micellar solutions of cetyltrimethylammonium chloride (CTAC) in 1-hexanol-cyclohexane/water was investigated through absorption and fluorescence measurements under varying the hydrogen-ion concentration in a water pool, the mole fraction of 1-hexanol in a bulk solvent and the water to surfactant molar concentration ratio. RB exhibited equilibria between the cationic, zwitterion and lactone forms of the dye as a cause of the spectral changes, indicating a change in the RB distribution among the reversed micellar water pool, interface and bulk solvent. Furthermore, RB was used as a probe to develop a method for determining the critical micelle concentration (CMC) in CTAC solutions. Abrupt variations in the intensities and wavelengths of the absorption and emission maxima of RB were observed at the CMC. The standard free energy of micellization was also evaluated from the CMC data.

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Quantitative analysis of pharmaceutical compounds up to Nano gram levels is highly recommended to introduce feasible and sensitive tool for determination of the compounds in the pharmaceutical and biological samples. Nirmatrelvir plus ritonavir was recently approved in the US, the UK and Europe as a new co-packaged dosage form for the treatment of COVID-19. The objective of this work was to develop a more sensitive TLC method based on using β-cyclodextrin as a chiral selector additive in the mobile phase for simultaneous determination of nirmatrelvir and ritonavir in pure form, pharmaceutical formulation and spiked human plasma. The analysis procedures were developed using TLC aluminum silica gel plates and methanol–water- 2% urea solution of β-cyclodextrin (40:10:.5, by volume) as a mobile phase with UV detection at 215 nm. The developed method was successfully applied over a linearity range of 10–50 ng/band for both nirmatrelvir and ritonavir. The method was validated for limits of detection and quantitation, accuracy, precision, specificity, system suitability, and robustness. Furthermore, the eco-friendliness of the proposed method was assessed using the analytical eco-scale and the green analytical procedure index. The described method exhibited compliance with green analytical chemistry principles based on common green metric values.

A highly sensitive flow-injection (FI) method was developed for the determination of ascorbic acid using chemiluminescence (CL) based detection. This method involved the following processes: (1) reduction of tetrachloroaurate(III) in hydrochloric acid with ascorbic acid; (2) on-line extraction of the residual Au(III) with rhodamine B from the aqueous hydrochloric acid solution into toluene, followed by the separation of the Au(III)-containing organic phase from the aqueous phase through a microporous Teflon membrane in the flow system; and (3) the measurement of CL produced in a flow cell upon mixing of the extract stream of Au(III) in toluene with luminol in the reversed micellar medium of cetyltrimethylammonium chloride-water in 1-hexanol-cyclohexane, which was injected into a CL reagent stream. In this procedure, a reduction in the CL intensity occurred due to the addition of ascorbic acid to the Au(III) solution. The CL signal of Au(III) decreased with increasing concentration of ascorbic acid in the aqueous sample solution. The proposed procedure allowed the indirect quantitative determination of ascorbic acid in the range of 1.0 × 10 to 1.0 × 10 M with a correlation coefficient of 0.987 and relative standard deviation of 2.1% (n = 6) at 1.0 × 10 M. The proposed FI-CL methodology was successfully applied for quantitative determination of ascorbic acid in fruit juices and pharmaceutical samples.