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A novel, simple, sensitive and rapid spectrophotometric method for the determination of selenium(iv) in an acidic medium using rhodamine B hydrazide (RBH) has been developed. The method is based on the micellar mediated oxidation of RBH by Se(iv) in an acidic medium to produce a pinkish violet color of rhodamine B, which was monitored spectrophotometrically at λmax 585 nm. The sensitivity of the method was found to increase when the reaction was performed in a micellar medium. Beer's law was obeyed in the concentration range of 0.002-0.032 μg mL-1. The reaction variables such as time, temperature, reagent concentration, and acidity have been optimized for the reaction. Sandell's sensitivity and molar absorptivity for the reaction system were found to be 0.00004 μg cm-2 and 42.52 × 106 L mol-1 cm-1, respectively. The developed method was successfully applied for the determination of Se(iv) in several real samples with quantitative results.

A tetraphenylethene functionalized rhodamine sensor RbTPE has been synthesized by the condensation of tetraphenylethene-aldehyde and rhodamine B hydrazide. RbTPE exhibited an aggregation-induced emission effect in the THF/water system, and displayed high selectivity and sensitivity for HCl vapor in the solid state. The solid-state emission of RbTPE can be reversibly switched between blue and red due to the stronger protonation of the rhodamine amino group by HCl. A satisfactory nonlinear relationship was observed upon exposure to HCl vapor in the range of 0–500 ppm, and the detection limit was as low as 20 ppm. After exposing the post-test product RbTPE–HCl to NH3 vapor for a few minutes, the spirolactam ring closed and the signals restored, which showed that RbTPE could be used as a “naked-eye” and reversible sensor for detecting HCl and NH3.

A simple, sensitive, and rapid spectrophotometric method is proposed for the determination of the trace amount of thallium. The method is based on the oxidation of rhodamine B hydrazide by thallium(I) in acidic medium to give a pinkish violet radical cation, having a maximum absorption at 565 nm. The sensitivity of the method was found to increase when performed in micellar medium. Beer's law is valid over the concentration range of 0.005 μg mL−1 to 6.4 μg mL−1 with molar absorptivity and Sandell's sensitivity of 6.305 × 104 L mol−1 cm−1 and 0.008 mg cm−1 respectively. The tolerance limits for interfering ions are discussed. All variables were studied in order to optimize the reaction conditions. The validity of the method was checked by its simultaneous determination in synthetic samples.