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In present work, rhodamine B hydrazide and rhodamine 6G hydrazide were synthesized and the chemiluminescence performance has been investigated. Based on the chemiluminescence of rhodamine 6G hydrazide‑chromium(VI), a selective and sensitive method for the direct detection of chromium(VI) was developed. The chemiluminescence intensity was linearly related to the concentration of chromium(VI) in the range of 2.60 × 10− 8–8.00 × 10− 6 mol/L with a correlation coefficient of r = 0.998 and a detection limit of 1.4 × 10− 8 mol/L (S/N = 3). The results indicated rhodamine 6G hydrazide was an excellent chemiluminescent probe for chromium(VI) without reduction of chromium(VI) to chromium(III). A possible mechanism of CL emission was also suggested.

In this article, we successfully designed and synthesized a novel chemosensor PW bearing rhodamine B hydrazide and 8-formyl-7-hydroxyl-4-methylcoumarin, which displayed both colorimetric and “turn-on” fluorescence responses for CN− in DMSO/H2O (1 : 1, v/v, pH = 7.20) solution. The probe could distinguish CN− via a deprotonation process and the mechanism of intramolecular charge transfer (ICT), which was proved by 1H NMR titration, ESI-MS and DFT calculations. The detection limit of the sensor PW towards CN− was 1.592 × 10−7 M. Moreover, the sensor PW was successfully utilized to detect CN− in bitter almond. Test strips containing PW were also prepared, which could act as a colorimetric tool to detect CN− in practical application.

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.

Rhodamine B hydrazide (RBH) was prepared as a new derivatizing reagent for residual formaldehyde in a drug such as N-butyl-2-cyanoacrylate (NBCA). RBH reacted with formaldehyde rapidly at room temperature, and the resulting derivative can be detected sensitively at 238 nm. After optimizing the derivatization and chromatographic separation conditions, RBH as a pre-column derivatizing reagent has been successfully used for the analysis of formaldehyde in real NBCA samples by high-performance liquid chromatography (HPLC). The detection limit of the method is 0.004 μg/mL for formaldehyde, and the recovery is 94.0%-96.6%. Most notably, compared with the previous HPLC methods, the developed method has the advantages of mild derivatization temperature, short derivatization time and high sensitivity.

N-acryloyl rhodamine B hydrazide, a non-responsive control of a colorimetric Cu(2+) sensor, was used as a turn-on fluorescent sensor for Hg(II) from HgCl2 in the presence of AgNO3. The detection was highly selective and sensitive, and a large number of environmentally and biologically relevant metal ions, such as Na(+), K(+), Ca(2+), Mg(2+), Fe(3+), Cu(2+), Zn(2+), Cr(3+), Pb(2+), Ni(2+), Fe(2+), Mn(2+), Co(2+), Cd(2+), including Hg(II) from the easy dissociated salts, did not show significant interference. The fluorescence of the sensor (10 μM) was enhanced 74 folds by 10 equiv. of Hg(II) from HgCl2 in THF/HAc-NaAc (1/1, v/v, pH = 6) aqueous buffer solution containing 20 equiv. of AgNO3. The maximal fluorescence intensity increased linearly with the concentration of Hg(II) in the range of 0-70 μM. The detection limit of Hg(II) was 0.59 μM. The sensing mechanism was explored by Job's plot experiment, reversible experiment, mass spectrum analysis, spectroscopic analysis, and thin-layer chromatography.

A novel spectrofluorimetric method for the determination of sulfite using rhodamine B hydrazide as fluorogenic reagent in the presence of polyoxyethylene sorbitan monooleate (Tween 80) surfactant micelles is described. The method is based on the mixture of sulfite with rhodamine B hydrazide, a colorless, non-fluorescent substance in Tween 80 surfactant micelles which gives rhodamine B-like fluorescence emission. The fluorescence intensity increase is linearly related to the concentration of sulfite in the range 5–800 ng ml −1 with a detection limit of 1.4 ng ml −1 (3 σ ). The optimal conditions for the detection of sulfite are evaluated and the possible detection mechanism is also discussed. The method has been successfully applied to the determination of total sulfite in wines and compares well with the standard iodimetric method.

A novel method for the determination of peroxynitrite using rhodamine B hydrazide as a fluorogenic probe is described. The method is based on the oxidation of rhodamine B hydrazide, a colorless, non-fluorescent substance, by peroxynitrite to give rhodamine B-like fluorescence emission. The fluorescence increase is linearly related to the concentration of peroxynitrite in the range of 7.5×10 −8 –3.0×10 −6 mol l −1 with a detection limit of 2.4×10 −8 mol l −1 (3 σ ). The optimal conditions for the detection of peroxynitrite were evaluated and the possible detection mechanism was also discussed in this paper.