Use of Surfactant as Mobile Phase Additive in LC for Simultaneous Determination of Metal-Pyrrolidine Dithiocarbamate Chelates

Reversed phase liquid chromatography using UV detection was developed for the simultaneous analysis of Hg(II), Pb(II), Cd(II), Ni(II), Fe(III) and V(V) ions after their complexation with pyrrolidine-dithiocarbamate (PDC). Optimum chromatographic conditions were a μ-Bondapak C₁₈ column and an isocratic mobile phase consisting of 40 mmol L^?1 SDS, 34 mmol L^?1 TBABr and 68% acetonitrile in 10 mmol L^?1 phosphate buffer pH 3.5. The separation of six PDC complexes was achieved within 8 min. Analytical performances and method validation were investigated. The detection limits ranged from 0.16 μg L^?1(Fe(III)) to 5.40 μg L^?1(Pb(II)). Recoveries obtained for all the studied samples including tap water, whole blood and vegetables were 72–98%. The results obtained from the proposed method were not significantly different compared to those obtained from atomic absorption spectrometry (P = 0.05).     

Detection of silver(I) ion based on mixed surfactant-adsorbed CdS quantum dots

Mixed cationic and anionic surfactants were adsorbed on cadmium sulfide quantum dots (CdS QDs) capped with mercaptoacetic acid. The CdS QDs can be extracted into acetonitrile with 98 % efficiency in a single step. Phase separation only occurs at a molar ratio of 1:1.5 between cationic and anionic surfactants. The surfactant-adsorbed QDs in acetonitrile solution display stronger and more stable photoluminescence than in water solution. The method was applied for determination of silver(I) ion based on its luminescence enhancement of the QDs. Under the optimum conditions, the relative fluorescence intensity is linearly proportional to the concentration of silver(I) ion in the range between 50 pmol L^?1and 4 μmol L^?1, with a 20 pmol L^?1 detection limit. The relative standard deviation was 1.93 % for 9 replicate measurements of a 0.2 μmol L^?1 solution of Ag(I).

Enhancement of the Fluorescence Quenching Efficiency of DPPH<Superscript>•</Superscript> on Colloidal Nanocrystalline Quantum Dots in Aqueous Micelles

Luminescent CdS quantum dots capped with thioglycolic acid (CdS-TGA QDs) were demonstrated to serve as a fluorescence probe for a model organic radical, 2,2-diphenyl-1-picrylhydrazyl radical (DPPH^•), employing the quenching of the CdS-TGA QDs emission signal by the radical. Under the optimum conditions, the quenching efficiency of DPPH^• on CdS-TGA QDs was proportional to the concentration of DPPH^•, following Stern-Volmer relationship. Different types of surfactants (cationic, anionic and neutral surfactants) were introduced to CdS-TGA QDs in order to increase the detection sensitivity. The fluorescence intensity of CdS-TGA QDs was greatly enhanced by cationic and neutral surfactants. Moreover, the quenching efficiency of DPPH^• on the QDs in the presence of micelles was remarkably ca. 13 times higher than that in the system without micelles. Effects of pH and concentration of surfactants on the fluorescence quenching of CdS-TGA QDs were investigated. Electron spin resonance (ESR) spectroscopy was also used to monitor the DPPH radical species in CdS-TGA QDs mixtures with and without micelles. Fluorescence quenching mechanisms of CdS-TGA QDs by DPPH^• in the presence and in the absence of CTAB were proposed.     

Determination of arsenic based on quenching of CdS quantum dots fluorescence using the gas-diffusion flow injection method

A sequential injection analysis system for determination of arsenic based on hydride generation and fluorescence quenching of mercaptoacetic acid capped cadmium sulfide quantum dots (CdS-MAA QDs) is described. The generated arsine diffused across the PTFE membrane in a gas-diffusion unit and subsequently interacted with CdS-MAA QDs. The parameters affecting the arsine generation and the fluorescence quenching of QDs were studied. Under the optimum conditions, it was observed that a increase in the concentration of As(III) corresponded well to a decrease in fluorescence intensity according to the Stern-Volmer relationship. The extent of quenching was dependent on the concentration of arsenic in the range of 0.08-3.20 mmol L⁻¹, with the detection limit of 0.07 mg L⁻¹. The precision (%RSD) from eight replicates of the determination of As(III) 1.0 mg L⁻¹ was found to be 1.4%. The proposed method was applied to the determination of arsenic in ground water samples with satisfactory recoveries.