Xirong Huang

Determination of tin in canned foods by UV/visible spectrophotometric technique using mixed surfactants

The complex of tin(IV) with bromopyrogallol red (BPR) in the presence of nonyl phenoxy polyethoxyethanol (OP) and cetyltrimethylammonium bromide (CTAB) has a sensitive absorption peak at 304 nm. Under the optimal conditions, Beers law is obeyed over the range 0.1-2.5 mug ml(-1) Sn(IV) with molar absorptivity being 8.2 x 10(4) l mol(-1) cm(-1) and detection limit 0.018 mug ml(-1). As compared with the visible method which also uses BPR as chromogenic reagent (lambda(max) = 550 nm), our method is sensitive and selective because of the complexs high, sharp absorption peak. In addition, the present method is simple and rapid, no heating or standing is needed. By means of the mixed surfactants the precipitation caused by the ion association of cetyltrimethylammonium cation and I(-)(3) anion is avoided if iodide is used for separating micro amounts of tin(IV) from a sample matrix. An application of the proposed method to the determination of Sn(IV) in a canned food was made with satisfactory results.

Determination of chromium in waste-water and cast iron samples by fluorescence quenching of rhodamine 6G.

A new simple, selective and sensitive fluorescence quenching method was developed to determine chromium with rhodamine 6G. The method is based on the oxidation of rhodamine 6G by chromium(VI) in sulfuric acid solution. The linear calibration graph was obtained in the range 8-80 ng ml(-1) chromium(VI). The detection limit is 0.8 ng ml(-1). The method was applied successfully to the determination of chromium in waste water and cast iron samples.

STUDY ON A FLUORESCENCE-ENHANCED SYSTEM OF 1,2,4-TRIHYDROXYANTHROQUINONE-BE2+-DNA

Fluorescence-enhancement of 1,2,4-trihydroxyanthroquinone (THAQ)-Be2+ complex enhanced by nucleic acid was studied. Experimental results revealed that double-stranded DNA can enhance remarkably the fluorescence intensity of THAQ-Be2+, while RNA cannot. Based on these results, a fluorescence method for the selective determination of DNA in the presence of RNA was developed. Maximum fluorescence intensity was found in the pH range 3.6-4.5 with maximum excitation and emission wavelengths at 510 and 565 nm, respectively. Under optimum conditions, the calibration graph was linear over the range 0.08-18 micrograms ml-1 for double-stranded fish sperm DNA (fsDNA) with the detection limit being 2.75 x 10(-8) g ml-1. The method was applied for the determination of DNA in synthetic samples. The relative S.D. for five replicates was within 4%. In addition, the interaction mechanism of THAQ-Be2+ with DNA was also discussed.

Fluorimetric determination of hydrogen peroxide in water using acetaminophen

A fluorimetric procedure for the determination of hydrogen peroxide, based on the oxidation of acetaminophen with hydrogen peroxide in acidic medium, is described. The calibration graph was linear in the range 5.0 x 10(-8) - 2.4 x 10(-5) M hydrogen peroxide at an emission wavelength of 333 nm with excitation at 298 nm. The method has been applied to the determination of hydrogen peroxide in rain water, and the recoveries in milk samples were good.

Mixed micellar medium for the spectrophotometric determination of molybdenum in molybdenum/tungsten mixtures

Effects of cetyltrimethylammonium bromide (CTAB) and/or nonylphenoxypolyethoxyethanol (OP) on the absorption spectra of the complexes of molybdenum and tungsten with bromopyrogallol red (BPR) were studied. Based on these effects, a mixture of CTAB and OP was thus selected as a medium for the selective and sensitive determination of Mo in Mo/W binary mixtures. Under the optimum conditions, Beers law was obeyed over the range 0.06-0.8 mug ml(-1) Mo with molar absorptivity being 1.3x10(5) l mol(-1) cm(-1) and detection limit 0.025 mug ml(-1). For 1.0 mug Mo, at least 20 mug W did not interfere in the determination of Mo with average recovery and relative standard deviation being 99.5% and <2%, respectively. The method developed maintained the features of simplicity and rapidity and, moreover, its selectivity and sensitivity enhanced greatly due to the use of CTAB/OP mixed micellar medium. When coupled with a compatible concentration method, the proposed method could be used for the determination of trace Mo in natural waters.

Spectrophotometric determination of Sb(III) in Sb(III)/Sb(V) binary mixtures using sodium dodecylsulfate/nonylphenoxy polyethoxyethanol mixed micellar media

Different micellar media had different effects on the absorption spectra of the complexes of bromopyrogallol red with Sb(III) and Sb(V). The mixed micellar medium composed of 0.7 ml of 0.2% sodium dodecylsulfate (SDS) and 0.3 ml of 2% nonylphenoxypolyethoxyethanol (OP) at 80 degrees C could be used for the sensitive determination of Sb(III) in Sb(III)/Sb(V) binary mixtures. Under the optimal conditions, Beers Law was obeyed over the range 0.1-2.3 mug ml(-1) Sb(III) with molar absorptivity at 538 nm being 4.8 x 10(4) l mol(-1) cm(-1) and detection limit 0.04 mug ml(-1). For 10 mug Sb(III), more than 100 mug Sb(V) could be tolerated (error < 3%) in the presence of SDS/OP micellar medium as compared with 0.1 mug Sb(V) in the absence of SDS/OP micellar medium. In addition, the sensitivity of Sb(III) in the micellar medium was much higher than that in pure water medium. As compared with conventional extraction spectrometry, the proposed method produced a reproducible result. It did not need the conversion of Sb(III) to Sb(V) and a time-consuming extraction process. A detailed discussion on the selection of surfactants, the effect of temperature, and the role played by the mixed surfactants were also made.

Facile method for fabrication of self-supporting nanoporous gold electrodes via cyclic voltammetry in ethylene glycol, and their application to the electrooxidative determination of catechol

AbstractA method is described for in-situ electrochemical preparation of nanoporous gold electrodes (np-GEs) via alloying and dealloying using ethylene glycol (EG) as a solvent. The np-GEs were prepared via cyclic voltammetry from a gold electrode in the presence of ZnCl2 in EG. Effects of temperature, number of scan cycles and scan rate were investigated. It is concluded that the process involves formation of interfacial elemental zinc and the formation of a gold-zinc alloy. At axa0temperature of 120xa0°C, the alloy is formed already after the first scan cycle, and ten further cycles do not cause substantial further changes in the morphology. Changes in the morphology were corroborated by data on the electroactivity of the np-GEs. The mechanism of the formation of np-GEs in EG obviously is different from that in other solvents due to the superior smoothing ability of EG for electroplating. This results in more uniform alloy layers andxa0in a more evenly distributed porous structure. The self-supporting np-GE without any further modification displays an amperometric response to catechol (at a working voltage of 420xa0mV vs. SCE) in the 0.050 to 1.0xa0mM concentration range, with a detection limit of 1.78xa0μM (at an S/N of 3), indicating that the np-GE can be applied to convenient and effective determination of catechol.n Graphical AbstractA facile in-situ electrochemical alloying and dealloying route using ethylene glycol as the solvent is introduced for the fast fabrication of axa0self-supporting nanoporous gold electrode. Itxa0exhibits good electrocatalytic activity towards the oxidation of catechol.

Effect of Polyvinylpyrrolidone on the States of Water in Water-in-Oil Microemulsions with Betaine Surfactant

A water-in-oil (w/o) microemulsion was prepared with the zwitterionic surfactant dodecyl betaine (C12BE), n-pentanol (C5OH), n-heptane (C7H16) and water. Effects of polyvinylpyrrolidone (PVP) with different molecular weight on the state of water in w/o microemulsions at a given water/C12BE molar ratio were investigated by FT-IR and differential scanning calorimetry (DSC). The experimental results showed that addition of PVP resulted in an increase of the content of the bound water in water pool of a w/o microemulsion, but a decrease of the amount of the bulky water. The higher the molecular weight of PVP, the more bound water; and the less bulk water. The change of the trapped water was not obvious due to the interference of C5OH.

Fluorescence property on solutions of zwitterionic surfactant tetradecylbetaine in the presence of macromolecules

The fluorescence property of zwitterionic surfactant tetradecylbetaine (C14BE) solutions in the presence of polyvinylpyrrolidone (PVPk30 and PVPk90), or Xanthan (Xc) have been investigated by steady-state fluorescence probe. The intensity ratio of the first and third peaks (I1/I3) of the monomer and that of the excimer to monomer (Ie/Im), and the aggregation number of the aggregates have been monitored. The results showed that C14BE/PVP and C14BE/Xc interactions mostly occur at the micelle surface. The C14BE clusters or micelles are bound to macromolecule chains by electrostatic force for PVP and by hydrogen-bonding for Xc, respectively.

Proton nuclear magnetic resonance study of the solubilization site of bromopyrogallol red in aqueous cationic/nonionic mixed micellar solutions

Abstract The solubilization site of bromopyrogallol red (BPR) in cetyltrimethylammonium bromide (CTAB)/Triton X-100(TNX) mixed micellar solutions was studied by the pulsed FT NMR technique. The changes in the chemical shifts of the individual groups of protons in the two surfactant molecules indicated that BPR was localized near the ammonium head group of CTAB and the benzene ring of TNX. Diluting the mixed micellar solution made BPR move a little toward the outer portion of the micelle while increasing the mole fraction of TNX made BPR move a little toward the inner portion of the micelle.