Yun'e Zeng

Fluorination with polytetrafluoroethylene slurry in electrothermal vaporization-inductively coupled plasma-atomic emission spectrometry

Abstract A method was developed to determine refractory elements by inductively coupled plasma-atomic emission spectrometry (ICP-AES) with sample introduction by electrothermal vaporization (ETV). A slurry of polytetrafluoroethylene (PTFE) was used as fluorinating reagent to promote the vaporization of refractory elements from a graphite furnace and to avoid the formation of difficult volatile carbides. With this treatment the refractory elements can be efficiently vaporized, and subsequently introduced into the plasma. The detection limits of this method were in the picogram to sub-nanogram range and superior to those obtained with conventional nebulization systems, and were comparable with those obtained with similar ETV—ICP-AES techniques. The analyte vaporization and transport process was systematically explored, and the corresponding vaporization and transport mechanisms of refractory elements in this system have been proposed. The matrix effects and sample particle size effects in fluorination assisted ETV—ICP-AES were significantly reduced. Therefore, an effective method for lowering the matrix interferences has been proposed.

Flow-injection stopped-flow spectrofluorimetric kinetic determination of total ascorbic acid based on an enzyme-linked coupled reaction

Abstract A flow-injection enzymatic kinetic spectrofluorimetric procedure for determining total ascorbic acid in solution by combining the merging zones principle with the stopped-flow technique is described. It is based on the oxidation of ascorbic acid catalysed by laccase to dehydroascorbic acid, which then reacts with o -phenylenediamine to form a fluorescent quinoxaline. Total ascorbic acid is determined in the range of 0.025–1.0 μg ml −1 at 30 determinations per h. The procedure is applied to the determination of total ascorbic acid in wine, beer, urine and pharmaceutical preparations.

Single-mismatch detection using nucleic acid molecular 'light switch'

A novel nucleic acid molecular light switch method is developed for the sensitive recognition and detection of a single-base mismatched oligonucleotides. The detection limit of oligonucleotide of perfect double stranded and that with single-base, two-base and three-base mismatched are 0.11, 0.17, 0.34 and 1.5 ng ml(-1), respectively. It was found that Ru(phen)(2)(dppx)(2+) (phen=1,10-phenanthroline, dppx=7,8-dimethyl-dipyridophenazine) can be used to detect and recognize the perfect double stranded oligonucleotides from mismatched and random targets by the intensity of fluorescence and temperature. This method can be used to recognize and quantitatively detect target DNA with specific sequence. The advantage of this method is that no requisites are needed to separate the coexisting random targets in the case of a mixed solution containing perfect, mismatched and random targets, which make the recognition analysis of oligonucleotide simple and fast. Moreover, it has potential in the study of dynamic process of DNA hybridization.

A novel method for determination of DNA by use of molecular 'Light Switch' complex of Ru(bipy)2(dppx)2+

Abstract A novel fluorimetric method was developed for selective determination of DNA with the molecular ‘Light Switch’ complex of Ru(bipy) 2 (dppx) 2+ . The maximum fluorescence intensity was produced in the pH range of 9.3–11.5, and the maximum excitation and emission wavelengths were 467 and 595xa0nm, respectively. Under the optimum conditions, the fluorescence intensity was in proportion to the concentration of DNA. The linear range for calfthymus DNA, Salmon sperm DNA and Herring sperm DNA were 0–0.4, 0–0.35 and 0–0.4xa0μg/ml, respectively. The limits of detection for Calfthymus DNA, Salmon sperm DNA and Herring sperm DNA were 0.75, 0.66 and 1.49, respectively. A satisfactory result was obtained when the proposed method was used to determine DNA in the presence of some coexisting substances.

Micelle Enhanced Spectrofluorimetric Determination of Norfloxacin Using Terbium as Fluorescent Probe

Abstract Terbium(III) forms highly fluorescent complex with norfloxacin. The presence of surfactant can enhance greatly fluorescence intensity. In this paper, the fluorescence characteristics of complex in presence of surfactant has been investigated. It was found that norfloxacin could form stable complex with terbium in the pH 6.5–8.5 media. The fluorescence intensity of complex in SLS media is three folds more than complex itself. A new micelle enhancement spectrofluorimetry for the determination of norfloxacin has been developed. The detection limit of proposed method is 0.017 μg/ml. It has been satisfactory for the determination of trace norfloxacin in serum with 95.2%∼101.2% recoveries.

Processing and error analysis of signals in flow-injection analysis

Abstract The processing and error analysis of signals in flow-injection systems were systematically studied by simulation and experimental measurements. The content includes an error analysis for peak-height and peak-area signal, a least-squares filtering procedure applied to the flow-injection curve and a peak recognition to remove interferences from air bubbles. Simulation results were obtained by statistical processing of peak-height and peak-area values from Gaussian curves to which noise had been added. The experimental measurements were done by an automatic flow-injection device to obtain detailed information for each individual point of a peak. 2-(2-Arsenophenylazo)-7-(2,6-dichlorophenylazo-4-sulphonic acid)-1,8-dihydroxynaphthalene-3,6-disulphonic acid (DCSA) was used for measuring physical dispersion alone, and Fe(II)- o -phenanthroline for the measurement of both physical dispersion and chemical reaction. The results from computer simulation and experiments agreed well.

Spectral studies on the interaction of DNA and Ru(bipy)2(dppx)2

The interaction of Ru(bipy)2(dppx)2+ (bipy = 2.2-bipyridine,dppx = 7,8-dimethyldipyrido phenazine) with the calfthymus DNA has been studied with fluorescence and ultraviolet visible absorption spectroscopy. The results of fluorescence quenching and salt effect show that Ru(bipy)2(dppx)2+ intercalate into the double helix of DNA. The ultraviolet visible absorption spectrum of Ru(bipy)2(dppx)2+, calfthymus DNA, and their interaction indicate that Ru(bipy)2(dppx)2+ intercalate into the double helix of DNA via the ligand dppx.

Development of a Chemiluminescence Method for the Simultaneous Determination of Ascorbic and Tartaric Acids Based Upon Their Reaction with Cerium(IV) in the Presence of Rutheniumtrisdipyridine

Abstract A time-resolved chemiluminescent method for the determination of ascorbic and tartaric acid has been developed. The method is based on the differential rate of the chemiluminescent reaction of Ru(bipy)3 2+, ascorbic and tartaric acid with Ce(IV). The ascorbic acid system gives the highest chemiluminescence intensity at 2s, whereas the tartaric acid system gives its most intense chemiluminescence emission at 40s. Ascorbic acid (1.7×10−6~ 5.2 ×10−8M) and tartaric acid (1.4×10−4~1.4 10−6M) in wines were determined simultaneously with refative standard deviations of better than 5%(n=5). The detection limit of ascorbic acid and tartaric acid were 4.8×10−8 M and 8.4×10−7 M, respectively.

Chemiluminescence Determination of Sulfite and Sulfur Dioxide Using Tris(1,10-Phenanthroline)Ruthenium-KMnO4 System

Abstract The emission produced by sulfite after oxidation by potassium permanganate in acidic solution in the presence of Ru(phen)3 2+ is used to determine 1.0 × 10−7 to 2.5 × 10−5 mol/L sulfite. The limit of detection is 4.5 × 10−9 mol/L and the relative standard deviation is 3.1% for a 1 × 10−5 mol/L sulfite solution (n=8). The method was also applied satisfactorily to the determination of sulfur dioxide in air by using triethanolamine (TEA) as absorbent material.

Pulse injection analysis with chemiluminescence detection: determination of cinnamic acid using the Ru(bipy)32+-KMnO4 system

Abstract A new chemiluminescence method for the determination of cinnamic acid is described. This method is based on the chemiluminescence produced in the reaction of Ru(bipy) 3 2+ (bipyxa0=xa02,2′-bipydyl) and cinnamic acid with KMnO 4 . Under optimal conditions, the linear range and detection limit of cinnamic acid are 3.0xa0×xa010 −9 xa0–xa03.0xa0×xa010 −6 xa0gxa0ml −1 and 1.2xa0×xa010 −9 xa0gxa0ml −1 , respectively. The relative standard deviation is 2.2% for the determination of 1.0xa0×xa010 −7 xa0gxa0ml −1 cinnamic acid ( n xa0=xa011). The proposed method allows the determination of cinnamic acid with 2–3 orders of magnitude higher sensitivity than that of other reported methods based on various analytical techniques. It is simple, sensitive and easy to operate and can be used for the determination of cinnamic acid in human urine. A discussion on the possible reaction mechanism is presented.