摘要:

Most authors have used the fluorescence of Se-DAN complex for the fluorimetric determination of Se in biological samples. A considerable variation of the analytical conditions of this fluorimetric determination has been observed. All the original Se-compounds in the sample must be converted to selenite. Therefore, a previous step of mineralization of samples and reduction to selenite is required for the fluorimetric determination. The conditions for the digestion of samples may be chosen as a function of the sample to be analyzed. Heating with HCl for a variable time is usually used in the reduction step. For the complete formation of Se-DAN complex and to obtain the maximum fluorescent signal, the pH must be adjusted to values between 1-3 and then heated for a variable time depending on the temperature chosen. Application of organic solvents, surfactants and cyclodextrins has been studied to increase the fluorescent intensity and improve the sensitivity of the fluorimetric determination in aqueous medium. It is necessary to improve analytical methods in order to obtain adequate information about speciation studies. There are other fluorimetric methods alternative to the use of Se-DAN complex such as the use of 2,3-diamino-1,4-dibromonaphthalene (Br2-DAN) to obtain the fluorophrore complex or the oxidation of non-fluorescent 2-(α-pyridyl)-thioquinaldinamide (PTQA) to a fluorescent compound in acidic medium by Se(IV).

ISSN:0003-2719    

DOI:10.1080/00032719908542927

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

A disposable bienzymic sensor for the reliable determination of dithiocarbamate fungicides was developed. Aldehyde dehydrogenase and a highly stable NADH oxidase were immobilized on the surface of a disposable Pt-sputtered carbon paste screen printed electrode by using photocrosslinkable poly(vinylalcohol) bearing styrylpyridinium groups. Due to the very poor solubility of ethylenebis(dithiocarbamates), a preliminary transformation of these compounds in a highly soluble sodium form was carried out using EDTA, disodium form. The advantages of performing this previous step was both to solubilize the compounds and to use a commercial disodium ethylenebis(dithiocarbamate), i.e. nabam, as calibration compound. The sensor was used for the determination of EDTA/Na2-transformed zineb and the results showed a good correlation with those achieved with nabam. As low as 8 ppb of pesticide has been detected in these first experiments, whereas the detection limit of the recommended spectrophotometric method is about 400 ppm.

ISSN:0003-2719    

DOI:10.1080/00032719908542928

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

A highly selective disposable glucose biosensor based on the dispersion of cupric-hexacyanoferrate and glucose oxidase within a screen-printable carbon ink is described. The dispersed metal-hexacyanoferrate catalyst offers a marked decrease of the overvoltage for the reduction of the enzymatically-liberated hydrogen peroxide, and a stable response at physiological pH. Such efficient catalytic activity allows tuning of the detection potential to a region (around – 0.1V) where interfering reactions are negligible. Such operation eliminates the need for an anti-interference membrane barrier, and along with the one-step dispersion of the enzyme and electrocatalyst, greatly simplifies the sensor fabrication. The high selectivity and simplified fabrication hold great promise for thick-film biosensors for testing glucose and other important substrates of other oxidases.

ISSN:0003-2719    

DOI:10.1080/00032719908542929

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The generation of large changes in the crystal frequency is a highly sought-after goal in designing a successful thickness-shear mode (TSM) acoustic wave sensor application. We examined the potential for modulating the mass loading and viscoelastic properties of a swellable polymeric coating to achieve this goal. Using a 10 MHz AT-cut crystal with an immobilized coating of a styrene-divinylbenzene copolymer, a high molecular weight target analyte with complementary ionic and molecular binding properties was selected. Injection of the antibiotic cefoperazone in a sodium acetate buffer generated exceptionally large changes in frequency, in the range 500 - 5000 Hz. The rate of change in frequency is proportional to the analytical concentration. A multi-step regeneration protocol allows the coating to be reused multiple times. These results suggest that TSM sensor sensitivities can be significantly enhanced for selected analytes by the judicious selection of an appropriate swellable polymer coating.

ISSN:0003-2719    

DOI:10.1080/00032719908542930

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Three voltammetric enzyme-linked immunoassays based on new systems of o-, m- and p-aminophenol-H2O2-horseradish peroxidase (HRP) have been developed and used for the detection of α-fetoprotein (α FP) in human serum. HRP or labelled HRP catalyzes the oxidation reactions of o-, m- and p-aminophenol with H2O2, the products of which produce three sensitive voltammetric peaks at potentials of −0.87 V, −0.46 V and −0.45 V (vs. SCE) in Britton-Robinson (BR) buffer solution, respectively. By using these voltammetric peaks, the detection limits of α FP are 1.25 ng/mL, 0.5 ng/mL and 0.2 ng/mL, respectively, and the linear ranges 1.25-400 ng/mL, 0.5-400 ng/mL and 0.2-400 ng/mL, respectively. The detection limits of α FP with these methods are lower than that with the enzyme-linked immunosorbent spectrophotometric assay (ELISA).

ISSN:0003-2719    

DOI:10.1080/00032719908542931

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

9,10-anthraquinone (AQ), a photochemically reactive substrate, has been conjugated together with human serum albumin (HSA), and the photoinduced fluorogenic reaction of the HSA-AQ conjugate was studied. This conjugate shows a greatly enhanced photochemical fluorimetric activity compared with that of free AQ. The spectral characteristics of the photoreduction product of the HSA-AQ conjugate was investigated and large blue shifts in both the excitation and emission bands, compared with those of free AQ, were observed. The kinetic behavior of the photoinduced fluorogenic reaction and the effects of some experimental conditions were also investigated. The enhancement in the photoinduced fluorogenic reactivity of HSA-AQ was utilized in the sensitive detection of HSA by a simple in-situ photoinduced kinetic fluorimetric method. The calibration graph was linear over the range 0-1.0x10−6mol/L HSA. The detection limit was 6.5x10−10mol/L HSA and the relative standard deviation was 2.7% for 6.0x10−8mol/L HSA (n=6).

ISSN:0003-2719    

DOI:10.1080/00032719908542932

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

A novel immunoassay of methyltestosterone (MT) in serum is developed. We synthesized the antigen of MT (AgMT) by covalently bonding it to BSA and raised its antibody (AbMT) from rabbit. AbMTwas conjugated to poly-N-isopropylacrylamide (p-NIPAAm) to form AbMTbound thermally reversible hydrogel (p-NIPAAm-AbMT). A competitive immunoassay method based on the competition of fluorescein isothiocyanate (FITC) labeled MT antigen (FITC-AgMT) and MT with limited amounts of p-NIPAAm-AbMTwas established. The separation in the assay process was achieved by precipitation of the immuno-complex above its critical solution temperature. The detection limit of MT is 50 ng/ml. The recoveries of MT in human serum are above 93%.

ISSN:0003-2719    

DOI:10.1080/00032719908542933

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

A simple spectrophotometric method for the determination of ruthenium in the presence of platinum in Pt-Ru-Ge catalyst applied in fuel cells has been developed. Platinum catalyst (20% Pt) with carbon support containing 0.5% Ru and 5% Ge was digested in the mixture of HCl+HNO3(6+1). Carbon was separated from the examined sample by filtration after dissolution of the metals. Ruthenium was converted into a complex with thiourea (λmax=640 nm, ε = 2.9·1031 mol−1cm−1) in the medium of 5 M in HCl and 1% in thiourea after 15 min heating at 70 °C. Platinum does not interfere with the determination of ruthenium. Germanium is converted into volatile GeCl4and escapes from the examined sample during the digestion step. The content of ruthenium determined in the examined samples of catalyst amounted to 0.49% (RSD = 0.14%).

ISSN:0003-2719    

DOI:10.1080/00032719908542934

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

5-amino-1,3,4-thiadiazole-2-thiol groups attached on a silica gel surface have been used for adsorption of Cd(II), Co(II), Cu(II), Fe(III), Ni(II), Pb(II) and Zn(II) from aqueous solutions. The adsorption capacities for each metal ion were (in mmol.g−1): Cd(II)= 0.35, Co(II)= 0.10, Cu(II)= 0.15, Fe(III)= 0.20, Hg(II)= 0.46, Ni(II)= 0.16, Pb(II)= 0.13 and Zn(II)= 0.15. The modified silica gel was applied in the preconcentration and quantification of trace level metal ions present in water samples (river, and bog water).

ISSN:0003-2719    

DOI:10.1080/00032719908542935

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Two new electrochemiluminescence (ECL) reactions in aqueous solution involving cadmium(II) ions are reported. The ECL reaction occurs in the presence of a common co-reactant, tripropylamine (TPA), and either of two organic ligands, 2,2′:6′,2″-terpyridine or 2,2′-bipyridine. The reaction is presumed to arise from the metal-ligand complex and the co-reactant. Conditions for ECL emission were optimised and a calibration graph constructed. Emission was linear over the range 10-1 000 ppb. The calculated limits of detection (LOD) were 8 and 50 ppb using terpyridine and bipyridine, respectively. Comparison with a previously reported reaction involving cadmium(II) ions and 1, 10-phenathroline is made.

ISSN:0003-2719    

DOI:10.1080/00032719908542936

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor