摘要:

Molecularly imprinted polymers prepared using acrylamide as the hydrogen bonding functional monomer exhibited good enantiomeric recognition properties in aqueous solutions. Our results indicate that the recognition improved with increased mobile phase water percentage and ionic strength, and was also very much pH dependent upon the ionisation properties of the sample molecules. The results can be interpreted in terms of specific hydrophobic interactions between the enantiomeric species and the recognition sites of imprinted polymers. A study of substrate selectivity showed differences between a pure organic system and a water/organic system as the mobile phases. The hydrophobicity of the test compounds was found to be an important parameter in determining the selectivity.

ISSN:0003-2719    

DOI:10.1080/00032719708001728

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Simultaneous detection of multiple signals for common biochemical/electrochemical reactions is a challenging area of research for comparative studies. Based on our previous work with electrochemcially assisted thermal biosensors, a hybrid biosensor has been developed for the simultaneous monitoring of the electrochemically generated current and the thermal signal produced in association with enzymatic catalysis. The sensor combined the two measurement principles of electrochemical regeneration of substrate and flow injection biocalorimetry. The enzyme column was constructed of a platinum foil in electrical contact with a poly (pyrrole)-coated reticulated vitreous carbon (RVC) matrix onto which tyrosinase was immobilized. The column functioned as enzyme reactor, working electrode and thermally sensitive element together with the thermistors. Catechol was oxidized by tyrosinase to form 1,2-benzoquinone which was subsequently regenerated electrochemically on the electrode surface. The primary heat production developed by the enzyme reaction could be measured calorimetrically. At the same time, the electrochemical reduction of 1,2-benzoquinone generated a current that was detected by the working electrode (enzyme column). Preliminary results showed good correlation of the two signals at both high and low oxygen concentrations in the buffer. A linear range between 12.5 and 250 μM catechol was obtained for the enzyme reaction. The sensitivity of the thermal measurement system was significantly enhanced by the recycling of catechol. The hybrid sensor provides a useful tool for comparative studies.

ISSN:0003-2719    

DOI:10.1080/00032719708001729

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Sulfur dioxide was detected and determined in air by a piezoelectric quartz crystal sensor coated with 4-aminoantipyrine 1-hydroxyetil-2-heptadecenyl imidazol (amine 220) solution (1:1 v/v in chloroform). The analytical response curve is linear over the concentration range from 0.70 to 5.0 ppm of SO2. Good linearities (r = 0.9990, 0.9995 and 0.9968) and sensitivities (18.0, 33.4 and 50.7 Hz/ppm) were found, respectively for exposure times of 30, 60 and 90 seconds. The sensor can be used for more than six months without loss in sensitivity and presented good reversibility and reproducibility. Among some possible interferents tested, only nitrogen dioxide and moisture caused major frequency changes.

ISSN:0003-2719    

DOI:10.1080/00032719708001730

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A new potentiometric membrane sensor responsive to uric acid has been developed. The membrane sensor is based on aliquat-urate, as an ion pair, and 2-NPOE as a plasticizer. The sensor exhibits fast, stable, and Nernstian response for the hydrogen urate over the concentration range 10−2–10−5M and pH 5–7. Many substances and ions cause no interference. A standard addition method has been used for determination of uric acid in serum, urine, and commercial standard uric acid and the results of determination were 3.0 to 7.2 mg%, 0.21 to 1.04 mg% and 4.5 × 10−5to 4.9 × 10−3mg%, respectively.

ISSN:0003-2719    

DOI:10.1080/00032719708001731

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A simple conductimetric system to determine ammonia concentration using a sensor based on a conductor polymer was developed. The sensitive element to ammonia is a thin polyaniline film deposited by chemical synthesis in an acrylic substrate prepared before hand with two graphite electrodes. The conductance of the polyaniline film decreases when exposed to the ammonia gas and this variation can be related to the ammonia concentration. To determine ammonia in fertilizer samples a system consisting of a measurement cell, a conductivity meter and a strip chart recorder was used. The results were compared with those obtained by three different laboratories employing a Kjeldahl method and are in good agreement. The detection range of the system was 0.6 to 3.7 μg.mL−1with a response time of 4 minutes. The relative standard deviation of the proposed method was about 5%.

ISSN:0003-2719    

DOI:10.1080/00032719708001732

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Laccase, polyphenol oxidase and peroxidase are widely distributed in both plants and micro-organisms. Among these enzymes, the identification of one particular activity in the presence of the others is often difficult as enzymes can often oxidise the same substrates. A method is described, that is suitable to differentiate the three activities on the same polyacrylamide gel electrophoresis. The method is based on the use of two substrates, 4-aminoN,N-diethylaniline and 4-tert-butyl-catechol, so that coloured spots appear corresponding to the different activities. Moreover, a comparison among different mushroom species belonging to the same genus is reported using the described method.

ISSN:0003-2719    

DOI:10.1080/00032719708001733

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A method for determining Ethinylestradiol (ETE) and Gestodene (GTD) in mixtures by first derivative spectrophotometry is described. The measurements are made at the zero-crossing wavelengths and the calibration graphs are linear up to 38 and 22 μg/mL of ETE and GTD, respectively. The method has been applied for determining both compounds in four different Spanish commercial contraceptives.

ISSN:0003-2719    

DOI:10.1080/00032719708001734

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A direct spectrophotometric method has been developed for quantitative determination of Diclofenac Sodium in gel-ointments. The reported technique does not require a separation step and it is based on only one extraction of Diclofenac Sodium from the gel-ointment and measurement of the absorbance at two wavelengths. This procedure allows also indirect quantitative determination of degradation products due to indolinone cyclization. The method is rapid, simple, specific, reproducible and stability indicating.

ISSN:0003-2719    

DOI:10.1080/00032719708001735

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The present paper describes the use of 1-(2-thiazolylazo)-p-cresol (TAC) for separation, preconcentration and determination of nickel (ng g−1) in alkaline salts using Inductively Coupled Plasma Atomic Emission Spectroscopy technique (ICP-AES). The method proposed is based on the liquid-liquid extraction of the complex formed between nickel(II) cation and 1-(2-thiazolylazo)-p-cresol (TAC). Parameters such as: TAC concentration, effect of pH, influence of the organic solvent on the extraction, back extraction and mineralisation of the organic phase were studied. The results demonstrated that nickel in the form of nickel(II)-TAC complex, in the pH range of 5.0 to 12.0, can be quantitatively extracted from saline solutions (up to 30% NaCl) using the following solvents: isoamyl alcohol, carbon tetrachloride, chloroform, xylene, hexane, butyl acetate or methyl isobutyl ketone. The solution for the nickel determination can be obtained by a back extraction using 5 ml of a 1M hydrochloric acid solution or also by the mineralisation of organic phase with evaporation of the organic solvent and digestion of the residue with concentrated nitric acid. The procedure was used for nickel determination in alkaline salts of analytical grade and food salts. The standard addition technique was used and the recoveries obtained revealed that the proposed procedure shows good accuracy and precision.

ISSN:0003-2719    

DOI:10.1080/00032719708001736

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The interaction of β-cyclodextrin(CD), hydroxypropyl-β-cyclodextrin(HP-β-CD) and γ-cyclodextrin(γ-CD) with the drug rutin has been investigated by using fluorescence spectroscopy. The stoichiometry of the complexes and their apparent formation constants have been estimated. The thermodynamic parameters(ΔH, ΔS) for the formation of complexes were obtained from the van't Hoff equation. The results show that the formation constants of rutin with several cyclodextrins exhibit the order HP-β-CD>β-CD>γ-CD with the same stoichiometry of the complexes 1:1. Rutin has no measurable fluoresence enhancement in α-CD system. The thermodynamics of the complex formation displays an enthalpy-entropy compensation effect. The complexing ability of HP-β-CD is remarkble stronger than β-CD and γ-CD.

ISSN:0003-2719    

DOI:10.1080/00032719708001737

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor