Stabilization of Sensing Assay within Polyelectrolyte-Coated Alginate Microspheres for Optical Urea Sensing

Abstract

A new absorbance-based enzymatic biosensor for determination of urea (in the range 0.01 to 6.7 mM) is described. Quantification using cresol red dye, immobilized in the nanofilm coatings assembled on alginate microspheres to immobilize the urease enzyme, has been accomplished using ratiometric absorbance measurements. The effect of salt concentration in polyelectrolyte nanofilms (on the stability of dye molecules) and buffer pH (on the enzyme stability) are reported. The results demonstrate excellent stability of sensing assay within alginate microspheres. Urea-sensing experiments demonstrate the potential to develop an optical urea sensor that is stable over a month.     

Simultaneous Determination of Micro Bromide and Iodide by Kinetic Spectrophotometric Method

ABSTRACT

ABSTRACTA new kinetic spectrophotometric method for the simultaneous determination of concentrations of micro bromide and iodide has been proposed. It is based on their catalytic effects on the reaction of m-cresol purple oxidized by potassium periodate in hydrochloride acid medium. The reaction rate was monitored by measuring the decrease in absorbance at 528nm and the increase in absorbance at 455nm. The total difference in absorbance of the sum of bromide and iodide is identical with determination of bromide was carried out after Cr(VI) oxidized I? to I₂, and I₂ was removed by extraction with CCI₄, and the amount of iodide was measured by subtracting the absorbance change of bromide from the total absorbance change in the presence of bromine and iodide. The optimum conditions influencing the reaction rate were studied. The linear range of determination is 0～4.0μg/ml for Br? and 0～3.0 μg/ml for I?. The detection limits are 0.032μg/ml for Br? and 0.059 μ/ml for I?. The method was successfully applied to the determination of micro amounts of bromide and iodide in food and life samples.     

Kinetic Spectrophotometric Determination of Manganese by Use of the Salicylaldehyde-Hydrogen Peroxide System

Abstract

A kinetic method is described for determining trace amounts of manganese(II), based on its catalytic effect on the oxidation of salicylaldehyde by hydrogen peroxide. The reaction is followed spectrophotometrically by measuring the rate of change of absorbance at 500 nm. The calibration graph is linear in the range 5–100 ng/ml with a relative error of ± 1.2%. The method has been applied to the determination of manganese in natural water.     

Colorimetric Determination of Microgram Quantities of Urea

Abstract

A sensitive colorimetric method of determining urea is described. It involves measurement of the absorbance of the red color formed when urea is heated with diacetyl monoxime and thiosemicarbazide under acidic conditions (phosphoric acid-sulfuric acid medium). The method is accurate and precise, and it permits determination of microgram amounts of urea in the presence of ammonium, nitrate, amino acids, amides, and amino sugars.     

Selective Kinetic Spectrophotometric Determination of Nitrite in Food and Water

Abstract

A highly selective and sensitive method for the kinetic spectrophothometric determination of sub-microgram amounts of nitrite has been development based on its reaction with Nile blue 2B in acidic medium. The reaction is monitored spectrophotometrically at 595 nm at a fixed time of 4.5 min. The change in absorbance at 595 nm is related to the concentration of nitrite in the range 0.005 - 1.100 μg.ml^?1 The detection limit is 0.001 μg.ml^?1. The relation standard deviation is 1% for 0.020 μg.ml^?1 of nitrite for ten replicate measurements. Most common anions and cations do not interfere. The procedure was applied to the determination of trace amounts of nitrite in sausage and water.     

Utilization of adsorption-immobilized urease in gas-diffusion flow injection

A gas-diffusion flow-injection system for the assay of urea is reported. Urea is enzymatically converted to ammonia, which is determined spectrophotometrically by detecting the change in absorbance of a mixed pH indicator. The enzyme is immobilized by addition of perfluoroalkyl chains to the free amine groups of the enzyme and then adsorption of this modified enzyme on a polytetrafluoroethylene gas-diffusion membrane. The method is applicable in the range 0.1–500 mM urea. The procedure was used in comparison assays using blood serum samples.     

Automation of the Batch Method for Reaction Kinetic Studies Using Flow Injection Analysis. Kinetic Study of Hydrolysis Of N4-Acetylsulfanilamide,Acetylsalicylic Acid and Phenyl Phosphate

Abstract

The automation of the discontinuous (batch) method for kinetic stucfies using flow-injection analysis (FIA) is described. Aliquots of the reaction mixture are automatically injected in an appropriate manifold and the kinetic profile of the reaction is obtained as a series of absorbance peaks. Observed reaction rate constants are calculated using the Guggenheim and non-linear fitting approaches. The new method is evaluated in the kinetic study of the acid hydrolysis of N⁴-acetylsulfanilamide by colorimetric monitoring of sulfanilamide, the alkaline hydrolysis of acetylsalicylic acid (aspirin) by colorimetric monitoring of salicylate, and the enzymic hydrolysis of phenyl phosphate with alkaline phosphatase by colorimetric monitoring of phosphate. The automated flow-injection batch method can be used in kinetic studies of reactions with t_1/2 greater than 200 s.     

Kinetic-Spectrophotometric Determination of Traces of Osmium by Its Catalytic Effect on the Oxidation of Pyrogallol Red by Hydrogen Peroxide

Abstract

A Kinetic-spectrophotometric method for the determination of ultra-trace amounts of osmium(VIII) is described. It is based on the catalytic action of osmium(VIII) on the oxidation of pyrogallol red with hydrogen peroxide, yielding a colorless product in neutral medium. The reaction is followed spectrophotometrically by measuring the rate of change in absorbance at 540 nm and 30°C. Os(VIII) in the range 0.005 -100 ng.ml^?1 can be determined. The proposed method is hardly subject to interferences. The relative standard deviation is 1.5% for 1 ng.ml^?1 of Os(VIII). The kinetic parameters of the catalyzed and uncatalyzed reactions are reported. The detection limit is 1 pg.ml^?1.     

Kinetic Flow Injection Spectrophotometric Determination of Nitrite by its Catalytic Effect on the Oxidation of Chlorophosphonazo-pN by Bromate

Abstract

A flow injection kinetic method has been developed for the determination of nitrite, based on its catalytic effect on bromate oxidation of chlorophosphonazo-pN in H₂SO₄ medium. The reaction is followed spectrophotometrically by measuring the decrease in the absorbance at 551 nm. The sampling frequency was 83 h^?1. The calibration curve was linear between 0.050 and 1.00 μg/ml, and the detection limit was 0.018 μg/ml. The proposed method was applied to the determination of nitrite in waters and soil with satisfactory results.     

Excess Zinc Ions Induce the Inhibition of Carboxypeptidase A Activity by the Conformational Change

Abstract

The mechanism for inhibition of enzyme activity by excess zinc ions has been studied by kinetic and equilibrium dialysis method at pH 8.2. Excess zinc ions were competitive inhibitor for both peptide and ester substrates. This behavior is believed to arise by the excess zinc ions fixing the enzyme in a conformation to which substrate cannot bind.     

A Kinetic Spectrophotometric Method to Determine the Insecticide Methyl Parathion in Commercial Formulations and the Aqueous Environment

Abstract

A simple kinetic-spectrophotometric method for the analysis of the organophosphate insecticide methyl parathien is presented. The method is based on the alkaline hydrolysis of the insecticide into its main metabolite p-nitrophenol. The influence of reaction variables (pH and temperature), and the effect of other pesticides, are discussed. The calibration graphs (initial rate, fixed time, fixed absorbance) were linear from 2 to 30μg/ml. The precision was calculated for the different methods applied, the relative standard deviation being 6.25% for 4μg/ml.

The proposed kinetic method can be applied directly to synthetic mixtures, commercial formulations and different aqueous environment, with recoveries close to 100%.     

Kinetics of the Oxidation of Phenylhydrazine by [Fe(CN)6]3− in Water‐in‐Oil Microemulsions

The oxidation reaction of phenyl hydrazine (Phh) by hexacyanoferrate ([Fe(CN)₆]^3?) has been studied in water‐in‐oil (w/o) microemulsion media. The kinetic profile of the reaction was investigated as a function of [Phh], droplet size, and droplet concentration. Comparison of the kinetic profiles of the reaction in microemulsion, water‐urea, and water‐AOT‐urea media indicates that the kinetic profile of the reaction in microemulsion shows a behavior similar to that of the reaction in water‐AOT‐urea medium at 4 M urea. An initial increase and then a decrease in k_obs is observed with increasing molar ratio, W_o(=[H₂O]/[AOT]) at constant [AOT] (=0.4 M), whereas k_obs decreases upon increasing the AOT concentration at constant molar ratio.     

Kinetic Spectrophotometric Determination of Vanadium (V) Based on its Inhibitory Effect on the Thionine – Ascorbic Acid Reaction

ABSTRACT

A simple and sensitive kinetic method for the determination of vanadium(V) based on its inhibitory effect on the reduction of thionine by ascorbic acid at pH=5 is described. The reaction rate is monitored spectrophotometrically by measuring the decrease in absorbance of thionine at 598 nm after a fixed time (10 min). The calibration graph is linear in the range of 10 ? 120 ng ml^?1 of vanadium(V) and the detection limit is 6 ng ml^?1. The relative standard deviation (RSD) for 80 ng ml^?1 of V(V) was 0.96% (n=10). The method was successfully applied to the determination of vanadium in a certified reference sample.     

Determination of Serum Urea with an Enzyme Thermistor Using Immobilized Urease

Abstract

The application of an enzyme thermistor device in a simple and accurate procedure for the determination of serum urea is described. The enzyme thermistor measures the heat produced when urea is passed through a small column containing immobilized urease. The stability and sensitivity as well as the performance with clinical serum samples of the system is evaluated. Advantages are the simplicity, the low enzyme cost and the insensitivity to the optical properties of the sample and interfering substances, which may affect the commonly used assay procedures.     

Optical Urea Biosensor Based On Ammonium Ion Selective Membrane

ABSTRACT

An optical urea biosensor was developed by immobilizing an urease enzyme layer on a thin ammonium-selective polymer membrane. The ammonium optical membrane utilized dichlorofluorescein octadecyl ester (DCFOE) as anionic chromophore and nonactin as neutral ionophore. The urease layer was coated on the top of the ammonium layer by gelatin entrapment combined with glutaradehyde cross-linking. Hydrolysis of urea catalyzed by urease produced ammonium ion, which was extracted into the-polymer film to form complexes with nonactin. A proton was released which resulted in a color change of the optical membrane due to charge neutrality principle. The biosensor     

Kinetic Spectrophotometric Determination of Traces of Manganese(II) by Its Catalytic Effect on Oxidation of 4‐Hydroxycoumarin with Potassium Permanganate in River Water Samples

Abstract

A new kinetic method for determination of traces of manganese(II) based on its catalytic effect on the oxidation of 4‐hydroxycoumarine with KMnO₄ at pH=1.35 and at a temperature of 25°C was proposed. The reaction was followed spectrophotometrically by measuring the decrease in the absorbance of the dye at 525 nm. The calibration graph is linear in the range 20–200 ng/cm³. The effects of certain foreign ions upon the reaction rate were determined for assessment by the selectivity of the method. The proposed method has been applied for determination of manganese(II) in river water samples with satisfactory results.     

Kinetic-Spectrophotometric Determination of Molybdenum(VI) Based on Its Catalytic Effect on the Thionine-Hydrazine Reaction

Abstract

A kinetic method for the determination of trace amounts of Mo(VI) (0.05-4 μg ml^?1) based on its catalytic effect on the reduction of thionine by hydrazine monochloride in strongly acidic media is reported. The reaction is monitored spectrophotometrically by measuring the decrease in absorbance of thionine at 605 nm after a fixed time (5 min.). The detection limit of the method is 23 ng ml^?1 and the relative standard deviation (RSD) for 0.05 μg ml^?1 of Mo(VI) is 1.2% (n=7). The method is almost free from interferences, especially from large amounts of tungsten. The procedure was successfully applied to the determination of trace amounts of molybdenum in steel.     

Enzymatic Determination of Ammonia in Lake Water Using a Semi-Automatic Analyser

Abstract

An enzymatic method was developed for the determination of ammonia concentrations in lake water. Lake water samples containing ammonia were mixed with a glutamate dehydrogenase (GIDH), reduced nicotinamide adenine dinucleotide phosphate (NADPH) and 2-oxoglutarate. The decrease in the absorbance intensity caused by the disappearance of NADPH by this reaction was measured at 340 nm. There was a linear relationship (r = 0.9997) between peak height and ammonia concentration over the range 0–29 μM. The detection limit was 0.29 μM for a sample volume of 250 μl. Interference of amino acids and urea at concentrations of 50 mg l^?1 was negligible. Good agreement was found between the enzymatic method and indophenol blue colorimetry.     

Kinetic determination of traces of manganese(II) by its catalytic effect on the autoxidation of 1,4-dihydroxy phthalimide dithiosemicarbazone

A kinetic method is described for the determination of trace amounts of manganese(II) based on its catalytic effect on the aerial oxidation of 1,4-dihydroxyphthalimide dithiosemicarbazone. The reaction is followed spectrophotometrically by measuring the rate of change in absorbance at 594 nm. The calibration graph (rate constant vs. manganese concentration) is linear in the range 10–90 ng Mn ml^-1. The preparation and properties of the reagent are described and the kinetic parameters of the reaction are reported. There are few interferences.