Construction of an immobilized asparaginase sensor and determination of asparagine and asparaginase in human blood serum

The sensor is based on asparaginase held on an ammonia gas sensor. Asparagine in the range 2.0 X 10-5-2.3 X 10-3 M gives a linear calibration graph with response times of 5-2 min. Asparagine can be determined in human serum. Asparaginase (0.01-0.2 U in 0.1 ml of sample) is determined in aqueous solution or serum by adding asparagine to the sample, and measuring the ammonia evolved. Results for both methods agree well with those obtained by the combined Conway-Russell method. © 1984

Construction of an immobilized asparaginase sensor and determination of asparagine and asparaginase in human blood serum

The sensor is based on asparaginase held on an ammonia gas sensor. Asparagine in the range 2.0 X 10-5-2.3 X 10-3 M gives a linear calibration graph with response times of 5-2 min. Asparagine can be determined in human serum. Asparaginase (0.01-0.2 U in 0.1 ml of sample) is determined in aqueous solution or serum by adding asparagine to the sample, and measuring the ammonia evolved. Results for both methods agree well with those obtained by the combined Conway-Russell method. © 1984

Kinetic determination of l-alanine and l-alanine dehydrogenase with an ammonia gas-sensing electrode

The ammonia gas-sensing electrode is used to assay l-alanine and l-alanine dehydrogenase. Alanine is de-aminated by bacterial alanine dehydrogenase in the presence of β-NAD+. The initial rate of ammonia release is proportional to alanine concentration or the enzyme activity. Optimal conditions for the assays are specified. Alanine (1.0 × 10-4-1.0 × 10-3 M in a 1-ml sample) and enzyme (0.181-0.181 U in a 0.1-ml sample) can eb determined. Application to the determination of alanine in human serum gave results that compared well with values obtained by the Yoshida method. © 1985

Kinetic microdetermination of manganese in natural waters and of osmium and ethylenediaminetetraacetic acid

Automatic spectrophotometric kinetic methods are described for the microdetermination of manganese and osmium, based on their catalytic effect on the periodate-acetylacetone reaction, and for the determination of EDTA, on the basis of its inhibitory effect on the manganese-catalyzed periodate-acetylacetone reaction; the time required for the formation of a small fixed amount of colored product is measured automatically and related directly to the catalyst or inhibitor concentration. Manganese at the 10-5-10-7 M level, and osmium and EDTA at the 10-7-10-6 M level, can be determined with an average error of ca. 2%. The method has been applied to the determination of manganese in natural waters, but is capable of more general applications. © 1978

Hemoglobin modified bilayer lipid membranes (BLMs) biosensor for carbon dioxide detection

The present paper describes the modification of self-assembled bilayer lipid membranes (s-BLMs) on a metal support with hemoglobin to develop a novel electrochemical minisensor for the rapid detection of carbon dioxide. Modification was achieved by the introduction of hemoglobin into the bulk electrolyte solution and ion conductivity of BLMs increased with additions of NaHCO3, in solution. The detection limit of CO, detection was 0.375 μM using BLMs containing 15% DPPA. The reversibility of the phenomenon of carbon dioxide binding to hemoglobin could be investigated by the use of s-BLMs. The present carbon dioxide sensor can be fabricated at low cost, with fast response times (about 10 s) and the capability of analyzing small volumes of samples. The long-term stability of the hemoglobin modified BLM-based biosensor is routinely over 48 h. The present paper describes the modification of self-assembled bilayer lipid membranes (s-BLMs) on a metal support with hemoglobin to develop a novel electrochemical minisensor for the rapid detection of carbon dioxide. Modification was achieved by the introduction of hemoglobin into the bulk electrolyte solution and ion conductivity of BLMs increased with additions of NaHCO3 in solution. The detection limit of CO2 detection was 0.375 μM using BLMs containing 15% DPPA. The reversibility of the phenomenon of carbon dioxide binding to hemoglobin could be investigated by the use of s-BLMs. The present carbon dioxide sensor can be fabricated at low cost, with fast response times (about 10 s) and the capability of analyzing small volumes of samples. The long-term stability of the hemoglobin modified BLM-based biosensor is routinely over 48 h

Kinetic micro-determination of manganese in natural waters and of iridium, nitrilotriacetic acid and 1,2-diaminocyclohexane-NNN′N′-tetraacetic acid

An automatic kinetic spectrophotometric method is described for the ultramicro determination of manganese and iridium, based on their catalytic effect on the periodate - phosphinate reaction. The method is also used for the determination of nitrilotriacetic acid (NTA) and 1,2-diaminocyclohexane- NNN′N′-tetraacetic acid (DCTA), on the basis of their activating and inhibiting effect, respectively, on the manganese-catalysed periodate - phosphinate reaction. The time required for the reaction to consume a fixed amount of periodate is measured automatically and related directly to the concentration of catalyst, activator or inhibitor. Manganese and iridium at the 10-8-10-7 M level and NTA and DCTA at the 10-6 M level were determined with average errors of about 2%. The method has been applied to the determination of manganese in natural waters

Electrochemical Transduction of Interactions of Atrazine with Bilayer Lipid Membranes

This work investigates the interactions of atrazine with bilayer lipid membranes (BLMs) that can be used for the direct electrochemical sensing of this herbicide. Egg phosphatidylcholine (PC) and dipalmitoylphosphatidic acid (DPPA) were used for the formation of solventless BLMs. The interactions of atrazine with these membranes were found to be electrochemically transduced by BLMs in the form of a transient current signal with a duration of seconds, which reproducibly appeared within 1 min after exposure of the membranes to atrazine. The sensitivity of the response was maximized by use of BLMs composed of 35% (w./w.) DPPA, and by alteration of the phase distribution within membranes by the introduction of calcium ions in bulk solution. The mechanism of signal generation was related to the adsorption of atrazine with a consequent rapid reorganization of the membrane electrostatics due to atrazine aggregation at the surface of BLMs. Hydrogen bonding between atrazine and the carbonyl group of the lipid was explored by addition of platelet-activating factor (PAF; an ether analog of PC) in BLMs composed of PC. Differential scanning calorimetry of vesicles composed of 15% DPPA was used to study the aggregation of atrazine in membrane domains enriched in the charged lipid. The magnitude of the transient current signal was linearly related to the concentration of atrazine in bulk solution with sub-micromolar detection limits. This electrochemical transduction of atrazine interactions with BLMs holds prospects for flow injection monitoring of triazine herbicides

Rapid electrochemical detection of propranolol and metoprolol in pharmaceutical preparations using stabilized lipid films

This work reports a technique for the rapid electrochemical detection of propranolol and metoprolol in pharmaceutical preparations using stabilized lipid films. Microporous filters composed of glass fibers (nominal pore sizes 0.7 and 1.0 μm) were used as supports for the formation and stabilization of these devices. The lipid film is formed on the filter by polymerization prior to its use. This stabilized after storage in air. Lipid films composed of phosphatidylcholine were used for the detection of propranolol and metoprolol in pharmaceutical preparations. The stabilized lipid membranes provided artificial ion gating events in the form of transient signals within about 60 and 34 s after exposure of the membranes to propranolol and metoprolol, respectively. The magnitude of the transient current signal was related to the concentration of propranolol and metoprolol in bulk solution in the micromolar range. The mechanism of signal generation was investigated by differential scanning calorimetric studies. These studies revealed that the adsorption of the drug is through the hydrophobic aryl terminal of the compound, whereas the hydrophilic groups were directed towards the electrolyte solution. This adsorption caused a rapid alteration of the electrochemical double layer of the lipid film (i.e., capacitance changes) that resulted in the transient ion current signal. The present technique was used for the rapid detection of propranolol and metoprolol in pharmaceutical preparations and can function for repetitive uses after storage in air. Future research is targeted to the determination of these chemicals in human biofluids such as urine of athletes

Construction of a N-Acetyl-L-Methionine Electrode and Determination of Acylase with an Ammonia Gas Sensor

The N-acetyl-L-methionine electrode is based on a coupled enzymatic system consisting of acylase and L-amino acid oxidase with an ammonia gas sensor;conditions of immobilization are optimized.N-acetyl-L-methionine in the range 4x10-5- 2xl0-3M gives a linear potential vs. log(concentl-ation)plot with a response time of 2–5 min over the range spccified.This electrode combined with an L-methionine e1ectrode, based only on L-amino acid oxidase and an ammonia gas sensor, can be used for the determination of both substrates in mixtures, thus extending the feasibility of the method.Acy]ase(0.1-2.0U) is determined in aqueous solutions by adding N-acetyl-L-me-thionine to the sample, and measuring the ammonia evolved with the gas-sensing electrode. © 1983, Taylor & Francis Group, LLC. All rights reserved

Kinetic ultramicrodetermination of chromium(III) and osmium(VIII) based on their accelerating effect on the periodate-arsenite reaction

A spectrophotometric kinetic method is described for the ultramicrodetermination of chromium (III) and osmium (VIII) based on their promoting and catalytic effect respectively on the periodate - arsenite reaction. For chromium(III) determination the decrease in absorbance within a fixed period of time is related directly to the chromium concentration. For osmium (VIII) determination the time required for the reaction to consume a fixed amount of periodate is measured automatically and related directly to the osmium concentration. Ultramicroamounts of chromium(III) in the 10-6-10-5M level and of osmium(VIII) in the 10-8-10-7M level were determined with a mean error of about 2%. The method has been applied to the determination of chromium in chrome ores. © 1978 Springer-Verlag