Amperometric method hydrogen peroxide detection

In a limited number of experiments, in which six different hydrogen peroxide concentrations were examined with four different pH values, the validity of the procedure used was checked by comparing the results obtained with the sensor electrode to those obtained by means of titration. The results obtained with the sensor electrode have a maximum divergence of 3% compared with the concentrations obtained by titration. The final aspect of the amperometrical detection method that was examined at laboratory scale is the stability in time of a calibrated sensor electrode. 

Mayer determined acetylcholine and choline by enzyme-mediated liquid chromatography with electrochemical detection [195]. The two compounds were separated by passing the eluted fractions through a post-column reactor containing immobilized Acetylcholineesterase and choline oxidase. In the presence of either compound, the dissolved oxygen was converted into hydrogen peroxide, which was detected amperometrically at a platinum electrode. This method was used to determine choline in rat brain homogenates. 

The concentration of hydrogen peroxide can be measured directly using amperometric detection. A change in H2O2 concentration in the medium appears as a variarion in the output current. The quantified parameters are m nitude of the sensor response, response time, and current response. It is desirable to measure signals in conditions when the linear relationship exists between the current value and the analyte concentration. At that point, the reactions are considered to be in steady state when pseudoequilibrium occurs between the species close to the sensor and their consumption at the indicative electrode. One of the serious problems associated with measurement of complex analytes is the possible interference of the redox species present in the sample. Several methods have been reported which aimed at reducing level of interference. These methods include use of perm-selective coatii, use of artificial mediators, or selective electrocatalysis. The use of mediators or selective electrocatalysis helps to lower the detection potential to the level when the majority of interferii species are electroinactive. ... 

After on-line dialysis of the milk sample, lactose is oxidized in the galactose oxidase reactor with release of hydrogen peroxide. The latter is detected by amperometric reduction of a mediator, oxidized by hydrogen peroxide in a peroxidase catalyzed reaction. The linear range of the method with 20 injection is in the range 0.05-300 mM. 

As the electrode moves closer to the cell surface, the amperometric current rises (Figure 17.1.3C). When the electrode is placed in contact with the cell surface, cholesterol is extracted from the membrane and moves across the thin membrane layer and partitions into the electrode-supported enzyme-modified lipid bilayer. Subsequent enzyme catalyzed oxidation of cholesterol by molecular oxygen produces hydrogen peroxide which is oxidized at the platinum electrode and detected. This is an efficient and simple method to determine cholesterol levels in the plasma membrane of cells which should find applicability in determining the role cholesterol plays in the organization of cellular membranes (51). 

Numerous studies have been reported of FIA based on immobilized enzyme columns and an electrode or thermistor. In particular, Saton et al. [70] proposed a FI method for the amperometric determination of GSH. The system comprises the immobilized enzyme column and a flow-through membrane-covered platinum/silver/silver chloride electrode pair for detection of hydrogen peroxide. The calibration graph for GSH was linear from 0.05 to 1.0 mM. The procedure is simple and selective. The assay took 3 min the sample volume was 200 pL. The RSD for 0.5 mM GSH was 2% (n = 10). 

In a third example case, p-carbolines are inhibitors of monoamine oxidases (MAO-A and MAO-B) and can be found in foods, hallucinogenic plants or certain plant dmgs. The referred article described a fast analysis method for p-carbolines based on the inhibition of MAO [79]. The MAO-A is inhibited by all three tested P-carbolines (harmane, norharmane and harmaline), while MAO-B is inhibited only by norharmane. The presence of norharmane in mixtures of p-carbolines can be identified based on the difference between the cumulative inhibition of MAO-A by all p-carbolines and MAO-B inhibition. The enzymes were immobilized on screen-printed electrodes modified with a stabilized film of Pmssian blue that contain also copper. Benzylamine was used as substrate for the enzymatic reaction and the hydrogen peroxide formed was measured amperometrically at —50 mV. The developed biosensors were used for food analysis. The detection limits obtained were 5.0 pM for harmane and 2.5 pM for both harmaline and norharmane. 

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