Peroxides In Solution Research Articles

Electrocatalytic reduction of hydrogen peroxide in solution in the presence of polyacrylic acid and copper ions: Application for gaseous hydrogen peroxide detection

A comprehensive voltammetric investigation into the electrocatalytic electrode mechanism for the reduction of hydrogen peroxide in an aqueous polyacrylic acid solution, in the presence of Cu2+ ions, is presented. The primary objective is to lay the groundwork for the development of a straightforward electrochemical sensor for the detection of gaseous H2O2. Various electrode reaction pathways have been observed depending on the potential applied to the glassy carbon electrode. At potentials approximately −0.400 V vs. Ag/AgCl (3 mol L−1 KCl), an electrochemical reduction of H2O2 occurs. In this context, the Cu2+/Cu+ redox couple, stabilized by polyacrylic acid, acts as a redox mediator, following the EC’ reaction scheme. Additionally, a complex Fenton-like spontaneous redox chemistry takes place between Cu2+/Cu+ and H2O2 within the bulk of the polyacrylic aqueous solution. This results in the generation of a variety of reactive oxygen species (ROS), with the superoxide anion and hydroxyl radical being the most probable intermediates. The electrochemical reduction of ROS species effectively recycles H2O2 near the electrode surface, constituting an electrocatalytic mechanism of the second order. This particular electrocatalytic process is evident as a prominent reduction current tail at potentials more negative than −0.400 V. This, in conjunction with the adsorption and stabilizing influence of polyacrylic acid, facilitates exceptional analytical sensitivity for the detection of gaseous H2O2. The sensor exhibits the capability to detect concentrations of gaseous H2O2 as low as 10−11 mol L−1, accomplished through the utilization of square-wave voltammetry and other advanced voltammetric techniques.

Theoretical and Experimental Investigations of Stable Arylfluorene-based Radical-type Mechanophores.

Radical-type mechanophores (RMs) can undergo homolytic cleavage of their central C-C bonds upon exposure to mechanical forces, which affords radical species. Understanding the characteristics of these radical species allows designing and developing bespoke mechanoresponsive materials. The thermal stability of the central C-C bonds and the oxygen tolerance of the generated radical species are crucial characteristics that determine the functions and applicability of such RM-containing mechanoresponsive materials. In this paper, we report the synthesis and characterization of two series of arylfluorene-based RM derivatives, i.e., 9,9'-bis(5-methyl-2-pyridyl)-9,9'-bifluorene (BPyF) and 9,9'-bis(4,6-diphenyl-2-triazyl)-9,9'-bifluorene (BTAF). The synthesis of BPyF and BTAF derivatives was accomplished without generating any peroxides initially, albeit that BPyF slowly converted to the corresponding peroxide in solution. DFT calculations revealed the importance of the thermodynamic stability and the values of the a-SOMO levels of the corresponding radical species for their thermal stability and oxygen tolerance. Furthermore, the mechanochromism of BTAF was demonstrated by ball-milling a BTAF-centered polymer, which was synthesized via atom-transfer radical polymerization (ATRP).

New Voltammetric Sensor Based on LDH and H2O2 for L-Proline Determination in Red and White Wines

Taking inspiration from our recent work in which a new sensor for hydrogen peroxide was proposed, our research group has now developed a simple, fast, and inexpensive voltametric system for determining proline concentration both in standard solutions and in real samples (red and white wines). This system uses a non-enzymatic sensor based on a working electrode of glassy carbon (GC) modified with a layered double hydroxide (LDH) compound, of the type GC-Ag(paste)-LDH-H2O2, with hydrogen peroxide in solution at fixed concentration, in a three electrode cyclic voltammetry setup. Using an increasing concentration of standard solutions of L-proline, the method shows a linearity range, in semilogarithmic coordinates, between 125 μmol L−1 and 3200 μmol L−1 of proline, with a limit of detection (LOD) value of 85.0 μmol L−1 and a limit of quantitation (LOQ) value of 95.0 μmol L−1. The developed method is applied to the determination of proline in several samples of commercial Italian wines. The results are compared with those obtained by applying the classic spectrophotometric method of ninhydrin, obtaining a good correlation of the results.

Luminol immobilized graphite electrode as sensitive electrochemiluminescent sensor for the detection of hydrogen peroxide

The present work, presents the Luminol immobilized electrochemiluminescence (ECL) for the detection of hydrogen peroxide. Herein, the ECL behavior of luminol immobilized on graphite as a paste electrode has been studied in nearly neutral solution (pH = 8) for the detection of hydrogen peroxide. Under the optimized conditions, a strong electron-transfer reaction occurs between luminol immobilized electrode and hydrogen peroxide in solution. Electrochemiluminescence response of proposed sensor for hydrogen peroxide was linear in the range of 1 × 10−8 to 1 × 10−3 μM with detection limit of 0.7 × 10−8 μM ​(S/N ​= ​3) at +0.6 ​V in PBS (pH ​= ​8). The sensor showed response for hydrogen peroxide concentration in less than 7 ​s. The prepared electrode is simple, fast, reproducible and stable. The effect of EDTA and other divalent interfering metal ions in the presence of hydrogen peroxide was also studied. The successful application of Luminol based ECL sensor was employed to study hydrogen peroxide in commercial hydrogen peroxide samples.

Generation of hydrogen peroxide in protein solutions under the influence of thermal and optical electromagnetic radiation

Using the method of induced chemiluminescence in solutions of bovine serum albumin (BSA) and bovine gamma globulin (BGG) under the influence of thermal and optical electromagnetic radiation, the formation of long-lived reactive protein species (LRPS) with a half-life of about 4-5 hours was registered. The oxygen effect was established, namely, the dependence of the chemiluminescence intensity of protein solutions on the concentration of dissolved oxygen. Using the enhanced chemiluminescence method in the luminol-p-iodophenol-peroxidase system, the ability of LRPS, induced by heat and laser radiation, to generate hydrogen peroxide in solution was studied. The dependence of the formation of H2O2 under the influence of LRPS at different times after exposure was established. Using the fluorescent probe coumarin-3-carboxylic acid, the formation of hydroxyl radicals in protein solutions after exposure to laser radiation and heat was detected. The obtained experimental data suggest that the generation of hydrogen peroxide by LRPS after exposure to thermal and optical electromagnetic radiation may be one of the mechanisms for activating protective cellular mechanisms that help overcome diseases, including those associated with oxidative stress.

Hibiscus sabdariffa L. Anthocyanins Immobilization on TiO2 Nanotubes and Its Electrochemical Characterization as a Hydrogen Peroxide Sensing Electrode

The antioxidant activity of the Hibiscus sabdariffa L. (H.s.) used in the food-processing industry inspired a low cost and environmentally friendly chemical modification for a nanostructured electrode. Titanium dioxide nanotubes (TiO2-Nts) grown by anodic oxidation from Ti foil are well-known for their richness of adsorption sites for organic compounds and also for their great electron mobility allowance, which makes them an excellent choice for modified electrode engineering. This study evidences the complexation of the anthocyanins from H.s. to the TiO2-Nts electrode through FTIR and UV-Vis spectroscopy and electrochemical characterization (cyclic voltammetry). This novel electrode showed remarkable stability and regeneration capability. This research also establishes a new method to quantify hydrogen peroxide in solution with a limit of linearity of 2.50 × 10−4 M and a detection limit of 4.50 × 10−6 M.

Leaching of yttrium from cathode ray tube fluorescent powder: Kinetic study and empirical models

In this paper, leaching kinetics of yttrium from cathode ray tubes in sulphuric acid and hydrogen peroxide solution was investigated. It was found that hydrogen peroxide concentration, followed by temperature, has the greatest influence on leaching rate. Leaching rate is clearly enhanced by the increase in H2O2 concentration. The leaching process without hydrogen peroxide follows the kinetic model controlled by the chemical regime, whereas in presence of H2O2 it follows the kinetic model controlled by diffusion through the product layer. The apparent activation energy was determined to be 40.0kJ/mol and 90.3kJ/mol with and without hydrogen peroxide in solution, respectively. Moreover, the experimental data were used to describe empirical mathematical models in order to predict the yttrium extraction as a function of sulphuric acid concentration, hydrogen peroxide concentration, temperature and time. From the analysis of the results and models, the optimal conditions to maximize the extraction of yttrium were inferred: 40°C, 10%vol hydrogen peroxide, 15min of reaction with 15%wt/vol pulp density, or alternatively at higher temperature (80°C) 15%wt/vol pulp density, 120–180min with 0% or 5%vol hydrogen peroxide in solution. Hence, yttrium is easily leached from CRTs powder at low temperature (40°C) with higher concentration of hydrogen peroxide, or by means of higher temperature (80°C) and lower concentration, even null, of hydrogen peroxide.

Determination by reactive absorption of the rate constant of the ozone reaction with the hydroperoxide anion

The reaction rate constant between the hydroperoxide anion (HO2−) and molecular ozone was evaluated from the reactive absorption method in the range of temperature from 20 to 35°C. This reaction is crucial in the initiation step of the ozone decomposition, especially using the peroxone process which combines ozone and hydrogen peroxide in solution. A stirred-cell operated semi-continuously was used for this purpose. A high initial concentration of tert-butanol (0.05molL−1) was applied to efficiently scavenge all radicals and to avoid any parasite reaction. Based on the dissolved H2O2 concentration decreasing and the outlet ozone concentration time-course, the stoichiometry of the initiation reaction was determined, with one mol of H2O2 consumed per mol of ozone transferred. The chemical conditions were thoroughly selected to reach a fast pseudo-first order absorption regime. The reaction rate constant increased from 1.91×106–2.40×106Lmol−1s−1 at 20°C to 5.68×106–7.31×106Lmol−1s−1 at 35°C.

An Experimental Model to Study the Impact of Lipid Oxidation on Contact Lens Deposition In Vitro

ABSTRACTPurpose: This study was to establish a controlled in vitro test system to study the effect of lipid oxidation on lipid deposition on contact lenses.Methods: Fatty acids with varying degree of unsaturation were oxidized using the Fenton reaction. The degree of lipid oxidation and the lipid moieties formed during the oxidation were identified and estimated by various lipid staining techniques following separation with thin-layer chromatography, and by measuring thiobarbituric acid reactive substances or peroxides in solution. Two different silicone hydrogel-based contact lenses (Balafilcon A and Senofilcon A) were incubated with fatty acids laced with radioactive tracer oxidized to varying degrees, and the amount of lipid deposition was measured using unoxidized lipid samples as controls.Results: The Fenton reaction together with the analytical methods to analyze the lipid oxidation can be used to control oxidation of lipids to a desired amount. In general, saturated fatty acids are not oxidized, the monounsaturated oleic acid produced peroxides while poly-unsaturated lipids initially produced peroxides and then fragmented into reactive aldehydes. Incubation with mildly oxidized lipids (most likely lipid peroxides) resulted in increased lipid deposition on Balafilcon A lenses compared to unoxidized lipids, but this was not observed for Senofilcon A lenses. Further oxidation of the lipids (carbon chain breakup) on the other hand resulted in diminished lipid deposition for both contact lens types.Conclusions: This study provides a method for inducing and controlling lipid oxidation so that the effect of lipid oxidation on contact lens binding can be compared. It could be shown that the degree of lipid oxidation has different effects on the lipid deposition on different contact lens types.

A cyanostilbene-boronate based AIEE probe for hydrogen peroxide—Application in chemical processing

We report a versatile cyanostilbene-boronate probe, which shows fluorescence emission enhancement in ethanol:HEPES buffer, attributed to aggregation-induced emission enhancement (AIEE), and detects hydrogen peroxide in solution, thin films as well as in industrial samples. The sensing protocol relies on the peroxide mediated transformation of the arylboronate moiety to phenol, and is well supported by various spectroscopic techniques and the theoretical studies. Industrial application, with no precedence, is unique as it can overcome inherent limitations of the qualitative determination method currently used in chemical processing industry.

Detection of prostate specific antigen based on electrocatalytic platinum nanoparticles conjugated to a recombinant scFv antibody

Highly sensitive and label free detection of prostate specific antigen (PSA) still remains a challenge in prostate cancer diagnosis. In this paper, we propose a sensitive electrochemical immunosensor based on electrocatalytic platinum nanoparticles conjugated to a recombinant scFv antibody. Gold disc electrodes functionalised with a l-Cysteine (Cys) self-assembled monolayer (SAM) were used to covalently bind PSA specific monoclonal antibody (anti-PSA) using N-ethyl-N′-(3-dimethylaminopropyl) carbodiimide and N-hydroxysuccinimide (EDC/NHS) chemistry. Immunosensing was completed using sandwich-type immunoreaction of the PSA–antigen (1–30ng/mL) between anti-PSA immobilized on the l-Cys modified electrode using label free electrochemical impedance (EIS) technique. Furthermore, highly specific in-house generated scFv fragments as receptor proteins were utilised for one step site-directed immobilisation on the surface of platinum nanoparticles (PtNPs). To improve the sensitivity of the immunoassay, these scFV labelled electrocatalytic PtNPs were then used for covalent hybridisation to the PSA modified electrode and then applied in a hybridisation assay to determine the concentration of the PSA by measuring the faradaic current associated with reduction of peroxide in solution. Semi-log plots of the PSA concentration vs. faradaic current are linear from 1 to 30ng/mL and pM concentrations can be detected without the need for molecular, e.g., PCR or NASBA, amplification.

Highly efficient detection of hydrogen peroxide in solution and in the vapor phase via fluorescence quenching.

Herein we report the highly efficient and sensitive detection of hydrogen peroxide in both aqueous solution and in the vapor phase via fluorescence quenching (turn-off mechanism) of the amplified fluorescent conjugated polymer-titanium complex induced by hydrogen peroxide. Inter- and intra-polymer energy migration leads to extremely high sensitivity.

One-Pot Synthesis of Protein-Embedded Metal–Organic Frameworks with Enhanced Biological Activities

Protein molecules were directly embedded in metal-organic frameworks (MOFs) by a coprecipitation method. The protein molecules majorly embedded on the surface region of MOFs display high biological activities. As a demonstration of the power of such materials, the resulting Cyt c embedded in ZIF-8 showed a 10-fold increase in peroxidase activity compared to free Cyt c in solution and thus gave convenient, fast, and highly sensitive detection of trace amounts of explosive organic peroxides in solution.

A Novel Ultra-Low Detection Limit Hydrogen Peroxide Sensor Based on Horseradish Peroxidase Immobilized Polyaniline Film

Hydrogen peroxide is a metabolic by-product and a kind of stable reactive oxygen species (ROS). When the ROS levels increase, it may causes several harmful effects of ROS on the cell structure, such as damage of DNA and protein oxidation, and this is known as oxidative stress. The oxidative stress is also the important clinical indicators of cause of aging, Alzheimer disease, and kidney diseases. Now the common test method of oxidative stress is Enzyme-linked immunosorbent assay (ELISA). ELISA needs color giving dyes, complicated preparation of sample, and optical system, so it is very expensive and inconvenient. In our study, we present a high sensitivity hydrogen peroxide sensor with ultra-low detection limit. The sensor can directly test the sample and only need very small amount of sample. And because of the simple structural design and fabrication, the sensor can be used as a cheap, efficient, and portable sensor system. In the future, the novel hydrogen peroxide sensor has various applications in studying oxidative stress and detecting reactive oxygen species for cells. Furthermore, we can combine the PANI sensor with different enzymes to fabricate other highly sensitive sensors to detect diverse materials, such as glucose, lactic acid and cholesterin. In our study, the PANI layer and gold electrodes were deposited on silicon nitride substrate, and the PANI was applied to fabricate a thin film between two electrodes. Then the PANI layer was sultonated by propane sultone and modified with HRP. During the measurement, the sensor was operated at 100mV and different concentrations of hydrogen peroxide citrate buffer solutions (pH=5.4) were dropped on it. The current change was measured when the hydrogen peroxide reacted with the HRP Immobilized PANI thin film. We tested the hydrogen peroxide solution from 0.1 nm to 1mM. The HRP-modified resistive sensors based on n-alkylated polyaniline(PANI) detect hydrogen peroxide in solution with very high sensitivity, ultra-low limit, and short response time. The sensitivity is higher than that of other sensing methods, such as electrochemical sensors or transistor sensors. The detection limit of PANI sensor is 0.7 nM (Figure 1. a, b). It is three orders smaller than that of other common methods with detection limit around 1 μM. To the best of our knowledge, it is the lowest detection limit that has ever been reported. And We combine the hydrogen peroxide sensor with glucose oxidase to build up the glucose sensor. In summary, the hydrogen peroxide sensor can provide a more exact hydrogen peroxide concentration and quick detection. The simple process for the sensor fabrication also allows the sensor to be cheap, disposable and combinable with other sensors to build up sensing system. This work was partially supported by National Science Council grant (No.99B20495A & 101-2221-E-007-102-MY3) and by the research grant (100N2049E1) at National Tsing Hua University.

Novel Cholesterol Sensor Based on Ultra-Low Detection Limit Hydrogen Peroxide Sensor

Hydrogen peroxide attracts a great interest due to its important role in food, pharmaceutical, and clinical applications. Hydrogen peroxide is also a by-product in many enzyme catalytic reactions, such as glucose oxidase, lactate oxidase, cholesterol oxidase, alcohol oxidase, urate oxidase, aldehyde oxidase, and oxalate oxidase, which are implemented to detect glucose, lactic acid, cholesterol, ethanol, urea, formaldehyde, and oxalate, respectively. These biomolecules are significant markers in many biologically metabolic reactions. In our study, we present a cholesterol sensor based on a high sensitivity hydrogen peroxide sensor with ultra-low detection limit. The sensor can directly test the sample and only need very small amount of sample. And because of the simple structural design and fabrication, the sensor can be used as a cheap, efficient, and portable sensor system. The HRP-modified resistive sensors based on n-alkylated polyaniline(PANI) detect hydrogen peroxide in solution with very high sensitivity, ultra-low limit, and short response time. The sensitivity is higher than that of other sensing methods, such as electrochemical sensors or transistor sensors. The detection limit of PANI sensor is 0.7 nM. It is three orders smaller than that of other common methods with detection limit around 1 μM. To the best of our knowledge, it is the lowest detection limit that has ever been reported. And we combine the hydrogen peroxide sensor with cholesterol oxidase to build up the cholesterol sensor. In our study, the PANI layer and gold electrodes were deposited on silicon nitride substrate, and the PANI was applied to fabricate a thin film between two electrodes. Then the PANI layer was sultonated by propane sultone and modified with HRP. After that, the device was combined with dialysis membrane which was modified with cholesterol oxidase. During the measurement, the sensor was operated at 100mV and different concentrations of cholesterol PBS solutions (pH=7.0) were dropped on it. The cholesterol reacted with the cholesterol oxidase and created hydrogen peroxide on the PANI thin film (Figure 1). The current change was measured when the hydrogen peroxide reacted with the HRP immobilized PANI thin film. According to regular cholesterol level in human blood, we tested the cholesterol solution from 100 mg/dl to 400 mg/dl ,and we get a very good linear result (Figure 2). In summary, the cholesterol sensor can provide a more exact cholesterol concentration detection. The simple process for the sensor fabrication also allows the sensor to be cheap, disposable and combinable with other sensors to build up sensing system. This work was partially supported by National Science Council grant (No.99B20495A & 101-2221-E-007-102-MY3) and by the research grant (100N2049E1) at National Tsing Hua University.

Syntheses and catalytic oxidation of tetrameric and polymeric copper(II) 1,3-propanediaminetetraacetates

Tetranuclear copper dihydrogen 1,3-propanediaminetetraacetate [Cu4Cl4(1,3-H2pdta)2] (1) was obtained from an acidic solution, which was converted to one dimensional coordination polymer [Cu(1,3-H2pdta)]n (2) and its hydrated derivative [Cu4(1,3-pdta)2(H2O)4]·H2O (3) respectively (H4pdta=1,3-propanediaminetetraacetic acid, C11H18N2O8) under heating condition. The four copper ions in 1 and 3 exist in quasi-symmetrical tetrahedral environments. Complex 1 consists of a tetrameric neutral unit [Cu4Cl4(H2pdta)2], which extents into a 3D supramolecular structure by inter-molecular hydrogen bonds [O3⋯Cl(1) 3.155(6)Å]. In 2, [1,3-H2pdta]2− ligand links each copper ion to generate a neutral polymeric chain [Cu(1,3-H2pdta)]n with strong intra-molecular hydrogen bonds [O4⋯O2 2.620(7)Å]. The protonated carboxy groups in 1 and 2 show weak coordination, while deprotonated nitrogen atoms are in coordination mode. All of the three complexes show catalytic activities to the conversions of cyclohexane to cyclohexanol and cyclohexanone with hydrogen peroxide in solution. This is attributed to the nano-constructed copper species (∼1.0nm) and the copper coordination polymer. The chloride ion seems not related to the conversion, while unsaturated configuration is considered favorably for the conversion.

Reactions of hydrogen peroxide with acetylacetone and 2-acetylcyclopentanone

A reaction of acetylacetone with equimolar amount of concentrated aqueous H2O2 in both organic solvents (ButOH, AcOH) and water at various temperatures gave the corresponding 3,5-dihydroxy-1,2-dioxolanes with different configuration of stereogenic centers. In the presence of an excess of H2O2, 3,5-dihydroxy-1,2-dioxolanes were converted to a mixture of 5-hydroperoxy-3-hydroxy-1,2-dioxolanes and further to a mixture of dimeric 1,2-dioxolan-3-ylperoxides. All the peroxides formed exist in solutions as equilibrium mixtures with the starting reagents. A prolonged reflux of solutions of 3,5-dihydroxy-1,2-dioxolanes in ButOH in the presence of a large excess of H2O2 led to the skeletal rearrangements of the substrates to a mixture of propionic acid and hydroxyacetone, which underwent further oxidative transformations. Unlike acetylacetone, 2-acetylcyclopentanone reacted with H2O2 in aqueous phase or in solutions in ButOH under thermodynamic or kinetic control with the formation of the corresponding 5-hydroperoxy-3-hydroxy-1,2-dioxolanes, rather than 3,5-dihydroxy-1,2-dioxolanes. Thermodynamically controlled process in solution in AcOH gave a mixture of all four possible hydroperoxyhydroxy-1,2-dioxolanes. These cyclic peroxides in solutions in ButOH or AcOH readily converted to a mixture of AcOH, glutaric, α-methyladipic, and α-hydroxy-α-methyladipic acids. An active α-hydroxylation of the substrate was observed upon reflux of a solution of 2-acetylcyclopentanone and H2O2 in AcOH.

Highly sensitive conductometric biosensors for total lactate, d- and l-lactate determination in dairy products

An original method combining two conductometric biosensors is proposed for the determination of total lactate, l- and d-lactate in dairy products. The biosensors were prepared through cross-linking of l-lactate oxidase from Pediococcus sp. (LODP) or a combination of LODP and horseradish peroxidase (HRP) at the surface of gold interdigitated microelectrodes using glutaraldehyde (GA) vapors. LODP is reported to catalyze specifically l-lactate oxidation into pyruvate and hydrogen peroxide in solution. In this work, we showed that LODP chiral selectivity was lost following enzyme cross-linking, rendering LODP sensor suitable for total lactate determination. Biosensor sensitivity towards both stereoisomers was 1.16±0.04μSμM−1. The addition of HRP significantly improved the linear range and stability of LODP biosensor, but also increased its sensitivity, the effect being more pronounced for d-lactate (+381%) than for l-lactate (+260%). This result was attributed to a modification in LODP chiral selectivity combined with the production of additional ions (acetate, H+ and HCO3−) via the HRP-catalyzed oxidation of pyruvate. A method, taking advantage of the difference in d- and l-lactate behaviours and combining the monoenzymatic and bienzymatic biosensors calibration data, was proposed for the calculation of their concentrations in unknown samples. Different parameters (HRP/LODP ratio, exposure time to GA vapors, pH and concentration of measurement medium) were optimized in order to achieve the best compromise between sensitivity and stability of the biosensors. The best limit of detection for l- and d-lactate, calculated as three times the signal to noise ratio was achieved with the bi-enzymatic sensor and was equal to 0.05μM. LODP/HRP biosensor response towards l-lactate was not significantly affected by glucose, fructose and lactose. The proposed biosensors were finally applied to the determination of total lactate, d- and l-lactate concentrations in yogurt samples. Results were in good agreement with those obtained using a reference colorimetric enzymatic method.

Development of a sensitive long path absorption photometer to quantify peroxides in aerosol particles (Peroxide-LOPAP)

Abstract. A new off-line instrument to quantify peroxides in aerosol particles using iodometry in long path absorption spectroscopy has been developed and is called peroxide long path absorption photometer (Peroxide-LOPAP). The new analytical setup features important technical innovations compared to hitherto published iodometric peroxide measurements. Firstly, the extraction, chemical conversion and measurement of the aerosol samples are performed in a closed oxygen-free (~ 1 ppb) environment. Secondly, a 50-cm optical detection cell is used for an increased photometric sensitivity. The limit of detection was 0.1 μM peroxide in solution or 0.25 nmol m−3 with respect to an aerosol sample volume of 1 m3. The test reaction was done at a constant elevated temperature of 40 °C and the reaction time was 60 min. Calibration experiments showed that the test reaction with all reactive peroxides, i.e. hydrogen peroxide (H2O2), peracids and peroxides with vicinal carbonyl groups (e.g. lauroyl peroxide) goes to completion and their sensitivity (slope of calibration curve) varies by only ±5%. However, very inert peroxides have a lower sensitivity. For example, tert-butyl hydroperoxide shows only 37% sensitivity compared to H2O2 after 1 h. A kinetic study revealed that even after 5 h only 85% of this inert compound had reacted. The time trends of the peroxide content in secondary organic aerosol (SOA) from the ozonolysis and photo-oxidation of α-pinene in smog chamber experiments were measured. The highest mass fraction of peroxides with 34% (assuming a molecular weight of 300 g mol−1) was found in freshly generated SOA from α-pinene ozonolysis. Mass fractions decreased with increasing NO levels in the photo-oxidation experiments. A decrease of the peroxide content was also observed with aging of the aerosol, indicating a decomposition of peroxides in the particles.

Real-time mapping of a hydrogen peroxide concentration profile across a polymicrobial bacterial biofilm using scanning electrochemical microscopy

Quantitative detection of hydrogen peroxide in solution above a Streptococcus gordonii (Sg) bacterial biofilm was studied in real time by scanning electrochemical microscopy (SECM). The concentration of hydrogen peroxide was determined to be 0.7mM to 1.6mM in the presence of 10mM glucose over a period of 2 to 8h. The hydrogen peroxide production measured was higher near the biofilm surface in comparison to Sg grown planktonically. Differential hydrogen peroxide production was observed both by fluorometric as well as by SECM measurements. The interaction between two different species in a bacterial biofilm of Sg and Aggregatibacter actinomycetemcomitans (Aa) in terms of hydrogen peroxide production was also studied by SECM. One-directional y-scan SECM measurements showed the unique spatial mapping of hydrogen peroxide concentration across a mixed species biofilm and revealed that hydrogen peroxide concentration varies greatly dependent upon local species composition.