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Introduction: A simple and inexpensive differential calorimetric sensor for rapid hydrogen peroxide (H2O2) quantification in industrial solutions was developed, characterized, and validated. An earlier method proposed by the authors, on which the developed sensor is based, was enhanced, allowing overcoming the issues with its practical application. Thus, the following goals were achieved: a response time of 195 s from sampling to the analytical result; the elimination of the influence of initial sample temperature on the precision of the result by a differential mode of measurement application; the elimination of the result precision degradation caused by the parasitic heat produced by the sample stirrer. A linear quantification range from 0.05 to 1.5 mol L-1 H2O2 with a limit of detection (LOD) of 0.035 mol L-1 H2O2 was reached by applying disposable catalyst holders with a lifetime of more than 50 quantifications. The catalyst surface area to sample volume ratio adjustment allows the sensor’s analytical characteristics adaptation to the industrial-technological process requirements. Background: Hydrogen peroxide is used as a reagent in the technological processes of several industrial branches, and the simple and fast monitoring of its concentration is critical for the maintenance of technological process stability. The common disadvantages of the existing sensors are the complex and long measuring procedures requiring sophisticated equipment and qualified personnel. Objective: This study’s objective is the development of a simple and inexpensive calorimetric sensor and measuring instrument for rapid H2O2 quantification in industrial solutions by nonqualified personnel. The sensor is based on the significant improvement of the reagent-less calorimetric method proposed by the authors earlier, allowing its simple and precise practical application. Drawbacks such as the result of precision degradation by the initial sample temperature and by parasitic heat production during the measurement were overcome by obtaining an economical, simple, rapid, and precise sensor. Methods: The temperature increase resulting from the heat generated during the catalytic H2O2 decomposition was recorded as a sensor response. A simple and inexpensive disposable acrylic ring covered by MnO2 serves as a specific catalyst for H2O2 decomposition. The sensor analytical characteristics were evaluated, and permanganate approach validation was conducted. Results: The developed sensor showed a linear response to H2O2 from 0.05 to 1.5 mol L-1 with a LOD of 0.035 mol L-1 and LOQ of 0.115 mol L-1 under optimized experimental conditions. The catalyst surface area to sample volume ratio adjustment allows the sensor’s analytical characteristics adaptation to the industrial process requirements. The results were validated using the permanganate approach application, obtaining recovery values of 98.7%–101.4%. Conclusion: A simple and economic calorimetric sensor for quick hydrogen peroxide quantification in industrial solutions was developed, characterized, and validated. Disposable catalyst-loaded rings were employed allowing 50 successive quantifications of 1 mol L-1 H2O2 with a relative error of 1.08%. The sensor construction enables easy catalyst replacement and adjustment of its analytical characteristics to the industrial technology requirements using catalyst rings with various catalyst surface areas.

A simple and rapid impedimetric sensor applicable for industrial lipase activity quantification was developed and characterized. It is based on the lipase catalyzed degradation by hydrolysis of a thin nanocomposite substrate sensitive layer deposited on a PCB stick electrode usable as disposable or regenerable. The sensitive layer degradation rate was evaluated by the impedance changes registration along time resulting from its thickness diminution applying a small amplitude AC voltage with a constant frequency. The AC current phase shift variations along the time caused by the impedance changes were registered as s sensor response. The sensor was characterized in terms of linear quantification range, LOD, precision and quantification time. The response time was found to be from 80 to 6 s for the linear concentration range from 0.99x10-2 to 1.68 U.S.P. U mL-1 with relative errors from 3.75% to 1.24% respectively and a LOD of 8x10-3 U.S.P. U mL-1. Finally, lipase spiked whey samples taken from milk industry were quantified and the results were validated by a titrimetric method revealing a good agreement (relative error less than 4.5%)

A simple and rapid reagent less nephelometric method for on-line H2O2 quantification in semiconductors etching solutions was developed, optimized, characterized and validated. The intensity of the light scattered by the oxygen gas suspension resulted from H2O2 catalytic decomposition by immobilized MnO2 was registered as analytical response. The influences of the light wave length, the agitation rate, the temperature and the catalyst surface area on the response amplitude were studied and optimization was done. The achieved linear concentration range from 10 to 150mmolL-1 at 0.9835 calibration curve correlation coefficient, precision from 3.65% to 0.95% and response time from 35 to 20s respectively, at sensitivity of 8.01µAmmol-1 L and LOD of 2.9mmolL -1 completely satisfy the semiconductor industry requirements.

An amperometric bi-enzyme sensor for detection of organophosphorus pesticides (OPs) with phenolic leaving groups, which are not electroactive, is presented in this work. The biosensing platform was created by a simple, controllable, and reproducible one-step electrodeposition onto the surface of a glassy carbon electrode of a chitosan bionanocomposite with entrapped carboxylated multi walled carbon nanotubes, organophosphorus hydrolase (OPH), and horseradish peroxidase (HRP). The OPs determination involved a sequence of OPH and HRP-catalyzed reactions resulting in phenolic radicals production, which were quantified by registering the current of their reduction at a potential of −50 mV vs. Ag, AgCl/KClsat.The developed sensor was applied for the determination of prothiofos, as an example. At optimized conditions (pH 7.25 and H2O2 concentration 200 μmol L−1), a LOD as low as 0.8 μmol L−1 was attained, while the linear concentration range was extended from 2.64 μmol L−1 up to 35 μmol L−1. The main advantage of the proposed bi-enzyme sensor is its selectivity toward the OPs with phenolic leaving groups, excluding the interference of the nitrophenyl-substituted OPs.

A simple, rapid, and reagent-less calorimetric method for H2O2 quantification, applicable automatically on-line was developed, analytically characterized and tested with real SC-1 alkaline etching solutions used in the semiconductor technology. Being based on H2O2 catalytic decomposition by immobilized solid catalyst, the proposed method possesses excellent specificity toward the H2O2 without any interference. The total quantification time was found to be less than 60s, RSD lies in the range from 4.7% to 1.8% for the linear concentration range from 2.8 10-2 to 2molL-1 respectively and the LOD was determined to be as low as 9.3 10-3molL-1.

The simultaneous voltammetric determination of species with close peak potentials presents some difficulties, because of the overlapping of their redox peaks at conventional solid electrodes. Therefore, two approaches were proposed to overcome this drawback: (i) chemometric resolution of the overlapped peaks by semi-derivative or multivariate analysis and (ii) development of chemically modified electrodes with better electrochemical performances, permitting peaks separation. However, the mathematical treatment habitually results in a precision decrease, while the electrode modification often requires the use of expensive materials and involves sophisticated techniques. Hence, another strategy for the direct simultaneous species determination is suggested in this work. It involves the application of Differential Alternative Pulses Voltammetry (DAPV) [1], which provides the great resolution of the second order voltammetric techniques, as Radio-Frequency Polarography, Second Harmonic AC Voltammetry, and Differential Faradaic Rectification Polarography (DFRP), in combination with the high sensitivity, precision, and instrumental and operational simplicity of the most common voltammetric technique, the differential pulse voltammetry (DPV). The second order voltammetric techniques including DAPV are based on the nonlinearity of the electrochemical system I/E characteristic yielding voltammograms shaped as a derivative of voltammetric peak resulting from small sinusoidal or rectangular bipolar deviations of the DC potential. Two single pulses of small amplitude, one cathodic and one anodic are successively applied in DAPV for every value of the scanned DC potential with delay time between the pulses equal to the delay time between the scan step and the first one (Fig. 1). The sum of the two pulse faradaic current components with opposite polarities is registered vs. the scanned potential as DAPV voltammogram. The experimentally determined half-width of the DAPV peaks (37 mV at 2 electrons reduction) is 1.22 times smaller than that of the most common voltammetric technique DPV (45.3 mV) at the same conditions and equals that obtained by the application of another second order technique, the DFRP. Thus, the DAPV voltammogram’s shape as second derivative of voltammetric wave combined with the small half-widths of the anodic and the cathodic peaks allows simultaneous quantification of species having very small peak potential difference. Taking advantage from the great resolution power of DAPV, it was applied for the simultaneous determination of a range of organic (catechol and hydroquinone [2]; o-nitrophenol, m-nitrophenol and p-nitrophenol [3]) and inorganic species (Cd2+/In3+; Tl+/Pb2+ [1, 4]) with close peak potential difference, as shown in Figs. 2-5. The proposed approach offers a very simple alternative route for the simultaneous determination of a broad range of species and overcomes the disadvantages of the currently applied strategies involving electrode modification or mathematical data processing. References 1. Zlatev, M. Stoytcheva, B. Valdez, J.P. Magnin, P. Ozil. Electrochem. Communications, 2006, 8, 1699-1706. 2. Ayala, M. Stoytcheva, R. Zlatev, Z. Velkova, V. Gochev, B. Valdez, G. Montero. Electroanalysis, 2018, 30, 1913-1917. 3. Stoytcheva, R. Zlatev, Z. Velkova, V. Gochev, A. Ayala, G. Montero, B. Valdez. Electroanalysis, 2019, 31, 652-660. 4. Zlatev, M. Stoytcheva, B. Valdez. Electroanalysis, 2018, 30, 1902-1905. Figures captions Fig. 1. DAPV potential-time waveform. M1-M4 are the current measuring intervals; DT is the wait time for the pulse capacitive current decay. Fig. 2. HQ (30 mmol L-1) and CC (10 mmol L-1) determination by DAPV. PBS 0.1 mol L-1, pH 7; Spectroscopic graphite electrode. Fig. 3. Nitrophenol (NP) isomers simultaneous determination by DAPV (m-NP 125 mmol L-1, p-NP 125 mmol L-1, and increasing o-NP concentrations: 25, 50, 75, 100 and 125 mmol L-1). PBS 0.1 mol L-1; pH 6.5; glassy carbon electrode modified by a nanocomposite of graphite nanopowder and Au nanoparticles. Fig. 4. Cd2+ and In3+ (E1/2 difference 45 mV) simultaneous determination by DAPV, 0.1 mol L-1 HCl; Hanging Mercury Drop Electrode. Fig. 5. Tl+ and Pb2+ (E1/2 difference 50 mV) simultaneous determination at 12:1 concentration ratio by DAPV and DPV. 0.1 mol L-1 HCl; Hanging Mercury Drop Electrode. Figure 1

In this study we describe a sensitive amperometric microbial biosensor that is fast, economic, reliable, and can compete with the existing proposed methods for vitamin B12 determination. Taking advantage of the bacterial strain Tetrasphaera duodecadis which oxidizes vitamin B12 with oxygen consumption, we shaped a promising alternative tool for the direct and specific determination of vitamin B12 in different samples without pre-treatment. For this purpose, a vitamin B12 amperometric microbial biosensor was constructed based on one-step immobilization of the bacterium by filtration of a concentrated bacterial mass through a 0.15 μm pore size cellulose filter and fixed on a Clark-type oxygen probe, serving as a transducer, and exploiting the described processes. The results obtained indicate a sensitive capability with a linear sensor concentration range from 10−7 mol L−1 to 10−5 mol L−1 and the response time of about 700 seconds at 10−6 mol L−1. Furthermore, the Tetrasphaera duodecadis membrane attached to the Clark type oxygen probe has an estimated 1 month lifetime at room temperature. In addition, the developed prototype allowed the assessment of B12 status directly in samples prepared for that purpose. The results were well correlated with those obtained with commercial samples, thus demonstrating that the proposed microbial sensor offers an accurate and useful analytical tool that can be easily applied to prevent diseases caused by the lack of vitamin B12.

The authors describe a graphite immobilized bismuth film electrode with enhanced sensitivity for the organophosphorus pesticide paraoxon. The film was formed by ex-situ electroplating of bismuth onto the large surface of a glassy carbon electrode modified with graphite nanopowder (Bi/Gr/GCE). The modified GCE was characterized by chronoamperometry using p-nitrophenol as a model nitro compound. The modification of the GCE results in an increase of the electroactive area (to 27.7 mm2) and of the electrocatalytic activity (the catalytic rate constant being 4140 L·mol−1·s−1). This results in an enhancement of the current for the electroreduction of paraoxon by a factor of 4.3 (compared to a plain GCE). The modified GCE was applied to the sensitive determination of paraoxon by differential pulse voltammetry. At a typical working potential of −0.45 V vs. Ag/AgCl, the LOD is 2 nmol·L−1 of paraoxon, which is comparable to the LOD of some cholinesterases-based electrochemical sensors and is lower than the LOD of the organophosphorus hydrolase-based electrochemical sensors for paraoxon. In addition, the new GCE is more stable than enzyme-based sensors, and it can be renewed.

It is imperative to understand and systematically compare the initial interactions between bacteria genre and surface properties. Thus, we fabricated a flat, anodized with 80 nm TiO2 nanotubes (NTs), and a rough Ti6Al4V surface. The materials were characterized using field-emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDX) and atomic force microscopy (AFM). We cultured in vitro Staphylococcus epidermidis (S. epidermidis) and Pseudomonas aeruginosa (P. aeruginosa) to evaluate the bacterial-surface behavior by FE-SEM and viability calculation. In addition, the initial effects of human osteoblasts were tested on the materials. Gram-negative bacteria showed promoted adherence and viability over the flat and rough surface, while NTs displayed opposite activity with altered morphology. Gram-positive bacteria illustrated similar cellular architecture over the surfaces but with promoted surface adhesion bonds on the flat alloy. Rough surfaces supported S. epidermidis viability, whilst NTs exhibited lower vitality. NTs advocated promoted better osteoblast organization with enhanced vitality. Gram-positive bacteria suggested preferred adhesion capability over flat and carbon-rich surfaces. Gram-negative bacteria were strongly disturbed by NTs but largely stimulated by flat and rough materials. Our work proposed that the chemical profile of the material surface and the bacterial cell wall characteristics might play an important role in the bacteria-surface interactions.

As known, the dissolved hydrogen undergoes electrochemical oxidation, the mechanism of which depends on the electrolyte pH. In alkaline solutions the OH- participates in the hydrogen oxidation according to the reaction: H+ OH-= H2O+2e-, while in acid solutions the electrochemical oxidation is direct: H2=2H++2e-. In both cases electrolyte acidifying occurs because of the OH- consumption or H+generation, making suitable the application of very acid electrolytes to avoid the sensor characteristics changes caused by a great pH changes over time. A 3-electrode probe similar to the Clark type oxygen probe construction was proposed, elaborated, and characterized as a dissolved hydrogen sensor. Its analytical characteristics such as LOD, sensitivity, response time, and linear response concentration range were determined as a function of the temperature, membranes materials, the electrolytes composition, and pH. Coulometric controlled electrochemical hydrogen generator was applied for standard solution preparation. The sensor characterization results are presented and discussed together with the results obtained from its application for the real time determination of the rate of hydrogen production by the varieties B10 and IR3 of the photosynthetic strain Phodobacter Capsulatus. Acknowledgement. This work was supported by CONACyT Mexico: Research grant No. 152961, CONACYT-SENER “Sustentabilidad Energética” 2010-01.

An approach for precision improvement in organophosphorus pesticide determination was developed, applied and characterized. The enzyme organophosphorus hydrolase was employed as a specific agent for electrode surface modification, and the pulsed amperometric detection for 66.6 ms was applied for the hydrolysis product detection. Pulsed electrochemical cleaning, i.e. oxidation at a very positive potential (+1.4 V vs. Ag, AgCl) was applied every 233 ms for 166.6 ms for elimination of the fouling effect, which degrades the determination precision. By this way a RSD of 0.41% at 40 μmol L−1p-nitrophenol determination was achieved after 10 determinations, instead of 43.93% without the pulsed cleaning application.

The rates of hydrogen production by B10 and the genetically modified IR3 varieties of the bacterial strain R. capsulatus employing DL-sodium lactate as a carbon source and parts of the visible spectrum light as energy source were compared. The influence of parameters such as: light spectrum (blue, green, red, white light), light luminance (from 2500 to 17000 lux), reactor geometry (flat and cylindrical), was studied to maximize the bacterial hydrogen production. Maximal results were achieved in a flat reactor at 700 nm (red light) and 2500 lux light luminance by both varieties, but the hydrogen production obtained by the genetically modified variety IR3 exceeded the B10 production up to 64 % in spite of the superior biomass quantity of the latter.

The Differential Alternative Pulses Voltammetry (DAPV) combining the high sensitivity of the Differential Pulse Voltammetry with the increased resolution of the second order voltammetric techniques was applied for on-site simultaneous determination of species as As(III), Pb(II) and Tl(I) in industrial solution without preliminary species separation. The limits of the species concentration ratios allowing simultaneous determination with preset precision of les than 10% were determined. The method was applied for determination in real industrial solutions.

Differential Alternative Pulses Voltammetry (DAPV), introduced by the authors earlier, was applied with HMDE for direct As(III) determination in the presence of Pb(II) in natural water without sample pretreatment. Distinguishable peaks of As(III) and Pb(II) were registered in 1 M HCl supporting electrolyte at a concentration ratio as high as 1 : 6, while complete peak overlapping occurs applying DPP at any concentration ratio at the same experimental conditions. In-situ As(III) determinations in the presence of Pb(II) in contaminated ground waters in Mexico were performed, using especially designed disposable safe mercury drop electrodes.

In this work are reported new results on the type of the immobilized acetylcholinesterase inhibition by specific and non-specific inhibitors, as well as the values of the characteristic enzyme reaction kinetic parameters in the absence and in the presence of inhibitors, identified applying an electrochemical approach. It was found that: -The kinetics of the process of acetylthiocholine hydrolysis catalyzed by the immobilized acetylcholinesterase is complicated by mass transfer constraints, at low substrate concentrations; -The inhibition of the immobilized acetylcholinesterase by specific inhibitors (trichlorfon, oxophosphol, galantamine, caffeine, atropine, nicotinic acid, and eserine) is of a competitive type, while quinine and thiamine acts as non-competitive inhibitors; -The character of acetylcholinesterase inhibition in heterogeneous phase by non-specific inhibitors (Hg2+, Cu2+, Cd2+, Mn2+, Fe3+, and AsO33-) is reversible and non-competitive. The reactivity of the inhibitors decreases in the order: Hg2+ → Cu2+ → Cd2+ → AsO33- → Fe3+ → Mn2+.

A simple and cheap type of disposable Au disc electrodes was developed and fabricated by PCB technology, massively used in electronic industry. This electrodes were successfully applied for "in-situ" As(III) determination in natural ground waters by the Square Wave Anodic Stripping Voltammetry (SWASV). A detection limit of 5.8 μg/L was reached at 20 s deposition time and -480 mV deposition potential. A conductometry based method was developed allowing the achievement of results reproducibility of 7.8 % to 1.5 % for the As(III) concentrations in the range from 5.8 μg/L to 250 μg/L by surface reproducibility correction of the disposable electrodes.

A novel electrochemical biosensor integrating the strictly autotrophic bacterial strain Leptospirillum ferrooxidans as a recognition element and a Clark type oxygen probe as a transducer was designed, metrologically and analytically characterized and applied for the specific Fe(2+) determination. The bacterial Fe(2+) oxidation involves O(2) consumption, thus the quantification was performed registering the decrease of the oxygen reduction current. The limit of detection was found to be 2.4 micromol L(-1) and the sensitivity of the determinations-3.94 nAL micromol(-1). The response time of the biosensor is 18s for Fe(2+) concentrations of 10(-5) to 10(-4) mol L(-1). The biosensor was applied as well for the indirect determination of Fe(2+) oxidizing species such as Cr(2)O(7)(2-), reaching a sensitivity of 2.47 nAL micromol(-1). The transducer characteristics were evaluated and optimized to obtain short response time and high sensitivity. The analytical performances of the biosensor subject of the present work were found to be similar to that of the At. ferrooxidans based one developed by the authors earlier, avoiding however the sulfur compounds interference, because of the substrate specificity of the applied bacterial strain.

PurposeTo develop and test a rapid method for evaluation of the corrosion protection (CP) of carbon steel (CS) by vapour corrosion inhibitors (VCI) films.Design/methodology/approachThe determination of the CP by VCI on CSs is commonly carried out in a chamber applying neutral salt spray (NSS) and usually it takes many days. The common disadvantage of the various rapid methods created until now is the need of special laboratory equipment making their application complicated and inconvenient for field tests. The method for CP measurement of VCI films on CS described in this study is based on measurement of the height of the anodic peak under galvanostatic condition applied earlier on other types of films and coatings. By means of a calibration plot: peak height (V) vs NSS protection time (s), CP of VCI films on CS specimens expressed in hours NSS is determined in a few seconds without using an NSS chamber. Measurements of CP by VCI films under field conditions are performed applying a hand held tester.FindingsTwo groups of CS UNS G10180 steel specimens with increasing thickness of VCI films were studied – one in an NSS chamber and the second by the application of a corrosion tester. The correlation between the results obtained for the two groups of specimens was found and a calibration plot was made.Practical implicationsBased on this method, a special corrosion tester was developed, able to measure under field conditions as well.Originality/valueThe method subject of the paper is a further development of a galvanostatic method developed by the authors for CP evaluation of chromate films of Zn and Cd coatings. The method was modified according to the properties of VCI films

An amperometric bacterial sensor with current response to Fe 2+ and S 2 O 3 2− ions has been designed by immobilizing an acidophilic biomass of Acidithiobacillus ferrooxidans on a multi disk flat-front oxygen probe. The bacterial layer was located between the oxygen probe and a membrane of cellulose. A filtration technique was used to yield the bacterial membranes having reproducible activity. The decrease of O 2 flow across the bacterial layer is proportional to the concentration of the dosed species. The dynamic range appeared to be linear for the Fe 2+ ions up to 2.5 mmol L −1 with a detection limit of 9 × 10 −7 mol L −1 and a sensitivity of 0.25 A L mol −1 . The response of the biosensor is 84 s for a determination of 2 × 10 −4 mol L −1 Fe 2+ . Optimizing the Fe 2+ determination by A. ferrooxidans sensor was carried out owing to Design of Experiments (DOE) methodology and empirical modelling. The optimal response was thus obtained for a pH of 3.4, at 35 °C under 290 rpm solution stirring. S 2 O 3 2− concentration was determined at pH 4.7, so avoiding its decomposition. The concentration range was linear up to 0.6 mmol L −1 . Sensitivity was 0.20 A L mol −1 with a response time of 207 s for a 2 × 10 −4 mol L −1 S 2 O 3 2− concentration.

A bioelectrocatalytical method is applied to study the influence of some pharmaceuticals (atropine, caffeine, thiamine, nicotinic acid, quinine and eserine) on the acetylcholinesterase activity. The measuring principle is based on the process of acetylthiocholine hydrolysis, catalyzed by the acetylcholinesterase, immobilized on a graphite electrode surface. The product of this reaction is electroactive and its oxidation current is registered. The kinetics of the process, occurring with the participation of the above mentioned substances, is studied. It is found that competitive (eserine, nicotinic acid, atropine, caffeine) and noncompetitive (thiamine, quinine) inhibition takes place; kinetic parameters of the enzymic reaction (apparent Michaelis constants and constants of inhibition) are determined using electrochemical data, in the absence and in the presence of the inhibitors. It is observed that some of the tested substances behave as activators, under certain conditions. It was found that atropine, caffeine, thiamine, nicotinic acid and quinine do not show any electrochemical activity under the described conditions. Only eserine is oxidized; this however, does not interfere with the enzyme determination in a certain concentration range. Calibration plots, useful for the quantitative analysis, are constructed.

A virtual instrumentation (VI) system called VI localized corrosion image analyzer (LCIA) based on LabVIEW 2010 was developed allowing rapid automatic and subjective error-free determination of the pits number on large sized corroded specimens. The VI LCIA controls synchronously the digital microscope image taking and its analysis, finally resulting in a map file containing the coordinates of the detected probable pits containing zones on the investigated specimen. The pits area, traverse length, and density are also determined by the VI using binary large objects (blobs) analysis. The resulting map file can be used further by a scanning vibrating electrode technique (SVET) system for rapid (one pass) “true/false” SVET check of the probable zones only passing through the pit’s centers avoiding thus the entire specimen scan. A complete SVET scan over the already proved “true” zones could determine the corrosion rate in any of the zones.

International audience; A new voltammetric technique providing high resolution – Differential Alternative Pulses Voltammetry (DAPV) based on the nonlinearity of I/E characteristic of the electrochemical systems was developed, suitable for simultaneous determination of species without their preliminary separation. Superimposition of couples of single rectangular pulses separated by a constant delay time and having same amplitude and opposite polarity, combined with appropriate signal processing yields first derivative of peak shaped curve. The DAPV faradaic current response equation for reversible electrochemical reactions was theoretically derived, graphically presented and experimentally tested. DAPV was applied for determination of species having very near E1/2 potentials: Pb2+/Tl+ and In3+/Cd2+ under increasing concentration ratios. The experimental results compared with those obtained by Differential Pulse Polarography (DPP) and Second Harmonic Alternating Current Polarography show superiority of DAPV resolution power which is combined with high sensitivity, similar to that providing by DPP, employing a simple electronic equipment.

A highly sensitive lipase activity sensor was developed and tested. It is based on the application of SiO2 nanoparticle loaded olive oil as a lipase substrate, deposited on a QCM crystal. The heavier nanoparticles’ release during the substrate enzymatic degradation causes a QCM frequency response enhancement proportional to the nanoparticle/substrate mass ratio.

Preliminary analytical characterization of a simple, rapid, sensitive, and cost effective spectrophotometric method for determination of lipase activity is presented in this work. It is based on the spectrophotometric monitoring of the lipolysis of olive oil, deposited on disposable transparent PET strips, and assembled with Fe2O3 nanoparticles, which play a role of a light barrier. The removal of nanoparticles along with oil degradation evolution provokes a diminution of the light absorption, proportional to the enzyme activity.

The Reversible Hydrogen Electrode (RHE) potential depends on the pH and the H2 pressure which determines the disolved hydrogen concentration according to the Henry law. RHE was applied as hydrogen sensor for real time bacterial hydrogen production rate evaluation employing the photosynthetic Rodobacter Capsulatus strain IR3 in 10 ml reactor containing RCV medium. The reliable determination of the produced H2 volume for determination of the process rate requires big reactor volumes since the H2 production rate is small, measured in mL/hour and the precise measurements of small gas volumes is very complicated. The RHE potential monitoring however allows real time determination of the generated H2 and hence the process rate without consumption of great reagent amounts.

In this work is suggested a Clark type electrode with disposable enzyme membrane for phe- nols determination. This approach allows avoiding the electrode fouling by recording the oxygen re- duction current, and obtaining a stable and reproducible sensor response. An appropriate method for enzyme membrane fabrication by cellulose acetate filters coating with tyrosinase through the use of biocompatible hydrogels was proposed and tested. The sensitivity of the catechol determination, as an example, was found to be 0.89 ∝A mmol -1 L. The detection limit equaled 1 ∝mol L -1 . The achieved RSD was 1.22%.