Journal of the Air Pollution Control Association, 1986
This paper deals with a comparative screening of existing air quality models based on their abili... more This paper deals with a comparative screening of existing air quality models based on their ability to simulate the distribution of sulfur dioxide data in the Venetian area. Investigations have been carried out on sulfur dioxide dispersion in the atmosphere of the Venetian area. The studies have been mainly focused on transport models (Gaussian, plume and K-models) aiming at meaningful
The current flowing at a band ultramicroelectrode in a rectangular channel under mass transfer-li... more The current flowing at a band ultramicroelectrode in a rectangular channel under mass transfer-limited conditions is computed numerically. The procedure is based on the "hopscotch" algorithm and on an appropriate space transformation, 6 = tanh(x/a).
The calibration uncertainty associated with the determination of metals at trace levels in a drin... more The calibration uncertainty associated with the determination of metals at trace levels in a drinking water sample by ICP-MS was estimated when signals were affected by two error contributions, namely instrumental errors and operational condition errors. The calibration uncertainty was studied by using J concentration levels measured I times, as usual in experimental calibration procedures. The instrumental error was random in character whilst the operational error was assumed systematic at each concentration level but random among the J levels. The presence or the absence of the two error contributions was determined with an F-test between the ordinary least squares residual variance of the mean responses at each concentration and a pooled variance of the replicates. The theory was applied to the calibration of 30 elements present in a multi-standard solution and then to the analysis of boron, calcium, lithium, barium and manganese in a real drinking water sample. The need of using the proposed approach as calibration for almost all the analyzed elements resulted evident. The presence or the absence of the two error contributions was determined with an F-test between the ordinary least squares residual variance of the mean responses at each concentration and a pooled variance of the replicates. It was found that in the former instance the uncertainty determined using a two-components variance regression was greater than that obtainable from the one-variance regression.
... 0.0014 ppm is easily achieved and consequently ION CHROMATOGRAPHY O1-' NITRITE ... solut... more ... 0.0014 ppm is easily achieved and consequently ION CHROMATOGRAPHY O1-' NITRITE ... solution to a flowing solution, using an appropriate thin-layer detector, a ... RATIOS FOR THE DIFFERENT ELUENT DETECTOR COMBINATIONS INVESTIGATED Eluen t Conductometric ...
This paper reports the combined use of the nonparametric Theil-Sen (TS) regression technique and ... more This paper reports the combined use of the nonparametric Theil-Sen (TS) regression technique and of the statistics of Lancaster-Quade (LQ) concerning the linear regression parameters to solve typical analytical problems, like method comparison, calculation of the uncertainty in the inverse regression, determination of the detection limit. The results of this new approach are compared to those obtained with appropriate reference methods, using simulated and real data sets. The nonparametric Theil-Sen regression technique appears a new robust tool for the problems considered because it is free from restrictive statistical constraints, avoids searching for the error nature on x and y, which may require long analysis times, and it is easy to use. The only drawback is that the intrinsic nature of the method may lead to a possible enlargement of the uncertainty interval of the discriminated concentration and to the determination of larger detection limits than those obtainable with the commonly used, less robust, regression techniques.
Cyclic voltammetry has been successfully used to study the oxidation of nicotinamide adenine dinu... more Cyclic voltammetry has been successfully used to study the oxidation of nicotinamide adenine dinucleotide (NADH) at single-wall carbon-nanotube-paste (CNTP) electrodes modified with p-methylaminophenolsulfate (p-MAP) and 3,4-dihydroxybenzaldehyde (3,4-DHB). Diffusion-like behaviour was observed for p-MAP-modified electrodes, and a diffusion coefficient of 2.4×10-6 cm2 s-1 was calculated for p-MAP in the paste. The behaviour of 3,4-DHB-modified CNTP electrodes was typical of that of surface-confined mediators.
A new mediated carbon nanotube paste (CNTP) amperometric biosensor for fructose is described. The... more A new mediated carbon nanotube paste (CNTP) amperometric biosensor for fructose is described. The biosensor is formed by a CNTP electrode modified with an electropolymerized film of 3,4‐dihydroxybenzaldehyde (3,4‐DHB) and is based on the activity of a commercial available D‐fructose dehydrogenase (FDH) immobilized on an immobilon membrane placed on the top of the electrode surface. Analytical parameters such as enzyme
The effectiveness of isotopically and non-isotopically labelled internal standards in reducing ma... more The effectiveness of isotopically and non-isotopically labelled internal standards in reducing matrix-induced effects is evaluated. The question is addressed in the quantitative analysis by gas chromatography/mass spectrometry (GC/MS) of dimethyl sulphide, chosen as a typical example of volatile sulphur compounds, in wine matrices. When matrix/run effects are not cancelled out the use of a variance component model (VCM) to handle the linear calibrations obtained by regression technique is successful. The method implies the estimation of an overall calibration straight line, which properly takes into account the uncertainty due to different matrices, the calibration run and the measurement error, making the use of an isotopically labelled internal standard not necessary. The obtained results show that the benefits of lowering times and costs for routine analyses compensate for the small increase in uncertainty in the concentration values obtained in the regression analysis and the slight increase in the detection limit.
Soil samples were suspended in a suitable aqueous solvent and a solid phase microextraction (SPME... more Soil samples were suspended in a suitable aqueous solvent and a solid phase microextraction (SPME) fibre was used to sample the headspace (HS) for five volatile chlorinated compounds (VOX). Their determination was made by GC-ECD technique in the splitless mode. Preliminary studies on the effects of methanol and of the sand/clay ratio on the fibre extraction were made. Four experimental factors, namely, extraction time, extraction temperature, pH and NaCl%, able to affect distribution of the analytes among the four different phases, were varied in suitable ranges. A multivariate approach applied to the face centred cube (FCC) experimental design, was used to try to optimise the overall sample response. The suitable set of factors found for the determination of chloroform, 1,2-dichloroethane, trichloroethylene, 1,1 ,2-trichloroethane, 1,1,2,2-tetrachloroethane, was a compromise among the relevant optimal factor sets of the single analytes. Detection limits of 0.003 ng, 0.022 ng, 0.001 ng, 0.015 ng and 0.002 ng were found respectively for the five cited analytes. The method was successfully used to determine the analyte contents in two real soils sampled in an industrial area.
Stir bar sorptive extraction (SBSE)-thermal desorption (TD) procedure combined with gas chromatog... more Stir bar sorptive extraction (SBSE)-thermal desorption (TD) procedure combined with gas chromatography mass spectrometry (GC-MS) and the statistical variance component model (VCM) is applied to the determination of semi-volatile compounds including organochlorine and organophosphorus pesticides in various synthetic and real fruit-based soft drink matrices. When the matrix effects are corrected using isotopically labelled or non labelled internal standard, but matrix/calibration run-induced deviations are still present in the measurements, the adoption of a variance component model (VCM) in the quantitative analysis of various matrices via an overall calibration curve is successful. The method produces an overall calibration straight line for any analyte accounting for the uncertainty due to all the sources of uncertainty, namely matrix-induced deviations, calibration runs performed at different times, measurement errors. Small increases in the detection limits and in uncertainty in the concentration values obtained in the inverse regression face favourably the decrease in times and costs for routine analyses.
Currently used operating conditions for analysing volatile organic compounds (VOCs) by purge-and-... more Currently used operating conditions for analysing volatile organic compounds (VOCs) by purge-and-trap gas chromatography/mass spectrometry (GC/MS) produced non-linear calibration curves with non-uniform variance. Second-order polynomial models therefore had to be used in weighted regression analysis of measurements of replicates spiked at various concentrations. A transparent procedure based on a reported method of very low computational complexity allowed calculation of the parameters of second-order models, confidence bands of regression lines, prediction bands, and confidence intervals of discriminated analyte concentrations. Tolerance intervals were introduced for this last purpose. Critical, detection and quantification levels drawn from the calibration curves were compared with those calculated by the EPA method.
The paper summarizes critically the current approaches for the calculation of the limits of detec... more The paper summarizes critically the current approaches for the calculation of the limits of detection and quantification.
The electrochemical behaviour of acidic and neutral pharmaceutical active compounds (PhACs) was s... more The electrochemical behaviour of acidic and neutral pharmaceutical active compounds (PhACs) was studied by cyclic voltammetry and pulse voltammetric techniques on mercury, carbon nanotube paste, carbon paste and gold electrodes. The best results, in terms of sensitivity, linearity range and detection limits, were obtained by differential pulse voltammetry (DPV) for ofloxacin (LOD 5.2 M), differential pulse polarography (DPP) for clofibric acid (LOD 4.7 M) and normal pulse voltammetry (NPV) for diclofenac (LOD 0.8 M) and propranolol (LOD 0.5 M).
Articles Articles, All fields, Author, Advanced search. Images Images, Journal/Book title, Volume... more Articles Articles, All fields, Author, Advanced search. Images Images, Journal/Book title, Volume, Issue, Page, Search tips. Font Size: Decrease Font Size Increase Font Size. ... a Department of Physical Chemistry, University of Venice, Calle Larga S. Marta, 2137, 30123, Venice, Italy ...
International Journal of Environmental Analytical Chemistry, 2005
A new method for measuring the oxygen permeability (Dk) of common polymer membranes based on an a... more A new method for measuring the oxygen permeability (Dk) of common polymer membranes based on an amperometric sensor was developed. The system was successfully applied to food wrapping and storing films. The method is based on measurement of oxygen concentration variations in time, by means of an amperometric oxygen sensor (Clark electrode), covered with the polymer film and secured with a proper cap. Measurements were carried out under a constant flow of oxygen in order to be independent of initial oxygen concentration. The oxygen permeability of various commercially available food wrapping films was determined according to Fick's first law of diffusion. The method was tested using a reference material of different thickness, Hydrofilcon-43, with a known permeability value. This method gave more reproducible results compared with the ISO measurement systems. The influence of time, use and hydration degree on oxygen permeability was also tested by exposing the tested films for 36 h to UV radiation and keeping them for 50 days in a dryer under vacuum. Results showed that oxygen permeability is proportional to the degree of hydration of the film.
The effect of oxygen on the mediated electrocatalytic oxidation of nicotinamide adenine dinucleot... more The effect of oxygen on the mediated electrocatalytic oxidation of nicotinamide adenine dinucleotide (NADH) by diaphorase from Clostridium kluveri (DI) was studied using cyclic voltammetry, UV-vis spectrophotometry and NMR spectrometry. The enzyme was found to be able to use molecular oxygen as an electron acceptor. NADH could therefore be oxidized by two competitive electron acceptors: a redox mediator, for istance p-methylaminophenolsulfate (MAP) or ferrocene monocarboxylic acid (FMCA) properly added to the solution, and molecular oxygen. Some considerations on the consequence of the use of diaphorase from Clostridium kluveri in amperometric biosensors were also reported.
ABSTRACT The method based on the confidence limits of a regression straight line is applied to th... more ABSTRACT The method based on the confidence limits of a regression straight line is applied to the linear portion of the calibration curve of a biosensor in order to determine the limit of detection. A practical application gives a detection limit of an ethanol biosensor greater than that calculated by using the method of the signal-to-noise-ratio, S/N=3, but the value is more reliable because it accounts for the variability in the response at analyte additions. A simple approximation of the method is also presented.
The diaphorase-catalyzed electrochemical oxidation of NADH with the aid of quinones (MAP) or ferr... more The diaphorase-catalyzed electrochemical oxidation of NADH with the aid of quinones (MAP) or ferrocene derivatives (FMCA) as electron transfer mediators was studied by cyclic voltammetry under variable conditions of concentration polarization of NADH near the electrode surface. The suppression of this polarization was obtained by the redox L-lactate dehydrogenase-catalyzed reaction between L-lactate and NAD . The addition of pyruvate inhibits the formation of NADH owing to the thermodynamically unfavorable (uphill) electron transfer from L-lactate to NAD . The role played by the uphill/downhill character of the last step of the catalytic chain was illustrated by regenerating NADH using the redox couple gluconolactone/glucose with glucose dehydrogenase as catalyst. The influence on the catalytic wave of the presence of a downhill or uphill step between diaphorase and NAD /NADH couple was also rationalized via the digital simulation technique using experimental data reported in the literature.
Journal of the Air Pollution Control Association, 1986
This paper deals with a comparative screening of existing air quality models based on their abili... more This paper deals with a comparative screening of existing air quality models based on their ability to simulate the distribution of sulfur dioxide data in the Venetian area. Investigations have been carried out on sulfur dioxide dispersion in the atmosphere of the Venetian area. The studies have been mainly focused on transport models (Gaussian, plume and K-models) aiming at meaningful
The current flowing at a band ultramicroelectrode in a rectangular channel under mass transfer-li... more The current flowing at a band ultramicroelectrode in a rectangular channel under mass transfer-limited conditions is computed numerically. The procedure is based on the "hopscotch" algorithm and on an appropriate space transformation, 6 = tanh(x/a).
The calibration uncertainty associated with the determination of metals at trace levels in a drin... more The calibration uncertainty associated with the determination of metals at trace levels in a drinking water sample by ICP-MS was estimated when signals were affected by two error contributions, namely instrumental errors and operational condition errors. The calibration uncertainty was studied by using J concentration levels measured I times, as usual in experimental calibration procedures. The instrumental error was random in character whilst the operational error was assumed systematic at each concentration level but random among the J levels. The presence or the absence of the two error contributions was determined with an F-test between the ordinary least squares residual variance of the mean responses at each concentration and a pooled variance of the replicates. The theory was applied to the calibration of 30 elements present in a multi-standard solution and then to the analysis of boron, calcium, lithium, barium and manganese in a real drinking water sample. The need of using the proposed approach as calibration for almost all the analyzed elements resulted evident. The presence or the absence of the two error contributions was determined with an F-test between the ordinary least squares residual variance of the mean responses at each concentration and a pooled variance of the replicates. It was found that in the former instance the uncertainty determined using a two-components variance regression was greater than that obtainable from the one-variance regression.
... 0.0014 ppm is easily achieved and consequently ION CHROMATOGRAPHY O1-' NITRITE ... solut... more ... 0.0014 ppm is easily achieved and consequently ION CHROMATOGRAPHY O1-' NITRITE ... solution to a flowing solution, using an appropriate thin-layer detector, a ... RATIOS FOR THE DIFFERENT ELUENT DETECTOR COMBINATIONS INVESTIGATED Eluen t Conductometric ...
This paper reports the combined use of the nonparametric Theil-Sen (TS) regression technique and ... more This paper reports the combined use of the nonparametric Theil-Sen (TS) regression technique and of the statistics of Lancaster-Quade (LQ) concerning the linear regression parameters to solve typical analytical problems, like method comparison, calculation of the uncertainty in the inverse regression, determination of the detection limit. The results of this new approach are compared to those obtained with appropriate reference methods, using simulated and real data sets. The nonparametric Theil-Sen regression technique appears a new robust tool for the problems considered because it is free from restrictive statistical constraints, avoids searching for the error nature on x and y, which may require long analysis times, and it is easy to use. The only drawback is that the intrinsic nature of the method may lead to a possible enlargement of the uncertainty interval of the discriminated concentration and to the determination of larger detection limits than those obtainable with the commonly used, less robust, regression techniques.
Cyclic voltammetry has been successfully used to study the oxidation of nicotinamide adenine dinu... more Cyclic voltammetry has been successfully used to study the oxidation of nicotinamide adenine dinucleotide (NADH) at single-wall carbon-nanotube-paste (CNTP) electrodes modified with p-methylaminophenolsulfate (p-MAP) and 3,4-dihydroxybenzaldehyde (3,4-DHB). Diffusion-like behaviour was observed for p-MAP-modified electrodes, and a diffusion coefficient of 2.4×10-6 cm2 s-1 was calculated for p-MAP in the paste. The behaviour of 3,4-DHB-modified CNTP electrodes was typical of that of surface-confined mediators.
A new mediated carbon nanotube paste (CNTP) amperometric biosensor for fructose is described. The... more A new mediated carbon nanotube paste (CNTP) amperometric biosensor for fructose is described. The biosensor is formed by a CNTP electrode modified with an electropolymerized film of 3,4‐dihydroxybenzaldehyde (3,4‐DHB) and is based on the activity of a commercial available D‐fructose dehydrogenase (FDH) immobilized on an immobilon membrane placed on the top of the electrode surface. Analytical parameters such as enzyme
The effectiveness of isotopically and non-isotopically labelled internal standards in reducing ma... more The effectiveness of isotopically and non-isotopically labelled internal standards in reducing matrix-induced effects is evaluated. The question is addressed in the quantitative analysis by gas chromatography/mass spectrometry (GC/MS) of dimethyl sulphide, chosen as a typical example of volatile sulphur compounds, in wine matrices. When matrix/run effects are not cancelled out the use of a variance component model (VCM) to handle the linear calibrations obtained by regression technique is successful. The method implies the estimation of an overall calibration straight line, which properly takes into account the uncertainty due to different matrices, the calibration run and the measurement error, making the use of an isotopically labelled internal standard not necessary. The obtained results show that the benefits of lowering times and costs for routine analyses compensate for the small increase in uncertainty in the concentration values obtained in the regression analysis and the slight increase in the detection limit.
Soil samples were suspended in a suitable aqueous solvent and a solid phase microextraction (SPME... more Soil samples were suspended in a suitable aqueous solvent and a solid phase microextraction (SPME) fibre was used to sample the headspace (HS) for five volatile chlorinated compounds (VOX). Their determination was made by GC-ECD technique in the splitless mode. Preliminary studies on the effects of methanol and of the sand/clay ratio on the fibre extraction were made. Four experimental factors, namely, extraction time, extraction temperature, pH and NaCl%, able to affect distribution of the analytes among the four different phases, were varied in suitable ranges. A multivariate approach applied to the face centred cube (FCC) experimental design, was used to try to optimise the overall sample response. The suitable set of factors found for the determination of chloroform, 1,2-dichloroethane, trichloroethylene, 1,1 ,2-trichloroethane, 1,1,2,2-tetrachloroethane, was a compromise among the relevant optimal factor sets of the single analytes. Detection limits of 0.003 ng, 0.022 ng, 0.001 ng, 0.015 ng and 0.002 ng were found respectively for the five cited analytes. The method was successfully used to determine the analyte contents in two real soils sampled in an industrial area.
Stir bar sorptive extraction (SBSE)-thermal desorption (TD) procedure combined with gas chromatog... more Stir bar sorptive extraction (SBSE)-thermal desorption (TD) procedure combined with gas chromatography mass spectrometry (GC-MS) and the statistical variance component model (VCM) is applied to the determination of semi-volatile compounds including organochlorine and organophosphorus pesticides in various synthetic and real fruit-based soft drink matrices. When the matrix effects are corrected using isotopically labelled or non labelled internal standard, but matrix/calibration run-induced deviations are still present in the measurements, the adoption of a variance component model (VCM) in the quantitative analysis of various matrices via an overall calibration curve is successful. The method produces an overall calibration straight line for any analyte accounting for the uncertainty due to all the sources of uncertainty, namely matrix-induced deviations, calibration runs performed at different times, measurement errors. Small increases in the detection limits and in uncertainty in the concentration values obtained in the inverse regression face favourably the decrease in times and costs for routine analyses.
Currently used operating conditions for analysing volatile organic compounds (VOCs) by purge-and-... more Currently used operating conditions for analysing volatile organic compounds (VOCs) by purge-and-trap gas chromatography/mass spectrometry (GC/MS) produced non-linear calibration curves with non-uniform variance. Second-order polynomial models therefore had to be used in weighted regression analysis of measurements of replicates spiked at various concentrations. A transparent procedure based on a reported method of very low computational complexity allowed calculation of the parameters of second-order models, confidence bands of regression lines, prediction bands, and confidence intervals of discriminated analyte concentrations. Tolerance intervals were introduced for this last purpose. Critical, detection and quantification levels drawn from the calibration curves were compared with those calculated by the EPA method.
The paper summarizes critically the current approaches for the calculation of the limits of detec... more The paper summarizes critically the current approaches for the calculation of the limits of detection and quantification.
The electrochemical behaviour of acidic and neutral pharmaceutical active compounds (PhACs) was s... more The electrochemical behaviour of acidic and neutral pharmaceutical active compounds (PhACs) was studied by cyclic voltammetry and pulse voltammetric techniques on mercury, carbon nanotube paste, carbon paste and gold electrodes. The best results, in terms of sensitivity, linearity range and detection limits, were obtained by differential pulse voltammetry (DPV) for ofloxacin (LOD 5.2 M), differential pulse polarography (DPP) for clofibric acid (LOD 4.7 M) and normal pulse voltammetry (NPV) for diclofenac (LOD 0.8 M) and propranolol (LOD 0.5 M).
Articles Articles, All fields, Author, Advanced search. Images Images, Journal/Book title, Volume... more Articles Articles, All fields, Author, Advanced search. Images Images, Journal/Book title, Volume, Issue, Page, Search tips. Font Size: Decrease Font Size Increase Font Size. ... a Department of Physical Chemistry, University of Venice, Calle Larga S. Marta, 2137, 30123, Venice, Italy ...
International Journal of Environmental Analytical Chemistry, 2005
A new method for measuring the oxygen permeability (Dk) of common polymer membranes based on an a... more A new method for measuring the oxygen permeability (Dk) of common polymer membranes based on an amperometric sensor was developed. The system was successfully applied to food wrapping and storing films. The method is based on measurement of oxygen concentration variations in time, by means of an amperometric oxygen sensor (Clark electrode), covered with the polymer film and secured with a proper cap. Measurements were carried out under a constant flow of oxygen in order to be independent of initial oxygen concentration. The oxygen permeability of various commercially available food wrapping films was determined according to Fick's first law of diffusion. The method was tested using a reference material of different thickness, Hydrofilcon-43, with a known permeability value. This method gave more reproducible results compared with the ISO measurement systems. The influence of time, use and hydration degree on oxygen permeability was also tested by exposing the tested films for 36 h to UV radiation and keeping them for 50 days in a dryer under vacuum. Results showed that oxygen permeability is proportional to the degree of hydration of the film.
The effect of oxygen on the mediated electrocatalytic oxidation of nicotinamide adenine dinucleot... more The effect of oxygen on the mediated electrocatalytic oxidation of nicotinamide adenine dinucleotide (NADH) by diaphorase from Clostridium kluveri (DI) was studied using cyclic voltammetry, UV-vis spectrophotometry and NMR spectrometry. The enzyme was found to be able to use molecular oxygen as an electron acceptor. NADH could therefore be oxidized by two competitive electron acceptors: a redox mediator, for istance p-methylaminophenolsulfate (MAP) or ferrocene monocarboxylic acid (FMCA) properly added to the solution, and molecular oxygen. Some considerations on the consequence of the use of diaphorase from Clostridium kluveri in amperometric biosensors were also reported.
ABSTRACT The method based on the confidence limits of a regression straight line is applied to th... more ABSTRACT The method based on the confidence limits of a regression straight line is applied to the linear portion of the calibration curve of a biosensor in order to determine the limit of detection. A practical application gives a detection limit of an ethanol biosensor greater than that calculated by using the method of the signal-to-noise-ratio, S/N=3, but the value is more reliable because it accounts for the variability in the response at analyte additions. A simple approximation of the method is also presented.
The diaphorase-catalyzed electrochemical oxidation of NADH with the aid of quinones (MAP) or ferr... more The diaphorase-catalyzed electrochemical oxidation of NADH with the aid of quinones (MAP) or ferrocene derivatives (FMCA) as electron transfer mediators was studied by cyclic voltammetry under variable conditions of concentration polarization of NADH near the electrode surface. The suppression of this polarization was obtained by the redox L-lactate dehydrogenase-catalyzed reaction between L-lactate and NAD . The addition of pyruvate inhibits the formation of NADH owing to the thermodynamically unfavorable (uphill) electron transfer from L-lactate to NAD . The role played by the uphill/downhill character of the last step of the catalytic chain was illustrated by regenerating NADH using the redox couple gluconolactone/glucose with glucose dehydrogenase as catalyst. The influence on the catalytic wave of the presence of a downhill or uphill step between diaphorase and NAD /NADH couple was also rationalized via the digital simulation technique using experimental data reported in the literature.
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