Božidar S. Grabarić

Glucose determination in blood samples using flow injection analysis and an amperometric biosensor based on glucose oxidase immobilized on hexacyanoferrate modified nickel electrode

Abstract A very simple amperometric enzyme-based glucose sensor is applied as detector in flow injection analysis (FIA) of diabetic patients blood glucose. The enzyme glucose oxidase (GOD) is immobilized by a glutaraldehyde/bovine serum albumin crosslinking procedure on the surface of an alkali nickel hexacyanoferrate thin film electrocrystallized on the nickel electrode. An alkali nickel hexacyanoferrate modified nickel electrode catalyzes the reduction of the hydrogen peroxide, formed by selective biocatalytic GOD action on glucose oxidation by oxygen present in sample solutions. The developed glucose sensor has shown good sensitivity at low negative operating potentials ( −300 to −100 mV vs. Ag AgCl ), sufficiently wide linear glucose concentration range (5 μM–2.9 mM), relatively long operating time (during three months of operation the initial sensitivity decreased only 30%) and no influence of the most common interferences present in human blood like proteins, ascorbic and uric acids.

The study of some possible measurement errors in clinical blood electrolyte potentiometric (ISE) analysers

The understanding of the most important sources of error in potentiometric blood analyser which might contribute to better instruments measurement repeatability is very often marginalized in fabrications and daily operation of some commercial blood analysers. In this paper ISEs-potentiometric measurements were performed and validated in Clinical Institute of Laboratory Diagnosis of the Zagreb University School of Medicine and Clinical Hospital Centre, using a carefully designed and constructed fully automated (computerised) homemade ISE-based blood electrolyte analyser constructed with an in-line five-channel flow-through measuring cell. The influence of electrolyte concentration of the salt bridge is reported. Special attention has been paid to the reference electrode design, and constructions which can operate in open liquid junction and membrane restricted liquid junction modes are described.

Determination of small amounts of analytes in the presence of a large excess of one analyte from multi-analyte global signals of differential-pulse voltammetry and related techniques with the signal ratio resolution method

The signal ratio resolution method was applied to the determination by differential-pulse voltammetry and related techniques of two analytes in presence of a large excess of a third analyte in ternary mixtures of known qualitative composition. Using the signal ratio resolution method, a global signal is divided by the individual signal of the major component, multiplied by a factor, in order to obtain a height as close as possible to the estimated contribution of the major component to the global signal. To establish possible influence of resolving the signal on the quantification, simulated differential-pulse polarograms (DPPs) were divided by the individual major component DPP having a different peak current height and different current translation values. Using theoretically simulated DPPs, it was found that two minor components can be determined with a relative error <1% for different resolving parameters (peak current height of resolving functions, current translation values and peak separations). The method was then verified on a system containing Cd at 0.3, Tl at 200 and Pb at 0.5 µmol l–1 using differential-pulse anodic stripping voltammograms. It was shown that using this method and a system with favourable reversibility and amalgam formation, cadmium can be determined in a 200-fold and lead in a 120-fold excess of thallium, with a relative error of <10%. The main advantage of the method over other deconvolution methods is the removal of the contribution of one component from the global signal, revealing the contributions of the other components in a peak-shaped form that is linearly proportional to the analyte concentrations.

Application of adsorptive stripping voltammetry for indirect measurement of nonelectroactive ions using competitive complex formation reactions

It is shown that adsorptive stripping voltammetry can be used for indirect determinations of non-electroactive species. Determination of fluoride was selected to demonstrate this concept which can be used in environmental, clinical and other applications.The fluoride determination is based on competitive complex formation reactions between zirconium and organic ligands, viz. Alizarin Red S (ARS) and Acid Alizarin Violet N (AAVN) and fluoride ions in acidic media (0.1M HNO3 or HClO4). Free ARS ligand is adsorbable on mercury electrode and its voltammetric peak increases with fluoride concentration due to ARS displacement from the Zr-ARS complexes with fluoride forming more stable Zr-fluoride complexes. Using AAVN as a ligand Zr-AAVN complexes are adsorbable on a mercury electrode and the voltammetric peak decreases with increasing fluoride concentration due to formation of more stable Zr-fluoride complexes.The sensitivity of the method is down to 0.1 μM of fluoride. Overall fluoride recovery from synthetic water samples at micromolar concentration level was within 1% of the concentration added, with overall reproducibility of 5 independent measurements of ± 2.5% and ± 1.8% with ARS and AAVN ligand, respectively. Some interferences possibly present in water have been investigated.

On determination of formaldehyde in air by differential pulse polarography and related techniques

SummaryFormaldehyde collection efficiency from air and its determination by DC and DP polarography and linear sweep voltammetry at mercury electrode in basic and acidic solutions are scrutinized. Some statements from older literature about this subject are found to be too conservative. The experimental conditions and reliable procedure for formaldehyde sampling from air, standardization and determination from solution using polarographic and related techniques are presented. Detection limits of formaldehyde determination by these techniques are estimated.ZusammenfassungDie Anreicherung von Formaldehyd aus Luft und dessen Bestimmung mittels DC-und DP-Polarographie sowie mittels linearer Voltammetrie an der Quecksilber-Elektrode in basischem und saurem Milieu wurde eingehend geprüft. Gewisse Feststellungen in der älteren Literatur erwiesen sich als ungeeignet. Die experimentellen Voraussetzungen zur Probenahme, die Standardisierung und Bestimmung aus Lösung mit Hilfe polarographischer und ähnlicher Verfahren wurden angegeben. Die Nachweisgrenzen wurden ermittelt.

Monitoring of pyrocatechol indoor air pollution

Abstract Spectrophotometric and electrochemical methods for monitoring of pyrocatechol (PC) indoor air pollution have been investigated. Spectrophotometric determination was performed using Fe(III) and iodine methods. The adherence to Beers law was found in the concentration range between 0 and 12 μg ml− for iodine method at pH = 5.7 measuring absorbance at 725 nm, and in the range 0–30 μg ml− for Fe(III) method at pH = 9.5 measuring absorbance at 510 nm. The former method showed greater sensitivity than the latter one. Differential pulse voltammetry (DPV) and chronoamperometric (CA) detection in flow injection analysis (FIA) using carbon paste electrode in phosphate buffer solution of pH = 6.5 was also used for pyrocatechol determination. The electrochemical methods allowed pyrocatechol quantitation in submicromolar concentration level with an overall reproducibility of ± 1%. The efficiency of pyrocatechol sampling collection was investigated at two temperatures (27 and 40°C) in water, 0.1 M NaOH and 0.1 M HCl solutions. Solution of 0.1 M HCl gave the best collection efficiency (95.5–98.5%). A chamber testing simulating the indoor pollution has been performed. In order to check the reliability of the proposed methods for monitoring of the indoor pyrocatechol pollution, the air in working premises with pyrocatechol released from meteorological charts during mapping and paper drying was analyzed using proposed methods. The concentration of pyrocatechol in the air during mapping was found to be 1.8 mg m−3 which is below the hygienic standard of permissible exposure of 20 mg m−3 (≈ 5 ppm). The release of pyrocatechol from the paper impregnated with pyrocatechol standing at room temperature during one year was also measured. The proposed methods can be used for indoor pyrocatechol pollution monitoring in working premises of photographic, rubber, oil and dye industries, fur and furniture dyeing and cosmetic or pharmaceutical premises where pyrocatechol and related compounds are in use.

Spectrophotometric determination of beryllium in bronzes with Chrome Azurol S

SummarySpectrophotometric Determination of Beryllium in Bronzes with Chrome Azttrol S Some remarks on the spectrophotometric determination of beryllium in bronzes using Chrome Azurol S (CAS) are given. The determination was performed at pH=6.5 and 10.0 using hexamethylene-tetramine and ammoniacal buffers, respectively. It was demonstrated that the determination of Be with CAS at pH=10.0 is slightly less sensitive, but it has two advantages which are important in obtaining reliable results. First, is the shorter time to reach the equilibrium between Be and CAS, and second, is lower pH sensitivity so that a better precision of the results at pH=10.0 overcompensate the slightly lower sensitivity at this pH in comparison with that at pH=6.5.

Potentiometric Determination of Anionic and Nonionic Surfactants in Surface Waters and Wastewaters

Surfactants are used in almost all branches of industry, in everyday life as home and industrial cleaning compounds, in cosmetics, in pharmaceuticals, in foods, in crop protection, etc. Their waste belongs to the most widespread organic pollutants, representing a global environmental problem, giving thus a great importance for their monitoring in the environment. The existing methodology for the monitoring of anionic and nonionic surfactants in effluents is based on the time-consuming extraction-spectrophotometric procedures connected with numerous drawbacks: considerable chemicals consumption, use and disposal of toxic organic solvents, etc. Potentiometric methods with surfactant sensors (surfactant-selective electrodes) sensitive to the surfactants overcome almost all of these disadvantages offering an attractive alternative to the existing methods. The biggest challenge in surfactant analysis is the determination of low levels in environmental samples.