Analytica Chimica Acta (v.445, #1)

A critical review presented is of the literature concerning the use of acidic solutions of potassium permanganate to generate chemiluminescence during the oxidation of both organic compounds and inorganic species. A brief overview of the reagent’s historical origin is followed by a chronological survey of its analytical applications, from what we believe to be the first report in 1975 through to those published up until mid-2001. This review does not include those papers where potassium permanganate has been used either in alkaline conditions or in conjunction with other chemiluminescence reagents.
Keywords: Review; Chemiluminescence; Potassium permanganate;

The separation of Ru(II)) tris-diimine enantiomers was performed by chiral capillary electrophoresis (CE). A highly sensitive laser-induced fluorescence (LIF) detection system was employed for detection of transition metal complexes present in solution at the low micromolar range. An argon ion laser (457.9 nm, 0.15 mW) was used as an excitation source. The enantiomers of the [Ru(diimine)3]2+ complexes were separated using either potassium antimonyl-d-tartrate or dibenzoyl-l-tartrate (l-DBT) as chiral resolving agents. The concentration limit of detection (LOD) for the tris(1,10-phenanthroline) Ru(II) complex was 12.5 μM and the LOD for the tris(2,2′-bipyridine) ruthenium(II) complex was 1.0 μM. These limits represent an improvement in the overall LOD by three-orders of magnitude relative to that obtained via UV–VIS detection. The CE–LIF system was also used to assess the stereoselective interactions between tris(1,10-phenanthroline) Ru(II) complexes and B-form deoxyribonucleic acid (B-DNA).
Keywords: Capillary electrophoresis; Laser-induced fluorescence; Ruthenium complexes; DNA binding;

Determination of triazine herbicides by capillary liquid chromatography with on-column focusing and temperature gradient by M.E León-González; L.V Pérez-Arribas; L.M Polo Dı́ez; C Panis; M.P San Andrés (29-34).
The combination of capillary liquid chromatography, temperature gradient and on-column focusing with large injection volumes offers a powerful tool for the determination of very low concentrations of triazines and their degradation products when very polar degradation products are present. A temperature gradient from subambient temperatures up to 70°C allows separation of eight triazines in 24 min. The focusing step makes it possible to increase 50 times the sample volume that can be injected into a capillary column. Detection limits (3×noise) are improved by a factor between 50 and 125 to 9 ng l−1 for hydroxyatrazine and 45 ng l−1 for atrazine. The chromatographic method, combined with solid phase extraction, was applied to the determination of eight triazines in ground water.
Keywords: Capillary liquid chromatography; Temperature programming; Column focusing; Triazine herbicides; Water;

A modulated tandem source consisting of a microwave plasma torch and an atmospheric-sampling glow discharge is investigated as a means of generating atomic and molecular mass spectra in a rapid, sequential manner. Conceptually, the pair operates by using the microwave plasma torch to produce atomic ions, and the atmospheric-sampling glow discharge for production of molecular fragmentation mass spectra. The mass spectra of several volatile organic compounds representative of both atomic and molecular modes of operation are presented, and the latter directly compared to mass spectra produced by an electron-impact ionization source. Unique aspects of the experimental construction and performance of this pair are considered.
Keywords: Microwave plasma torch; Atmospheric-sampling glow discharge; Tandem source; Modulated source; Mass spectrometry;

Conductometric formaldehyde sensitive biosensor with specifically adapted analytical characteristics by Sergei V. Dzyadevych; Valentina N. Arkhypova; Yaroslav I. Korpan; Anna V. El’skaya; Alexey P. Soldatkin; Nicole Jaffrezic-Renault; Claude Martelet (47-55).
A conductometric enzyme biosensor for determination of formaldehyde in aqueous solutions has been developed using interdigitated thin-film planar electrodes and immobilised alcohol oxidase from Hansenula polymorpha. The biosensor steady-state response was reached after about 1 min. Its dynamic range can vary from 0.05 to 500 mM formaldehyde and depends on the time of enzymatic membrane cross-linking by glutaraldehyde and on the buffer concentration used. The biosensor developed was not completely specific and selective. It demonstrated no response to primary alcohols and other substrates alone. Unfortunately, the response of this biosensor in a mixture of formaldehyde and methanol was decreased in comparison to the one observed for pure formaldehyde, even if no response was obtained with the interfering specie alone. The operational stability was not <20 h and the relative standard deviation appeared to be about 3%. Moreover, the storage stability was more than 1 month.
Keywords: Conductometric biosensor; Interdigitated planar electrodes; Formaldehyde; Alcohol oxidase;

A new pH selective microelectrode has been developed and tested. The described microelectrode is based on the neutral chromoinophore ETHT 2418 which is incorporated into a liquid membrane of variable composition. The microelectrode is based on an optimized membrane composition and exhibits a linear dynamic response function from pH <1 to 9, a response time <3 s, and resistance of about 35±8 (n=7) GΩ for a tip diameter of about 1 μm. These characters make the electrode suitable for measurements at normal physiological intracellular pH as well as in acidic physiological media. Such electrodes with tip diameters from 0.5 to 5 μm display a sensitivity of 57.5±0.5 mV/pH unit from pH <1 to 9. The discrimination of Na+, K+, Mg2+, and Ca2+ is sufficient for extra- and intracellular measurement of pH at the typical ionic backgrounds encountered. The influence of the composition of the solvent polymeric membrane, the plasticizer, the additives, and the H+-selective carrier on the electrode’s response was studied. The electrode shows a wide dynamic range, high stability and good reproducibility. Finally, pH profiles of a wet instant noodle was revealed for the first time with the presented pH microelectrode. The average pH in the noodle is around 4.14.
Keywords: Neutral carrier; H+-selective ionophores; pH profile; ETHT 2418; Microelectrode; Instant noodle;

Recovery of phenolic compounds from Olea europaea by Danielle Ryan; Helen Lawrence; Paul D. Prenzler; Michael Antolovich; Kevin Robards (67-77).
The recovery of biophenols from olive drupes by simple extraction (free phenolics) was compared to that from acid- and base-treated extracts. Quantitative data are presented for levels of phenols obtained by the different procedures. The major phenol in green olives, oleuropein, was significantly affected by both acid- and base-treatment, and resulted in the liberation of hydroxytyrosol glucoside. The level of hydroxytyrosol glucoside produced after 24 h of acid-treatment was approximately 50 times that produced in base-treated extracts.
Keywords: Olive; Phenolic compounds; Hydrolysis; Liquid chromatography;

In relation to the application of sequential extraction procedures to soil samples or sediments, arise the problems of the non-selectivity of the extractants and the potential for redistribution of trace metals among phases during the extraction, so that these procedures are said to be operational. Our aim was to re-examine these problems by giving a particular attention to the role of H+ ions which are a necessary element of the reactivity of every aqueous reagent, and seem to be one of the main factors to be taken into account in order to explain some of the discrepancies. Some elements explaining the H+ consumption and its relation with final pH will be given and discussed in terms of selectivity and refixation.
Keywords: Sequential extraction; Soil trace metals; Speciation; Soil compartments;

Application of potentiometry to characterize acid and basic sites in humic substances by Maria Marta de Souza Sierra; Karine Arend; Andreia Neves Fernandes; Marcelo Giovanela; Bruno Szpoganicz (89-98).
Acid–base properties of seven fulvic (FA) and two humic acids (HA) from mangrove sediments were investigated by potentiometry using the BEST7 program to resolve the titration curves. With the aim of testing the applicability of this software to humic substances (HS), a mixture containing three benzene-carboxylic acids (3,5-dihydroxybenzoic acid; 2,4-dihydroxybenzoic acid and phthalic acid) presenting pK a values from 2.77 to 10.54 was studied first. The acidity contents as well as the pK a values obtained for each of the three compounds were very close to those of theoretical and reported data, attesting the validity of the application. When the same methodology was applied to HS it was possible to detect two sites, the first being attributed to carboxylic and the second to phenolic groups. Acidity values were very uniform for the set of samples studied and they were within the range usually shown in the literature for HS from distinct environments. Carboxylic acidity ranged from 1.83 to 3.23 meq g−1 and was lower than phenolic acidity (3.23–5.18 meq g−1), both for FA and HA. Such an inverted trend relative to results normally reported is discussed in terms of the origin of the samples as well as of the classical wet chemical methodologies customarily employed to assess HS acid–base properties. The pK a values as an average of HS carboxylic groups ranged from 5.51 to 5.99, the higher values, in general, being relative to HA, probably due to the higher surface electronic density of these molecules compared to FA. The pK a values of phenolic groups ranged from 9.09 to 9.85, the average being near to the pK a of the first catechol deprotonation (9.30). Distribution of HS species as a function of pH are also shown.
Keywords: Acid–base properties; Humic substances; Potentiometry; BEST7 program;

Preparation of a soil reference material for the determination of radionuclides by M Llauradó; J.M Torres; J Tent; A Sahuquillo; H Muntau; G Rauret (99-106).
Method performance in analytical chemistry is checked using certified reference material (CRM). Due to their high production cost, CRMs cannot be used routinely in daily laboratory work, therefore, laboratory reference materials (LRMs) is preferred. This paper describes the preparation of an LRM for the determination of radionuclides in soil. The LRM was prepared by mixing three soils — two from areas affected by the Chernobyl NPP accident, which present condensed radioactivity contamination, and one non-contaminated soil from inland Catalonia. The resulting solid dilution contained condensed radioactive contamination at environmental levels and natural radionuclides ( 137 Cs , 90 Sr , 40 K , 212 Pb , 214 Pb , 208 Tl , 214 Bi and 228 Ac ). Bulk homogeneity was checked before soil was bottled and, once bottled, final homogeneity and stability studies were performed. Analysis of variance was carried out with the results. No statistically significant differences were observed for within- or between-bottle results. Neither the storage temperature nor the time of the determination after bottling affected the results. Therefore, the material prepared is considered homogeneous and stable and will be used in a future intercomparison exercise for radiochemical laboratories in Spain.
Keywords: Soil reference material; Radionuclides;

A high-temperature catalytic oxidation (HTCO) method was evaluated and compared with the Kjeldahl method for determining total dissolved N (TDN) in 0.025 M K2SO4 soil extracts used to assess soil microbial biomass nitrogen. First the HTCO method was evaluated for routine analysis for TDN in K2SO4 solutions. Nitrogen recoveries measured by HTCO exceeded 98% for compounds containing organic and inorganic N and for concentrations up to 10 mg N l−1. The proposed indirect injection of sample into the furnace safeguards the catalyst and quartz combustion tube. In these conditions, the drift of signal sensitivity during sequence analysis was negligible implying that HTCO can be used for the routine analysis of samples in a 0.025 M K2SO4 matrix. The HTCO and Kjeldahl methods were then compared for determining soil microbial biomass nitrogen in different types of soil using the fumigation-extraction method. The TDN concentrations in K2SO4 soil extracts measured with both methods were well correlated. Some discrepancies however, were, observed for TDN concentrations >10 mg N l−1 due to a probable underestimation of N in the soil extracts with the Kjeldahl method. The calculated extractable microbial biomass values resulting from the difference in TDN between control and fumigated soils were in good agreement for both methods. HTCO thus provides a very rapid and reliable method for measuring TDN in K2SO4 soil extracts used to determine soil microbial biomass nitrogen.
Keywords: Microbial biomass nitrogen; Total dissolved nitrogen; High-temperature catalytic oxidation; Kjeldahl method;

New way of application of the bromate–bromide mixture in kinetic analysis by G. López-Cueto; M. Ostra; C. Ubide (117-126).
The bromine generated in situ by the bromate–bromide mixture has usually been used in kinetic analysis to determine either individual species that give reaction with bromine or the total concentration of mixtures of those analytes. In this paper the bromate–bromide mixture is proposed as a reagent for multicomponent kinetic determinations. Mixtures of acetylsalicylic acid (ASA) and paracetamol (AAP) have been used to test the discriminating ability of reactions with bromine. The reaction between bromine and AAP is fast and the reaction between bromine and ASA is negligible. However, ASA slowly hydrolyzes to yield salicylic acid (SA) and acetic acid, and the reaction between bromine and SA can be considered fast in the reaction conditions. This complex behaviour contains enough information to resolve mixtures of ASA and AAP after applying partial least squares regression (PLS) to the kinetic photometric data. After optimization, errors around 5–6% were found for the determination of ASA and AAP. Quimiometric considerations on the calibration models are made. The method has been successfully applied to the determination of ASA and AAP in pharmaceuticals.
Keywords: Multicomponent kinetic determinations; Partial least squares regression; Principal component analysis; Bromate–bromide mixture; Acetylsalicylic acid; Paracetamol;