Analytical and Bioanalytical Chemistry (v.355, #1)

To clarify the mechanism of mercury adsorption on gold surfaces thin epitaxial gold films have been exposed to trace amounts of gaseous mercury under laboratory conditions for different periods of time. The changes in the surface morphology of the thin films caused by the exposure have been studied by scanning tunneling microscopy (STM). The evolution of the surface structures with time has been also investigated, in the course of a few days after the exposure. The adsorption of mercury on the gold surfaces has caused drastic changes in the morphology of the surfaces. Pits and islands of 2 to 30 nm in diameter have appeared on the surface, their size and density per unit area depending on the amount of exposure to mercury. The formation of pits and islands followed a certain path of events.

Space and time-resolved studies of laser induced plasmas in air at atmospheric pressure are presented. Photovoltaic solar cells have been used as samples. The second harmonic (532 nm) of a Nd: YAG laser at an irradiance of 18 × 1012 W/cm2 has been used. The precise focus of the beam allows a microanalysis at a 0.02 mm2 surface area working in single-shot mode. The use of an intensified charge-coupled device (CCD) detector has allowed time-resolved studies in both imaging or spectroscopy modes. The two-dimensional capability of the CCD has enabled the study of atomic and ionic species distribution along the plume. Most data have been recorded using single-laser shot experiments. Spectral lines have been assigned to transitions in atomic components of the material under investigation in the neutral or ionic states of the corresponding atoms. Effects of delay in improving spectral resolution and some examples of spectral characterization of species as a function of its decay are shown.

Laser induced breakdown spectroscopy (LIBS) is applied to analyze aqueous solutions of Li+, Na+, Ca2+, Ba2+, Pb2+, Cd2+, Hg2+ and Er3+ and suspensions of ErBa2Cu3Ox particles (d = 0.2 μm). An excimer (308 nm) pumped dye laser with laser pulse at 500 nm and pulse energy at 22 ±2 mJ is used to produce plasma in aqueous solution. Plasma emission lines of the elements are detected by a photodiode array detector. Detection limits of the metal ions are 500 mg/l for Cd2+, 12.5 mg/l for Pb2+, 6.8 mg/l for Ba2+, 0.13 mg/l for Ca2+, 13 μg/l for Li+ and 7.5 μg/l for Na+. No mercury and erbium emission can be detected, even at Hg2+ and Er3+ concentrations of up to the g/l range. On the other side, for Er in suspensions of ErBa2Cu3Ox particles a more than 103 times higher sensitivity is found than for dissolved Er3+. This result gives a possibility to analyze colloid-borne metal ions with an increased sensitivity.

Hexacyanoferrate-based composite ion-sensitive electrodes for voltammetry by Heike Düssel; Aleš Dostal; Fritz Scholz (21-28).
Composite electrodes made of graphite, paraffin and metal hexacyanoferrates exhibit a voltammetric response of the hexacyanoferrate ions, the potential of which depends linearly on the logarithm of concentration of alkali and alkaline-earth metal ions. This behaviour has been observed on account of the fact that the electrochemical reaction is accompanied by an exchange of these ions between the solution and the zeolitic lattice of the hexacyanoferrates for charge compensation. The voltammetric determination of the formal potential of these electrodes in a solution allows the quantitative analysis of the ions which are exchanged between the metal hexacyanoferrates and the aqueous solutions. Iron(III), copper(II), silver(I), nickel(II) and cadmium(II) hexacyanoferrates have been studied for the determination of H+, Li+, Na+, K+, Rb+, Cs+, NH4su{+}, Mg2+, Ca2+ and Ba2+. In some cases, the selectivity constants are as low as 3·10−4, or even so small that their exact value is inaccessible. Electrodes made of iron (III), copper (II), silver (I), nickel (II) and cadmium (II) hexacyanoferrates are most suitable for the determination of potassium ions. Electrodes with nickel (II) and cadmium (II) hexacyanoferrates are also suitable for the determination of caesium ions. The working range of the electrodes also depends on the conductivity of the solutions and can range from 10−5 to 1 moll−1. Typical standard deviations of the potential measurements are 3 mV.

First- and second-derivative spectrophotometric methods for the simultaneous determination of aluminium and iron in their mixtures are described. The methods are based on the colored complexes formed by aluminium and iron with hematoxylin in the presence of cetyltrimethylammonium bromide as a surfactant. The zero-crossing method has been utilized to measure the first- and second-derivative value of the derivative spectrum. Aluminium (0.05–1 μg ml−1) could be determined in the presence of iron (0.09–1.6 μg ml−1) and vice versa. The detection limits of aluminium and iron are 0.01 and 0.09 μg ml−1, respectively in the first-derivative mode and 0.014 and 0.1 μg ml−1 in the second-derivative mode. The proposed method has been applied to the simultaneous determination of aluminium and iron in glasses, phosphate rocks, cement and magnesite alloy.

A selective and sensitive spectrophotometric method for the determination of Th(IV) has been based on the reaction with thorin and subsequent extraction of the red-orange coloured complex with N-hydroxy-N,N′-diphenylbenzamidine (HDPBA) in benzene as floated complex at pH 2.2. The complex in ethanol exhibits a maximum absorbance at 495 nm, with a molar absorptivity of 6.0 × 104 lmol−1 cm−1, with a Sandell’s sensitivity of 3.9 × 10−3 μg cm−2. The method follows Beer’s law up to 3.0 μg Th(IV)ml−1. None of the common cations and anions tested interfere. The detection limit of the method is 0.04 μg Th(IV) ml−1, the RSD (n =10) is 1.4%. The method has been successfully employed for the determination of thorium in various standard and monazite samples.

In hydraulic high-pressure nebulization (HHPN) an aerosol is produced by means of an HPLC-pump and a special nebulization nozzle, applying a pressure of about 200 bar. This spray technique has been employed for sample introduction of mineral oil samples in flame atomic absorption/flame emission spectrometry. The determination of the trace elements Al, Cr, Cu, Fe, K, Na, Ni, Pb, Si and V has been investigated. Viscosity hardly acts upon the sensitivity of the determination, thereby avoiding a time consuming dilution of oil samples. By means of two interconnecting sampling valves a calibration method based on the standard addition technique can be performed which is both simple and easy to carry out. In samples of used oils, results for Cu and Pb equalled those of XRF-analysis. Regarding Fe traces, data obtained from AAS and XRF measurement correlate. In comparison with sample uptake by pneumatic nebulization, which is restricted to diluted oil samples, detection limits decrease by a factor of 2 to 4, indicating the dilution required in pneumatic nebulization.

The determination of cadmium in different sample types has been carried out by electrothermal atomization atomic absorption spectrometry with D2-background correction using a unpyrocoated graphite tube, after pressurized microwave-assisted digestion. Five chemical modifiers [(NH4)2HPO4, Pd(NO)3)2, Ni(NO3)2, thiourea and Triton X-100] have been assayed and nickel nitrate has been found to be most effective for an accurate determination of cadmium in mussel tissue, pig kidney and sewage sludge. The characteristic mass of the method is of the order of 1 pg and the limit of detection is lower than 0.1 ng/ml.

A reversed-phase PB LC-MS method was used for the determination and unequivocal identification of vitamin K1 in some vegetable samples. The method was also applied to the identification of other constituents in the food analyzed. LC-MS experiments were carried out in both EI and negative-ion CI modes. Preliminary sensitivity studies on vitamin K1 showed a detection limit of 2 ng (signal-to-noise ratio = 3) in negative-ion operation and in single-ion monitoring at m/z 450. Quantitative results obtained with LC-MS for the extracts of four vegetables were compared with those of LC-UV analyses performed at 247 nm.

Three approaches based on continuous flow methodology are assessed for the purpose of extending the dynamic range of flame atomic absorption spectrometry. The determination of several elements in infant liquid and powdered milk and water samples is used to check the performances of the manifolds. Two of the systems are fully computer-controlled and permit a calibration graph to be obtained by using a single standard solution. The results confirm that continuous flow methodology is a reliable alternative to the time-consuming common dilution procedures based on glassware. Since the systems are versatile and permit a wide range of degrees of dilution to be obtained, they can be easily adapted for the automated or semi-automated analysis of other liquid samples which are too concentrated to be aspirated directly into the atomic absorption spectrometer.

Chemometrical approaches to evaluate analytical data from aquatic macrophytes and marine algae by J. A. Stratis; V. Simeonov; G. Zachariadis; T. Sawidis; P. Mandjukov; S. Tsakovski (65-70).
The possibility of using aquatic macrophytes and algae as bioindicators of water pollution is investigated. The use of cluster analysis enables the treatment of the analytical data in a global way, revealing hidden clusters of similar behaviour between various biological species or sampling sites. A great number of species was collected from four rivers and fourteen coastal sites in Greece and were analysed for zinc, copper, cadmium, lead and manganese. The analytical data obtained were treated by hierarchical clustering, for marine algae and aquatic macrophytes separately.

Biomimetic oxidation of plant protecting agents by Till Einig; Gerhard Görlitz; Bernd Neidhart (71-77).
The suitability of two in vitro oxidation systems as chemical models for the biological degradation of plant protecting agents has been investigated. As representative herbicides diclofop, fenoxaprop, isoproturon, linuron and monolinuron have been oxidised by two systems, the Fentons’ reagent and the ascorbic acid oxidation system (AAOS) and the results compared to those of the known metabolic pathways of these compounds. The herbicides have been oxidised by Fentons’ reagent (hydroxy radicals). The main products were isolated by preparative scale HPLC and identified with 1H-NMR and MS. Some of the products have been identified by comparing their retention times and UV/Vis-spectra to those of standard compounds. Several products known from biological degradation are also found after chemical oxidation, however, notable differences between the two pathways have been observed, for instance in the case of diclofop. Oxidation by the AAOS leads to comparable results. Reaction rates for the oxidation with the AAOS have been studied and compared with data known from degradation studies of the herbicides in soil. Compounds which are slowly degraded in soil are oxidised more slowly in the biomimetic process than those with a fast degradation in soil.

Entrapment of both glucose oxidase and peroxidase in regenerated silk fibroin membrane by Yongcheng Liu; Haiying Liu; Jianghong Qian; Jiaqi Deng; Tongyin Yu (78-82).
Two enzmyes, glucose oxidase and peroxidase, were for the first time simultaneously immobilized in regenerated silk fibroin membrane. The structure and morphology of the regenerated silk fibroin membrane containing both glucose oxidase and peroxidase were investigated with IR spectra and SEM. The bienzymes do not change the structures of the regenerated silk fibroin in the membrane, which has an islands-sea structure. For the first time, an amperometric methylene green mediating sensor for glucose based on co-immobilization of both glucose oxidase and peroxidase in regenerated silk fibroin was constructed. Cyclic voltammetry and amperometry were used to test the suitability of methylene green shuttling electrons between peroxidase and the glassy carbon electrode. The bienzyme-based system offers fast response and high sensitivity of the sensor to glucose. The effects of pH, temperature, and the concentration of the mediator on the response current were evaluated, and the dependence of the Michaelis-Menten constant Km aPP on the concentration of the mediator was investigated.

An algorithm is described for the theoretical calculation of the slopes of calibration lines for the elements of the K-series in multi element X-ray fluorescence analysis of thin films using polychromatic excitation with X-ray tubes producing widely differing primary radiation intensity profiles. The mathematical equations used to calculate slopes as a function of atomic number are based on the fundamental relationship between fluorescent intensity and atomic number, fluorescent yield, concentration and mass absorption coefficients of the analyte for primary radiation. A normalisation procedure based on a single known slope in the series ensured that the calculated slopes were correct for the particular measuring conditions.

The preparation of a fast response Ag/Ag2SO4 reference electrode by G. Finoly; W. Leidert; M. Bickel (86-86).
A procedure for the preparation of a fast response Ag/Ag2SO4 reference electrode to be used for the detection of the endpoint of a coulometric titration is described.

The difference in the peak potentials of In(III) and Cd(II), whose reduction potentials are very close to each other, becomes large in the presence of poly β-cyclodextrin in sodium perchlorate medium. The relationships between the peak currents for these two ions and their concentrations are linear, suggesting that the simultaneous determination of the ions is possible in the presence of this reagent.

Determination of zinc by flow injection with fluorimetric detection in a micellar medium by N. Gañán Gutiérrez; F. Sánchez Rojas; J. M. Cano Pavón (88-91).
A room-temperature flow injection spectrofluorimetric method is presented for the determination of Zn(II), based on the use of salicylaldehyde thiocarbohydrazone in the presence of Triton X-100 and sodium acetate-acetic acid buffer. Various physical and chemical variables affecting the reaction in the flow system were evaluated. The proposed method is very selective. The calibration graph is linear over the range 10–1000 ng/ml, with a detection limit of 5 ng/ml and a relative standard deviation at the 50 ng/ml level of 1.8 %. The method was successfully applied to the determination of Zn(II) in drinking waters and biological samples.

Three methods for the determination of chlorophenols in surface water have been evaluated. Two of them utilize solid phase extraction followed by derivatization either in aqueous phase or in organic solvent. The third method is based on liquid-liquid extraction with simultaneous in-situ derivatization. This method was found to be not applicable for samples of surface water. The surfactants present in the samples prevent the separation of the hexane layer at a ratio of 1: 20 or higher. Both methods using solid phase extraction gave acceptable results; however, the derivatization in aqueous phase proved its priority.

A solvent-soluble membrane filter is proposed for the simple and rapid preconcentration and spectrophotometric determination of ascorbic acid based on the reduction of 1, 10-phenanthroline (phen)-iron (III), which is collected on a nitrocellulose membrane filter as an ion-associate of the cationic complex of tri,phen-iron (II) [ferroin, Fe(phen) 3 2+ ] with an anionic surfactant (of dodecyl sulfate). The ion-associate collected is dissolved in a small volume of 2-methoxyethanol together with the filter. The colour intensity is measured at 510 nm against the reagent blank and is proportional to the content of ascorbic acid in the range 2.5–50 μg ascorbic acid in 5 ml of solvent with excellent reproducibility (RSD 3.2% for 200 μg 1−1 ascorbic acid), the enrichment factor achieves 100-fold and detection limits better than 2.0 μg 1−1 can be obtained. Diverse components of organic and inorganic compounds normally present in fruits, vegetable, beverages and urine do not interfere. The recoveries of the ascorbic acid added to the samples are quantitative.

Quantitative determination of transferrin in cerebrospinal fluid using an enzyme linked immunosorbent assay by G. F. Van Landeghem; P. C. D’Haese; L. V. Lamberts; M. E. De Broe (96-97).
An enzyme linked immunosorbent assay (ELISA) based method for the determination of transferrin in cerebrospinal fluid (CSF) is described. This method allows transferrin determinations in ultra-small (≤ 5 μL) sample volumes. The proposed method offers the possibility to determine transferrin at very low concentrations at which existing methodologies fail because of their insufficient detection limits. The accuracy of the proposed technique was validated by comparing the results of 20 CSF samples obtained by ELISA to those measured by nephelometry yielding mean ± SD values of 21.1 ± 5 mg/L and 20.6 ± 6 mg/L, respectively (y = 1.13X – 2.97, r = 0.899). The interassay CV was below 10% whereas the detection limit was 2.9 μg/L.