Showing papers in "Analytical and Bioanalytical Chemistry in 1996"

An Energy-dispersive Miniprobe Multielement Analyzer (EMMA) for direct analysis of Pb and other trace elements in peats.

Abstract: An Energy-dispersive Miniprobe Multielement Analyzer (EMMA) was designed and constructed for sensitive, rapid, and non-destructive analysis of trace elements (As, Cr, Cu, Fe, Ga, Ge, Hf, Mn, Ni, Pb, Rb, Se, Sr, Th, Y, U, Zn) in small (e.g. 50 μm) samples such as individual mineral grains from rocks. An alternative configuration of the EMMA instrument is described here for use with larger samples such as powders of coal, soil, sediments, and plant materials. To minimize heterogeneity problems, a larger X-ray beam size (0.1 × 6 mm) was used by installing a different collimator, and the sample holder rotated 25 times per minute. Using this approach, Rb, Sr, Cu, Zn and Pb were measured in peat samples collected from bogs in Switzerland and northern Scotland. The detection limit for Pb, for example, is approximately 0.3 μg/g which is one order of magnitude better than conventional XRF analyzers. For comparison, Pb was also measured in acid digests of the same samples using GFAAS. The Pb results obtained using EMMA are comparable to the GFAAS data for the continental peat samples. However, in the Cl-rich samples from the maritime bogs, the GFAAS signal was strongly suppressed, and an accurate comparison of the two methods was not possible. The EMMA technique, therefore, has three advantages over conventional GFAAS: first, no sample dissolution is required; second, several elements of interest are determined simultaneously; and third, the EMMA technique is not subject to matrix interferences.

Laser induced breakdown spectroscopy (LIBS) as an analytical tool for the detection of metal ions in aqueous solutions

Abstract: Laser induced breakdown spectroscopy (LIBS) is applied to analyze aqueous solutions of Li(+), Na(+), Ca(2+), Ba(2+), Pb(2+), Cd(2+), Hg(2+) and Er(3+) and suspensions of ErBa(2)Cu(3)O(x) particles (d=0.2 microm). 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 Cd(2+), 12.5 mg/l for Pb(2+), 6.8 mg/l for Ba(2+), 0.13 mg/l for Ca(2+), 13 microg/l for Li(+) and 7.5 microg/l for Na(+). No mercury and erbium emission can be detected, even at Hg(2+) and Er(3+) concentrations of up to the g/l range. On the other side, for Er in suspensions of ErBa(2)Cu(3)O(x) particles a more than 10(3) times higher sensitivity is found than for dissolved Er(3+). This result gives a possibility to analyze colloid-borne metal ions with an increased sensitivity.

Comparison of metal concentrations in three species of mosses and metal freights in bulk precipitations

Abstract: Concentration of 25 trace metals in mosses (Hylocomium splendens, Pleurozium schreberi and Hypnum cupressiforme) are compared with bulk deposition freights (Bergerhoff method) at 3 sites in Switzerland, one on the plateau, a second in the northern prealps and a third in the southern alps. The three moss species are interchangeable and the atmospheric background deposition can be estimated with sufficient accuracy for Ag, Al, As, Cd, Ce, Co, Cr, Cu, Fe, Ga, Ge, La, Li, Mo, Nb, Ni, Pb, Th, Ti, U, V, W, Y, Zn. For Hg this study does not give definite results. No seasonal differences in moss concentrations from spring to autumn can be shown.

Tributyltin biomonitoring using prosobranchs as sentinel organisms.

Abstract: Tributyltin (TBT) compounds, some of the most toxic xenobiotics, produce a variety of pathological reactions in animals. A reliable biomonitoring method to assess the degree of environmental TBT pollution has been described based on investigations of virilization phenomena in prosobranch snails (Mollusca: Gastropoda). Examples are the imposex phenomenon in marine and freshwater species, the intersex reaction in littorinids and the reduction of female sexual glands and offspring numbers in further species resulting mainly in a sterilization of females. The degree of imposex or intersex in populations is determined by different biomonitoring indices which allow to assess the TBT pollution of the environment at low costs with high precision. The effectiveness of TBT legislations is analysed by extensive surveys in France and Ireland indicating that there is still a continuing threat to sensitive marine organisms. TBT disturbs the biosynthesis of steroid hormones on the level of estrogen biosynthesis. The observed virilization phenomena seem due to an inhibition of the cytochrome P-450 dependent aromatase by this organotin compound.

Platinum metal concentrations in urban road dust and soil in the United Kingdom

Abstract: Concentrations of Pt, Pd, Rh and Au in soils and road dusts taken from areas of high and low traffic flows in the London Borough of Richmond and from a section of the Kingston bypass (A3) at New Malden, Surrey, have been measured. High concentrations of platinum are associated with high traffic densities. Samples taken from streets of lower traffic flows were found to contain the lower concentrations of the ranges. These values correlated well with the levels of lead which were also high at roundabouts. If the preliminary results obtained in this study apply more generally throughout the UK, then the potential for exposure to enhanced levels of Pt would appear to be higher for road users and for those living in urban environments or along major highways.

Hexacyanoferrate-based composite ion-sensitive electrodes for voltammetry.

Abstract: 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.

Determination of boron isotopic variations in aquatic systems with negative thermal ionization mass spectrometry as a tracer for anthropogenic influences.

Abstract: A technique for precise boron isotope ratio measurements with a high detection power has been developed by negative thermal ionization mass spectrometry (NTIMS). Relative standard deviations in the range of 0.03-0.3% have been obtained for the determination of the 11 B/ 10 B isotope ratio using nanogram amounts of boron. Ba(OH) 2 has been applied as ionization promoter for the formation of negative thermal ions. By adding MgCl 2 better reproducibilities of the measurement have been achieved. A possible interference of BO 2 - ions at mass number 42 by CNO - could be excluded by the sample preparation technique used. Contrary to other NTI techniques no dependence of the measured isotope ratio on the boron amount used has been observed. Anthropogenic and natural saline influences in ground water have been successfully identified by boron isotope ratio determinations with this NTIMS method, due to the different isotopic composition of boron in natural and anthropogenic substances. In sewage, the boron isotope ratio is substantially influenced by washing powder, which contains low 11 B/ 10 B ratios (expressed in δ 11 B values normalized to the standard reference material NIST SRM 951). In contaminated ground water, low δ 11 B values are normally correlated with high boron and high chloride concentrations. On the other hand, δ 11 B shifts to higher values in less contaminated samples. For ground water with saline influences, only the δ 11 B determination, and not the boron or chloride content, allowed the correct identification of this natural source of contamination.

Atmospheric heavy metal pollution in Slovenia derived from results for epiphytic lichens.

Abstract: In 1992, a monitoring survey has been started on the national scale in Slovenia using the epiphytic lichen Hypogymnia physodes (L.) Nyl. The primary aim has been to analyse lichens using the k0-based INAA method to obtain information about the levels of elements in the atmosphere and to identify significant pollution sources. Monte Carlo-Assisted Factor Analysis was applied to a data set of the 28 elements As, Ag, Ba, Br, Ce, Cd, Co, Cr, Cs, Fe, Ga, Hf, Hg, K, La, Mo, Na, Rb, Sb, Sc, Se, Sr, Sm, Tb, Th, U, W and Zn, which have been selected from the elements determined as the most important ones for the identification of pollution sources. A Monte Carlo approach has been used to give more insight into the uncertainties and significance levels of the factor analysis results. It has been found that concentration patterns in lichens yielded 9 factors (source types) which are presented and discussed in detail. The geographical patterns of the contributions of all factors are also shown.

Vitality fertilization of Scots pine stands growing along a gradient of heavy metal pollution: short-term effects on microbial biomass and respiration rate of the humus layer

Abstract: In 1992 forest vitality fertilization experiments were established on a heavy metal deposition gradient with four treatments in three replications at distances of 0.5, 4 and 8 km from a Cu-Ni smelter in order to estimate their impact on the disturbed forest ecosystem. The increase in Cu concentration in the humus (F/H) layer of the Calluna site type Scots pine (Pinus sylvestris) stands from ca. 300 to 8000 mg kg–1 d.m. (dry matter) along the 8 km long transect towards the smelter resulted in declining soil microbial biomass and soil respiration activity. Three independent measurements of microbial biomass: Cmic-FE (fumigation extraction), Cmic-SIR (substrate induced respiration), and ATP have been used together with an indicator of fungal biomass (ergosterol) and microbial activity (soil respiration). Within this Cu pollution range, all the measured microbial biomass levels declined to 10%–28% of the control plot values and activity assessed by respiration was lowered to 16%. Liming has increased the Cmic-SIR and respiration rate. Treatments with test fertilizer, made from grounded apatite, did not result in different microbial biomass and respiration rate values compared to the respective controls along the whole gradient. Nitrogen + lime treatments resulted in similar changes to lime alone. No changes, as compared to the respective control, could be detected with nitrogen fertilization at the less polluted end of the gradient.

Decomposer animal communities in forest soil along heavy metal pollution gradient.

Abstract: Responses of soil decomposer animals to heavy metal contamination and to concomitant changes in organic matter quality and quantity and in soil microbial biomasses have been studied along a pollution gradient from a Cu-Ni smelter. Samples have been taken separately for nematodes, enchytraeids and microarthropods 0.5, 2 and 8 km from the smelter. Special attention has been paid to the changes in the collembolan fauna. The sampling sites have been located in homogeneous Scots pine (Pinus sylvestris) forests with podsolic soil profiles. In addition, an experiment has been carried out in which intact soil cores have been transferred in mesh baskets between the sites 2 and 8 km from the smelter (control samples have been transferred within the sites). Although most soil animals seemed to be quite resistant to direct and indirect effects of heavy metals, results indicate that certain soil animals like enchytraeids can be useful and easy to monitor when the effects of heavy metals on soil decomposition systems are assessed.

Chlorophyll fluorescence biosensor for the detection of herbicides.

Abstract: A biosensor is described for the detection of triazine and phenylurea herbicides in drinking water by kinetic measurements of endogenous chlorophyll fluorescence in isolated chloroplasts from higher plants. The pocket-size device uses a diode laser for simultaneous excitation of sample and reference channels, and photodiodes for detection of the emitted light. The biological material can be supplied as a freeze-dried powder, stable for 21 days at room temperature, for 6 weeks at 4 °C or for at least 9 months at −20 °C. The detection of 0.1 μg/l of a single herbicide, as required by European Community legislation on drinking water quality, can be achieved without prior extraction of the sample.

Non-spectral interferences encountered with a commercially available high resolution ICP-mass spectrometer.

Abstract: Results of a systematic study concerning non-spectral interferences observed with a commercially available high resolution ICP-mass spectrometer are reported and compared to observations made with a quadrupole-based instrument. In general, matrix effects were observed to be to a large extent comparable for both instruments used. In all cases, the matrix-induced signal suppression or enhancement was seen to depend in a regular way on the mass number of the nuclides monitored. In most cases, the ionization potential of the nuclides has little or no influence on the extent of suppression or enhancement. For As, Se and Te, the introduction of 2.5 % ethanol, 0.5 mol/l H2SO4, or to a lesser extent 0.5 mol/l H3PO4, leads to an exceptional increase in the signal intensity for both instruments. Registration of signal behaviour plots (signal intensity as a function of the nebulizer gas flow rate) in different matrices revealed that both the height of the plot and the optimum nebulizer gas flow rate are a function of the matrix composition. Finally, no indication was found that the acceleration of the extracted ions over 8000 V with the high resolution instrument would lead to an alleviation of space charge effects when compared to a quadrupole-based ICP-mass spectrometer.

Heavy metals as stressing factors in the red wood ants (Formica polyctena) from industrially polluted forests.

Abstract: Relations between metal contaminations in social groups of ants from colonies of Formica polyctena, from 5 localities variously contaminated by industrial pollution, and their metabolic and detoxifying strategies have been investigated. Cd, Pb, Zn, Mn, Cu levels have been measured in social groups of workers and pupae throughout the season. Patterns of metabolic, transport and detoxifying enzymes have been assayed and phosphoadenine nucleotides and the energy charge (AEC) have been determined. The metal content is a measure of the level of contamination and has been the highest in foragers returning to the nest. Body burdens of Cd, Pb and Zn diminished progressively from the surface workers to those from the inner part of the hill. The concentration of total adenylates was slightly lower than stated in Finnish ants poisoned with Cd, but the AEC index was always above 0.8, with high variations between the social groups. Carboxylesterases showed a positive correlation of activity pattern with the metal load in foraging workers, with the highest value for cadmium load in ants from a locality in the middle of a pollution gradient. The pattern of superoxide dismutase activity has been site-dependent, but it did not correlate well with the metal load in workers.

Determination of Platinum-Group Elements (PGE) from catalytic converters in soil by means of docimasy and INAA.

Abstract: The nickelsulfide fire assay (docimasy) for the enrichment of platinum-group elements (PGEs) has been modified for the use with small samples and combined with instrumental neutron-activation analysis (INAA). This procedure has been applied to the determination of PGEs exhausted from catalytic converters and deposited in soil near the Wiesbadener Kreuz (highway A3, Frankfurt-Koln). Our results show a considerable enhancement of the Pt (up to 330 ng/g), Pd (6.6 ng/g) and Rh (7.5 ng/g) contents close to the highway.

Metal body burdens and detoxifying enzymes in spiders from industrially polluted areas.

Abstract: Detoxifying enzymes have been assayed and metal concentrations have been monitored in four species of spiders from differently contaminated localities in Southern Poland. A behavioural feeding activity and the life style decide on sensitivity and vulnerability of spiders. Wolf-spiders, more active than the web-spinners, cumulate higher amounts of metals, reflecting quantitatively and qualitatively the pollution level in their environment. Detoxifying systems in spiders appeared inducible and efficient to maintain normal physiological responses. Within web-spinning spiders the linyphiids seem to be the most effective regulators of metal burdens. Their detoxifying capabilities correlate well with increased industrial contaminants. The analysis of biochemical biomarkers of exposure confirmed earlier ecological findings that species of the family Linyphiidae are more favoured than the Araneidae. Differences in their feeding activity, behaviour of web-spinning and the size of animals would explain alterations in detoxifying abilities between Meta segmentata and Araneus diadematus.

Direct quantitative analysis of peptides using matrix assisted laser desorption ionization.

Abstract: The protocol and various matrices were examined for quantification of biomolecules in both the low ca. 1200 amu and mid mass 6000–12000 amu ranges using an internal standard. Comparative studies of different matrices of MALDI quantitative analysis showed that the best accuracy and standard curve linearity were obtained for two matrices: (a) 2,5-dihydroxybenzoic acid (DHB) combined with a comatrix of fucose and 5-methoxysalicylic acid (MSA) and (b) ferulic acid/fucose. In the low mass range, the quantitative limit was in the 30 fmol range and in the mid mass range the quantitative limit was in the 250 fmol range. Linear response was observed over 2–3 decades of analyte concentration. The relative error of the standard curve slope was 1.3–1.8% with correlation coefficients of 0.996–0.998.The main problem for quantitative measurement was suppression of the signal of the less concentrated component (analyte or internal standard) by the more concentrated component. The effect was identified with saturation of the matrix by the analyte. The threshold of matrix saturation was found to be in the range of 1/(3000–5000) analyte/matrix molar ratio. To avoid matrix saturation the (analyte+internal standard) to matrix molar ratio should be below this threshold. Thus the internal standard concentration should be as low as possible.DHB/MSA/fucose and ferulic acid/fucose matrices demonstrated good accuracy and linearity for standard curves even when the internal standard had chemical properties different from the analyte. However, use of an internal standard with different chemical properties requires highly stable instrumental parameters as well as constant (analyte+internal standard)/matrix molar ratio for all samples.

A FIA-system for As(III)/As(V)-determination with electrochemical hydride generation and AAS-detection.

Abstract: A flow-injection system with electrochemical hydride generation and atomic absorption detection for As(III)/As(V) determination is described. A simple electrolytic flow-through cell has been developed and optimized. Several cathode materials like Pt, Ag, Cu, C and Pb have been tested. The influence of the electrolysis current, concentration of sulfuric acid, carrier stream, flow rate, sample volume and interferences by other metals on the arsenichydride generation have been studied. For the determination of total inorganic arsenic, As(V) is reduced to As(III) on-line by postassium iodide or L-cysteine at 95° C. The influence of the temperature and the reduction medium on this pre-reduction step has been tested. The calibration curve is linear in the range of 5 to 50 μg/L for As(III) and total inorganic arsenic and shows a higher sensitivity than in case of reduction with sodium tetrahydroborate. The detection limit is 0.4 μg/L for As(III) and 0.5 μg/L for total inorganic arsenic at a sample volume of 1 mL.

Toxicity of cadmium species on luminescent bacteria.

Abstract: The toxicity of cadmium compounds against luminescent bacteria has been measured using the MicrotoxR toxicity bioassay and has been related to the cadmium species. Since the MicrotoxR test is carried out in NaCl (2%) and cadmium forms stable chloro complexes, NaNO3 and NaClO4 have been tested successfully as alternative to sodium chloride to provide the adequate osmotic protection of the bacteria. The influence of medium and ionic strength as well as different exposure times on EC50 values has been evaluated.

Particle analysis of car exhaust by ETV-ICP-MS

Abstract: Particulates of platinum group elements (Pt, Rh, Pd, Ir) emitted in automotive catalyst exhaust were measured down to the pg/m3 level. Samples were taken from a standard type three-way catalyst equipped gasoline engine, running on a computer controlled dynamometer. Particulates in catalyzed car exhaust were sampled fractionated according to size by using the cascade impactor with separate targets mounted underneath each nozzle. The targets, small flat discs made of pure graphite, were subsequently analyzed by ETV-ICP-MS without any preparatory steps.

Speciation of metals and metalloids in sediments with LTGC/ICP-MS.

Abstract: Low temperature GC on-line coupled with an ICP/MS has been used as analytical device to detect organometallic and -metalloid compounds from various sediments of rivers and harbours in West Germany. The different species have been volatilized by derivatization with NaBH4 and cryofocussed in a trap. Different alkylated species of As, Sn and Sb have been identified, while only methylated compounds of the elements Ge, Se, Te, Hg and Bi could be detected.

Microwave digestion methods for the determination of trace elements in brain and liver samples by inductively coupled plasma mass spectrometry.

Abstract: Two microwave digestion systems (open-focused and closed-pressurized) were tested for the mineralization of human brain and bovine liver (NIST SRM 1577a) as dissolution steps prior to the determination of 16 trace elements (Bi, Cd, Co, Cs, Cu, Fe, Hg, Mn, Mo, Pb, Rb, Sb, Sn, Sr, Tl, and Zn) by inductively coupled plasma mass spectrometry (ICP-MS). Digestion parameters (mass of sample, digestion mixture, and power/time steps) were optimized using temperature and pressure sensors. Digestions with the open-focused microwave system require larger volumes of conc. HNO3 and 30% H2O2 than digestions with the closed-pressurized system. Both systems produce correct results for the bovine liver samples. The concentrations obtained for the digests of the open-focused system tend to be less precise than the concentrations from the “closed-pressurized” digests. Because the “open-focused” digests must be diluted to 50 mL to bring the acid concentration to 0.7–2.0 mol/L required by the ICP-MS (closed-pressurized digests need to be diluted to only 20 mL), the detection limits for the system with the open-focused digestion are higher than for the system with the closed-pressurized digestor. The open-focused digestor cannot handle more than 150 mg brain tissue, whereas the closed-pressurized system can mineralize 470 mg. The latter method gave better results with brain tissue than the open-focused system. The preparation of brain tissue as reference material for the determination of trace elements in brain samples is described.

Applications of laser-induced breakdown spectrometry (LIBS) in surface analysis.

Abstract: The applicability of laser-induced breakdown spectrometry (LIBS) for surface analysis is presented in terms of its lateral and depth resolution. A pulsed N(2) laser at 337.1 nm (3.65 J/cm(2)) was used to irradiate solar cells employed for photovoltaic energy production. Laser produced plasmas were collected and detected using a charge-coupled device. An experimental device developed in the laboratory permits an exact synchronization of sample positioning using an XY motorized system with laser pulses. Multielement analysis with lateral resolution of up to 30 microm is feasible with the present system. Three-dimensional capabilities of the system are used for studies on the distribution of carbon impurities at the surface of the solar cells.

Determination of heavy metal concentrations in plants exposed to different degrees of pollution using ICP-AES

Abstract: Plant samples (Plantago lanceolata - narrow leaf plantain and Cichorium endiviae - endive) were collected in the surroundings of heavy metal emission sources and in other less contaminated areas After digestion in a closed microwave system using HNO(3), the concentrations of Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, and Zn were determined using ICP-AES Detection limits for all the elements of interest are given Differences in heavy metal uptake rate between both plant species were observed The uptake is more intensive for endive than for narrow leaf plantain High concentrations of some heavy metals were determined in the unwashed plant samples as a result of exposure to aerosols Tukey's statistical test was used to confirm the discrepancy of Cr concentration in plant samples from various areas Washing the leaves with water was found to remove a large amount of water-soluble aerosols

Direct determination of copper and iodine in milk and milk powder in alkaline solution by flow injection inductively coupled plasma mass spectrometry.

Abstract: The development and evaluation of a flow injection inductively coupled plasma mass spectrometric (FI-ICP-MS) method for the determination of copper and iodine in milk and milk powder has been described. The sample preparation is based simply on the dilution of the sample by an alkaline solution containing 0.05 mol/l potassium hydroxide and 0.07 mol/l tetramethylammonium hydroxide. Possible matrix interferences on the determination of copper were alleviated by the use of standard addition calibration. Detection limits (3s) were 0.94 microg l(-1) and 0.45 microg l(-1) for copper and iodine, respectively. Four different certified milk powder reference materials were analysed and the concentrations found were in a good agreement with the certified values indicating that the method is unbiased. Due to the simplicity of the method a high sample throughput is possible, approximately 90 samples can be analysed in one day. More than 100 samples of Danish raw milk were analysed and median values of 0.050 mg kg(-1) of Cu and 0.084 mg kg(-1) of I were found.

Detection of trace radioisotopes in soil, sediment and vegetation by glow discharge mass spectrometry.

Abstract: The possibility for the determination of some radioisotopes of cesium, strontium, plutonium, uranium and thorium by glow discharge mass spectrometry (GDMS) in soils, sediments and vegetations is investigated. The preparation of samples is described as a combination of the use of a conductive host matrix and a secondary cathode in order to decrease the dilution effect of the blending material for the trace level determination and to gain a stable discharge. Effects of interferences arising from the nature of the conductive host matrix and of the secondary cathode on the sensitivity of the method are discussed. The determination of (137)Cs and (90)Sr has been attempted and the results obtained were in agreement with those from other analytical techniques. Accuracy, internal and external precisions have been also evaluated. GDMS is shown to be a helpful technique for the determination of radioisotopes in environmental samples. Radioisotopes can be determined according to the matrix of the sample (e.g. grass), also in presence of isobaric interferences. However, limitations still exist on the application of GDMS.

New concept for the non-invasive determination of physiological glucose concentrations using modulated laser diodes.

Abstract: The detection of small absorption differences is one of the basic requirements for the non-invasive determination of blood substrates. As conventional spectrometers are limited in their detection capabilities of small absorption changes, semiconductor lasers are applied for this purpose. By using a special modulation scheme, physiological glucose concentrations could be successfully predicted. The results demonstrate the feasibility of using small and inexpensive laser diodes for the spectroscopic determination of glucose in aqueous solutions as a step towards a portable non-invasive glucose sensor for self- monitoring of diabetic patients.

Kinetic aspects of the reduction of mercury ions by humic substances

Abstract: A combination of a computer controlled titration device with a cold vapour atomic absorption spectrometer was set up to examine the kinetics of the reaction between humic substances and Hg(II). Subsequent injections of Hg(II) into an excess of humic acid produce data about short and long term changes in the reaction velocity of humic substances. This experimental design is suitable for the examination of the effects of pH, reaction time, light and interfering substances like chloride on the formation of elemental mercury. The obtained data agree with data from the literature. With the accumulation of the produced elemental mercury on a gold net it is possible to enhance the sensitivity of the method. This enables examinations at environmental concentrations.

Monitoring of high hydrogen peroxide concentrations by voltammetryc.

Abstract: Different electrode systems have been investigated as possible voltammetric sensors for in-line measurements and monitoring of high concentrations of hydrogen peroxide (up to 30 g/l) as used in alkaline textile bleaching liquor. With most of the tested electrodes insurmountable ohmic potential losses are encountered, resulting in a saturation of the sensor output current. Taking accuracy and stability with time into consideration promising results are obtained with a rotating glassy carbon electrode, an ultra-micro platinum electrode and stationary titanium and zirconium electrodes, in decreasing order of preference when selectivity versus the many possible additives used in industry are not yet taken into account.

A thermodynamic surface model for caesium sorption on bentonite

Abstract: Caesium sorption on Wyoming bentonite MX-80 has been studied in solutions of NaCl, KCl, MgCl2, CaCl2, NaNO3 and Ca (NO3)2 of concentrations varying between 0.025 and 1 mol/L, as well as in a weakly saline (I=0.004 ml/L) and a strongly saline (I=0.46 mol/L) natural groundwater. These experiments have been used to derive a thermodynamic model for the interaction of caesium with the bentonite surface in accordance with a surface chemical model, including acid/base reactions developed recently for montmorillonite. The sorption behaviour of caesium on bentonite can be described, within the experimental and model uncertainties, in terms of a one-site ion exchange model. The ion exchange constant obtained for the reaction NaX+Cs+⇆ CsX+Na+ (where X represents the ion exchange sites on montmorillonite) is log10 K0 ex=1.6. Impurities in the bentonite, influencing the concentrations of competing cations, such as Na+, K+, Mg2+ and Ca2+, have a crucial impact on the sorption of caesium. This impact can be adequately quantified with the present model. The model predictions compare well with sorption data published in the open literature on both Wyoming bentonite MX-80 and other types of bentonite. Distribution coefficients from the literature obtained from both batch and diffusion experiments and varying over four orders of magnitude are reproduced and explained successfully by the model.

Syn/anti isomerization of 2,4-dinitrophenylhydrazones in the determination of airborne unsymmetrical aldehydes and ketones using 2,4-dinitrophenylhydrazine derivation.

Abstract: Aldehydes and ketones readily react with 2,4-dinitrophenylhydrazine (2,4-DNPH) to form the corresponding hydrazones. This reaction has been frequently used for the quantification of airborne carbonyl compounds. Since unsymmetrical aldehydes and ketones are known to form isomeric 2,4-dinitrophenylhydrazones (syn/ anti-isomers), the influence of isomerization on the practicability and accuracy of the 2,4-DNPH-method using 2,4-dinitrophenylhydrazine-coated solid sorbent samplers has been studied with three ketones (methyl ethyl ketone (MEK), methyl isopropyl ketone (MIPK), and methyl isobutyl ketone (MIBK)). With all three ketones the reaction with 2,4-DNPH resulted in mixtures of the isomeric hydrazones which were separated by HPLC and GC and identified by mass spectroscopy and (1)H nuclear magnetic resonance spectroscopy. The isomers show similar chromatographic behaviour in HPLC as well as in GC, thus leading to problems in quantification and interpretation of chromatographic results.