Slurry Technique Research Articles

Electrothermal atomic absorption spectrometric determination of cadmium in bangladeshi vegetables with a metal tube atomizer and slurry sampling technique

Ultrasonic slurry sampling electrothermal atomic absorption spectrometry with a molybdenum tube atomizer has been applied for the determination of cadmium in vegetable samples in Bangladesh. The suspension-stabilizing medium was 10% glycerol solution. The optimum pyrolysis temperature was 300°C. The detection limit was 13 fg (3S/N). Matrix element interference was studied and it was found that thiourea as a chemical modifier eliminated the interference. The results for the determination of cadmium in vegetable samples by the proposed method were in good agreement with those measured in dissolved acid-digested samples. The method enables rapid calibration, and simple and rapid analysis of cadmium in vegetable samples at low cost.

Method development for the determination of iron in milligram amounts of rice plants (Oryza sativa L.) from cultivation experiments using graphite furnace atomic absorption spectrometry.

The amount of sample that is available for analysis in laboratory plant cultivation experiments is usually very limited. Highly sensitive analytical techniques are therefore required, even for elements that are present in the plants at mg g(-1) concentrations, and graphite furnace atomic absorption spectrometry (GFAAS) was chosen in this work because of its micro-sampling capability, and its relatively simple operation. Four micro-methods were investigated for the determination of iron in roots and leaves of rice plants: i) a micro-digestion with nitric and hydrochloric acids, ii) a slurry procedure using tetramethylammonium hydroxide (TMAH) tissue solubilizer, iii) a slurry prepared in 1.4 mol L(-1) nitric acid, and treated in an ultrasonic bath, and iv) the direct analysis of solid samples. The micro-digestion was suffering from high blank values and contamination problems, so that it could not be recommended for routine purposes. The TMAH method exhibited poor precision and occasional low recoveries, particularly for real samples. Direct solid sampling analysis gave results similar to those obtained with the slurry technique with ultrasonic agitation for the determination of iron in certified reference materials with iron content up to about 100 microg g(-1), but was too sensitive for the investigated rice plants, which had an iron content up to several mg g(-1). The slurry technique with ultrasonic treatment of the samples, suspended in dilute nitric acid, was finally adopted as the method of choice. The method was then applied for the determination of iron in the leaves and in different compartments of the roots of two rice cultivars, one sensitive to iron toxicity, an important nutritional disorder, and the other one resistant to iron toxicity. The results suggest that the higher resistance to iron toxicity of the second cultivar is due to a smaller uptake of iron from the soil, resulting in lower iron levels in all compartments of the plant.

Metsulfuron methyl sorption-desorption in field-moist soils.

Pesticide sorption coefficients (K(d)) are generally obtained using batch slurry methods. As a consequence, the results may not adequately reflect sorption processes in field-moist or unsaturated soil. The objective of this study was to determine sorption of metsulfuron methyl, a weak acid, in field-moist soils. Experiments were performed using low density (i.e., 0.3 g mL(-)(1)) supercritical fluid carbon dioxide (SF-CO(2)) to convert anionic metsulfuron methyl to the molecular species and remove it from the soil water phase only, thus allowing calculation of sorption coefficients (K(d)) at low water contents. K(d) values for sorption of the metsulfuron methyl molecular species on sandy loam, silt loam, and clay loam soil at 11% water content were 120, 180, and 320 mL g(-)(1), respectively. Using neutral species K(d) values, the pK(a) of metsulfuron methyl, and the pH of the soil, we could successfully predict the K(d) values obtained using the batch slurry technique, which typically has a predominance of anionic species in solution during the sorption characterization. This application of supercritical fluid extraction to determine sorption coefficients, combined with sulfonylureas' pK(a) values and the soil pH, will provide an easy method to predict sorption in soil at different pH levels.

Cordierite–mullite coating for SiCf/SiC composites

Abstract A glass of suitable composition for coating of SiCf/SiC composites has been developed. The resulting coating is a crystalline cordierite-mullite material. The SiCf/SiC composites were coated by a simple and low cost slurry technique: a slurry made of glass powder and ethanol was put on the as-received SiCf/SiC composite and heat treated at 1180 °C for 1 h in order to obtain a uniform, pore-free and crystalline coating through the “glass–ceramic method”. The thermal analysis could not reveal any residual glass transition in the obtained coating material and the melting point of the crystalline phases formed in the coating during the coating process (cordierite, 2MgO–2Al2O3–5SiO2 and mullite, 3Al2O3–2SiO2 rate of 3:1 wt. %) was measured at about 1430 °C.

Oxidation protective multilayer coatings for carbon–carbon composites

An oxidation protective double layered coating was deposited on a carbon–carbon composite (C/C) using a simple and low cost method. A surface modification of the C/C was obtained by direct reaction of liquid silicon with the C/C, promoting the formation of a 5–10 μm β-SiC layer on the composite surface. The inner layer, in contact with the C/C, is a composite made with a barium borosilicate glass matrix (SABB) and boron carbide particles; the outer layer is another composite layer formed by a SABB glass matrix and yttrium oxide particles. The layers are deposited by a slurry technique. Oxidation tests were carried out in a furnace in air, in order to verify the coating stability and its effectiveness. No mass loss of the C/C composite was observed after 100 h at 1200°C, while after 150 h at 1300°C the C/C mass loss did not exceed 1%.

Custom-made interface between electrothermal vaporiser and inductively coupled plasma-mass spectrometer: determination of nickel by isotope dilution in plant samples

ICP-mass spectrometer Perkin Elmer Elan 6000 was adapted for ETV analysis by coupling with GBC GF 3000 graphite furnace atomiser. Both instruments were connected by a 25 cm long PTFE tubing of 6 mm i.d. and a custom-made interface. The apparatus was applied to nickel determination using isotope dilution technique. The efficiency of analyte transfer through the interface was approximately 20%, however the incomplete transfer did not influence the blank values. Measured isotope ratio was very stable, whereas the magnitude of ion signal showed a little shift. CRM samples were analysed after microwave decomposition and by slurry technique as well. Obtained results were compared with those of pneumatic sample nebulisation after nickel separation on Chelex column. All tested techniques gave accurate results with comparable precision. However, the slurry technique allowed significant decreasing of the blank values and the limit of detection. The duration of analysis run can also be substantially shortened from several hours to a few minutes.

Slurry sampling for electrothermal atomic absorption spectrometric determination of chromium, nickel, lead and cadmium in sewage sludge

The slurry technique was applied for determination of chromium (Cr), nickel (Ni), lead (Pb) and cadmium (Cd) in sewage sludge by electrothermal atomic absorption spectrometry. The graphite furnace temperature programme was optimised. Suspensions prepared in a medium containing 0.5 and 5.0% (v/v) HNO 3 and 0.5 and 5.0 HNO 3 with 0.5% (m/v) glycerol were introduced directly into the furnace. The reliability of the procedure was proved by analysing certified reference material CRM 144R sewage sludge. The contents of Cr, Ni, Pb and Cd in two sludge samples from Poland (Poznań area) ranged between 1.2 and 7.2 mg kg −1 for Cr; 4.5 and 44.9 mg kg −1 for Ni; 0.93 and 103.1 mg kg −1 for Pb and 0.28 and 1.65 mg kg −1 for Cd. The detection limit was calculated as 0.087, 0.054, 0.068 and 0.005 mg kg −1 for Cr, Ni, Pb and Cd, respectively. The relative standard deviation (R.S.D.) measurements for the slurry sampling method was 2.7–4.5% (CRM 144R) and 7.1–9.4% (sewage sludge from Poland).

Glass coating for SiCf/SiC composites for high-temperature application

This work reports on the fabrication of a self-healing, oxidation-resistant glass coating for SiCf/SiC composites. The glass-coating material is a thermally stable boro-silicate glass with excellent wetting properties and viscosity.Some glass-coated composites were prepared by a simple and low-cost slurry technique, then treated in air for 100 h at 1200°C. Three-point bending tests were performed on the glass-coated composites after the thermal treatment, and the results were compared with the bending strength of the uncoated SiCf/SiC before and after the same thermal treatment. The mechanical behavior of the glass-coated composite remained almost virtually unaffected after being heated at 1200°C in air for 100 h.

Determination of nickel, chromium and cobalt in wheat flour using slurry sampling electrothermal atomic absorption spectrometry

The slurry technique was applied to the determination of Ni, Cr and Co in wheat flour by electrothermal atomic absorption spectrometry (ETAAS). The influence of the graphite furnace temperature programme was optimized. Optimum sensitivity was obtained by using a mixture of 15% HNO3–10% H2O2 as suspended medium for a 3% w/v slurry in the determination of Ni; lower concentrations of HNO3 were necessary for the determination of Co and Cr (viz. 5 and 10%). The precision of direct analyses of the slurries was improved by using mechanical agitation between measurements; thus, the RSD of the measurements was ca. 5% for repeatability. The direct slurry sampling (SS) technique is suitable for the determination of Ni and Cr in wheat flour samples at levels of 150–450 and 30–72 ng g−1, respectively, as it provides results similar to those obtained by ashing the sample. However, the typically low level of Co in these samples precluded its determination by the proposed method (the study was made in an SRM spiked wholemeal flour), at least in those samples that were contaminated with elevated concentrations of the metal (viz. more than 90 ng of Co per g of flour). The method provides a relative standard deviation of 6, 8, and 4% for Ni, Cr, and Co, respectively.

Determination of tellurium in indium antimonide by slurry sampling electrothermal atomic absorption spectrometry

A method for the determination of tellurium dopant concentration in indium antimonide (InSb) by Zeeman effect electrothermal atomic absorption spectrometry using the slurry sampling technique was developed. The effects of chemical modifier type and mass on the absorbance-peak characteristics of tellurium in InSb slurried samples were studied. The atomization behavior of tellurium in InSb slurries could be greatly improved by the use of palladium nitrate as a chemical modifier. The detection limit of the optimized procedure was 0.4 µg g –1 . In the determination of tellurium at the concentration level of 16 µg g –1 , a relative standard deviation of 7% was obtained. Good agreement of the results obtained by the slurry sampling technique with those obtained by solution electrothermal atomic absorption spectrometry and inductively coupled plasma mass spectrometry was found.

The influence of true simultaneous internal standardization and background correction on repeatability for laser ablation and the slurry technique coupled to ICP emission spectrometry

For the solid sampling techniques laser ablation and the slurry technique, the influence of simultaneous measurement vs. sequential measurement of the signal and background and the internal standard was investigated on an identical data set. The experiments were carried out with an array spectrometer, which generates spectra rather than single points. These spectra, typically measured around the analyte wavelength, are measured simultaneously. The ICP spectrometer used has a `profiling' mode, whereby the entrance slit is moved fourfold and the spectra are recorded with a small spectral shift in a sequential manner. These images are then combined to form a spectrum which is composed of simultaneous and sequential measured data. Hence, by carefully selecting the data points in a measured spectrum, the difference between simultaneous and sequential measurements can be estimated from an identical data set. In the example studied, simultaneous background correction and simultaneous internal standardization (typical for array ICP-OES) gave a mean RSD of 3.6%, sequential background correction and simultaneous internal standardization (typical for simultaneous ICP-OES) produced an average RSD of 6.1% and sequential background correction and sequential internal standardization (typical for sequential ICP-OES) resulted in a mean RSD of 6.4%. The RSDs reflect the solid sampling procedure. Some applications of laser ablation and slurry sampling are presented.

Direct determination of metal concentrations in freshwater algae by total reflection X-ray fluorescence spectrometry

A direct TXRF method for the determination of metal impurities by applying three different freshwater algae, viz., Chlorella keslerii, Synehococcus sp. and Cylindrospermopsis raciborskii, was developed. The applicability of the slurry sampling technique was confirmed by comparing the analytical results obtained with those obtained by total digestion of the algae. The concentration data showed an acceptable agreement for Cu, Fe, Mn and Zn. The calculated accumulation factors for the metals detected were highest for Chlorella keslerii.

The influence of true simultaneous internal standardization and background correction on repeatability for laser ablation and the slurry technique coupled to ICP emission spectrometry

Micro-samples of human fingernails were analyzed for lead using Rhenium-cup, in-torch vaporization (ITV) sample introduction and inductively coupled plasma atomic emission spectrometry (ICP-AES). Lead concentrations were found to be in agreement with those reported in the literature. Direct elemental analysis of micro-samples of fingernails, minimum sample pre-treatment and, overall, increased speed of analysis are the main advantages of the approach.

Slurry sampling electrothermal atomic absorption spectrometry for trace element analysis of high-purity tungsten trioxide

A slurry sampling ETAAS method for the determination of trace concentrations of Ca, Co, Cr, Cu, Fe, K, Mg, Na and Ni in tungsten trioxide is presented. A high background absorption appearing with large sample amounts during atomization at high temperatures was the only matrix interference observed. It could be significantly reduced by volatilization of the matrix in the pyrolysis step. Calibration curves recorded with aqueous standards could be used for calibration in all cases excluding the determination of very low analyte concentrations of Co and Fe which required the use of the standard additions method. The results obtained by this method showed an excellent agreement with those determined in digests by ETAAS. The detection limits achievable by the slurry technique were between 1 (Ca, K, Mg, Na) and 210 (Cu) ng/g. They were mostly by more than one order of magnitude better than those of the solution techniques.

Application of the Slurry Technique to the Determination of Selenium in Fish Samples by Electrothermal Atomic Absorption Spectrometry

A slurry technique was applied in the development of a sensitive and precise method for selenium determination in fish samples without sample pre-treatment. Several pyrolysis curves were investigated and different chemical modifiers were tested. Ammonium oxalate was used to improve the selectivity. Calibration within the range 2.5–25.0 µg l -1 Se was performed with aqueous standards. The detection limit was calculated as 0.33 µg l -1 and the RSD of the measurements was 5.9% for repeatability and 9.2% for reproducibility. The reliability of the entire procedure was confirmed by analysis of a standard reference material and by comparison with a microwave digestion procedure.

Evaluation of Various Sample Preparation Procedures for the Determination of Chromium, Cobalt and Nickel in Vegetables

Three methods for the determination of Cr, Co and Ni in vegetables were tested with a view to the evaluation of various sample preparation procedures involving dry ashing, the direct slurry technique and continuous flow microwave-assisted digestion. NIST SRM 1572 Citrus Leaves was used for this purpose. For the determination of the analytes by AAS, the temperature programmes of the graphite furnace were optimized and the use of some chemical modifiers was studied. Direct slurry analyses of vegetables (in samples prepared at a 2% m/v concentration in 1% HNO 3 containing 10% H 2 O 2 ) were generally accurate and precise for Co and Ni, but gave low recoveries (about 85%) for Cr. Continuous digestion of the samples in a microwave oven was necessary for the reliable determination of Cr (about 100% recovery) by use of 5% HNO 3 as the digesting reagent. The best method for each application was used for the determination of Cr, Co and Ni in a variety of vegetables, using direct calibration with aqueous standards.

Application of the response surface methodology for potassium determination in soils by AAS using the slurry technique

The response surface methodology has been used in the analysis of soil samples in order to determine the optimum combination of the variables that have direct influence on the atomic absorption signal and to study their interactions as well as their effect on the total potassium concentration. The application of this methodology leads to a knowledge of the dependence between the analytical signal and the nitric acid concentration, time and temperature of the ultrasonic agitator. The optimum experimental responses were obtained in the isoresponse zone at 10% v/v of nitric acid, an ultrasonic time of 105 min, and a temperature of 42°C.

Mechanism of solid–solid resolution of pantolactone

The enantioselective solid–solid clathration of (S)-pantolactone (1) into (R,R)-trans-2,3-bis(diphenylhydroxymethyl)-1,4-dioxaspiro[4·4]nonane (2) and -[4·5]decane (3) was studied preparatively and mechanistically using atomic force microscopy (AFM) measurements and crystal packing data. Short-distance solid-to-solid sublimation mechanisms occur in both cases with initial formation of epitaxial floes along the b-axis in 2 and random craters in 3. The bulk control in the phase rebuilding stage is understood from the particular crystal packings. Bulk control was largely lost in the phase transformation stage when passivation of the surfaces occurred in both cases. The host lattices of 2 and 3 exhibit closed molecular double layers with all hydroxyl groups inside and lacking access for intercalation of 1. The reaction has to start at isolated surface defects. Once started, new doors for further entrance of guest molecules (S)-1 are opened in the double layer. For practical use, both the crystallographic difficulties and the passivation have to be overcome. A slurry technique involving addition of stoichiometric amounts of water to the solids provided useful conditions for the preparative resolution of (R/S)-1 or further racemates exhibiting passivation, whereas heating alone speeded up the resolution of 2-methylpiperazine with 2. © 1996 John Wiley & Sons, Ltd.

Mechanism of solid-solid resolution of pantolactone

The enantioselective solid–solid clathration of (S)-pantolactone (1) into (R,R)-trans-2,3-bis(diphenylhydroxymethyl)-1,4-dioxaspiro[4·4]nonane (2) and -[4·5]decane (3) was studied preparatively and mechanistically using atomic force microscopy (AFM) measurements and crystal packing data. Short-distance solid-to-solid sublimation mechanisms occur in both cases with initial formation of epitaxial floes along the b-axis in 2 and random craters in 3. The bulk control in the phase rebuilding stage is understood from the particular crystal packings. Bulk control was largely lost in the phase transformation stage when passivation of the surfaces occurred in both cases. The host lattices of 2 and 3 exhibit closed molecular double layers with all hydroxyl groups inside and lacking access for intercalation of 1. The reaction has to start at isolated surface defects. Once started, new doors for further entrance of guest molecules (S)-1 are opened in the double layer. For practical use, both the crystallographic difficulties and the passivation have to be overcome. A slurry technique involving addition of stoichiometric amounts of water to the solids provided useful conditions for the preparative resolution of (R/S)-1 or further racemates exhibiting passivation, whereas heating alone speeded up the resolution of 2-methylpiperazine with 2. © 1996 John Wiley & Sons, Ltd.

Seasonal variation in rates of heterotrophic nitrogen fixation (acetylene reduction) in Zostera noltii meadows and uncolonised sediments of the Bassin d'Arcachon, south-west France

Nitrogen fixation (acetylene reduction) rates were measured over an annual cycle in meadows of the seagrass Z. noltii and uncolonised sediments of the Bassin d'Arcachon, south-west France, using both slurry and whole core techniques. Measured rates using the slurry technique in Z. noltii colonised sediments were consistently higher than those determined in isolated cores. This was probably due to the release of labile organic carbon sources during preparation of the slurries. Thus, in colonised sediments the whole core technique may provide a more accurate estimate of in situ activity. Acetylene reduction rates measured by the whole core technique in colonised sediments were 1.8 to 4-fold greater, dependent upon the season, in the light compared with those measured in the dark, indicating that organic carbon released by the plant roots during photosynthesis was an important factor regulating nitrogen fixation. In contrast acetylene reduction rates in uncolonised sediments were independent of light.