Time-resolved characterization of laser-induced plasma from fresh potatoes

Optical emission of laser-induced plasma on the surface of fresh vegetables provides sensitive analysis of trace elements for in situ or online detection of these materials. This emergent technique promises applications with expected outcomes in food security or nutrition quality, as well as environment pollution detection. Characterization of the plasma induced on such soft and humid materials represents the first step towards quantitative measurement using this technique. In this paper, we present the experimental setup and protocol that optimize the plasma generation on fresh vegetables, potatoes for instance. The temporal evolution of the plasma properties are investigated using time-resolved laser-induced breakdown spectroscopy (LIBS). In particular, the electron density and the temperatures of the plasma are reported as functions of its decay time. The temperatures are evaluated from the well known Boltzmann and Saha-Boltzmann plot methods. These temperatures are further compared to that of the typical molecular species, CN, for laser-induced plasma from plant materials. This comparison validates the local thermodynamic equilibrium (LTE) in the specific case of fresh vegetables ablated in the typical LIBS conditions. A study of the temporal evolution of the signal to noise ratio also provides practical indications for an optimized detection of trace elements. We demonstrate finally that, under certain conditions, the calibration-free LIBS procedure can be applied to determine the concentrations of trace elements in fresh vegetables.     

Enhanced trace element analysis of plant materials after accelerated pulsed UV digestion

A method for measuring trace concentration of Fe, Co, Ni, Cu, Zn and Pb in plant materials was developed, optimized, validated and compared using reference standards and fresh samples. The method is based on rapid material digestion by radicals produced with laser-assisted pulsed UV (PUV) photolysis of aqueous solutions containing H₂O₂. Metals in the resulting solution were pre-concentrated as carbamates. Samples were analyzed with particle induced X-ray emission (PIXE). Combined PUV digestion and pre-concentration techniques resulted in enhanced detection levels of selected trace elements in foods and non-food commodities. The method was applied to measure trace elements in wastewater irrigated fruits, vegetables and crops.     

Microwave assisted sample preparation for determining water-soluble fraction of trace elements in urban airborne particulate matter: evaluation of bioavailability

The feasibility of using two different microwave-based sample preparation methods was investigated to determine the total and water-soluble trace metal fraction in airborne particulate matter. The extraction techniques were then applied to urban particulate matter of different sizes in order to evaluate their bioavailability of associated trace metals. While a combination of HNO₃-HF-H₂O₂ was used for the total trace metal fraction of particulate matter, water was employed for the microwave-assisted extraction of water-soluble trace metal fractions. Inductively coupled plasma-mass spectrometry (ICP-MS) was used for the analysis of trace elements. The experimental protocol for the microwave assisted digestion was established using two different SRMs (1648, urban particulate matter and 1649a, urban dust). In the case of water-soluble trace metal fraction, the quantities extracted from the SRMs were compared between ultrasonic and microwave-assisted extractions, and there was a good agreement between the two extraction methods. Blanks values and limits of detection (LODs) for total and water-soluble trace metal concentrations were determined for three different filter substrates (Teflon, Zeflour, and Quartz). Subsequently, the proposed digestion method was evaluated for its extraction efficiency with these filter substrates. Finally, the real-world application of the proposed microwave-based sample preparation methods was demonstrated by analyzing trace elements in airborne particulate samples collected from different outdoor environments in Singapore. The solubility of 11 trace elements detected in the particulate samples is quantified.     

Differentiation of Detection of Ascorbic Acid and Dehydroascorbic Acid Using Hydrodynamic Amperometry and Anodic Stripping Voltammetry on Modified Aluminum Electrodes

An electroanalytical strategy for the simultaneous determination of ascorbic acid (AA) and dehydroascorbic acid (DHA), is described. A palladized Al electrode is used for hydrodynamic amperometry of AA. While the decrease of anodic stripping voltammetry current of the K₂UO₂[Fe(CN)₆]‐Pd/Al electrode prepared in the presence of DHA was the principal of the DHA determination. The calibration graph for both methods was linear over the concentration range 1–50 μM. The detection limit was found to be 0.5 μM. Some fresh fruit juices and vegetables of trace level of AA and DHA were analyzed as the typical example of application.     

A study of some trace elements in infant foods

Seven trace elements were determined in milk formulas, powder milk and infant food. Instrumental neutron activation analysis was used for the analysis of Fe, Zn, Co, Cr and Rb, while As and Cu content was determined using radiochemical neutron activation analysis. Differences were found in the trace element content of foods of the same type. Milk formulas are comparable with human milk according to the results obtained for the elements analyzed. The samples of powder cow's milk presented similar concentrations of the elements studied. Liver with vegetables was found to have the highest Cu content. A meal prepared at home, made of beef and fresh vegetables showed a higher trace element content than its similar commercial one. An estimation of the daily intake of the elements analyzed was made and compared with minimum recommended daily ingestion.     

Application of iminodiacetate chelating resin muromac A-1 in on-line preconcentration and inductively coupled plasma optical emission spectroscopy determination of trace elements in natural waters

On-line system incorporating a microcolumn of Muromac A-1 resin was used for the developing of method for preconcentration of trace elements followed by inductively coupled plasma (ICP) atomic emission spectrometry determination. A chelating type ion exchange resin has been characterized regarding the sorption and subsequent elution of 24 elements, aiming to their preconcentration from water samples of different origins. The effect of column conditioning, pH and flow rate during the preconcentration step, and the nature of the acid medium employed for desorption of the retained elements were investigated. A sample (pH 5) is pumped through the column at 3 ml min⁻¹ and sequentially eluted directly to the ICP with 3 M HNO₃/HCl mixtures. In order to remove residual matrix elements from the column after sample loading a short buffer wash was found to be necessary. The effectiveness of the matrix separation process was illustrated. The procedure was validated by analyzing several simple matrices, Standard River water sample as well as artificial seawater. Proposed method can be applied for simultaneous determination of In, Tl, Ti, Y, Cd, Co, Cu and Ni in seawater and for multielement trace analysis of river water. Recovery at 1 μg l⁻¹ level for the determination of investigated 24 elements in pure water ranged from 93.1 to 96% except for Pd (82.2%) and Pb (88.1%). For the same concentration level for seawater analysis recovery was between 81.9 and 95.6% except for Hg (38.2%).     

贵阳地区蔬菜中微量元素的研究

研究了贵阳地区主要蔬菜中微量元素的含量水平及分布状况 ,为发展该地区高微特种蔬菜的研究与生产 ,把蔬菜产业做大、做强、做好提供科学的依据     

Direct determination of trace rare earth elements in high purity Y2O3 using fluorination assisted electrothermal vaporization inductively coupled plasma atomic emission spectrometry with slurry sampling

A new method for the determination of trace amounts of 14 rare earth elements in high purity Y₂O₃ using fluorination assisted electrothermal vaporization inductively coupled plasma atomic emission spectrometry with slurry sampling was developed. A polytetrafluoroethylene (PTFE) emulsion was used as a fluorinating reagent to promote the vaporization of the analytes from graphite furnace. The main factors affecting analytical signals were investigated systematically. The interference of matrix could be minimized in the presence of PTFE. Under optimum conditions, the detection limits for rare earth elements were 0.032 ng～2.52 ng and the relative standard deviations were in the range of 1.4% to 4.3%. The proposed method was applied to the direct analysis of high purity Y₂O₃ powder with satisfactory results.     

Direct determination of trace rare earth elements in high purity Y2O3 using fluorination assisted electrothermal vaporization inductively coupled plasma atomic emission spectrometry with slurry sampling

A new method for the determination of trace amounts of 14 rare earth elements in high purity Y₂O₃ using fluorination assisted electrothermal vaporization inductively coupled plasma atomic emission spectrometry with slurry sampling was developed. A polytetrafluoroethylene (PTFE) emulsion was used as a fluorinating reagent to promote the vaporization of the analytes from graphite furnace. The main factors affecting analytical signals were investigated systematically. The interference of matrix could be minimized in the presence of PTFE. Under optimum conditions, the detection limits for rare earth elements were 0.032 ng∼2.52 ng and the relative standard deviations were in the range of 1.4% to 4.3%. The proposed method was applied to the direct analysis of high purity Y₂O₃ powder with satisfactory results. Received: 19 June 1999 / Revised: 10 December 1999 / Accepted: 16 December 1999     

Residue analysis of ethylenethiourea in vegetables by high-performance liquid chromatography with amperometric detection

Summary A method for the residue analysis of ethylenethiourea (ETU) in vegetables by HPLC with amperometric detection was developed. ETU was separated with Nucleosil C₁₈ as stationary phase and methanol-water (5:95, v/v) containing 0.05 mol/l ammonium acetate as eluent. The voltage of the working electrode (glassy carbon) was set at +1150 mV vs. Ag/AgCl. The limit of detection for ETU was found to be 0.3 ng. The method was applied to the determination of trace amounts of ETU in tomatoes and cucumbers. The minimum quantitation level was 0.01 ppm. The method can be performed easily; it is selective and highly sensitive.     

Isolierung von Magnesium aus biologischem Material für die massenspektrometrische Isotopenanalyse

Magnesium is precipitated as hydroxide after elimination of interfering elements by means of ion-exchange procedures (phosphate, iron, trace elements) and masking with EDTA (calcium). The sample is applied in form of MgCl₂ to the tungsten filament of an 1-filament-ion-source for surface ionization.     

Neutron activation analysis of high purity nickel by solvent extraction using 2-benzylpyridin/benzene

A radiochemical neutron activation analysis using solvent extraction has been applied for the determination of trace impurities in high purity nickel. Because of the high activity of⁵⁸Co produced by the nuclear reaction,⁵⁸Ni(n,p)⁵⁸Co, cobalt should be separated from the impurities. Removal of cobalt from the other trace elements in the aqueous acidic solution containing 1M thiocyanate ion (KSCN) was achieved by extraction with 1M2-benzylpyridin (BPy) in benzene. From the result of tracer experiments, cobalt was completely separated from most other elements except Fe, Mo and Zn. To determine the experimental accuracy, NIST SRM 673 nickel oxide was analyzed and the results agreed well within 10% deviation. This established radiochemical method was applied to the analysis of high purity nickel samples.     

Trace analysis of ceramic surfaces by laser ionization mass spectrometry

Summary Laser ionization mass spectrometry (LIMS) is an analytical method for the simultaneous determination of concentrations of trace elements in solid samples and for the analysis of layers with thicknesses >1 m. This laser-induced surface analytical method is limited by the laser focus and crater depth of the laser system applied. Results of mass spectrometric trace analysis on a silicon carbide surface, ZrO₂ and high-T_c superconducting ceramics are discussed.     

Study of the adsorption behavior ¶of heavy metal ions on nanometer-size ¶titanium dioxide with ICP-AES

A new method using nanoparticle TiO₂ as solid-phase extractant coupled with ICP-AES was proposed for simultaneous determination of trace elements. The adsorption behavior of nanometer TiO₂ towards Cu, Cr, Mn and Ni was investigated by ICP-AES, and the adsorption pH curves, adsorption isotherms and adsorption capacities were obtained. It was found that the adsorption rates of the metal ions studied were more than 90% in pH 8.0～9.0, and 2.0 mol L^–1 HCl was sufficient for complete elution. Nanometer TiO₂ possesses a significant capacity for the sorption of the metal ions studied which is higher than the capacity of silica, the commonly used extractant. The method has been applied to the analysis of some environmental samples with satisfactory results.     

Microwave assisted digestion of atmospheric aerosol samples followed by inductively coupled plasma mass spectrometry determination of trace elements

A microwave digestion method in a closed vessel was developed for the determination of trace metals in atmospheric aerosols using inductively coupled plasma mass spectrometry (ICP-MS). A recovery study for the elements V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Cd, Sb, and Pb was conducted using multi-elemental standard solutions, NIST 1633b Trace Elements in Coal Fly Ash, and NIST 1648 Urban Particulate Matter. A simple digestion method using only HNO₃/H₂O₂ gave good recoveries (90%–108%) for all elements except Cr in SRM 1648, but yielded low recoveries for SRM 1633b. A more robust method using HNO₃/H₂O₂/HF/H₃BO₃ yielded higher recoveries (82%–¶103%) for the lighter elements (V – Zn) in SRM 1633b, and improved the Cr recovery in SRM 1648, but decreased the Se recovery in both SRMs. A comparative analysis of aerosol samples obtained at a remote mountain location Nathiagali, Pakistan (2.5 km above mean sea level), and Mayville, New York, downwind from the highly industrialized Midwestern United States, was carried out using Instrumental Neutron Activation Analysis (INAA) for the elements Cr, Mn, Fe, Co, Zn, As, Se, and Sb. The simple digestion method yielded excellent agreement for Cr, Fe, Zn, As, Se, and Sb, with slopes of the ICP-MS vs. INAA regressions of 0.90–1.00 and R² values of 0.96–1.00. The regressions for Mn and Co had slopes of 0.82 and 0.84 with R² values of 0.83 and 0.82, respectively. Addition of HF/H₃BO₃ did not improve the correlation for any of the elements and degraded the precision somewhat. The technique provides sensitivity and accuracy for trace elements in relatively small aerosol samples used in atmospheric chemistry studies related to SO₂ oxidation in cloud droplets. The ability to determine concentrations of a very large number of elements from a single analysis will permit source apportionment of various trace pollutants and hence strategies to control the sources of air pollution. This is particularly important as the health effects of particulate matter are increasingly recognized.     

Development of a combined method to carry out a multielement analysis for environment preser vation

The paper discusses the possibilities of energy dispersive X-ray fluorescence spectroscopy and instrumental neutron activation analysis in the investigation of environmental pollutions. The X-ray fluorescence spectroscopy of samples was performed using the MECA-1044A analyzer (XR-500, LINC SYSTEMS, Great Britain) with a pulsed X-ray tube with a silver target as a source of excitation. Neutron activation analysis was carried out on the basis of two reactors: IBR-2 LNP JINR, Dubna, and TWR ITEP, Moscow. The optimal regimes of measurement for both methods as well as the detection limits corresponding to these regimes are given. To illustrate the perspectives of the methods, the ecological problem of the consequences of introducing into soil of the now available meliorator CaSO₄·2H₂O is solved in the paper. Data on absorption of trace elements in a wide range including rare-earth elements by agricultural plants are presented. This paper may be of interest for specialists in analytical chemistry and ecology.     

Application of RF GDMS for trace element analysis of nonconducting La0.65Sr0.3MnO3 ceramic layers

Radio-frequency glow discharge mass spectrometry (RF GDMS) has been applied to the determination of trace elements in ceramic perovskite layers (La_0.65Sr_0.3MnO₃) using synthetic standards. For the preparation of these standards high-purity powder of the basic material (La_0.65Sr_0.3MnO₃) was doped with trace elements in concentrations from 20 to 500 μg/g and the mixture was pressed to compact samples. The resulting calibration curves and the calculated relative sensitivity factors (RSF) differed only from 0.4 to 2 for different elements. For nearly all elements the standard deviations in the determination of trace elements in La_0.65Sr_0.3MnO₃ were better than 15% and detection limits (using the 3σ-criterion) were below 10 μg/g. Changes of the discharge parameters (RF power, pressure of the discharge gas (Ar) in the RF glow discharge) have no significant influence on the sensitivity to elements.     

Application of k0-method in instrumental neutron activation analysis to glass matrix: test study for low power research reactor GHARR-1

In this work k₀-INAA (via IAEAk₀-software) has been applied on glass samples to determine major, minor and trace element concentration. As many as 50 elements were detected and quantified with 3–5 mg of 0.1 % AuAl comparator monitor (0.1 % gold–99.9 %Alumimum wire). The average concentration of SiO₂, Na₂O, CaO, Al₂O₃ and MgO ranged between 76–96 %, 11.15–12.66 %, 5.26–10.71 %, 1.13–2.73 % and 3.51–6.23 % respectively. The relative concentrations of impurity elements; Cr, Fe, Mn and Co determined from the glass samples were used to match the physical appearance (color) of the glass based on general knowledge of colored glass production. The analytical procedure was validated using SRM 610 (glass matrix) and SRM GBW07106 (rock matrix) both as control samples which indicated a relative uncertainty of 15 and 6 % respectively for SRM 610 and SRM GBW07106. The relative sensitivity at which some of the elements were detected in major, minor and trace levels have indicated, that the k₀-method in instrumental neutron activation analysis using low power research reactor is a useful technique in glass analysis and could equally be used for forensic and archeological glass characterization.     

Quasi ‘non-destructive’ laser ablation-inductively coupled plasma-mass spectrometry fingerprinting of sapphires

A homogenized 193 nm excimer laser with a flat-top beam profile was used to study the capabilities of LA-ICP-MS for ‘quasi’ non-destructive fingerprinting and sourcing of sapphires from different locations. Sapphires contain 97–99% of Al₂O₃ (corundum), with the remainder composed of several trace elements, which can be used to distinguish the origin of these gemstones. The ablation behavior of sapphires, as well as the minimum quantity of sample removal that is required to determine these trace elements, was investigated. The optimum ablation conditions were a fluency of 6 J cm⁻², a crater diameter of 120 μm, and a laser repetition rate of 10 Hz. The optimum time for the ablation was determined to be 2 s, equivalent to 20 laser pulses. The mean sample removal was 60 nm per pulse (approx. 3 ng per pulse). This allowed satisfactory trace element determination, and was found to cause the minimum amount of damage, while allowing for the fingerprinting of sapphires. More than 40 isotopes were measured using different spatial resolutions (20–120 μm) and eight elements were reproducibly detected in 25 sapphire samples from five different locations. The reproducibility of the trace element distribution is limited by the heterogeneity of the sample. The mean of five or more replicate analyses per sample was used. Calibration was carried out using NIST 612 glass reference material as external standard. The linear dynamic range of the ICP-MS (nine orders of magnitude) allowed the use of Al, the major element in sapphire, as an internal standard. The limits of detection for most of the light elements were in the μg g⁻¹ range and were better for heavier elements (mass >85), being in the 0.1 μg g⁻¹ range. The accuracy of the determinations was demonstrated by comparison with XRF analyses of the same set of samples. Using the quantitative analyses obtained using LA-ICP-MS, natural sapphires from five different origins were statistically classified using ternary plots and principal multi-component analysis.     

Major and trace element assessment of Tietê river sediments, São Paulo, Brazil

The objective of this study was to quantify major and trace elements present in sediments collected from the one of Brazil’s most important rivers, Tietê River. Sediments from 5 different sampling points (P₀–P₄), in 3 campaigns (2008/2009), from the headwaters to Suzano County upstream from São Paulo city were collected. X-ray fluorescence was applied for measuring total concentration of major elements and instrumental neutron activation analysis (INAA) for trace elements. The elements Cd, Hg and Pb were determined by atomic absorption spectrometry after digestion using the US EPA 3,051 procedure. These metal concentrations were compared to the PEL and TEL oriented values from CCME. The sampling sites P₃ and P₄, near industrialized areas, showed the highest concentrations for potentially bioavailable metals, mainly Pb and Hg. The results obtained by INAA were compared to upper continental crust values. A strong enrichment was found for the elements As, Br, Sb, Th, U and Zn. These results evidenced contamination by industrial effluents and sewage even relatively close to the Tietê River headwaters. The worst biological effects (acute toxicity) on benthonic organism Hyalella azteca were also observed at P₃ and P₄.