Direct Determination Of Trace Elements Research Articles

Direct Determination of Trace Elements in Meat Samples via High-Resolution Graphite Furnace Atomic Absorption Spectrometry

This work presents a direct and straightforward approach for the determination of trace elements in fish muscle, oyster, and bovine liver via direct solid sample analysis (SS) using high-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS GF AAS). The preliminary studies revealed the presence of spectral interferences at the analytical line of Ni at 231.096 nm, which could be corrected subtracting the spectrum of SiO and PO from the sample spectra using least-squares background correction. Moreover, all meat samples were proven homogeneous according to the homogeneity factor (H e) (all values were <10 mg½). Pyrolysis (Tp) and atomization (Ta) temperatures were studied and optimized as 800 °C (Tp) and 2500 °C (Ta) for Mn, 700 °C (Tp) and 2600 °C (Ta) for Ni, and 600 °C (Tp) and 2500 °C (Ta) for Rb. Calibration against aqueous standards was proven feasible for Mn determination, whereas Ni and Rb required calibration against solid standards for their quantification. The detection limits achieved were demonstrated adequate for application to food analysis (0.005 μg g−1 for Mn, 0.002 μg g−1 for Ni, and 0.1 μg g−1 for Rb). The developed method was successfully applied for the elemental analysis of fish muscle, oyster, and bovine liver and three certified reference materials, demonstrating good agreement with the certified values and with the reference technique at a 95 % statistical confidence level.

Direct determination of trace elements in austenitic stainless steel samples by ETV-ICPOES

Electrothermal vaporization (ETV) coupled to inductively coupled plasma optical emission spectrometry (ICPOES) was applied to the direct analysis of austenitic stainless steel powders using external calibration with increasing amounts of urban particulate matter (NIST 1648a) certified reference material.

Possibilities of High Resolution Inductively Coupled Plasma Optical Emission Spectrometry in the Determination of Trace Elements in Environmental Materials

This paper presents new quantitative data for the spectral interferences obtained by high resolution 40.68 MHz radial viewing inductively coupled plasma optical emission spectrometry (HR-ICP-OES) in the determination of Zn, Cd, Sb, Cu, Mn, Pb, Sn, Cr, U, and Ba in environmental materials in the presence of a complex matrix, containing Al, Ca, Fe, Mg, and Ti. The �� -concept for quantification of spectral interferences was used. The optimum line selection for trace analysis of a variety of multicomponent matrices requires the choice of prominent lines, which are free or negligibly influenced by line interference problems. The versatility of �� -concept as basic methodology was experimentally demonstrated in the determination of trace of elements in soil and drinking water. The detection limits are lower in comparison with corresponding threshold concentration levels for soil and drinking water in accordance with environmental regulations. This paper shows the possibilities of present day ICP-OES equipment in the direct determination of trace elements (without preconcentration of impurities) in environmental samples.

Determination of trace elements in biological fluids

Main approaches to the trace element analysis of biological fluids and problems appearing in this case are considered. The specific character of these approaches is illustrated by the examples of the analysis of real samples for various trace elements. The advantage of methods for the direct determination of trace elements in these samples is demonstrated.

A novel total reflection X-ray fluorescence procedure for the direct determination of trace elements in petrochemical products

A total reflection X-ray fluorescence (TXRF) procedure was developed for the determination of metal traces in petrochemical end products or intermediates for surfactant synthesis. The method combines a fast and straightforward sample preparation, i.e. deposition on the sample holder and evaporation of the sample matrix, with an efficient quantification method based on internal standardization (organic gallium standard). The method developed showed detection limits below 0.05μgg(-1) and in most cases below 0.005μgg(-1). Fifteen elements (Ca, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Rh, Sn, Sr, V and Zn) were determined in matrices such as paraffins, n-olefins, linear alkylbenzenes, long-chain alkyl alcohols and esters: typical metal contents were below 1μgg(-1). The results were compared with the reference method ASTM D5708 (test method B) based on inductively coupled plasma optical emission spectroscopy: advantages and drawbacks of the two procedures were critically evaluated. The TXRF method developed showed comparable precision and absence of bias with respect to the reference method. A comparison of the performances of the two methods is presented.

Direct determination of trace elements in boron nitride powders by slurry sampling total reflection X-ray fluorescence spectrometry

The use of slurry sampling total reflection X-ray fluorescence spectrometry (SlS-TXRF) for the direct determination of Ca, Cr, Cu, Fe, Mn and Ti in four boron nitride powders has been described. Measurements of the zeta potential showed that slurries with good stabilities can be obtained by the addition of polyethylenimine (PEI) at a concentration of 0.1 wt.% and by adjusting the pH at 4. For the optimization of the concentration of boron nitride in the slurries the net line intensities and the signal to background ratios were determined for the trace elements Ca and Ti as well as for the internal standard element Ga in the case of concentrations of boron nitride ranging from 1 to 30 mg mL − 1. As a compromise with respect to high net line intensities and high signal to background ratios, concentrations of 5 mg mL − 1 of boron nitride were found suitable and were used for all further measurements. The limits of detection of SlS-TXRF for the boron nitride powders were found to range from 0.062 to 1.6 μg g – 1 for Cu and Ca, respectively. Herewith, they are higher than those obtained in solid sampling and slurry sampling graphite furnace atomic absorption spectrometry (SoS-GFAAS, SlS-GFAAS) as well as those of solid sampling electrothermal evaporation inductively coupled plasma optical emission spectrometry (SoS-ETV-ICP-OES). For Ca and Fe as well as for Cu and Fe, however, they were found to be lower than for GFAAS and for ICP-OES subsequent to wet chemical digestion, respectively. The universal applicability of SlS-TXRF to the analysis of samples with a wide variety of matrices could be demonstrated by the analysis of certified reference materials such as SiC, Al 2O 3, powdered bovine liver and borate ore with a single calibration. The correlation coefficients of the plots for the values found for Ca, Fe and Ti by SlS-TXRF in the boron nitride powders as well as in the before mentioned samples versus the reference values for the respective samples over a concentration range from 2.5 to 1470 μg g – 1 were found to be 0.995, 0.991 and 0.997, respectively.

Direct multielement determination of trace elements in boron carbide powders by slurry sampling ETV-ICP-OES

The use of slurry sampling electrothermal evaporation inductively coupled plasma optical emission spectrometry (SlS-ETV-ICP-OES) for the direct determination of trace elements in boron carbide powders with different particle size distributions was investigated. It was found that the addition of 6 mL min−1 of Freon R12 (Cl2F2C) to the 500 mL min−1 Ar carrier gas flow as a thermochemical reagent resulted in an increase of the net line intensity for Ti by a factor of 25 in SlS-ETV-ICP-OES, when analyzing 20 μL of a slurry containing 1% of the boron carbide powder BC-1. After heating the dry residue of 20 μL of a slurry of 1% of boron carbide for 12 s to 2600 °C on a L'vov platform the residues on the platforms were analyzed by total reflection X-ray fluorescence spectrometry (TXRF). The evaporation efficiency for Ti was found to have increased from 12 to 97% by the addition of 6 mL min−1 of R12 as compared to evaporation in Ar only. When heating dry residues of boron carbide slurries on L'vov platforms to temperatures ranging from 2000 to 2600 °C without adding R12 to the Ar, it could be observed visually that only a small fraction of the boron carbide matrix is evaporated. However, when heating at 2600 °C under the addition of R12 almost no residues were found on the platform after the evaporation step. For the analysis of boron carbide powders with SlS-ETV-ICP-OES the limits of detection were found to be between 0.002 and 2 μg g−1 for the elements Al, Ca, Co, Cr, Cu, Fe, Mg, Mn, Na, Ni and Ti. For Fe a wide variety of samples could be analyzed by SlS-ETV-ICP-OES with one calibration under the use of R12. This was shown for different samples, namely three boron carbide powders, three boron nitride powders, an aluminium oxide powder (NIST 699), silicon carbide powder (BAM S-003), powdered apple leaves (NIST 1515), a reference sample for trace elements in natural water (NIST 1643d) and an aqueous standard solution. When plotting the net line intensities versus the accepted concentrations a coefficient of determination of 0.990 is obtained. By SlS-ETV-ICP-OES under the addition of R12 the values obtained were found to be between 78 to 128% of the mean of the results of slurry sampling-TXRF and of ICP-OES subsequent to wet chemical digestion. 11 trace elements with concentrations ranging from 0.7 to 370 μg g−1 for Co and Fe, respectively, could be determined in two boron carbide powders with particle size distributions of d90 = 3.5 μm and d90 = 9.2 μm, respectively.

The synergy of elemental and biomolecular mass spectrometry: new analytical strategies in life sciences

The application of mass spectrometry with soft ionization techniques (ESI, electrospray ionization, and MALDI, matrix-assisted laser desorption ionization) in the life sciences for the detection and identification of biomolecules is already well established, whereas the application of elemental mass spectrometry and in particular inductively coupled plasma mass spectrometry (ICP-MS) for the determination of metals, metalloids and non-metals in biomolecules is rather new and there is some hesitation in accepting this analytical method, although it offers many advantages. Therefore, it is the aim of this tutorial review to highlight new analytical strategies consisting of the combined applications of elemental and molecular mass spectrometric techniques. In fact, elemental and biomolecular mass spectrometric methods are highly complementary: elemental mass spectrometry methods, such as ICP-MS, offer very sensitive element analysis in the trace and ultra-trace concentration range with multielement capability and the excellent and uniform sensitivity is structure-independent and can be used analytically for accurate quantification as well as for fast screening of specific elements even in complex samples. Laser ablation (LA) ICP-MS, as a solid state mass spectrometric technique, allows the direct determination of trace elements in biological and environmental samples and is applied for microlocal analysis with spatial resolution in the mum range. In contrast, molecular weight determination and structural information is completely lost during the ionization step so that these features have to be provided by biomolecular mass spectrometry and in particular by ESI- and MALDI-MS. On the basis of selected examples, it will be shown that only the combination of different elemental and biomolecular mass spectrometric techniques can solve analytical problems in the life sciences and environmental research in a synergistic way where neither technique alone would be successful. This synergy will be demonstrated by selected applications from various areas: food and nutrition, toxicology, clinical and pharmaceutical research, biochemistry and in particular proteomics. Future developments and trends will be discussed concerning instrumental developments of new mass spectrometric techniques providing high sensitivity with lower detection limits for many elements measured quasi-simultaneously so that new analytical information about biological systems can be drawn from isotopic information and the application of stable non-radioactive isotopic tracers. In addition, elemental labels enable the development of new high-throughput screening techniques based on multiplexed biomarkers. Advanced powerful surface mass spectrometric techniques are required for the imaging of elemental and molecular information in order to analyse tissue samples and to develop novel array-based biochips.

Direct Determination of Trace Elements in Powdered Samples by In-Cell Isotope Dilution Femtosecond Laser Ablation ICPMS

A method has been developed for the direct and simultaneous multielement determination of Cu, Zn, Sn, and Pb in soil and sediment samples using femtosecond laser ablation inductively coupled plasma mass spectrometry (fs-LA-ICPMS) in combination with isotope dilution mass spectrometry (IDMS). The in-cell isotope dilution fs-LA-ICPMS method proposed in this work was based on the quasi-simultaneous ablation of the natural abundance sample and the isotopically enriched solid spike, which was performed using a high repetition rate laser and a fast scanning beam device in a combined manner. Both the sample preparation procedure and the total analysis time have been drastically reduced, in comparison with previous approaches, since a unique multielement isotopically enriched solid spike was employed to analyze different powdered samples. Numerous experimental parameters were carefully selected (e.g., carrier gas flow rate, inlet diameter of the ablation cell, sample translation speed, scanner speed, etc.) in order to ensure the complete mixing between the sample and the solid spike aerosols. The proposed in-cell fs-LA-ICP-IDMS method was tested for the analysis of two soil (CRM 142R, GBW-07405) and two sediment (PACS-2, IAEA-405) reference materials, and the analysis of Cu, Zn, Sn, and Pb yielded good agreement of usually not more than 10% deviation from the certified values and precisions of less than 15% relative standard deviation. Furthermore, the concentrations were in agreement not only with the certified values but also with those obtained by ICP-IDMS after the microwave-assisted digestion of the solid samples, demonstrating therefore that in-cell fs-LA-ICP-IDMS opens the possibility for accurate and precise determinations of trace elements in powdered samples reducing the total sample preparation time to less than 5 min. Additionally, scanning electron microscope measurements showed that the aerosol generated by in-cell fs-LA-ICP-IDMS predominantly consisted of linear agglomerates of small particles (in the order of few tens of nanometers) and a few large spherical particles with diameters below 225 nm.

Direct inductively coupled plasma-atomic emission spectrometry analysis of trace elements in muscle tissues of hairtail using electrothermal vaporization with slurry sampling.

A procedure for direct determination of trace elements in muscle tissue of hairtail was developed using inductively coupled plasma-atomic emission spectrometry and electrothermal vaporization with slurry sampling. Due to use of polytetrafluoroethylene as the chemical modifier, the vaporization behaviors of analytes from the slurry and the aqueous standard solutions were very similar. In this case, the aqueous standards could be used for the calibration of slurry samples. The main factors influencing this method were studied systematically. The detection limits for Cr, Ni, Zn, Cd, and Pb were 3.1, 10.5, 176, 6.9, and 83 ng/mL, respectively, and the relative standard deviations were less than 10%. The proposed method was applied to the determination of trace Cr, Ni, Zn, Cd, and Pb in hairtail samples with satisfactory accuracy and precision. A certified reference material of mussel (GBW 08571) was analyzed, and good agreement was obtained between the results from the proposed method and certificate values.

Direct Determination of Trace Elements in High Purity Gallium by High Resolution Inductively Coupled Plasma Mass Spectrometry

An analytical method using high resolution inductively coupled plasma mass spectrometry (HR-ICP-MS) for rapid simultaneous determination of Be, Mg, Al, Si, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ge, As, Mo, Ag, Cd, In, Sb, Ba, Pb, and Bi elements in high purity gallium was described. The sample was dissolved in HNO 3 and HCl by microwave digestion, then the above 22 elements in the solution were detected directly by HR-ICP-MS. Most of the spectral interferences could be avoided by measuring in the high resolution mode (HRM). The matrix effects because of the presence of excess HCl and Ga were evaluated. Correction for matrix effects was made using Sc, Rh and Tl as internal standards. The conditions of the determination were optimized and discussed. The result showed that the detection limit of the method was in the range of 0.001–0.21 μ g l −1, the relative standard deviation (RSD) was less than 3.3% and the recovery of the samples was in the range of 89.8%–111.6%.

Derivative flame atomic absorption spectrometry and its application in trace analysis

Flame atomic absorption spectrometry (FAAS) is an accepted and widely used method for the determination of trace elements in a great variety of samples. But its sensitivity doesn’t meet the demands of trace and ultra-trace analysis for some samples. The derivative signal processing technique, with a very high capability for enhancing sensitivity, was developed for FAAS. The signal models of conventional FAAS are described. The equations of derivative signals are established for FAAS, flow injection atomic absorption spectrometry (FI-FAAS) and atom trapping flame atomic absorption spectrometry (AT-FAAS). The principle and performance of the derivative atomic absorption spectrometry are evaluated. The derivative technique based on determination of variation rate of signal intensity with time (dI/dt) is different from the derivative spectrophotometry (DS) based on determination of variation rate of signal intensity with wavelength (dI/dλ). Derivative flame atomic absorption spectrometry (DFAAS) has higher sensitivity, lower detection limits and better accuracy. It has been applied to the direct determination of trace elements without preconcentration. If the derivative technique was combined with several preconcentration techniques, the sensitivity would be enhanced further for ultra-trace analysis with good linearity. The applications of DFAAS are reviewed for trace element analysis in biological, pharmaceutical, environmental and food samples.

Partitioning behaviour of trace elements in a stoker-fired combustion unit: An example using bituminous coals from the Greymouth coalfield (Cretaceous), New Zealand

In order to understand trace element behaviour during combustion of coals from the Greymouth coalfield, combustion tests were performed on three seam composite samples. The major and trace elements from sub-samples of feed coal, bottom ash, fly ash, and flue gas were analysed by different techniques including inductively coupled plasma mass spectrometry (ICP-MS), inductively coupled plasma-atomic emission spectrometry (ICP-AES), wavelength dispersive X-ray fluorescence (WD-XRF), and scanning electron microscopy with energy-dispersive X-ray analyser (SEM-EDXA). To help better understand trace element partitioning in combustion ash, float–sink and sequential leaching experiments were also employed to determine the association of trace elements with mineral matter or organic matter. Instrumental Neutron Activation Analysis (INAA) was also employed to determine trace element content in float and sink fractions of fly ash as well as in three major phases in the bottom ash. The partitioning behaviour of trace elements, including some that are environmentally sensitive, was also investigated through the use of float–sink tests and direct determination of trace elements in different combustion ash types and phases. Mass balance and partitioning of major and trace elements have been studied to determine the fate of trace elements after combustion. The partitioning of trace elements, especially hazardous air pollutants (HAPs), in different combustion ashes can be summarised as follows: 1. Most trace elements, especially As, Ba, Co, Cr, Mn, Ni, are partitioned in the glassy and refractory bottom ash fractions. 2. A significant proportion of trace elements of As, Se, and Pb are partitioned into fly ash fractions. 3. Some volatile elements (e.g. > 90% of S and Hg and up to 64% of Cl) and, to a lesser extent, B (up to 44%) and Cd (up to 50%) are partitioned in the flue gas fraction. 4. Although the low ash yield of Greymouth coal seams have the advantage of generating less solid combustion ash, one of the accompanying consequences is that resultant trace elements tend to be enriched in the ash to a greater magnitude than other more clastic sediment influenced coals.

Electrothermal vaporization in inductively coupled plasma atomic emission spectrometry for direct multielement analysis of food samples with slurry sampling

Slurry sampling followed by electrothermal vaporization (ETV) was used as sample introduction technique in inductively coupled plasma atomic emission spectrometry (ICP-AES) for the direct determination of trace elements in food samples. A polytetrafluoroethylene (PTFE) emulsion was used as a fluorinating reagent to promote vaporization and the transportation of analytes. The main factors affecting the analytical signals were investigated in detail. Under optimum operating conditions, the detection limits (DL) for this method varied from 1.8 (Cu) to 215 ng/mL (Zn), while the relative standard deviations (RSD) were in the range 2.6% (Cu)-7.2% (Zn). The proposed method was successfully applied to the direct determination of trace amounts of V, Cu, Cr, Fe, Zn, and La in rice without any chemical pretreatment. The precision was evaluated by analyzing a standard reference material (tea leaves, GBW 07605) and comparing the results from this method with results obtained by pneumatic nebulization (PN) ICP-AES after the wet-chemical decomposition of the same sample.

Preconcentration and determination of trace elements with 2,6-diacetylpyridine functionalized Amberlite XAD-4 by flow injection and atomic spectroscopy

An on-line flow injection method for the direct determination of trace elements in environmental samples is described. A mini-column packed with 2,6-diacetylpyridine functionalized Amberlite XAD-4 was used to preconcentrate and separate 8 trace metals (Cd, Co, Cu, Mn, Ni, Pb, U and Zn) from water and extracts from solid samples. The metals were eluted with 0.1 M HNO(3) directly to the detection system (either inductively coupled plasma-mass spectrometry (ICP-MS) or flame atomic absorption spectrometry (FAAS)). As well as demonstrating that the resin could be used to preconcentrate ultra-trace analytes from natural waters, it was also shown to work well at a pH of 5.5. Therefore, after treatment of sample digests with sodium fluoride, samples that contain extremely large concentrations of iron may be analysed for trace analytes without the excess iron overloading the capacity of the resin. To this end, the analytes Cd, Co, Cu and Ni were preconcentrated from acid extracts of certified soil/sediment samples and then eluted with nitric acid to be determined on-line. Limits of detection (3sigma) of Cd = 0.33 microg l(-1), Co = 0.094 microg l(-1), Cu = 0.34 microg l(-1), Mn = 0.32 microg l(-1), Ni = 0.30 microg l(-1), Pb = 0.43 microg l(-1), U = 0.067 microg l(-1) and Zn = 0.20 microg l(-1) for the FI-ICP-MS system and Cd = 22 microg l(-1), Co = 60 microg l(-1), Cu = 10 microg l(-1) and Ni = 4.8 microg l(-1) for the FI-FAAS system were obtained. Analysis of certified reference materials showed good agreement with the certified values using the two methods.

Slurry Sampling Electrothermal Vaporization Combined with ICP-AES for Direct Analysis of Environmental Samples

In this article, a polytetrafluoroethylene (PTFE) slurry was used as a chemical modifier for direct determination of trace elements in environmental samples by electrothermal vaporization inductively coupled plasma atomic emission spectrometry (ETV-ICP-AES) with slurry sampling. The vaporization behaviors of the analytes in slurry and solution were comparatively studied in the presence of PTFE. The main influence factors for this method were examined. Under the optimum operating conditions, the precision of this method was better than 7% with the detection limits varying from 1.7 ng mL−1 (Cu) to 203 ng mL−1 (Zn). The proposed method has been applied to the direct determination of the trace elements in camphor tree leaves and standard reference material (the combined sample of branch and leaf of shrub, GBW 07603) with satisfactory results.

Direct determination of trace elements in sea-water using reaction cell inductively coupled plasma mass spectrometry

A method is described for the direct determination of several transition elements in sea-water by reaction cell (RC)-inductively coupled plasma mass spectrometry (ICP-MS) using ammonia as a reaction gas. Results show significant improvement over standard quadrupole (Q) ICP-MS performance for direct sea-water analysis and were comparable to high resolution (HR) ICP-MS. In this study, the RC-ICP-MS was used to determine chromium, copper, manganese, nickel and vanadium in sea-water. Ammonia gas was passed through the reaction cell to reduce molecular ion interference. These interferences normally lead to false positive results when low resolution quadrupole ICP-MS (Q-ICP-MS) is used to analyze sea-water. Good recoveries were obtained for V-51, Cr-52 and Mn-55 in the 1∶10 diluted sea-water, CASS-4, NASS-4 and SLEW-3. Molecular ion interference was reduced significantly but not completely for Ni-58 and Cu-63, giving rise to a positive bias typically no more than 0.3 µg l−1. A matrix blank subtraction or matrix matched external calibration can be used to further improve the accuracy for these elements at levels below 0.5 µg l−1. Detection limits in the undiluted sea-water range from 0.02 µg l−1 for chromium to 0.3 µg l−1 for copper. The precision and accuracy of the method were checked against three certified reference standards.

Application of laser-induced breakdown spectrometry for direct determination of trace elements in starch-based flours

Spatially resolved laser-induced breakdown spectrometry (LIBS) was investigated to evaluate the feasibility as a quick and simple method to analyze trace elemental concentrations in starch-based flour samples. A Nd∶YAG laser beam (λ = 1064 nm, 30 mJ pulse−1) has been used for generation of laser-induced plasma on sample surface under reduced pressure of argon atmosphere. A series of starch powder samples containing different concentrations of Sr, Mg, Al, Cu, Cr, K, Mn, Rb, Cd, and Pb were used to construct the calibration curves and estimate detection limits of measurements. The calibration graphs for all elements show good linearity (correlation coefficient, r > 0.99) in the range 0–160 µg g−1 or within three orders of magnitude. Detection limits achieved were below 18 µg g−1 for all elements studied in this work. The lowest detection limit (0.3 µg g−1) was obtained from Sr measurement. Precision (%RSD) for the selected analysis was in the range 2–10%. The standard addition method was applied to assess the accuracy of LIBS using a NIES standard rice sample. The concentrations of Mg and Mn in NIES standard rice sample determined by spatially resolved LIBS technique have good agreements with those of certified value within an error range. The results indicate that spatially resolved LIBS has been shown to be an accurate technique for determining trace elements of ppm (µg g−1) level in starch-based food samples directly with an acceptable precision without any tedious digestion and dilution procedure.

Direct determination of trace elements in terephthalic acid by laser induced breakdown spectroscopy

The feasibility of laser induced breakdown spectroscopy (LIBS) as an online tool for trace metal analysis in terephthalic acid (TA) was evaluated. Millions of metric tonnes of TA are produced each year as a raw material for various kinds of polyesters used to make many consumer and industrial products. The conventional techniques used for trace metal analysis in TA are electrothermal atomization atomic absorption spectrometry (ETA-AAS) and inductively coupled plasma optical emission spectroscopy (ICP-OES). However, these techniques require digestion of the sample and dissolution and so are very time consuming and are not suitable for online analysis. LIBS, if it meets the sensitivity and accuracy requirements, will be a very effective tool for online analysis of the production of terephthalic acid and other organic particles. In this work, the main elements of interest, including Mn, Co, Fe, and Na, were studied. The strongest emission line of each element was chosen to obtain the best detection limit. The experimental parameters, including delay time, gate time, sample stage moving speed, and laser repetition rate, were optimized to maximize the signal-to-noise and signal-to-background ratios. Two sampling methods were studied: compressed pellet and loose powder on sticky tape. The preliminary results indicated that there was no difference between these two sampling methods in term of sensitivity and precision. Therefore, the loose powder on sticky tape was preferred for making online analysis of loose powders possible. One unknown and two certified samples were used to determine the accuracy of the method, and the results were compared to those obtained by ICP-OES.

Temporally Resolved Boltzmann Plots and Excitation Temperatures of Iron Atoms in a Helium Radiofrequency Atomization/Excitation Source for Atomic Emission Spectrometry

A polychromator that allows simultaneous measurements of the emission intensities of multiple lines with different excitation energies was constructed. Thus, temporally resolved Boltzmann plots of iron atomic levels became measurable. The polychromator was applied to a helium radiofrequency atomization/excitation source that was developed for direct determination of trace elements in liquid and solid samples of small size. To examine the excitation characteristics and the nonthermal equilibrium in the plasma, temporally resolved excitation temperatures on low and high energy levels of iron atoms and of iron ions were calculated. The observed results indicate that the excitation temperatures fluctuate depending on the change in plasma density and sample vaporization.