Analytical evaluation of electrothermal vaporization/low-pressure inductively coupled plasma atomic emission spectrometry for trace elemental analysis in microliter samples

A novel method for the determination of trace elements in microliter samples using the tantalum filament electrothermal vaporization/low-pressure inductively coupled plasma (ETV/LP-ICP) atomic emission spectrometry has been developed. An improved tantalum filament ETV was directly coupled with LP-ICP system for efficient vaporization of microliter samples and further quantitative analysis. The experimental parameters including ETV current, rf power and mass flow rate of argon carrier gas were optimized using the copper emission signal produced by 5 μl of standard solution (5 μg/ml). Under the optimized condition, the analytical performances including linearity, precision and detection limit for the developed system were investigated. Absolute detection limits in the range of 22–391 pg for selected eight elements (Fe, Cu, Cr, Mn, Pb, K, Zn and Mg) were obtained with satisfactory precision (<8.9% RSD). The feasibility of the developed system has been demonstrated by analyzing wheat gluten NIST standard sample.     

Determination of trace amounts of rare earth and other elements in rice samples by ICP-AES with sample introduction by tungsten-coil electrothermal vaporization

Summary A device with tungsten-coil electrothermal vaporization for sample introduction into ICP has been proposed. It was applied to the determination of trace amounts of rare earth and other elements in rice samples. Several influencing factors were investigated in detail, such as drying and vaporization parameters, carrier gas flow rate, volume of vaporization chamber and matrix effects. Under optimal experimental conditions, the detection limits for Mg, Cu, Mn, Cr, Fe, Co, Ni and eight rare earth elements are of the order of 10⁻⁹−10⁻¹¹ g. The detection limits for the rare earth elements tested by the present method are comparable to and, in most instances, exceed those for the GFAAS and conventional pneumatic nebulisation-ICP-AES. A precision with RSD<6% was obtained.     

Application of low temperature electrothermal vaporization ICP-AES for determination of refractory yttrium with 1-(2-pyridylazo)-2-naphthol as chemical modifier

A low temperature electrothermal vaporization inductively coupled plasma atomic emission spectrometry (ETV-ICP-AES) method was developed for the determination of the refractory yttrium, using 1-(2-pyridylazo)-2-naphthol (PAN) as chemical modifier. The trace yttrium was vaporized as PAN complex into plasma from a graphite furnace at a comparatively low temperature of 1200 °C. The operation conditions were optimized, and the vaporization behavior of Y-PAN chelate and the main factors affecting the determination were investigated in detail. Under the optimized conditions, the detection limit of Y was 0.7 ng ml⁻¹, and the relative standard deviation (R.S.D.) for 0.1 μg ml⁻¹ Y was 4.5% (n=9, v=10 μl). The linear range of calibration curve covered three orders of magnitude. The recommended approach has been applied for analysis of three biological samples with satisfactory results. The accuracy of the method was demonstrated by analyzing two standard reference materials.     

Determination of vanadium and titanium in steel by inductively coupled plasma atomic emission spectrometry with modified use of a tungsten boat furnace atomizer for atomic absorption spectrometry

For electrothermal sample introduction, a commercially available tungsten boat atomizer for atomic absorption spectrometry (AAS) was transferred to a vaporizer for inductively coupled plasma atomic emission spectrometry (ICP-AES). The modification retained as much of the original design of the atomizer as possible, so that the apparatus could be switched easily between conventional tungsten boat furnace (TBF)-AAS and TBF-ICP-AES. By using this system, a procedure for the determination of vanadium and titanium in steel was investigated. The detection limits (S/N=3) of vanadium and titanium were 3.9 and 1.5 ng ml^?1, respectively. The relative standard deviations for five replicate determinations were ca. 3% for both elements. The calibration graphs were linear up to 100 μg ml^?1 vanadium(V) and 10 μg ml^?1 titanium(IV). Results of analyses of some low-alloy steel samples are given.     

Thermal analysis of high-speed high-temperature reactions of refractory carbide synthesis

A new thermoanalytikal method, called electrothermal explosion (ETE) is described in which uniform heating of samples at extremely high rates (up to 10⁵ deg. sec^?1) is achieved. Heating is by direct passing of an electric current through the sample in the initial stages and by chemical heat release after the ignition conditions have been attained. ETE is the only direct method that allows the macrokinetics of heterogeneous reactions occurring in condensed systems to be studied at high temperature and at short conversion times, which are prohibitive for traditional thermoanalytical devices (up to 3500 K and 10^?2 sec respectively). Kinetic data on high-temperature, high-speed interactions in powder mixtures of carbon with titanium, silicon and tantalum are presented. The rate of heat release in the Ti?C system depends only to a small extent on temperature after the metal has melted, being mainly determined by the solution rate of carbon particles. The interaction mechanism in the Si?C system is similar to that in Ti?C, but the high enthalpy of carbon solution in liquid silicon results in a bulk activation energy ofE=55 kcal. mol^?1. Synthesis of tantalum carbide from the elements in the temperature range 1500–3000 K occurs by the mechanism of reaction diffusion and proceeds with strong self-retardation.     

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.     

Determination of lead in sea water by electrothermal atomic absorption spectrometry after electrolytic accumulation on a glassy carbon furnace

Lead in sea water is determined by combining in situ preconcentration of the analyte on a proper glassy carbon furnace from flowing solutions, with electrothermal atomic absorption spectrometry. The apparatus is a modified version of a prototype previously tested for lead determination in different salt solutions and for mercury determination in sea water. The effects of experimental parameters such as pH, flow rate, electrolysis current, electrolysis time, etc., are described and the optimum conditions for determination of lead are given. The relative standard deviation at 1.5 ng Pb ml^-1 is ±1%, and the detection limit (twice the standard deviation of the blank) is 0.03 ng ml^-1.     

Preconcentration of trace lead by adsorption onto a tantalum wire for electrothermal atomization atomic absorption spectrometry with a tungsten tube atomizer

A preconcentration method of lead in waters by adsorption on a tantalum wire was developed for electrothermal atomization atomic absorption spectrometry with a tungsten tube atomizer. After the preconcentration, the tantalum wire was directly inserted into the tungsten tube atomizer. In the preconcentration (adsorption) process for lead, the optimal immersing time was 90 s and the best pH was 4. Under the optimal conditions, the detection limit for lead by the tantalum wire preconcentration method was 6.0 pg mL^− 1 (3S/N) and the relative standard deviation was 6.1%. The influences of large amounts of concomitants on the preconcentration of lead were evaluated. Even though 10³ to 10⁴-fold excess of matrix elements existed in aqueous solution, the lead absorption signal was not significantly affected by the matrix elements. The method with preconcentration on a tantalum wire was applied to the determination of lead in river waters and proved to be sensitive, simple, and convenient. Because this preconcentration method can be utilized in the in-situ treatment of trace lead in environmental water samples, it was unnecessary to carry the water samples to the analytical work place. The present technique was shown to be useful for the determination of lead in environmental water samples at 0.1−1 μg L^− 1.     

Determination of platinum, palladium and rhodium in biological and environmental samples by low temperature electrothermal vaporization inductively coupled plasma atomic emission spectrometry with diethyldithiocarbamate as chemical modifier

A novel method for inductively coupled plasma atomic emission spectrometry (ICP-AES) determination of trace amounts of Pt(II), Pd(II) and Rh(III), based on gaseous compounds introduction into the plasma as their diethyldithiocarbamate complexes by electrothermal vaporization (ETV), was developed. At the temperature of 1100 °C, the trace amounts of Pt, Pd and Rh were vaporized into plasma. The factors affecting the formation of the chelates and their vaporization behaviors, such as ashing temperature and time, vaporization temperature and time, pH and the concentration of chelating reagents were studied in detail. Under the optimized conditions, the limits of detection (LODs) (3σ) of Pt, Pd and Rh for tested solutions were 5.4, 1.4 and 0.8 ng ml⁻¹, and for actual sample (auto-catalyst NIST SRM 2557) were 0.27, 0.07 and 0.04 μg g⁻¹, respectively. The relative standard deviations (RSDs) for Pt, Pd and Rh were 1.4, 2.6 and 2.4% (C_Pt=0.5 μg ml⁻¹, C_Pd,Rh=0.25 μg ml⁻¹, n=7), respectively. The linear ranges of calibration graphs for Pt, Pd and Rh cover three orders of magnitude. Compared with conventional electrothermal vaporization technique, using the reagent of diethyldithiocarbamate as chemical modifier could not only enhance the analytical sensitivities, but also reduce the vaporization temperature. By combination with a separation/preconcentration step, the proposed method had been successfully applied to the analysis of the artificial seawater, tap water and urine with recoveries ranging from 91 to 106%. The two certified reference material meager platinpalladium ore GBW 07293 and auto-catalyst NIST SRM 2557 was also analyzed for validation, and the determined values obtained were in good agreement with the certified values.     

Electrothermal vaporization inductively coupled plasma atomic emission spectrometry determination of gold, palladium, and platinum using chelating resin YPA(4) as both extractant and chemical modifier

A new method for determination of trace gold (Au), palladium (Pd), and platinum (Pt) in environmental and geological samples by electrothermal vaporization (ETV)-inductively coupled plasma atomic emission spectrometry (ICP-AES) with the use of chelating resin YPA₄ as both solid phase extractant and chemical modifier has been developed. The resin loaded with analytes was prepared to slurry and directly introduced into the graphite furnace without any pretreatment. The factors affecting the vaporization behaviors of Au, Pd, and Pt were investigated in detail. It was found that, in the presence of YPA₄, Au and Pd could be quantitatively vaporized at lower vaporization temperature of 1900 °C. Compared with the conventional electrothermal vaporization, the vaporization temperature was decreased by 700 °C, and the detection limits for Au and Pd was decreased by a three-fold. However, a little effect of YPA₄ on the ETV-ICP-AES determination of Pt was found. Under the optimized conditions, the detection limits (3σ) of Au, Pd, and Pt for this method are 75, 60, and 217 pg, respectively; and their relative standard deviations (R.S.D.) are 4.4, 5.6, and 3.7%, respectively (n=9, C=0.2 μg ml⁻¹). The proposed method has been applied to the determination of trace Pd and Pt in sewage sludge, and the results well agreed with the recommended values. In order to further verify the accuracy of the developed method, a GBW07293 certified geological reference material and an auto catalyst NIST SRM 2557 reference material were analyzed, and the determined values coincided with the certified values very well.     

Study on volatilization of ytterbium as 1-(2-pyridylazo)-2-naphthol chelate from electrothermal vaporizer for sample introduction in inductively coupled plasma atomic emission spectrometry

Based on the formation of a volatile 1-(2′-pyridylazo)-2-naphthol (PAN) chelate, a novel method was described for the determination of trace ytterbium by electrothermal vaporization (ETV)-inductively coupled plasma atomic emission spectrometry (ICP-AES). It was found that in the presence of PAN, the trace Yb was quantitatively vaporized from a graphite furnace into ICP at a low temperature of 1100 °C. The main factors affecting the formation and vaporization of the Yb-PAN chelate were investigated in detail. Under the optimized conditions, the 3σ detection limit of Yb for this method was 0.4 ng ml⁻¹ and the relative standard deviation (R.S.D.) for 0.1 μg ml⁻¹ Yb was 3.7% (n=9, v=10 μl). The linear range of calibration spanned three orders of magnitude. The content of Yb in the standard reference material (shrub, GBW 07603) determined by the proposed method was in good agreement with the certified value.     

Determination of aluminum and silicon in biological materials by inductively coupled plasma atomic emission spectrometry with electrothermal vaporization

An atomic emission spectrometric method is described for the determination of trace elements in microvolume samples especially of biological materials. Based upon the arrangement of a commercial electrothermal vaporizer and a 40-MHz inductively coupled plasma, the direct determination of aluminum and silicon in human body fluids such as urine and serum and aluminum in hemodialysis solution is performed. The instrumental system involves vaporizing the sample from a modified graphite electrode followed by atomization and excitation of the vapors in the ICP discharge. Compromise experimental conditions are reported and calibration functions compared. Limits of detection in 5-μl samples were 8 pg Al and 2.5 ng Si, and after preconcentration of Al with a poly(acrylamidoxime) resin, the detection limit was 1 pg Al. Recovery of 5 μg $\text{Si}\text{ml}$ and 10 ng $\text{Al}\text{ml}$ from aqueous and synthetic standards was 80–85% and 96–103%, respectively.     

Direct determination of arsenic in fresh and saline waters by electrothermal vaporization inductively coupled plasma mass spectrometry

A method is described for the direct determination of arsenic in fresh and saline waters by electrothermal vaporization inductively coupled plasma mass spectrometry. Arsenic could be determined directly in waters containing up to 10 000 μg ml⁻¹ NaCl without interference from the formation of ⁷⁵ArCl⁺. For non-saline waters, arsenic was determined directly with the addition to both aqueous calibration standards and samples of 0.1 μg each of Pd and Mg to act as physical carriers. For the analysis of highly saline waters, the use of Pd and Mg chemical modifier served to thermally stabilize arsenic up to a temperature of 1000°C, while the separate addition of 8 mg of ammonium nitrate was used to remove chloride from the sample. This eliminated serious spectral interference on ⁷⁵As⁺ from ⁷⁵ArCl⁺. Although the ArCl⁺ spectral interference was completely eliminated, residual Na co-volatilized with As caused signal suppression, requiring the use of the method of standard additions for calibration. An absolute limit of detection limit for As of 0.069 pg was obtained corresponding to 6.9 pg ml⁻¹ in a 10 μl sample.     

Determination of the rare earth elements La, Eu, and Yb using solidified floating organic drop microextraction and electrothermal vaporization ICP-MS

We have developed a method for the determination of trace levels of the rare earth elements La, Eu, and Yb in biological and environmental samples. It is based on solidified floating organic drop microextraction using 1-(2-pyridylazo)-2-naphthol (PAN) as a chelator, followed by electrothermal vaporization (ETV) and quantification by inductively coupled plasma mass spectrometry. PAN also acts as a modifier in ETV. The effects of pH, amount of PAN, extraction time, stirring rate, volume of sample solution, and temperature program were examined. Under optimized conditions, the detection limits are 2.1, 0.65 and 0.91 pg mL^?1 for the elements La, Eu and Yb, respectively. The relative standard deviations are <6.0 % (c?=?0.1 ng mL^?1, n?=?9). When applied to the analysis of (spiked) natural water samples, the recoveries range from 92 to 105 %. The accuracy was validated with certified reference materials (combined sample of branch and leaf of shrub: GBW 07603 and human hair: GBW 07601), and the results were in good agreement with the certified values.

Determination of sulphur in fuel oils by absorption spectrometry of electrothermally generated carbon sulphide molecules

Molecular absorption spectra of CS are observed during the vaporization of crude and fuel oils in an electrothermal atomizer. The CS absorbance at 257.6 nm is used to determine the sulphur content of the oil, based on measurements in a conventional electrothermal atomic absorption spectrometer. The results for various fuel oils generally agree with those obtained by x-ray fluorescence spectrometry (ASTM D2622). The detection limit referred to the undiluted oil is 50 mg kg^?1, and the repeatability is 3% at the 250 mg kg^?1 level. Some oils exhibit uneven vaporization of sulphur species.     

D. Purves,trace-element contamination of the environment : Elsevier,Amsterdam, 1977, xi + 260 pp., price Dfl. 85, U.S. $34.75

A study of the dissolution rate of magnetite electrodes required a reasonably precise method for the determination of iron in aqueous solutions containing 1 mol kg^-1 sodium perchlorate. Atomic absorption spectrometry with electrothermal atomization in the wavelength range 248–392 nm with ashing at 1600°C proved to be the most satisfactory method. Iron concentrations in the range 0.1–100 μg ml^-1 were determined with 1-μl samples. The addition of low flow rates of acetylene to the nitrogen purge gas improved the reproducibility and increased the carbon rod lifetime.     

Direct determination of trace rare earth elements in ancient porcelain samples with slurry sampling electrothermal vaporization inductively coupled plasma mass spectrometry

A method for the direct determination of trace rare earth elements in ancient porcelain samples by slurry sampling fluorinating electrothermal vaporization inductively coupled plasma mass spectrometry was developed with the use of polytetrafluoroethylene as fluorinating reagent. It was found that Si, as a main matrix element in ancient porcelain sample, could be mostly removed at the ashing temperature of 1200 °C without considerable losses of the analytes. However, the chemical composition of ancient porcelain sample is very complicated, which makes the influences resulting from other matrix elements not be ignored. Therefore, the matrix effect of ancient porcelain sample was also investigated, and it was found that the matrix effect is obvious when the matrix concentration was larger than 0.8 g l^− 1. The study results of particle size effect indicated that when the sample particle size was less than 0.057 mm, the particle size effect is negligible. Under the optimized operation conditions, the detection limits for rare earth elements by fluorinating electrothermal vaporization inductively coupled plasma mass spectrometry were 0.7 ng g^− 1 (Eu)–33.3 ng g^− 1(Nd) with the precisions of 4.1% (Yb)–10% (La) (c = 1 μg l^− 1, n = 9). The proposed method was used to directly determine the trace rare earth elements in ancient porcelain samples produced in different dynasty (Sui, Ming and Qing), and the analytical results are satisfactory.     

Determination of the total carbon in soft drinks by tungsten coil electrothermal vaporization inductively coupled plasma spectrometry

A method is developed for the direct determination of carbon in soft drinks by electrothermal vaporization inductively coupled plasma atomic emission spectrometry. A tungsten coil is used as the electrothermal vaporizer, and is extracted from a commercially produced 150 W, 15 V microscope bulb. The standard additions method is employed to correct any matrix effects from the samples. Carbon emission is monitored at 193.091 nm. Carbon content determined for the samples was in the range of 13 to 60 g in one 8 fl oz serving, and these values agreed with the label values in the range 93 to 137% (except for one sample, Orange Fanta, which provided a 200% recovery. This was likely due to non-carbohydrate carbon-containing species in that sample). The precision of the technique was always better than 20% relative standard deviation (n = 10). The detection limits for carbon range from 0.4 to 3 mg L^{− 1}, and absolute detection limits range from 12 ng to 90 ng for a 30 μL aliquot of sample on the coil. This method could be an alternative approach for determining the carbon content of nonvolatile compounds, and complement HPLC–ICP-AES determination of those same species.     

Application of an ETV-ICP system for the determination of elements in human hair

When determining element contents in hair samples without sample digestion it is necessary to analyze large sample volumes in order to minimize problems of inhomogeneity of biological sample materials. Therefore an electrothermal vaporization system (ETV) is used for solid sample introduction into an inductively coupled plasma (ICP) for the determination of matrix and trace elements in hair. This paper concentrates on the instrumental aspects without time consuming sample preparation. The results obtained for optimization tests, ETV operating parameters and ICP operating parameters, are shown and discussed. Standard additions are used for calibration for the determination of Zn, Mg, and Mn in human hair. Studies including reproducibility and detection limits for chosen elements have been carried out on certified reference materials (CRMs). The determination of reproducibility (relative standard deviation (RSD) of n = 10) and detection limits (DLs) of Zn (RSD < 8.5%, DL < 0.8 μ g⁻¹), Mn (RSD < 14.1%, DL < 0.3 μ g⁻¹), and Mg (RSD < 7.4%, DL < 6.6 μ g⁻¹) are satisfactory. The concentration values found show good agreement with the corresponding certified values. Further sample preparation steps, including hair sampling, washing procedure and homogenization for hair, relating to measurements of real hair samples are described.     

Evaluation and application of internal standardization in atomic absorption spectrometry with electrothermal atomization

A new dual-channel system developed for use in atomic absorption spectrometry is used to assess the internal standard technique for electrothermal atomization. Cobalt was found to be a suitable internal standard for iron determinations, and is used for determination of 7—330 ng Fe ml^-1 in water samples. With use of the internal standard technique, fluctuations caused by atomizer variables are reduced and interferences from many cations are also decreased.