Determination of trace Ag, Au, Ge, Pb, Sn and Te by microwave plasma torch atomic emission spectrometry coupled with an electrothermal vaporization sample introduction system

An electrothermal vaporization (ETV) sample introduction device tantalum filament was combined with microwave plasma torch atomic emission spectrometry (MPT-AES) for determination of several trace elements. Some operating parameters of the system were optimized. The effects of easily ionized elements (EIEs) on the emission intensities of the tested elements were studied in detail. It was revealed that there was no interference resulting from small amount of sample matrix; while with the existence of large amount of sample matrix, the method of standard addition could be used to determine trace elements in samples. So, no modifier was required in this method. The results indicated that ETV-MPT-AES not only has the advantage of micro sample consumption (a volume of 3 mul for each injection), but also offers high sensitivities for the determination of Ag, Au, Ge, Pb, Sn and Te as compared with those obtained with pneumatic nebulization (PN) MPT-AES.     

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.From Zhurnal Analiticheskoi Khimii, Vol. 60, No. 3, 2005, pp. 286–290.Original English Text Copyright © 2005 by Chen.This article was submitted by the author in English.     

Chelation of urinary cadmium with ammonium pyrrolidine dithio-carbamate prior to determination by tungsten-coil inductively coupled plasma atomic emission spectrometry

Cadmium in the urine samples of patients with age-related disease forms a complex with a chelating agent, ammonium pyrrolidine dithio-carbamate, and the complex is extracted with methyl isobutyl ketone. One milliliter of urine provides three separate 200-μl aliquots of extract, so a preconcentration factor of 5/3 is observed. In this manner, the Cd is effectively separated from the complex urine matrix. An internal standard, Bi, is added to improve both precision and accuracy. The extracts are analyzed by inductively coupled plasma atomic emission spectrometry using a tungsten-coil as an electrothermal vaporizer. A 20-μl aliquot of the extract is injected directly onto the coil. Two Cd atomic emission lines are observed simultaneously: 228.8 nm and 226.5 nm. The limits of detection at these wavelengths are 0.04 and 0.2 μg/l, respectively. Without the extraction technique, the detection limit is 0.4 μg/l at the 228.8-nm line. With the internal standard technique, the accuracy as measured with a urine standard reference material is 98%. Six urine samples collected from patients with age-related diseases are found to contain Cd levels in the range 0.9 to 4.1 μg/l. The precision associated with the measurement of these real samples is 6.2% relative standard deviation. The technique provides off-wavelength background correction and simultaneous determination at two different wavelengths, so samples that are limited in volume can still be analyzed with a high degree of confidence.     

Microliter sample introduction into an inductively-coupled plasma by electrothermal carbon cup vaporization

An atomic emission spectrometric system is described for quantifying trace elements in microvolume samples. The system involves vaporizing the sample by electrothermal carbon cup vaporization followed by the atomization and excitation of the vapor cloud in an inductively coupled plasma (i.c.p.). The detection limits for 21 elements in 10-μl samples are at ng ml^-1 and sub-ng ml^-1 levels with linear dynamic ranges of over four orders of magnitude. Carbon cups coated with pyrolytic graphite are overcoated with tantalum carbide. These cups have resulted in improved detection levels (performances) for Al, As, Bi, Co, Cu and Sn relative to those not containing tantalum. However, cups not treated with tantalum are superior for Au, Cd, Ge, Hg, K, Li, Mg, Mn, Rb and Zn. Comparisons between the two types of carbon cups are presented and discussed. Results also are compared with literature values available for other electrothermal vaporization systems.     

Multi-Element Analysis Based on an Automated On-Line Microcolumn Separation/Preconcentration System Using a Novel Sol-Gel Thiocyanatopropyl-Functionalized Silica Sorbent Prior to ICP-AES for Environmental Water Samples

A sol-gel thiocyanatopropyl-functionalized silica sorbent was synthesized and employed for an automated on-line microcolumn preconcentration platform as a front-end to inductively coupled plasma atomic emission spectroscopy (ICP-AES) for the simultaneous determination of Cd(II), Pb(II), Cu(II), Cr(III), Co(II), Ni(II), Zn(II), Mn(II), Hg(II), and V(II). The developed system is based on an easy-to-repack microcolumn construction integrated into a flow injection manifold coupled directly to ICP-AES’s nebulizer. After on-line extraction/preconcentration of the target analyte onto the surface of the sorbent, successive elution with 1.0 mol L⁻¹ HNO₃ was performed. All main chemical and hydrodynamic factors affecting the effectiveness of the system were thoroughly investigated and optimized. Under optimized experimental conditions, for 60 s preconcentration time, the enhancement factor achieved for the target analytes was between 31 to 53. The limits of detection varied in the range of 0.05 to 0.24 μg L⁻¹, while the limits of quantification ranged from 0.17 to 0.79 μg L⁻¹. The precision of the method was expressed in terms of relative standard deviation (RSD%) and was less than 7.9%. Furthermore, good method accuracy was observed by analyzing three certified reference materials. The proposed method was also successfully employed for the analysis of environmental water samples.     

电热蒸发进样电感耦合等离子体原子发射光谱（ETV－ICP－AES）联用技术研究

本文采用国产部件组装了一套ＥＴＶ－ＩＣＰ－ＡＥＳ仪器体系，对装置的连接及操作参数进行优化。深入系统地考察了分析物的蒸发过程和传输过程，提出了难熔元素的蒸发和传输机理。研究了ＥＴＶ－ＩＣＰ－ＡＥＳ中基体效应，提出了以聚四氟乙烯为氟化剂，氟化辅助ＥＴＶ－ＩＣＰ－ＡＥＳ测定难熔元素的新方法，应用于环境和生物标样中痕量元素分析，获得满意结果。     

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.

Development of an electrothermal vaporization ICP–MS method and assessment of its applicability to studies of the homogeneity of reference materials

A method has been developed for measurement of the homogeneity of analyte distribution in powdered materials by use of electrothermal vaporization with inductively coupled plasma mass spectrometric (ETV–ICP–MS) detection. The method enabled the simultaneous determination of As, Cd, Cu, Fe, Mn, Pb, and Zn in milligram amounts of samples of biological origin. The optimized conditions comprised a high plasma power of 1500 W, reduced aerosol transport flow, and heating ramps below 300?°C s^–1. A temperature ramp to 550?°C ensured effective pyrolysis of approximately 70% of the organic compounds without losses of analyte. An additional hold stage at 700?°C led to separation of most of the analyte signals from the evaporation of carbonaceous matrix compounds. The effect of time resolution of signal acquisition on the precision of the ETV measurements was investigated. An increase in the number of masses monitored up to 20 is possible with not more than 1% additional relative standard deviation of results caused by limited temporal resolution of the transient signals. Recording of signals from the nebulization of aqueous standards in each sample run enabled correction for drift of the sensitivity of the ETV–ICP–MS instrument. The applicability of the developed method to homogeneity studies was assessed by use of four certified reference materials. According to the best repeatability observed in these sample runs, the maximum contribution of the method to the standard deviation is approximately 5% to 6% for all the elements investigated.     

Optimization of the operating conditions of solid sampling electrothermal vaporization coupled to inductively coupled plasma optical emission spectrometry for the sensitive direct analysis of powdered rice

Two different approaches were used to improve the capabilities of solid sampling (SS) electrothermal vaporization (ETV) coupled to inductively coupled plasma optical emission spectrometry (ICP-OES) for the direct analysis of powdered rice. Firstly, a cooling step immediately before and after the vaporization step in the ETV temperature program resulted in a much sharper analyte signal peak. Secondly, point-by-point internal standardization with an Ar emission line significantly improved the linearity of calibration curves obtained with an increasing amount of rice flour certified reference material (CRM). Under the optimized conditions, detection limits ranged from 0.01 to 6 ng g⁻¹ in the solid, depending on the element and wavelength selected. The method was validated through the quantitative analysis of corn bran and wheat flour CRMs. Application of the method to the multi-elemental analysis of 4-mg aliquots of real organic long grain rice (white and brown) also gave results for Al, As, Co, Cu, Fe, Mg, Se, Pb and Zn in agreement with those obtained by inductively coupled plasma mass spectrometry following acid digestion of 0.2-g aliquots. As the analysis takes roughly 5 min per sample (2.5 min for grinding, 0.5–1 min for weighing a 4-mg aliquot and 87 s for the ETV program), this approach shows great promise for fast screening of food samples.     

Electrothermal vaporization for the determination of halogens by reduced pressure inductively coupled plasma mass spectrometry

Trace level quantities of some halogen elements are determined by coupling tungsten filament electrothermal vaporization (ETV) with reduced pressure argon inductively coupled plasma mass spectrometry (ICP-MS). Microliter aqueous samples of chlorides, bromides and iodides were loaded on the tungsten wire, where they were dried at constant current and then vaporized by using a high-capacity condenser discharge. On decreasing the pressure of the plasma, analyte intensity increased sharply. The reduced pressure ICP is seen to give a much narrower, more intense signal profile. The detection limits for bromine and chlorine improved about 10 times compared with an atmospheric pressure ICP ionization source. An electron collision ionization mechanism may contribute most to halogen ionization for reduced pressure ICP. The linear dynamic range was over three orders of magnitude. The precision was generally between 3–8%. Matrix effect was investigated with Na as a matrix element. Absolute detection limits for the elements studied are in the picogram to subnanogram range.     

Determination of refractory elements in atmospheric particulates using slurry sampling electrothermal vaporization inductively coupled plasma optical emission spectrometry and inductively coupled plasma mass spectrometry with polyvinylidene fluoride as chemical modifier

Electrothermal vaporization (ETV) inductively coupled plasma optical emission spectrometry (ICP-OES) and inductively coupled plasma mass spectrometry (ICP-MS) with polyvinylidene fluoride (PVDF) as chemical modifier are critically compared for the determination of refractory elements in coal fly ash and airborne particulates. The atmospheric particulates that collected on a PVDF filter were introduced into the graphite furnace in the form of a slurry by dissolving the filter in dimethylformamide, and the dissolved filter PVDF, along with additional added PVDF powder, was used as a chemical modifier for subsequent ETV-ICP-OES and ETV-ICP-MS determination. The vaporization behaviors of analytes (Ti, Zr, V, Mo, Cr, La) in ETV-ICP-OES/MS were studied in detail, and the optimal ETV operating parameters were obtained. Under the optimized operating conditions, the detection limits of target elements were 0.08-2.7 ng m(-3) for ETV-ICP-OES and 0.5-50 pg m(-3) for ETV-ICP-MS, respectively, with analytical precisions of 3.5-7.3% for ETV-ICP-OES and 3.9-9.6% for ETV-ICP-MS, respectively. The tolerable amounts of matrix elements for ETV-ICP-OES are higher than for ETV-ICP-MS. Both ETV-ICP-OES and ETV-ICP-MS were used to directly determine the trace refractory elements in coal fly ash and airborne particulates and the analytical results are comparable.     

Determination of Mercury and Thallium in Seawater by Electrothermal Vaporization Inductively Coupled Plasma Mass Spectrometry

Electrothermal vaporization inductively coupled plasma mass spectrometry (ETV‐ICP‐MS) has been applied to the determination of Hg and Tl in seawater samples. Various modifiers were tested for the best signal of these elements. After preliminary studies, 0.3% EDTA, 0.1%m/vTAC and 1% v/v HCl were added to the sample solution to work as the modifier. Since the sensitivities of Hg and Tl in various seawater matrices and aqueous standard solutions were quite different, standard addition method and isotope dilution method were used for the determination of Hg and Tl in these seawater samples. This method was applied to the determination of Hg and Tl in NASS‐4 and CASS‐3 reference seawater samples and seawater samples collected from the Kaohsiung area. Results obtained by isotope dilution method and method of standard additions agreed satisfactorily. Detection limits were in the range of 5‐15 and 0.4‐0.5 ng l^?1 for Hg and Tl in seawater, respectively, with the ETV‐ICP‐MS method. The precision between sample replicates was better than 18%) for all the determinations.     

Determination of cadmium by an improved double chamber electrothermal vaporization inductively coupled plasma atomic emission spectrometry

An improved double chamber electrothermal vaporization (ETV) system was designed. A new inner chamber and its bottom plate made of quartz glass were attached with carrier support gas inlet port for the determination of cadmium by inductively coupled plasma atomic emission spectrometry (ICP-AES). The use of the inner chamber in combination with the plate played important roles to transport the metal vapor efficiently into argon ICP. Ten-μl sample aliquots were dried at 100 °C and subsequently heated at 1000 °C on the tungsten boat furnace. The evolved vapor was swept into the ICP source through PTFE tubing and the inner chamber by a 0.8 l/min H₂ (7%)-Ar carrier gas. The performance parameters of ETV-ICP-AES such as temperature program and gas flow rate were evaluated using cadmium standard solution. Under the optimized experimental conditions, the best attainable detection limit at Cd II 214.438 nm line was 0.2 ng/ml with linear dynamic ranges of 50 to 10,000 ng/ml for cadmium. The instrumental precision expressed as the relative standard deviation (RSD) from ten replicate measurements of 10,000 ng/ml for cadmium by ETV-ICP-AES was 0.85%. The present method has been successfully applied to the determination of cadmium in zinc-base materials.     

Design and Critical Evaluation of Improved Electrothermal Vaporization Flame Atomic Absorption/Emission Spectrometry for Direct Determination of Trace Metals in Microliter Samples

Improved tantalum-filament electrothermal vaporization flame atomic absorption spectrometry (ETV-FAAS) was developed and used for the direct determination of trace metals in microliter samples. Studies have been made for optimizing the experimental parameters that affect the performance of sample introduction to the flame. Linear calibration graphs are shown for the elements Mn (10–200 ng), Pb (5–200 ng), Cu (5–100 ng), Cd (5–50 ng), Li (1–20 ng), Na (10–80 ng), and K (10–80 ng), using only 10 μl of standard solutions. The detection limits of the elements by ETV-FAAS were much lower than those of conventional FAAS. Absolute detection limits for all elements studied were less than 0.1 ng. The relative standard deviation values for the elements were <10%. The developed method was also applied to the determination of lead concentration in blood samples.     

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.     

Determination of Cd,Pb and Sr by Microwave Plasma Torch Atomic Emision Spectrometry Using an Electrothermal Vaporization Sample Introduction System

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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.     

Chromatographic Determination of Total Selenium in Biofortified Allium sp. following Piazselenol Formation and Micro-Solid-Phase Extraction

Herein, a method based on selective piazselenol formation is applied for total selenium determination in biofortified Allium species. Piazselenol is formed by reacting Se(IV) with an aromatic diamine, namely 4-nitro-1,2-phenylenediamine, in acidic medium. Samples were digested in a nitric acid/hydrogen peroxide open system, followed by selenate reduction in hydrochloric acid. Reaction conditions were optimized in terms of pH, temperature, reaction time, and other auxiliary reagents for interference removal, namely, EDTA and hydroxylamine. For the extraction of the selectively formed 4-nitro-piazselenol, micro-solid-phase extraction (μSPE) was applied, and the analysis and detection of the corresponding complex was performed by HPLC coupled with DAD. An external standard calibration curve was developed (R² = 0.9994) with good sensitivity, and was used to calculate the total selenium content from several Allium plants material, with good intermediate precision (RSD% < 16%). The accuracy of the method was evaluated using both, a comparison with an accepted reference method from our previously published data, as well as three certified reference material with recoveries between 84–126%. The limit of detection was determined to be 0.35 μg/g (in solids) and 1.1 μg/L (in solution), while the limit of quantification was 1.07 μg/g and 3.4 μg/L (in solution). Using the proposed method, selenium content can be quickly and accurately determined in several types of samples. In addition, this study present experimental conditions for overcoming the interferences that might be encountered in selenium determination using piazselenol.     

Speciation of Chromium in Water Samples by Cloud Point Extraction Combined with Low Temperature Electrothermal Vaporization ICP‐OES

Abstract

A new method based on cloud point extraction (CPE) separation and electrothermal vaporization inductively coupled plasma optical emission spectrometry (ETV‐ICP‐OES) detection was proposed for the determination of chromium species. Thenoyltrifluoracetone (TTA) was used as both an extractant for CPE of Cr(III) and a chemical modifier for ETV‐ICP‐OES determination. When the system temperature is higher than the cloud point temperature (CPT) of the selected surfactant, Triton X‐114, the complex of Cr(III) with TTA could enter the surfactant‐rich phase, whereas the Cr(VI) remained in aqueous solutions. Thus, an in situ separation of Cr(III) and Cr(VI) could be realized. The concentrated analyte was introduced into ETV‐ICP‐OES for determination of Cr(III) after proper disposal. Cr(VI) is reduced to Cr(III) prior to determining total Cr, and its assay is based on substracting of Cr(III) from total chromium. The main factors affecting cloud point extraction and the vaporization behavior of the analyte were investigated in detail. Under the optimized conditions, the limit of detection (LOD) for Cr(III) was 0.22 µg/L by preconcentration of a 10 mL sample solution, and the relative standard deviation (RSD) was 3.8% (C_Cr(III)=0.5 µg/mL, n=5). The proposed method was applied to the speciation of chromium in different water samples. In order to verify the accuracy of the method, a certified reference water sample was analyzed, and the results obtained were in good agreement with certified values.     

Observations on the determination of oxygen in silver halides using inductively coupled plasma-atomic emission spectrometry

This paper reports on a novel method for the determination of oxygen in silver halides using inductively coupled plasma-atomic emission spectrometry (ICP-AES). A heating system was designed and set up to heat the sample and to release oxygen which was then sent into the plasma by the argon carrier gas. A demountable extended ICP torch was assembled to prevent air from entering the analytical region of the ICP. The nonresonance near infrared atomic oxygen line, O(I) 777.19 nm, was used for the determination of oxygen. The detection limit of the method was 1.6 μg of oxygen. Pure oxygen was used for calibration. The method had a precision of 4.74% RSD for about 15 μg of oxygen in samples.