Direct determination of trace copper and chromium in silicon nitride by fluorinating electrothermal vaporization inductively coupled plasma atomic emission spectrometry with the slurry sampling technique

A method has been developed for the determination of trace impurities in silicon nitride (Si₃N₄) powders by fluorination assisted electrothermal vaporization (ETV) /ICP-AES using the slurry sampling technique. Polytetrafluoroethylene (PTFE) emulsion as a fluorinating reagent not only effectively destroys the skeleton of Si₃N₄, but also carries out selective volatilization between the impurity elements (Cu, Cr) and the matrix (Si). The experimental parameters influencing fluorination reactions were optimized. The detection limits for Cu and Cr are 1.05 ng/mL ( Cu) and 1.58 ng/mL (Cr), the RSDs are in the range of 1.9–4.2%. The proposed method has been applied to the determination of Cu and Cr in Si₃N₄ ceramic powders. The analytical results were compared with those obtained by independent methods.     

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.     

Direct analysis of tantalum powders by electrothermal vaporization inductively coupled plasma atomic emission spectrometry

A direct inductively coupled plasma atomic emission method for the determination of Ag, Al, As, Ca, Cd, Co, Cu, Fe, Ga, K, Li, Mg, Na and Pb in high-purity tantalum powders has been developed. The electrothermal vaporization technique using a modified longitudinally-heated Grün-ETAAS furnace with sample introduction on a platform and an automated sampling workstation provided the possibility of in situ analyte-matrix separation, freedom of blank, and applicability to routine analysis. Hard- and software were modified to allow signal recording and data processing independent of the spectrometer software. The extent of spectral interferences by Ta-emission at the analyte wavelengths used was determined and the analyte signals of each sample run were automatically corrected. Limits of detection ranging from 5 ng/g (Ag, Cu) to 250 ng/g (K, Pb) were obtained using optimized furnace and spectrometer conditions. The method was applied to the analysis of two tantalum samples and the results for Cu, Fe, K, Mg and Na were compared with those obtained by liquid and solid-samping ETAAS, showing satisfactory agreement.     

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.     

Determination of trace impurities in boron nitride by graphite furnace atomic absorption spectrometry and electrothermal vaporization inductively coupled plasma optical emission spectrometry using solid sampling

Two digestion-free methods for trace analysis of boron nitride based on graphite furnace atomic absorption spectrometry (GFAAS) and electrothermal vaporization inductively coupled plasma spectrometry optical emission (ETV-ICP-OES) using direct solid sampling have been developed and applied to the determination of Al, Ca, Cr, Cu, Fe, Mg, Mn, Si, Ti and Zr in four boron nitride materials in concentration intervals of 1–23, 54–735, 0.05–21, 0.005–1.3, 1.6–112, 4.5–20, 0.03–1.8, 6–46, 38–170 and 0.4–2.3 μg g^− 1, respectively. At optimized experimental conditions, with both methods, effective in-situ analyte/matrix separation was achieved and calibration could be performed using calibration curves measured with aqueous standard solutions. In solid sampling GFAAS, before sampling, the platform was covered with graphite powder and, for determination of Si, also the Pd/Mg(NO₃)₂ modifier was used. In the determination of all analyte elements by solid sampling ETV-ICP-OES, Freon R12 was added to argon carrier gas. For solid sampling GFAAS and ETV-ICP-OES, the achievable limits of detection were within 5 (Cu)–130 (Si) ng g^− 1 and 8 (Cu)–200 (Si) ng g^− 1, respectively. The results obtained by these two methods for four boron nitride materials of different purity grades are compared each with the other and with those obtained in analysis of digests by ICP-OES. The performance of the two solid sampling methods is compared and discussed.     

Direct determination of major elements in solid plant materials by electrothermal vaporization inductively coupled plasma atomic emission spectrometry

The present work demonstrates the capability of electrothermal vaporization (ETV) to become an important tool of solid sample introduction in ICP-AES for plant sample analysis. Direct determination of Al, Ca, Fe, K, Mg, Mn, Na and Zn was investigated in powdered plant samples. Obtaining good results for major elements in plant samples was governed by some special operating conditions. The sensitivity of the method necessitated the use of ICP in radial view configuration. The behavior of elements during vaporization was studied between 500 and 2600 °C. External calibration was carried out using solid external (cellulose) spiked with aqueous standard solutions. However, performances of the analytical method were found dependent of argon flow rates. Analytical accuracy of the method was tested in three reference materials. Analytical results agreed with certified values when cellulose was used in calibration. However, K could not be determined because of excessive sensitivity. Without cellulose, it was found that Fe results were underestimated and Zn results overestimated. Relative standard deviations varied from 3 to 23%. Limits of detection varied from 1 to 80 ng g⁻¹ from one element to the other for a typical mass sample of 2 mg.     

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.     

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.     

Analysis of aluminium-based ceramic powders by electrothermal vaporization inductively coupled plasma atomic emission spectrometry using a tungsten coil and slurry sampling

Slurry sampling followed by electrothermal vaporization was used as sample introduction technique for digestion-free analysis of aluminium nitride and aluminium oxide by inductively coupled plasma atomic emission spectrometry. The vaporizer consisted of a tungsten coil in a quartz chamber. Spectral interferences and background emission caused by tungsten ablation from the coil were reduced by coating it with tungsten carbide. Different approaches for background correction techniques were considered. The analytes Ca, Cd, Co, Cr, Cu, Fe, Mg, Ni and Zn were determined simultaneously, whereas Mn and Na were determined in the sequential mode. Calibration was performed using the standard additions method. The accuracy was checked by comparison of the results with those of independent methods. Detection limits between 0.01 (Mg) and 8.5 μg/g (Co) were achieved.     

Analysis of aluminium-based ceramic powders by electrothermal vaporization inductively coupled plasma atomic emission spectrometry using a tungsten coil and slurry sampling

Slurry sampling followed by electrothermal vaporization was used as sample introduction technique for digestion-free analysis of aluminium nitride and aluminium oxide by inductively coupled plasma atomic emission spectrometry. The vaporizer consisted of a tungsten coil in a quartz chamber. Spectral interferences and background emission caused by tungsten ablation from the coil were reduced by coating it with tungsten carbide. Different approaches for background correction techniques were considered. The analytes Ca, Cd, Co, Cr, Cu, Fe, Mg, Ni and Zn were determined simultaneously, whereas Mn and Na were determined in the sequential mode. Calibration was performed using the standard additions method. The accuracy was checked by comparison of the results with those of independent methods. Detection limits between 0.01 (Mg) and 8.5 μg/g (Co) were achieved. Received: 21 September 1998 / Revised: 30 October 1998 / Accepted: 3 November 1998     

Direct solid sampling electrothermal vaporization of alumina for analysis by inductively coupled plasma optical emission spectrometry

A procedure based on electrothermal evaporation (ETV) and inductively coupled plasma atomic emission spectrometry (ICP-OES) for the determination of trace impurities in Al₂O₃ powders without any sample pretreatment is presented. With the aid of matrix modifier the transport and the evaporation efficiency for refractory compounds could be increased by forming halides with a lower boiling point. As calibration is still a problem in direct solid sample analysis, different calibration approaches including the use of certified reference materials from NIST and standard addition of aqueous solutions of analytes were discussed. The accuracy obtained with calibration and with the standard addition method was shown up for the elements Ca, Fe, Ga, Mg, Mn, Na, Ni and V for the case of Al₂O₃ NIST standard reference material (SRM 699). The ETV–ICP-OES method was used for the analysis of Al₂O₃ powders with impurities in the low μg/g range and the results for the elements Ca, Fe, Ga, Mg, Mn, Na, Ni and V obtained with evaporation of discrete powder amounts with ETV–ICP-OES and slurry evaporation under the use of ultrasonic homogenization during the sampling and ETV–ICP-MS were shown to be in a good agreement.     

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     

Microhomogeneity assessments using ultrasonic slurry sampling coupled with electrothermal vaporization isotope dilution inductively coupled plasma mass spectrometry

Ultrasonic slurry sampling electrothermal vaporization inductively coupled plasma mass spectrometry (USS-ETV-ICP-MS) is a very powerful technique for the direct analysis of solid materials prepared as slurries. The use of isotope dilution USS-ETV-ICP-MS (USS-ETV-ID-ICP-MS) for micro-homogeneity characterization studies of powdered reference materials based on elemental analyses, was investigated. Slurry analysis conditions were optimized taking into consideration density, particle size, analyte extraction, slurry mixing, analyte transport and sampling depth. Slurries were prepared using 1–20 mg of material and adding 1.0 ml of 5% nitric acid diluent containing 0.005% Triton X-100®. Three reference materials were analyzed (RM 8431a Mixed Diet, SRM 1548a Typical Diet and SRM 2709 San Joaquin Soil). Cu and Ni were determined in each material and Fe was also determined in RM 8431a Mixed Diet. ETV conditions were optimized and the benefit of using Pd as a carrier to enhance transport, combined with oxygen ashing was demonstrated. The accuracy of the method was verified by comparing analytical results with certified values. The precision of the method was demonstrated by comparing R.S.D.'s for slurry samples and aqueous standards and elemental ‘homogeneity’ was quantified based on the slurry sampling variability. The representative sample mass analyzed was calculated taking into consideration extraction of analyte into the liquid phase of the slurry. Representative sample masses of approximately 4 mg of RM 8431a provided slurry sampling variabilities of 10% or less for Cu, Fe and Ni. Representative sample masses of approximately 10 mg of SRM 1548a provided slurry sampling variabilities of approximately 10% for Cu and Ni. Representative sample masses of approximately 0.3 mg of SRM 2709 resulted in total analytical variabilities of less than 7%, highlighting the fact that the San Joaquin Soil is clearly the most homogeneous of the materials characterized.     

Plasma behavior during electrothermal vaporization sample introduction in inductively coupled plasma atomic emission spectrometry

Electrothermal vaporization (ETV) sample introduction in inductively coupled plasma atomic emission spectrometry suffers from severe matrix effects. In the present study, the differences between wet and dry plasma conditions are studied. In addition, the influence of the sample composition was investigated. An inductively coupled plasma optical emission spectrometer, with detection based on charge transfer, allowed the simultaneous measurement of ionic and atomic emission line intensities during the transient signal. Mg and Cr were the test elements. The ion-to-atom line ratio increases at higher power settings, but the changes were larger when a nebulizer was used for sample introduction than with ETV sample introduction. The decrease of ion-to-atom line ratios at increasing observation height was more pronounced when ETV was used, due to the absence of water vapor. The gas flow rate showed a stronger influence for nebulization than for ETV. In the presence of a calcium matrix, lower ion-to-atom line ratios were observed, but the ratio did not change significantly within the transient emission signal. Similar line ratios were observed for different amounts of calcium matrix. The values of ion-to-atom line ratios for Mg and Cr indicate that the plasma ionization and thermal characteristics are not modified due to the presence of the calcium matrix.     

Speciation of chromium(III) and chromium(VI) by in situ separation and sequential determination with electrothermal vaporization inductively coupled plasma atomic emission spectrometry

A novel method for the speciation of chromium(III) and chromium(VI) by in situ separation and sequential determination with electrothermal vaporization-inductively coupled plasma-atomic emission spectrometry (ETV-ICP-AES) was developed. The reaction conditions between Cr(III) and 8-hydroxyquinoline (8-Ox) and the vaporization behavior of the chelate formed were investigated in detail. It was found that the Cr(III)-8-Ox chelate could be formed at room temperature and vaporized from graphite furnace under controlled experimental conditions, therefore, an in situ separation of Cr(III) from Cr(VI) was achieved. The retained Cr(VI) in graphite tube was then determined by using fluorination vaporization ETV-ICP-AES with PTFE slurry as chemical modifier. Under optimum experimental conditions, the detection limits for Cr(III) and Cr(VI) are 8.6 ng/ml and 11.3 ng/ml, and the relative standard deviations (R.S.D.s) are 3.8% and 4.1% (c=0.1 μg/ml, n=6), respectively. The linear ranges of the calibration curve for both Cr(III) and Cr(VI) covered three orders of magnitude. The proposed method has been applied to the speciation of Cr(III) and Cr(VI) in water samples with the satisfactory results.     

A comparison of slurry sampling electrothermal vaporization and slurry nebulization inductively coupled plasma mass spectrometry for the direct determination of trace impurities in titanium dioxide powder

A comparison of slurry sampling (SS)-ETV-ICP-MS and slurry nebulization (SN)-ICP-MS for direct determination of trace impurities in titanium dioxide powder is made. The particle size effect, matrix effect and analytical characteristics of SSETV-ICP-MS and SN-ICP-MS are compared. The results have shown that SSETV-ICP-MS has a lower particle size effect and matrix effect compared to SN-ICP-MS. The analytical performance of the two methods reveals that SSETV-ICP-MS and SN-ICP-MS have similar relative detection limits (in the nanogram per liter level); however, the former has a lower absolute detection limit than the latter. Although the precision for SSETV-ICP-MS is a little worse than that for SN-ICP-MS, it is still acceptable for real sample analysis. The two methods were successfully applied for the determination of trace impurities in titanium dioxide powder samples with particle sizes of less than 50 nm, but only SSETV-ICP-MS could be applied for the determination of trace impurities in titanium dioxide powder samples with a particle size of 1 microm.     

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.     

Possibilities of inductively coupled plasma atomic emission spectrometry with electrothermal vaporization in the analysis of high-purity reagents

Possibilities of electrothermal sample vaporization in inductively coupled plasma atomic emission spectrometry (ETV-ICP-AES) in the analysis of high-purity reagents were studied on an example high-purity waters, acid solutions, and trace impurity concentrates. The analytical and background signals in the injection of solutions into inductively coupled plasma (ICP) by pneumatic nebulization and electrothermal vaporization were compared and the of limits of detection in the analysis of high-purity reagents with impurity preconcentration by evaporation were estimated and compared.     

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.