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。     

Multiplexed electrothermal vaporization sample introduction system for inductively coupled plasma spectrometry

A multiplexed electrothermal vaporization (ETV) system for sample introduction into an inductively coupled plasma was designed in an effort to increase sample turn-around time. Tungsten filaments (300 W), originally designed for overhead projectors, were chosen for use as ETVs to avoid the high power requirements associated with other ETV devices, e.g. graphite furnaces (2–3 kW). In short, we have multiplexed the thermal stages have been multiplexed such that a vaporization event can take place every 20 s. This represents a significant increase in the throughput typically associated with ETV-ICPMS, which is normally approximately 20–30 samples/h. Evaluated with respect to common figure of merit criteria, the performance of the multiplexed ETV system is similar to that seen with conventional graphite furnace ETV systems. However, several mass spectral interferences can be introduced by the presence of W into the plasma, which hinder the analysis of certain metals (Hg, Mo, etc.). Thus, other low power vaporizers (e.g. Re, Ta) should be considered for use in future systems.     

Simultaneous electrothermal vaporization and nebulizer sample introduction system for inductively coupled plasma mass spectrometry

The novel analytical application of the combination of an inline electrothermal vaporization (ETV) and nebulization source for inductively coupled plasma mass spectrometry (ICP-MS) has been studied. Wet plasma conditions are sustained during ETV introduction by 200 mL/min gas flow through the nebulizer, which is merged with the ETV transport line at the torch. The use of a wet plasma with ETV introduction avoided the need to change power settings and torch positions that normally accompany a change from wet to dry plasma operating conditions. This inline-ETV source is shown to have good detection limits for a variety of elements in both HNO₃ and HCl matrices. Using the inline-ETV source, improved limits of detection (LOD) were obtained for elements typically suppressed by polyatomic interferences using a nebulizer. Specifically, improved LODs for ⁵¹V and ⁵³Cr suffering from Cl interferences (⁵¹ClO⁺ and ⁵³ClO⁺ respectively) in a 1% HCl matrix were obtained using the inline-ETV source. LODs were improved by factors of 65 and 22 for ⁵¹V and ⁵³Cr, respectively, using the inline-ETV source compared to a conventional concentric glass nebulizer. For elements without polyatomic interferences, LODs from the inline-ETV were comparable to conventional dry plasma ETV-ICP time-of-flight mass spectrometry results. Lastly, the inline-ETV source offers a simple means of changing from nebulizer introduction to inline-ETV introduction without extinguishing the plasma. This permits, for example, the use of the time-resolved ETV-ICP-MS signals to distinguish between an analyte ion and polyatomic isobar.     

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.     

Particle sample introduction system for inductively coupled plasma–atomic emission spectrometry

Development and characterization of a new, relatively inexpensive, computer-controlled, particle sample introduction (PSI) system for programmable delivery of small amounts of diluted powdered samples into an inductively coupled plasma (ICP) and measurement by atomic emission spectrometry (AES) is described. The PSI was developed for use with non-hygroscopic particles, in particular those with a particle weight in the ng range (i.e., with a diameter in low μm-range) and for solids that can be converted to a powder (i.e., a collection of particles). In this first report on PSI–ICP–AES, linearity of calibration curves and plasma loading concerns were addressed using three modes of operation. In the first mode, the PSI operated similar to a nebulizer and it delivered to the plasma for a period of 5–10 s a relatively constant amount of particles diluted with graphite. In the second mode, the PSI delivered to the plasma a small “puff” of a diluted sample, thus generating a transient, time-domain signal with duration of about a second. In the third mode, an even smaller “puff” was delivered to the plasma and, using high-speed data acquisition (in the kHz range), time-resolved emission signals from individual, μm-diameter and ng-weight particles were observed. Thus, the PSI can also be thought of as a nano-particle (i.e., ng rather than nm) sample introduction system. Similarly, the high-speed, wide-bandwidth single-channel time-resolved data acquisition mode enabled the determination of particle-size distribution. In addition, a dual-channel (or dual-element) mode enabled homogeneity studies on a per-individual-particle basis. In all modes, linear calibration curves were obtained (provided that plasma loading was avoided). Per-cent relative standard deviation ranged between 3.1% and 4.2% for Ni in certified reference materials but was as high as 50% for heterogeneous soil samples. Tungsten emission signals from refractory tungsten carbide powders were enhanced using mixed gases and by modifying the chemical environment of the ICP using SF₆. Furthermore, when coupled with high-speed data acquisition, PSI brought unique capabilities to ICP–AES for homogeneity studies from individual ng-weight particles and for the determination of particle size distributions. Overall, it was concluded that PSI is an attractive alternative to powder sample introduction systems described in the literature.     

Microwave desolvation for acid sample introduction in inductively coupled plasma atomic emission spectrometry

This study deals with the behaviour of a microwave desolvation system (MWDS) with acid solutions in inductively coupled plasma atomic emission spectrometry. Hydrochloric, nitric, sulphuric and perchloric acids at different concentrations (up to 0.6 mol l⁻¹) have been tested. Sample uptake rate (Q_l) was also varied. The parameters evaluated for each variable were analyte and solvent transport rates and emission intensity. The combination of low acid concentrations (0.05–0.1 mol l⁻¹) and low liquid flows (0.4 ml min⁻¹) leads to the highest analyte transport rate and emission signal and to the lowest solvent transport rate. For Q_l higher than 1.9 ml min⁻¹, the use of an impact bead is advisable. Among the acids tested, sulphuric and perchloric acids give rise to higher emission intensities than hydrochloric acid and nitric acid. Nonetheless, the limits of detection (LODs) obtained with the MWDS are about the same magnitude irrespective of the solution employed. The LODs reached when using the MWDS are similar to those obtained with a desolvation system based on infrared heating of the aerosol.     

Studies on transport phenomena in electrothermal vaporization sample introduction applied to inductively coupled plasma for optical emission and mass spectrometry

In the present work electrothermal vaporization (ETV) was used in both inductively coupled plasma mass spectrometry (ICP-MS) and optical emission spectrometry (OES) for sample introduction of solution samples. The effect of (Pd + Mg)-nitrate modifier and CaCl₂ matrix/modifier of variable amounts were studied on ETV-ICP-MS signals of Cr, Cu, Fe, Mn and Pb and on ETV-ICP-OES signals of Ag, Cd, Co, Cu, Fe, Ga, Mn and Zn. With the use of matrix-free standard solutions the analytical curves were bent to the signal axes (as expected from earlier studies), which was observed in the 20–800 pg mass range by ICP-MS and in the 1–50 ng mass range by ICP-OES detection. The degree of curvature was, however, different with the use of single element and multi-element standards. When applying the noted chemical modifiers (aerosol carriers) in microgram amounts, linear analytical curves were found in the nearly two orders of magnitude mass ranges. Changes of the CaCl₂ matrix concentration (loaded amount of 2–10 μg Ca) resulted in less than 5% changes in MS signals of 5 elements (each below 1 ng) and OES signals of 22 analytes (each below 15 ng). Exceptions were Pb (ICP-MS) and Cd (ICP-OES), where the sensitivity increase by Pd + Mg modifier was much larger compared to other elements studied. The general conclusions suggest that quantitative analysis with the use of ETV sample introduction requires matrix matching or matrix replacement by appropriate chemical modifier to the specific concentration ranges of analytes. This is a similar requirement to that claimed also by the most commonly used pneumatic nebulization of solutions, if samples with high matrix concentration are concerned.     

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.     

Efficiency of sample introduction into inductively coupled plasma by graphite furnace electrothermal vaporization

A laboratory constructed graphite furnace electrothermal vaporizer (GF-ETV) was used for studying transport efficiencies. This device enables collection of the vaporization products that exit the central sampling hole of the horizontal graphite tube. For determination of the transport efficiency between the GF-ETV and the ICP-torch three methods were tested: (1) deposition of the aerosol particles and the vapour of certain elements by mixing the vaporization product with supersaturated steam and subsequent condensation (direct method); (2) dissolution of the deposited sample fraction from the interface components (indirect method); and (3) calculation from line intensities when applying GF-ETV and pneumatic nebulization sample introduction methods using mercury as a reference element. The latter, `mercury reference method' required 100% transport efficiency for mercury with the ETV, which could be approximated with the use of argon as carrier gas (without halocarbon addition). With a 200 cm³/min flow rate of internal argon in the graphite tube, the transport efficiency was between 67 and 76% for medium volatility elements (Cu, Mn and Mg) and between 32 and 38% for volatile elements (Cd and Zn). By adding carbon tetrachloride vapour to the internal argon flow, the transport efficiency increased to 67–73% for the five elements studied.     

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.     

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.     

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.     

Peak broadening from an electrothermal vaporization sample introduction source into an inductively coupled plasma

Signal broadening using electrothermal vaporization with inductively coupled mass spectrometry (ETV-ICPMS) occurs at a rate much faster than would be predicted by simple longitudinal diffusion. A Monte Carlo simulation that focused on particle motion within the transport tubing was created to elucidate the causes of this dispersion within ETV-ICPMS. Several parameters, including the diffusion coefficient, tube diameter, transport tube length, and flow rate were varied to discern their role in signal broadening. Using typical instrumental parameters, the parabolic flow profile generated by laminar flow of the carrier gas was shown to be the primary cause of dispersion. Manipulating the aforementioned variables to lessen the effects of laminar flow led to a decrease in dispersion. Conversely, increasing the role of laminar flow promoted broadening. The broadening processes should be applicable to any transient introduction system where material must be transported to a detection system. Due to the difference in the rate of broadening expected for particles of different sizes, the simulation was used to calculate the average size of particles generated in the ETV using different mass amounts of sample. No change in particle size (∼1 nm) was seen for mass amounts ranging from 10–10 000 pg, which suggests that the particle number is increased with increasing sample mass rather than the average particle size. Using this method of determining particle size, it might be possible to further evaluate the mechanisms of physical ‘carrier’ action.     

Analyte transport efficiency with electrothermal vaporization inductively coupled plasma mass spectrometry

Reported are results for the quantitative determination of absolute transport efficiency in electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) for the Perkin-Elmer HGA-600MS electrothermal vaporizer. The absolute transport efficiencies for Mo, In, Tl and Bi were determined using experimental conditions typical of those applied to real analysis by ETV-ICP-MS. Experiments using an on-line filter trapping apparatus indicated that particles produced by the ETV device were smaller than 0.1 μm in diameter. The nature and condition of the ETV graphite surface, the length of the transfer tube, and the effect that diluted seawater and palladium modifiers have on analyte transport efficiency were investigated. Transport efficiency was comparable for all elements studied and was enhanced with previously used, rather than new, graphite tubes and when seawater and palladium carriers were present. When analyte was vaporized without carrier from a new graphite tube, the transport efficiency to the plasma was approximately 10%. Approximately 70% of the total amount of analyte vaporized was deposited within the ETV switching valve, 19% onto the transfer tubing and 1% onto the components comprising the torch assembly. These conditions represent the `worst case scenario', with analyte transport to the plasma increasing to approximately 20% or more with the addition of carrier.     

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.     

Analyte transport efficiencies in electrothermal vaporization for inductively coupled plasma mass spectrometry

A modified graphite furnace for solid-sampling atomic absorption spectrometry as an electrothermal vaporizer (ETV) was coupled to a Perkin–Elmer/Sciex ELAN 6000 ICP mass spectrometer. The integrals obtained from electrothermal vaporization of aliquots containing As, Cd, Cu, Co, Fe, Mn, Pb, Se, and Zn were compared with those obtained from pneumatic nebulization of the same aqueous standard solution. The pneumatic nebulizer was calibrated by weighing the mass of aqueous aerosol trapped on a filter. With “wet plasma” conditions maintained also for measurements with the ETV and reference signals for analyte signals obtained with the calibrated pneumatic nebulization, the transport efficiency of the ETV system, e.g. the ratio of the analyte amount introduced into the plasma to that amount dosed into the vaporizer, was determined. The transport efficiency of two different tube and interface designs has been evaluated. Investigations with and without the use of trifluoromethane as reactive gas, with different furnace heating rates, and with varying gas flows were performed. In general, the tube equipped with a nozzle led to generally higher transport efficiency than the standard tube. Without trifluoromethane transport efficiencies ranged from 10% to 35% with the standard tube and from 15% to 50% with the nozzle-type tube. With addition of 2 mL min^–1 trifluoromethane to the argon flow of 400 mL min^–1 through the tube, transport efficiencies from 20% to 70% and from 70% to100% were achieved with the standard and nozzle-type tubes, respectively.     

Analyte transport efficiencies in electrothermal vaporization for inductively coupled plasma mass spectrometry

A modified graphite furnace for solid-sampling atomic absorption spectrometry as an electrothermal vaporizer (ETV) was coupled to a Perkin-Elmer/Sciex ELAN 6000 ICP mass spectrometer. The integrals obtained from electrothermal vaporization of aliquots containing As, Cd, Cu, Co, Fe, Mn, Pb, Se, and Zn were compared with those obtained from pneumatic nebulization of the same aqueous standard solution. The pneumatic nebulizer was calibrated by weighing the mass of aqueous aerosol trapped on a filter. With "wet plasma" conditions maintained also for measurements with the ETV and reference signals for analyte signals obtained with the calibrated pneumatic nebulization, the transport efficiency of the ETV system, e.g. the ratio of the analyte amount introduced into the plasma to that amount dosed into the vaporizer, was determined. The transport efficiency of two different tube and interface designs has been evaluated. Investigations with and without the use of trifluoromethane as reactive gas, with different furnace heating rates, and with varying gas flows were performed. In general, the tube equipped with a nozzle led to generally higher transport efficiency than the standard tube. Without trifluoromethane transport efficiencies ranged from 10% to 35% with the standard tube and from 15% to 50% with the nozzle-type tube. With addition of 2 mL min(-1) trifluoromethane to the argon flow of 400 mL min(-1) through the tube, transport efficiencies from 20% to 70% and from 70% to 100% were achieved with the standard and nozzle-type tubes, respectively.     

Determination of lead and nickel in animal bone by microwave-induced plasma atomic emission spectrometry with sample introduction by electrothermal vaporization

Sulphuric/nitric acid digestion of the bone precedes introduction of the diluted digest into a helium microwave-induced plasma via a tantalum electrothermal vaporizer. Atomic emission is measured at the Ni I 352.454-nm and Pb I 405.781-nm lines. Detection limits (aqueous solution) are 1.1 × 10^?10 g Ni and 8 × 10^?11 g Pb. The technique was applied to the analysis of IAEA H-5 animal bone reference material.