High-Resolution continuum-source atomic absorption spectrometry in an inductively coupled plasma with photodiode array detection

Atomic absorption spectrometry (AAS) is a well established technique using flames and graphite furnaces. An inductively coupled plasma (ICP), however, is an attractive alternative atom/ion reservoir. A high-resolution continuum-source atomic absorption spectrometer with a photodiode array detector and an ICP as the atomization/ionization reservoir is described. Multi-wavelength capability permits the simultaneous determination of several elements by their atomic and/or ionic transitions. Each acquired spectrum is averaged for 10 s to improve the signal-to-noise ratios. Detection limits are calculated for 14 elements and compared with literature values.     

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.     

A helium inductively coupled plasma for atomic emission spectrometry

An annular helium inductively coupled plasma (He ICP) was generated at atmospheric pressure. No external cooling was used to stabilize the plasma. Aqueous solution was injected into the plasma without any difficulty. Preliminary results revealed that the annular He ICP was capable of exciting elements such as Cl and Br which possess high excitation energies. Atomic emission detection limits for Cl and Br were improved by factors of 63 and 34, respectively, as compared to the results obtained from the argon inductively coupled plasma. The excitation temperature of the annular He ICP (4180 K) was less than that of an Ar ICP (5570 K).     

Behaviour of a desolvation system based on microwave radiation heating for use in inductively coupled plasma atomic emission spectrometry

The present paper describes the preliminary results obtained with a desolvation system for inductively coupled plasma atomic emission spectrometry that incorporates a heating unit based on microwave (MW) radiation. This system has been called Microwave Desolvation System (MWDS). The results have proved that MW radiation can be considered as a good choice for aerosol heating in a sample introduction system. MW radiation seems to be a more uniform way of aerosol desolvation than conductive/convective heating (i.e. lower radial temperature gradients), the degree of vaporization of the droplets is less dependent on the liquid flow rate (Q_l), and also the background noise associated with the vaporization of droplets is reduced. As regards the results obtained with MWDS, in comparison with a conventional desolvation system (CDS), they are very dependent on Q_l. When heating is applied, the amount of analyte that leaves the heating step increases by 30–60% with the MWDS, irrespective of Q_l, whereas for the CDS this increase is very high (up to 300%) at low Q_l values (0.4 ml min⁻¹), but almost negligible at high Q_l values (2.4 ml min⁻¹). In agreement with this, the analytical figures of merit are favourable to the CDS at low flow rates, and to the MWDS at high liquid flows. Under all the conditions studied, the amount of solvent that leaves the condensation unit are lower for MWDS than for CDS.     

Interface for capillary electrophoresis coupled with inductively coupled plasma atomic emission spectrometry.

A modified concentric nebulizer was used as the interface to couple capillary electrophoresis (CE) to inductively coupled plasma atomic emission spectrometry (ICP-AES). The CE capillary replaces the central tube of the concentric nebulizer. The tip of the nebulizer tapers slowly to allow uncertainty in the position of the capillary. A platinum wire was inserted into the CE capillary to provide electrical connection to the CE power supply. pH changes inside the capillary due to electrolysis of the background buffer electrolyte was small and has minimal effects on the CE separation. The peak broadening effects due to the nebulizing gas flow, however, were significant. Resolution decreases quickly when the flow-rate of the carrier gas increases. Sample stacking technique was used to improve the resolution of species of opposite charge, e.g., Cr(VI) vs. Cr(III) ions. Detection limit of Cr based on peak area is approximately 10 ppb for the CE-ICP-AES system.     

Modified Babington nebulizer for inductively coupled plasma atomic emission spectrometry.

A PTFE Babingtonnebulizer equipped with a hood was investigated for inductively coupled plasma atomicemission spectrometry in conjunction with a PTFE cyclone chamber, in order to nebulize various sample solutions containing high salts, hydrofluoric acid and/or suspended solid. A hood of 3 mmphi (nozzle side) - 5 mmphi (outlet side) and 6 mm in length gave a comparable or higher sensitivity compared to a system with a commercially available concentric nebulizer and a glass cyclone chamber. Moreover, the present nebulizer was fully interchangeable with a concentric one at normal argon pressure, attaining sufficient stability, a short wash-out time and good nebulizing of high matrices solutions. The present system was successfully applied to the determination of trace impurities in highly pure silica powders.     

Development of transient data acquisition system for hyphenated techniques coupled with inductively coupled plasma atomic emission spectrometry

A transient data acquisition system for flow injection analysis (FIA), high performance liquid chromatography (HPLC), and electrothermal vaporization (ETV) combined with ICP-AES multi-element instrumentation was developed and successfully applied to the analysis of different types of samples, including human serum, human hair and tea, for simultaneous multi-element determinations. The accuracy of the method was verified with hair reference material. Good agreement between the experimental results and certified values, and also satisfactory recoveries from standard additions, were achleved.     

Quality of calibration in inductively coupled plasma atomic emission spectrometry

Calibration is a crucial step during the whole analytical process. A procedure is suggested to assess the quality of linear regression used for the calibration graph, based on the use of confidence limits for the concentration, as the regression coefficient is not appropriate for this purpose. This procedure has been applied to inductively coupled plasma atomic emission spectrometry. It indicates that the use of only three standards should be discouraged because of unacceptably high confidence limits for the concentration. Moreover, use of weighted regression is more adequate in performing the least squares method and provides more constant confidence limits over the concentration range used to construct the calibration graph. This procedure could be easily added to any commercially available ICP system software.     

Carbon-related matrix effects in inductively coupled plasma atomic emission spectrometry

In Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES), it has been observed that the emission intensity of some atomic lines is enhanced or depressed by the presence of carbon in the matrix. The goal of this work was to investigate the origin and magnitude of the carbon-related matrix effects in ICP-AES. To this end, the influence of the carbon concentration and source (i.e. glycerol, citric acid and potassium hydrogen phthalate), the experimental conditions and sample introduction system on the aerosol characteristics and transport, plasma excitation conditions and the emission intensity of several atomic and ionic lines of a total of 15 elements has been studied. Results indicate that carbon related matrix effects do not depend on the carbon source and they become more severe when the amount of carbon loaded into the plasma increases, i.e., when using: (i) carbon concentrations higher than 5 g L^− 1; (ii) high sample uptake rates; and (iii) efficient sample introduction systems. Thus, when introducing carbon into the plasma, the emission intensity of atomic lines with excitation energies below 6 eV is depressed (up to 15%) whereas the emission intensity of atomic lines of higher excitation energies (i.e. As and Se) are enhanced (up to 30%). The emission intensity of the ionic lines is not affected by the presence of carbon. The origin of the carbon-related interferences on the emission intensity of atomic lines is related to changes in the line excitation mechanism since the carbon containing solutions show the same aerosol characteristics and transport efficiencies as the corresponding aqueous solutions. Based on the previous findings, a calibration approach for the accurate determination of Se in a Se-enriched yeast certified material (SELM-1) has been proposed.     

Packed microcolumn SFC coupled with photodiode array UV detector and inductively coupled plasma detector (SFC-photodiode array UV-ICP)

Hyphenation of packed microcolumn SFC, a photodiode array UV detector, and an inductively coupled plasma spectrometer has been developed in order to evaluate the stability of acetylacetone complexes under supercritical conditions.     

电感耦合等离子体原子发射光谱法中Kalman滤波法解析重叠谱线的研究

考察了Kalman滤波技术校正ICP-AES中谱线重叠干扰的潜力。以新息序列的平均平方和为评价函数优化扫描光谱的峰位, 消除扫描过程中可能产生的波长定位误差, 从而保证滤波结果的准确性, 并使实际检出限显著改善。在中等分辨率光谱仪和扫描步长为1.5pm的条件下, 滤波器能有效地分辨峰间距只有4.8pm且峰形基本相同的重叠线对。对峰间距为9.8pm的重叠线时, 当线背比低至0.05左右时仍能获得满意结果。连续背景用理论描述, 因而样品溶液和纯组分溶液的光谱扫描无需扣除溶剂空白。     

Computer expert system for spectral line simulation and selection in inductively coupled plasma atomic emission spectrometry

This paper is an electronic publication in Spectrochimica Acta Electronica (SAE), the electronic section of Spectrochimica Acta, Part B (SAB). This hardcopy text, comprising the main body and an appendix, is accompanied by a disk with programs, data files and a brief manual. The main body discusses purpose, design principle and usage of the computer software for the inductively coupled plasma atomic emission spectrometry (ICP-AES) expert system. The appendix provides a brief instruction on the manipulation of the demonstration program and relevant information on accessing the diskette.The computer software of the expert system has been developed in C++ language to simulate spectra and to select analytical lines in ICP-AES. This expert system is based on a comprehensive model of non-LTE ICP-AES, which includes expertise in plasma discharges, analyte ionization and excitation, and spectral-line shapes. The system also provides several databases in which essential elemental and spectral data are stored. A logic reasoning engine is utilized for selection of the best analytical line with a main criterion of minimizing the true detection limit. The system is user-friendly with pop-up menus, an editor for database operation, and a graphic interface for the display of simulated spectra. The system can simulate spectra and predict spectral interferences with good accuracy.     

Use of magnesium as a test element for inductively coupled plasma atomic emission spectrometry diagnostics

To optimize the atomization and ionization processes in an inductively coupled plasma used as a source in atomic emission spectrometry, the Mg II 280.270-nm/Mg I 285.213-nm line intensity ratio is used. A theoretical ratio is calculated assuming a local thermodynamic equilibrium. A review of previously published experimental values of the ratio is given as a function of the parameters influencing the energy transfer between the plasma and the injected species. In particular, the effects of the power, the carrier gas flow-rate, the i.d. of the torch injector, the use of a sheathing gas and the presence of hydrogen are described. Values of the ratio close to the theoretical values are obtained with the use of a high power (> 1.4 kW), a low carrie gas flow-rate (< 0.6 1 min^?1 and a large i.d. of the injector (> 2 mm). This optimization can also be applied to the minimization of interference effects due to the presence of sodium.     

Comparison of atomic fluorescence and atomic emission spatial distribution profiles in the inductively coupled plasma

Extensive maps of fluorescence from calcium neutral atoms and ions have been measured. These measurements have been made using a readily available commercial torch (MAK Torch, Sherritt Research Centre, Fort Saskatchewan, Alberta, Canada) which has rigidly controlled dimension specifications in order to facilitate interlaboratory comparisons. The measurements were made for ground state Ca atoms and ions (15 point radial profiles) for each of five heights (10,13,19,25 and 31 mm above the load coil), four powers (0.75,1.0,1.25 and 1.5 kW) and three carrier gas flow rates (1,0.85 and 0.65 l/min). In addition complete lateral emission profiles of these same species have also been measured over the same range of conditions. The Ca atomic fluorescence and emission results are compared and as well the fluorescence results for the Sr ion are compared with ICP-mass spectrometric results. Finally, atomic fluorescence and emission results are presented for the Mo atom; these are contrasted with those for the Ca atom and preliminary results for the resonance fluorescence of excited state calcium ion are also presented.     

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.     

Determination of the ZnGeP2 composition by inductively coupled plasma atomic emission spectrometry

A procedure employing inductively coupled plasma atomic emission spectroscopy has been developed for the precise determination of the composition of Zn_{1 + x}Ge_{1 + x}P_{2 + x} alloys after their autoclave digestion. An optimal composition of the acid mixture has been chosen and the conditions preventing element losses in the digestion process have been found. To minimize the error of the developed procedure, the optimal concentration of Zn, Ge, and P in the analytes was found by calculating the results of analysis as atomic ratios Zn : Ge and P : Ge. The accuracy of the developed procedure was confirmed by the standard addition method and the comparison of the results with the results of an independent method. The relative standard deviation of the determination of atomic ratios was 0. 7–2.0%.     

Detection limits of rare earths by inductively coupled plasma atomic emission spectroscopy

Using a medium power (1.25–1.50 kW) ICP as an excitation source and a glass concentric nebulizer, aqueous solutions of rare earth elements are measured. Limits of detection for all the rare earth elements in both pure solution and in a mixture of all the rare earth elements combined are measured except for Pm. Analytical lines and ICP characteristics for such measurements are given.     

On-line monitoring of a frontal chromatographic separation using inductively coupled plasma atomic emission spectroscopy

A test array is described employing a destructive analytical technique for the long-term monitoring of an industrial-scale separation process. As an example, we chose frontal chromatography as the separation and ICP/AES as the analytical method. The feed solution of the process was conveyed by a process pump via the separation unit to a sample station, where a small portion was diverted and transported by a roller pump into the spectrometer. We equipped our array with different loops for operating the process, calibrating the instrument and verifying the calibration. We obtained identical results for the different loops by absorbing the pulsation of the process pump and arranging for identical suction lines of the spectrometer pump. Based on the results, we redesigned the sample station for a technical application using only commercially available parts.     

Correlation study of internal standardization in inductively coupled plasma atomic emission spectrometry

Correlation studies (calculation of the cross-correlation function and correlation coefficients) were carried out between fluctuations in the emission signals from various analyte and internal standard elements. Some statistics are presented which may help give a clearer picture of the utility of the internal standard principle. Improvements in precision brought about by the use of suitable standards are in the region of a factor of two. The use of argon emission lines as internal standards does not prove effective as an inverse correlation is observed between the emission of these lines and analyte lines.