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.     

Computerized simulation of aerosol-droplet desolvation in an inductively coupled plasma

A mathematical model for the desolvation of solvent droplets has been used in conjunction with an existing code for simulation of ICP fundamental parameters. The combination has been used for the calculation of droplet histories and desolvation behavior along the central channel of an ICP. Calculations have been performed for droplets of various sizes and under a variety of ICP operating conditions. As central-channel gas flow rate increases, the point of complete desolvation of the droplet shifts upward in the plasma, away from the load coil. This relationship is fairly linear. As forward power increases, the point of complete desolvation moves down in the discharge, closer to the load coil. This is approximately an inverse relationship. Finally, simulation of behavior for a log-normal size distribution of a large number of droplets (10⁸) shows that the number of surviving droplets falls sigmoidally with height above the load coil. For most nebulizer/spray chamber systems, the desolvation process is complete at a well-defined height in the plasma.     

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.     

Improvement of the capabilities of inductively coupled plasma optical emission spectrometry by replacing the desolvation system of an ultrasonic nebulization system with a pre-evaporation tube

The effect of replacing the desolvation system (i.e., heater/condenser (HC) and membrane desolvator (MD)) of an ultrasonic nebulizer (USN) system with a pre-evaporation tube (PET) that is heated to about 400 °C on the analytical capabilities of inductively coupled plasma optical emission spectrometry (ICP–OES) was investigated. A multivariate optimisation was conducted in each case to find operating conditions maximizing plasma robustness. Under optimum conditions, the analytical performance of ICP–OES was significantly improved (i.e., better sensitivity, detection limit and plasma robustness) with USN–PET compared to that achieved with both the commercially-available USN–HC–MD and a conventional pneumatic nebulizer/spray chamber sample introduction system. However, only the USN–PET approach allows the determination of Hg, which appears to otherwise be lost in the heater/condenser system. Using a simple external calibration, without any matrix matching, and using an argon emission line for internal standardization, the results obtained for the determination of trace elements in certified soil reference materials (SRM 2710 and 2711) by USN–PET were in good agreement with certified values. This is unlike with conventional sample introduction systems where internal standardization using an Ar line is unusual, as it does not compensate for physical interferences, and either internal standardization (with internal standards added to the sample and standard solutions) or matrix-matched calibration is required.     

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.     

Internal quality controls applied in inductively coupled plasma mass spectrometry multi-elemental analysis in the second French Total Diet Study

In 2006, the French Food Safety Agency (AFSSA) started the second French Total Diet Study to assess exposure to essential and non-essential elements through dietary intake by analysing 1352 food samples. A total of 21 elements were analysed to date by Inductively Coupled Plasma Mass Spectrometry after closed vessel microwave digestion, in 660 samples corresponding to at half of the study. This work presents and discusses the results of the various internal quality controls (IQC) applied to ensure that the analytical procedure is correctly carried out, from digestion to analysis, and to enable analytical chemists to validate the results obtained. The whole IQC allows to estimate uncertainties according to elements and to select those that should be discarded from the study or only given as indicative values for elements that were not within defined quality limits.     

Improving the analytical performances of inductively coupled plasma optical emission spectrometry by multivariate analysis techniques

The various multivariate analysis techniques which have been successfully applied to maximize the analytical performance of ICP-OES are reviewed. These include optimization procedures, spectral data processing and calibration methods as well as classification and pattern recognition techniques.     

Direct analysis of mineral components in wine by inductively coupled plasma optical emission spectrometry (ICP-OES)

A direct measuring method for the determination of 15 inorganic components in wine by ICP-OES was developed. It was applied to 17 white wines from 6 German wine-growing regions. In these investigations 15 elements (B, V, Mn, Zn, Fe, Al, Cu, Sr, Ba, Rb, Na, P, Ca, Mg and K) were involved. By using alcoholic calibration solutions the results of the direct measuring method are comparable with those of the control methods. Typical patterns of elements obtained by the multicomponent analyses can be evaluated by multivariate data analysis to recognize the origin of the wines. Received: 30 May 1996 / Revised: 2 July 1996 / Accepted: 5 July 1996     

Direct analysis of mineral components in wine by inductively coupled plasma optical emission spectrometry (ICP-OES)

A direct measuring method for the determination of 15 inorganic components in wine by ICP-OES was developed. It was applied to 17 white wines from 6 German wine-growing regions. In these investigations 15 elements (B, V, Mn, Zn, Fe, Al, Cu, Sr, Ba, Rb, Na, P, Ca, Mg and K) were involved. By using alcoholic calibration solutions the results of the direct measuring method are comparable with those of the control methods. Typical patterns of elements obtained by the multicomponent analyses can be evaluated by multivariate data analysis to recognize the origin of the wines. Received: 30 May 1996 / Revised: 2 July 1996 / Accepted: 5 July 1996     

Uncertainty budget for multi-elemental analysis of plant nutrients in conifer foliar material using inductively coupled plasma atomic emission spectrometry (ICP-AES)

Measurement uncertainties evaluated according to GUM were given in an uncertainty budget for the measurement of mass fractions of 12 elements in conifer tree needle materials. The measurement was performed using ICP-AES, with prior microwave digestion of the dried sample material. The uncertainty budget for Ca as an example showed that correction for a systematic error was the main source of measurement uncertainty. The key to reduced measurement uncertainty therefore lies in identifying the main sources of systematic errors, and reducing the uncertainty associated with their correction. The usefulness of the uncertainty budget was demonstrated in its application to method validation, to the design of a quality control program, and finally for guiding method optimization.     

Parametric analysis of the inductively coupled plasma

A systematic parametric study of an LTE (local thermodynamic equilibrium) mathematical model of pure inductively coupled argon plasma (ICAP) used for spectrochemical purposes was performed by means of computer simulations. The spatial distributions of temperature, gas velocity, magnetic field and energy losses were investigated under typical plasma operating conditions as function of the ICAP geometrical dimensions and dynamic parameters. These theoretical calculations can be used to predict the properties of the applied plasma in the course of practical work, to choose the optimal conditions by changing the operating parameters and to interpret existing analytical results.     

Influence of heated spray chamber desolvation on the detectability in inductively coupled plasma atomic emission spectrometry

 A comparison study has been made of the performance of a heated spray chamber desolvation system for sample introduction into inductively coupled plasma. The heated spray chamber system Mistral replaces the normal spray chamber of an ICP-spectrometer and improves the efficiency of both aerosol generation and transport to the plasma [1]. 27 elements in 6 sample solutions with different mineralization were measured with and without the heated spray chamber system. The higher the mineralization of the sample solution, the less was the increase of the intensity of the spectral lines of the elements determined. An increase of the intensity by the same factor for most of the elements was observed in different sample solutions like drinking water (factor 6), fresh water (factor 5), sea water (factor 1.5) and acid solutions resulting from the digestions of soil (factor 3–4) and rock (factor 2) samples. A few elements in drinking and fresh water were only detectable by using Mistral. A clear improvement of the detection limits was found, but compared to the increase of the intensity not for all elements by the same factor. The detection limits for water samples are in the lower μg/L- and the higher ng/L-level by using Mistral. So the Mistral is an alternative to the ultrasonic nebulizer. Received: 28 November 1995/Revised: 15 February 1996/Accepted: 21 February 1996     

Simplex optimization of a nitrogen-cooled argon inductively coupled plasma for multi-element analysis

A medium power (5 kW) nitrogen-cooled argon inductively coupled plasma (ICP) system was used in an investigation of the basic and modified simplex methods of optimization. The optimum operating conditions for the ICP system were established for 23 commonly determined elements covering a wavelength range from 180 to 340 nm and including an approximately equal number of atomic and ionic lines.Initially the optimization was carried out for individual elements on the basis of two responses: net signal-to-background ratio (SBR) and ionization interference (II).The simplex technique indicated a need to improve the nebulization system.In achievement of maximum SBR, interesting correlations were found between the optimum power required, on the one hand, and the difficulty of excitation of the elements and the optimum intermediate-gas flowrate, on the other.Finally a method for optimization of the conditions for the plasma in multi-element analysis, based on the sequential use of maximum SBR and minimum ionization interference (MII) responses, was devised and successfully tested against several routine analytical methods. Application of the conditions established during these optimizations result in an analytically useful plasma giving good detection limits as well as minimum ionization interference effects.     

Determination of arsenic by inductively coupled plasma mass spectrometry--comparison of sample introduction techniques

A comparison is made of four sample introduction techniques for the determination of As by inductively coupled plasma mass spectrometry. The techniques studied were 1) flow injection with pneumatic nebulization (FIA-PN), 2) direct electrothermal vaporization (ETV), 3) continuous hydride generation (HG) and 4) hydride generation with in situ trapping followed by electrothermal vaporization (HG-ETV). It was found that FIA-PN and ETV gave similar detection limits in concentration units (about 20 pg mL(-1)), although ETV had a much lower absolute detection limit (0.2 pg). Sample introduction by hydride generation gave an inferior detection limit (100-200 pg mL(-1)), also in combination with in situ trapping and ETV, owing to the blank signal from traces of As in NaBH4 which is difficult to eliminate. The results indicate that the more elaborate sample introduction techniques based on ETV and HG may not offer significant advantages compared to normal solution nebulization for the determination of As in simple sample matrices such as natural fresh waters, where matrix removal is not required.     

Intelligent flow-injection—inductively coupled plasma system for matrix matching

Water samples with variable salinity are analysed by a flow-injection—inductively coupled plasma (ICP) system. The sampling zone approach is used to level the sample and standard saline contents in order to compensate for matrix effects. Calibration graphs for Ca, Mg, Al, Fe, P and Si at three different sodium concentrations are obtained. The sample and standard salinity matching is done automatically by processing the sample sodium signal from the ICP with a microcomputer and adding a suitable amount of sodium. The decision process consists in choosing the appropriate standard solution and adjusting the commutation delay for the sampling zone, using a previously determined time—concentration curve. Sodium interference is minimized, allowing the analysis of water samples with a saline matrix up to 2.5% (w/v) NaCl. The proposed method is suitable for 60 samples h^?1.     

膜去溶-ICP-MS法测定高纯Eu_2O_3中14种痕量稀土杂质

研究了不需基体分离,膜去溶-ICP-MS法直接测定高纯Eu2O3中的14种痕量稀土杂质的分析方法。讨论了Eu基体产生的多原子离子对被测元素的质谱干扰。使用膜去溶后,待测元素灵敏度提高3倍左右,EuO/Eu产率从去溶前的0.016%降低为0.0007%。建立了Tm的数学校正方程,通过膜去溶结合数学校正可将Eu基体对Tm干扰完全消除。14种稀土杂质的检出限和(∑RE)为70 ng/L,测定下限和(∑RE)为0.54μg/g。对6N高纯Eu2O3样品进行了分析,样品回收率为96%~109%,RSD小于10%。所建立的方法对Eu2O3标准样品的测定结果与国家标准方法测定结果相一致。     

Characterization of particles made by desolvation of monodisperse microdroplets of analyte solutions and particle suspensions for nanoparticle calibration in inductively coupled plasma spectrometry

Particles produced by low-temperature desolvation of monodisperse microdroplets of analyte standard solution and nanoparticle suspensions in argon were collected on Si-wafers and studied applying scanning electron microscopy and X-ray microprobe techniques. At desolvation temperatures of about 150 °C, the particles from standard solutions are most often spherical and solid with good reproducibility and the analyte elements together with the unavoidable accompanying elements from trace contamination seem to be homogeneously distributed in the particles. However, there are surprising exceptions, particularly at higher temperatures, where analyte elements are separated in the particle by reduction or crystallization, as shown with Au and Ca standard solutions, respectively. Drying droplets of a diluted suspension of 250 nm gold particles at 200 °C revealed another interesting result, the production of relatively stable concave balloons of ∼ 3 µm in diameter including the Au particles. The balloon sheath was formed of compounds made of the contaminant elements in the suspension. The morphology of the particles is discussed in consideration of the Peclet number, the ratio of evaporation rate to analyte diffusion coefficient. The consequences of particle size and morphology for calibration purposes in nanoparticle characterization by ICP spectrometry are discussed.     

Design analysis of a laser ablation cell for inductively coupled plasma mass spectrometry by numerical simulation

A laser ablation setup including outer chamber, sample tube, sample holder and transport tubing was modelled and optimized using advanced computational fluid dynamics techniques. The different components of the setup were coupled and the whole device was modelled at once. The mass transport efficiency and transit times of near infrared femtosecond (fs) laser generated brass aerosols in pure argon and helium–argon mixtures were calculated at experimentally optimized conditions and a transient signal was constructed. The use of helium or argon did not influence the mass transport efficiency, but the signal structure changed. The signal fine structure was retrieved and experimentally validated. Bimodal peak structures were observed that seemed to originate from turbulent effects in the tubing connecting a Y-connector and the injector.     

Capabilities of a photodiode array based system for cataloguing the atomic emission spectra of the inductively coupled plasma

This paper describes a photodiode array based system and discusses its capabilities for cataloguing the atomic emission spectra emitted from an inductively coupled plasma. Dynamic range and line coverage are assessed and compared with those achievable with Fourier transform spectrometry.