Real-time internal standardization with an axially-viewed inductively coupled plasma for optical emission spectrometry

An evaluation of precision improvements using real-time internal standardization with an axially-viewed inductively coupled plasma (ICP) is presented. New findings are presented with respect to the nature of the noise in the analytical signals from the axial ICP. It is observed that a high degree of correlation exists in the line signals from the axial ICP. Using the yttrium ion line at 371.030 nm as the internal standard, the analytical precision after the application of real-time internal standardization is maintained between 0.1 and 0.2% relative standard deviation (RSD) for ion lines. Precision improvement factors of 3 to 4 are obtained by comparison with the uncorrected results. With atomic lines, real-time internal standardization using the yttrium ion line is less effective, yielding precision values between 0.2 and 0.7% RSD. The precision improvement factors for atomic lines are between 1.5 and 3. Thus, real-time internal standardization provides significant improvements in the RSDs of the line signals. The limits of these improvements are explored and an equation is presented which yields the fundamental shot noise limit for precision. Shot noise limited precision is demonstrated. However, this is not possible for all elements using a single internal standard signal. The effectiveness of real-time internal standardization is shown to be dependent on the nature of the specific spectral line. With the axially-viewed ICP, the dominant phenomenon preventing the full benefit of internal standardization from being obtained is the amplitude of the noise in the line signals and not the degree of correlation between analyte and internal standard signals. A trend is observed for atomic transitions in which lower excitation energy is correlated with higher relative noise amplitudes. This finding is in contrast with previously published work on the radially-viewed ICP. An explanation of this result is proposed which takes into account the influence of vaporizing sample droplets in the observation volume.     

Antimony speciation in environmental samples by interfacing capillary electrophoresis on-line to an inductively coupled plasma mass spectrometer

Antimony is a widely distributed trace element of ecotoxicological interest. A pathway via bioalkylation of inorganic Sb species is discussed in the literature, resulting in organically bound Sb species. Therefore, Sb speciation becomes increasingly a matter of interest for risk assessment in the environment. This contribution investigates the possibilities of CE on-line hyphenated to ICP-MS for Sb speciation. Two methods are employed, both highly resolving the species but only one preserving the species stability. The latter used Na2HPO4/NaH2PO4, 20 mM, pH 5.6 as the background electrolyte and NaOH or acetic acid as stacking electrolyte 1 or stacking electrolyte 2, respectively. Detection limits of 0.1 microgram/1-0.7 microgram/1, depending on species, were achieved. When analysing liquid phases from fouling and sewage sludge up to eight antimony species were detected. Sb (V) as well as methylated Sb species were found.     

Determination of lead in bone tissues by axially viewed inductively coupled plasma multichannel-based emission spectrometry

A new procedure for determining low levels of lead in bone tissues has been developed. After wet acid digestion in a pressurized microwave-heated system, the solution was analyzed by inductively coupled plasma multichannel-based emission spectrometry. Internal standardization using the Co 228.615 nm reference line was chosen as the optimal method to compensate for the matrix effects from the presence of calcium and nitric acid at high concentration levels. The detection limit of the procedure was 0.11 g Pb g^–1 dry mass. Instrumental precision at the analytical concentration of ~10 g l^–1 ranged from 6.1 to 9.4%. Precision of the sample preparation step was 5.4%. The concentration of lead in SRM 1486 (1.32±0.04 g g^–1) found using the new procedure was in excellent agreement with the certified level (1.335±0.014 g g^–1). Finally, the method was applied to determine the lead in various fish bone tissues, and the analytical results were found to be in good agreement with those obtained through differential pulse anodic stripping voltammetry. The method is therefore suitable for the reliable determination of lead at concentration levels of below 1 g g^–1 in bone samples. Moreover, the multi-element capability of the technique allows us to simultaneously determine other major or trace elements in order to investigate inter-element correlation and to compute enrichment factors, making the proposed procedure particularly useful for investigating lead occurrence and pathways in fish bone tissues in order to find suitable biomarkers for the Antarctic marine environment.     

Multivariate optimization by exploratory analysis applied to the determination of microelements in fruit juice by inductively coupled plasma optical emission spectrometry

A method for the direct determination (without sample pre-digestion) of microelements in fruit juice by inductively coupled plasma optical emission spectrometry has been developed. The method has been optimized by a 2³ factorial design, which evaluated the plasma conditions (nebulization gas flow rate, applied power, and sample flow rate). A 1:1 diluted juice sample with 2% HNO₃ (Tetra Packed, peach flavor) and spiked with 0.5 mg L^− 1 of Al, Ba, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Sb, Sn, and Zn was employed in the optimization. The results of the factorial design were evaluated by exploratory analysis (Hierarchical Cluster Analysis, HCA, and Principal Component Analysis, PCA) to determine the optimum analytical conditions for all elements. Central point condition differentiation (0.75 L min^− 1, 1.3 kW, and 1.25 mL min^− 1) was observed for both methods, Principal Component Analysis and Hierarchical Cluster Analysis, with higher analytical signal values, suggesting that these are the optimal analytical conditions. F and t-student tests were used to compare the slopes of the calibration curves for aqueous and matrix-matched standards. No significant differences were observed at 95% confidence level. The correlation coefficient was higher than 0.99 for all the elements evaluated. The limits of quantification were: Al 253, Cu 3.6, Fe 84, Mn 0.4, Zn 71, Ni 67, Cd 69, Pb 129, Sn 206, Cr 79, Co 24, and Ba 2.1 µg L^− 1. The spiking experiments with fruit juice samples resulted in recoveries between 80 and 120%, except for Co and Sn. Al, Cd, Pb, Sn and Cr could not be quantified in any of the samples investigated. The method was applied to the determination of several elements in fruit juice samples commercialized in Brazil.     

电感耦合等离子体发射光谱(ICP-OES)在地质样品中的研究进展

电感耦合等离子体发射光谱仪在地质样品无机元素分析测试中常用,具有灵敏度高,干扰小,测定线性范围广、稳定性好等优点。本文就电感耦合等离子体发射光谱法测定地质土壤,岩石样品时,综述了酸溶法、碱熔法、烧结法三种消解体系各自特点及消解剂的特性;详细分析了样品测定时外标法、内标法、标准加入法的选择及应用;探讨了样品测试时仪器条件的优化措施,同时对电感耦合等离子体发射光谱的干扰及校正做了分析。最后,对电感耦合等离子体发射光谱测定技术在地质样品中非金属元素分析物测定的应用及未来发展进行了展望。     

Ion-exchange method for separation and concentration of platinum and palladium for analysis of environmental samples by inductively coupled plasma atomic emission spectrometry

An ion-exchange procedure is proposed for determination of Pt and Pd in environmental samples, using a Dowex 1-X10 anion-exchange resin. Pt and Pd were separated from the matrix elements in the sample by selective retention on the column as anionic chloro complexes and subsequent elution by circulated thiourea at 60 °C. The eluent, containing Pt and Pd was analyzed by inductively coupled plasma (ICP) atomic emission spectrometry (AES). Average recoveries of 98% and detection limit of 15 ng/g for both metals were achieved. Analysis of Pt and Pd concentrations in road dust, sampled from several sites in Germany was performed. The comparison of the obtained data with the concentrations of Pt and Pd in the same samples, determined by ICP-MS showed a very good agreement.     

Multielement analysis of environmental samples by total-reflection X-ray fluorescence spectrometry, neutron activation analysis and inductively coupled plasma optical emission spectroscopy

Summary In environmental research and protection trace elements have to be determined over a wide range of atomic number, down to very low concentrations, and in quite different matrices. This challenge requires the availability of complementary analytical methods characterized by a high detection power and few sources of systematic errors. Besides, the capacity of multielement detection is often desired since it facilitates the tackling of many problems in which numerous trace elements are of direct concern. Total reflection X-ray fluorescence, neutron activation analysis and inductively coupled plasma optical emission spectroscopy, in principle, fulfill these requirements quite well. However, each method has its domain, and the application to certain sample species may be less promising. Under this aspect, the paper summarizes some recent developments and investigations, including intercomparisons as far as possible. Various matrices are considered: rainwater and airborne particulates, soil samples, river sediments and suspended particulate matter, river water filtrates, ovean water, and organic matrices. Capabilities and limitations are discussed. Sample preparation techniques are described if they are new or essential for achieving the results given.

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Multielementanalyse von Umweltproben mit Totalreflexions-Röntgenfluorescenzspektrometrie, Neutronenaktivierungsanalyse und ICP-Emissionsspektroskopie

Zusammenfassung Umweltforschung und Umweltschutz erfordern die Bestimmung von Spurenelementen über einen weiten Bereich der Ordnungszahl, z. T. bis in den extremen Spurenbereich und in ganz unterschiedlichen Matrices. Die Erfüllung dieser Aufgabe setzt die Verfügbarkeit einander ergänzender analytischer Verfahren voraus, die durch eine hohe Nachweisstärke und geringe systematische Fehler gekennzeichnet sein müssen. Hinzu kommt, daß vielfach Multielement-Eigenschaften wünschenswert sind, da bei manchen Fragestellungen zahlreiche Elemente von Interesse sind. Die Totalreflexions-Röntgenfluorescenzanalyse, die Neutronenaktivierungsanalyse und die optische Emissionsspektroskopie mit induktiv angeregter Plasmafackel erfüllen grundsätzlich diese Forderungen in hohem Maße. Jedoch besitzt jede Methode ihre besonderen Stärken, und Anwendungen auf bestimmte Probenarten können weniger erfolgreich sein. Der vorliegende Beitrag faßt unter diesem Aspekt einige neuere Entwicklungen und Untersuchungen zusammen, wobei nach Möglichkeit Vergleiche der verschiedenen Verfahren angestellt werden. Dabei werden die folgenden Matrices behandelt: Niederschlag und luftgetragene Partikel, Bodenproben, Flußsedimente und Schwebstoffe, Flußwasserfiltrate, Ozeanwasser und einige organische Matrices. Die Einsatzmöglichkeiten und die Leistungsgrenzen werden diskutiert. Die Probenvorbereitungstechniken werden beschrieben, sofern sie neu sind oder eine wesentliche Voraussetzung für die Erzielung der angegebenen Ergebnisse darstellen.

     

Oxygen bomb combustion of biological samples for inductively coupled plasma optical emission spectrometry

A rapid sample preparation method is proposed for decomposition of milk powder, corn bran, bovine and fish tissues, containing certified contents of the analytes. The procedure involves sample combustion in a commercial stainless steel oxygen bomb operating at 25 bar. Most of the samples were decomposed within 5 min. Diluted nitric acid or water-soluble tertiary amines 10% v/v were used as absorption solutions. Calcium, Cu, K, Mg, Na, P, S and Zn were recovered with the bomb washings and determined by inductively coupled plasma optical emission spectrometry (ICP-OES). Ethanol mixed with paraffin was used as a combustion aid to allow complete combustion. A cooling step prior releasing of the bomb valve was employed to increase the efficiency of sample combustion. Iodine was also determined in milk samples spiked with potassium iodide to evaluate the volatilization and collection of iodine in amine CFA-C medium and the feasibility of its determination by ICP-OES with axial view configuration. Most of the element recoveries in the samples were between 91 and 105% and the certified and found contents exhibited a fair agreement at a 95% confidence level.     

Radionuclide determination in environmental samples by inductively coupled plasma mass spectrometry

The determination of naturally occurring and anthropogenic radionuclides in the environment by inductively coupled plasma mass spectrometry has gained recognition over the last fifteen years, relative to radiometric techniques, as the result of improvement in instrumental performance, sample introduction equipment, and sample preparation. With the increase in instrumental sensitivity, it is now possible to measure ultratrace levels (fg range) of many radioisotopes, including those with half-lives between 1 and 1000 years, without requiring very complex sample pre-concentration schemes. However, the identification and quantification of radioisotopes in environmental matrices is still hampered by a variety of analytical issues such as spectral (both atomic and molecular ions) and non-spectral (matrix effect) interferences and instrumental limitations (e.g., abundance sensitivity).The scope of this review is to highlight recent analytical progress and issues associated with the determination of radionuclides by inductively coupled plasma mass spectrometry. The impact of interferences, instrumental limitations (e.g., degree of ionization, abundance sensitivity, detection limits) and low sample-to-plasma transfer efficiency on the measurement of radionuclides by inductively coupled plasma mass spectrometry will be described. Solutions that overcome these issues will be discussed, highlighting their pros and cons and assessing their impact on the measurement of environmental radioactivity. Among the solutions proposed, mass and chemical resolution through the use of sector-field instruments and chemical reactions/collisions in a pressurized cell, respectively, will be described. Other methods, such as unique sample introduction equipment (e.g., laser ablation, electrothermal vaporisation, high efficiency nebulization) and instrumental modifications/optimizations (e.g., instrumental vacuum, radiofrequency power, guard electrode) that improve sensitivity and performance will also be examined.     

Application of an orthogonal method for optimizing an inductively coupled plasma mass spectrometer.

The orthogonal method can be used to predict the optimum instrumental conditions and to guide the optimizing operations. This simplifies the ICP-MS optimization. In general, the final optimum parameter combination used in an analysis can be obtained after fine adjustments of the preferred parameters derived from the orthogonal experiment. This method can also be used to study the relationship between the parameter settings and the signal intensity deflection to improve the analysis of elements of a limited mass range or of isotopes.     

Alcohol and metal determination in alcoholic beverages through high-temperature liquid-chromatography coupled to an inductively coupled plasma atomic emission spectrometer

In the present work, an inductively coupled plasma atomic emission spectrometry (ICP-AES) system was used as a high temperature liquid chromatography (HTLC) detector for the determination of alcohols and metals in beverages. For the sake of comparison, a refractive index (RI) detector was also employed for the first time to detect alcohols with HTLC. The organic compounds studied were methanol, ethanol, propan-1-ol and butan-1-ol (in the 10-125 mg/L concentration range) and the elements tested were magnesium, aluminum, copper, manganese and barium at concentrations included between roughly 0.01 and 80 mg/L. Column heating temperatures ranged from 80 to 175 °C and the optimum ones in terms of peak resolution, sensitivity and column lifetime were 125 and 100 °C for the HTLC-RI and HTLC-ICP-AES couplings, respectively. The HTLC-ICP-AES interface design (i.e., spray chamber design and nebulizer type used) was studied and it was found that a single pass spray chamber provided about 2 times higher sensitivities than a cyclonic conventional design. Comparatively speaking, limits of detection for alcohols were of the same order for the two evaluated detection systems (from 5 to 25 mg/L). In contrast, unlike RI, ICP-AES provided information about the content of both organic and inorganic species. Furthermore, temperature programming was applied to shorten the analysis time and it was verified that ICP-AES was less sensitive to temperature changes and modifications in the analyte chemical nature than the RI detector. Both detectors were successfully applied to the determination of short chain alcohols in several beverages such as muscatel, pacharan, punch, vermouth and two different brands of whiskeys (from 10 to 40 g of ethanol/100 g of sample). The results of the inorganic elements studied by HTLC-ICP-AES were compared with those obtained using inductively coupled plasma mass spectrometry (ICP-MS) obtaining good agreement between them. Recoveries found for spiked samples were close to 100% for both, inorganic elements (with both HLTC-ICP-AES and ICP-MS) and alcohols (with both HTLC-ICP-AES and HTLC-RI hyphenations).     

Direct determination of trace elements in tungsten products using an inductively coupled plasma optical emission charge coupled device detector spectrometer

An echelle inductively coupled plasma optical emission spectrometer equipped with a segmented array of charge coupled device detectors was used for the direct determination of trace impurities in tungsten products. No sample preparation was necessary. The multicomponent spectral fitting software provided by the instrument was used for the correction of spectral interference and background. The detection limits of the trace elements Al, As, Bi, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Mo, Ni, P, Pb, Sb, Sn, Ti and V in tungsten matrix were obtained under optimized operating conditions. The accuracy of the proposed method was assessed using three National Reference Materials. As a result of their ultra-trace concentrations in the reference materials, As, Pb and Sn could not be determined satisfactorily. The concentrations found for the other elements agreed quite well with those of the certified values of the reference materials.     

Comparison between X-ray fluorescence and inductively coupled plasma atomic emission spectrometry in the analysis of sediment samples

Two multielemental analytical techniques, X-ray fluorescence analysis (XRF) and inductively coupled plasma atomic emission spectrometry (ICP-AES) were used for the analysis of the elemental composition of sediment samples from a marsh and standard reference materials. The sediment samples were pretreated with different methods which are widely used in practice. A comparison was made not only between the concentrations obtained by the different methods, but also between the statistical conclusions derived from the processing of the experimental results. Good agreement was found for some elements, e.g. Mn, Zn and Sr, while the concentrations and the statistical conclusions were shown to depend on the analytical method used in the case of other elements, e.g. Fe and Zr.     

Use of simplex optimization to improve the performance of an inductively coupled plasma in atomic emission spectrometry

Simplex methods are used in the optimization of many analytical techniques. In inductively coupled plasma—atomic emission spectrometry, various performance criteria can be used, including signal-to-background ratios, signal-to-noise ratios, detection limits, and the minimization of matrix effects. The simplex method can indicate deficiencies in equipment design that restrain performance. The threshold of auto-optimization of analytical instruments has been reached.     

Determination of237Np in environmental samples using inductively coupled plasma mass spectrometry

Ammonium uranates (AU) obtained by the addition of aqueous NH₄ OH to a solution of UO₂ (NO₃)₂ or the equilibrium reaction of UO₃ · 2H₂ O with the vapour over concentrated NH₄ OH have been studied by X-ray diffraction (XRD) analysis, diffuse reflectance Fourier transform infrared spectrometry (DR-FTIR) and chemical analysis. Ammonia can be present as either NH₃ or NH ₄ ⁺ . For precipitates obtained at a pH of 3.7, ammonia in the form of NH₃ is predominant. For ammonium uranate obtained by reaction over concentrated NH₄OH, most of the ammonia is bonded as NH ₄ ⁺ . The reaction mechanism and structures of the products are also discussed.     

Non-linear spectral interferences in an inductively coupled plasma optimized for simultaneous multi-element analysis of plant and soil samples by atomic emission spectrometry

Summary The spectral interferences by Al, Ca, Fe, K, Mg and Na in the direct simultaneous determination of As, Cd, Co, Cu, Hg, Pb and Se in plant and soil samples by ICP-AES are investigated, and a non-linear relationship between the apparent analyte concentration for As, Cd, Co, Hg and Se is observed. A correction method for non-linear spectral interferences is discussed and non-linear spectral correction coefficients are calculated.     

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.     

Laser vaporization of solid metal samples into an inductively coupled plasma

A laser vaporization-inductively coupled plasma system has been developed and tested for the direct analysis of solid metal samples. In this system the sample (normal emission spectroscopy metal disc standards) is vaporized utilizing a pulsed ruby laser and the vaporized material is swept into the ICP. Multichannel spectral data are simultaneously acquired using a photodiode array spectrometer. System parameters that have been investigated include ICP emission signal duration, number of laser shots to be used for a determination, the time between laser shots, free running or Q-switched laser operation, and the effect of laser focus. Analytical curves are presented for aluminum and brass samples.