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Research Article Electron Density from Balmer Series Hydrogen Lines

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Research Article Electron Density from Balmer Series Hydrogen Lines View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Crossref Hindawi Publishing Corporation International Journal of Spectroscopy Volume 2016, Article ID 7521050, 9 pages http://dx.doi.org/10.1155/2016/7521050 Research Article Electron Density from Balmer Series Hydrogen Lines and Ionization Temperatures in Inductively Coupled Argon Plasma Supplied by Aerosol and Volatile Species Jolanta Borkowska-Burnecka, WiesBaw gyrnicki, Maja WeBna, and Piotr Jamróz Chemistry Department, Division of Analytical Chemistry and Chemical Metallurgy, Wroclaw University of Technology, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw, Poland Correspondence should be addressed to Wiesław Zyrnicki;˙ [email protected] Received 29 October 2015; Revised 15 February 2016; Accepted 1 March 2016 Academic Editor: Eugene Oks Copyright © 2016 Jolanta Borkowska-Burnecka et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Electron density and ionization temperatures were measured for inductively coupled argon plasma at atmospheric pressure. Different sample introduction systems were investigated. Samples containing Sn, Hg, Mg, and Fe and acidified with hydrochloric or acetic acids were introduced into plasma in the form of aerosol, gaseous mixture produced in the reaction of these solutions with NaBH4 and the mixture of the aerosol and chemically generated gases. The electron densities measured from H ,H,H,andH lines on the base of Stark broadening were compared. The study of the H Balmer series line profiles showed that the values from H and H were well consistent with those obtained from H which was considered as a common standard line for spectroscopic 15 15 −3 measurement of electron density. The values varied from 0.56 ⋅ 10 to 1.32 ⋅ 10 cm and were the highest at loading mixture of chemically generated gases. The ionization temperatures of plasma, determined on the base of the Saha approach from ion-to-atom line intensity ratios, were lower for Sn and Hg (6500–7200 K) than those from Fe and Mg lines (7000–7800 K). The Sn II/Sn I and Hg II/Hg I, Fe II/Fe I, and Mg II/Mg I intensity ratios and the electron densities () were dependent on experimental conditions of plasma generation. Experimental and theoretically calculated ionization degrees were compared. 1. Introduction Typically, solutions are introduced into the plasma by means of pneumatic (PN) or ultrasonic nebulization(USN), Inductively coupled plasma (ICP) generated at atmospheric while chemical vapour generation (CVG) based on the pressure has been recognized as a one of the most commonly reduction of the element ions with NaBH4 in acidic medium applied techniques for both analytical purposes and spectro- has been widely employed to derivate elements into the form chemical investigations, including diagnostic studies. It has of volatile hydrides (e.g., As, Bi, Sb, Se, and Sn) or into cold become attractive for simultaneous determination of several vapours(Hg,Cd)[3,10].Systemswithoutphaseseparation, elements in a great variety of samples, namely, environmental, that is, allowing the simultaneous introduction of volatile industrial, geological, biological, clinical, and food materials species and sample aerosol using pneumatic nebulization, [1–3]. Additionally, although the method requires as a rule the canalsobeusedtodeterminebothhydrideandnonhydride liquid samples for measurements, the ability of hyphenation elements [3, 11–13]. of the ICP with electrothermal vaporization or laser ablation Experimental conditions have effects on ICP parameters, allows analysis of the samples in their solid state [4, 5]. On the for example, electron density ( ), plasma temperatures ( exc, other hand, plasma discharge appears as an interesting tool ion,and gas), or plasma robustness employing the ion-to- enabling us to get knowledge and to understand the processes atom intensity ratios (M II/M I). For the latter, the Mg II occurringintheplasmasource[6–9]. 280.3/Mg I 285.2 nm intensity ratio is usually considered. 2 International Journal of Spectroscopy Determination of is commonly carried out using the H compared experimental results with the predictions of three line profile. Excitation temperature is typically derived from theories that described laser-induced breakdown plasma. The atomic iron lines and the OH A-X 0-0 band serves usually for electron densities calculated from various H lines (with the gas plasma temperature measurements. A number of papers exception of H) were comparable. The other works on laser- have been devoted to ICP spectral diagnostics; however, induced plasma diagnostics concern mainly exploration of nebulization systems have been predominantly investigated the first-two Balmer series lines. For ICP only Batistoni et al. [6–9, 14–16] in comparison to the reports concerning CVG [19] measured the electron density in Ar-ICP for PN, CVG, [11,17–19].InthecaseofPN,theeffectofhydrogeninaddition and dry plasma by means of H and H lines and the results to the argon or combined effect with a desolvation step was obtained from the two lines were not consisted. also discussed [19–21]. The objective of the present study was determination Studies analysing the influence of CVG, PN, and com- and comparison of spectroscopic parameters of the induc- bined PN + CVG systems on ICP characteristic are relatively tively coupled plasma operating with pneumatic nebuliza- rare and not consisted. Grotti et al. [18] investigated effect of tion (aerosol), chemical vapour generation (gas mixture), operating conditions (power, carrier gas flow, and HCl and and pneumatic nebulization combined with CVG. For the NaBH4 concentrations) on exc, , and Pb II/Pb I ratio in electron density determination, the usage of the first-four an axially viewed ICP coupled with pneumatic nebulization hydrogen lines of the Balmer series was tested. Atomic and and ultrasonic nebulization associated with desolvation and ionic lines of Fe, Mg, Sn, and Hg served as thermometric with chemical vapour generation. At robust conditions and species. In considerations, effects of sample introduction the CVG system, the electron number density was about systems and related to the water, hydrogen, and mixture of 8% higher than at the PN system. Batistoni et al. [19] hydrogen and water loading into the plasma were analysed. determined and the H excitation temperature for the In addition, influence of the matrix of HCl and CH3COOH plasma with hydrogen from acidic NaBH4 hydrolysis and on spectroscopic parameters was examined. compared obtained values with those determined for PN and dry plasma. The increase in during NaBH4 hydrolysis with reference to the dry plasma and PN was about 50% and 40%, 2. Materials and Methods respectively [19]. In the other work [17], the values were 2.1. Instrumentation. All measurements were performed with above 70% higher at the CVG system than for dry plasma. the use of a Jobin Yvon sequential ICP-OES spectrometer Recently, spectroscopic and analytical characteristics of ICP (JY 38S) with a 1 m Czerny-Turner monochromator and with hydride generation with or without simultaneous intro- two holographic gratings (4320 and 2400 grooves/mm). duction of the sample aerosol were presented by Pohl and Spectra were recorded at the resolution of 0.01 nm in a Broekaert [11]. In this paper, the values determined from ex sequential mode. Additionally, the image system for quick Ar I, Au I, Bi I, and Fe I were found to be close together for data acquisition in the range of 190–780 nm was used. Work- the sample introduction systems studied although differences ing parameters for the ICP-OES measurements are given for particular species were noted. The highest values were inTable1.Therecordedlineintensitieswerebackground obtained for the combined PN and CVG system while the corrected and expressed as net signals. The mean values from values at CVG and PN mode were comparable [11]. three repeated measurements were used in all investigations. In the last years, attention has been paid to the use The precision of the signal measurements expressed as the of other than H hydrogen lines for the electron density relative standard deviation (RSD) ranged, depending on the determination [19, 22–32] in various plasma. Konjevicet´ experimental conditions, from 1 to 6%. al. [23] discussed difficulties appearing during experimental line profile analysis for higher members of Balmer series and compared theory versus experiments for low plasma 2.2. Sample Introduction Systems. The ICP spectrometer, diagnostics. Mijatovic´ et al. [24] tested the applicability of equipped with a modified cyclonic spray chamber and a the H lineasadiagnostictoolatmoderatelylowplasma parallel pneumatic nebulizer (Burgener), allowed nebulizing densities using a low-pressure pulsed arc operating in a solutions (PN) as well as attaining chemical vapour genera- H2:He gas mixture as a plasma source. Nikiforov et al. [29] tion (CVG) both separately and simultaneously with sample discussed applications of Stark broadening hydrogenated aerosol (PN + CVG). Solutions containing Sn(II), Hg(II), Mg(II), and Fe(II) at concentrations in the range of 5– (and nonhydrogenated) atomic lines for determination of −1 in atmospheric pressure plasma and presented equations for 50 gmL were used. The solutions were acidified to final −1 estimation based on measured broadening
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