Effect of the addition of non-ionic surfactants on the emission characteristic of direct current atmospheric pressure glow discharge generated in contact with a flowing liquid cathode Krzysztof Greda, Piotr Jamroz and Pawel Pohl * A direct current atmospheric pressure glow discharge generated in contact with a flowing liquid cathode was used to study the effect of the concentration of two non-ionic surfactants, i.e., Triton x-45 and Triton x-405 added to electrolyte solutions, on the emission characteristic of the excitation source by using optical emission spectrometry. The emission intensity of different molecular and atomic species as well as the background level were measured. Selected spectroscopic parameters, i.e., rotational temperatures of OH and N 2 molecules, excitation temperatures of Co and H atoms, the electron number density and the intensity ratio for Mg II to Mg I lines, were also determined. The net intensity of atomic emission lines of several metals (Cs, Cu, Hg, Mg, Mn and Pb) was found to be enhanced by more than 4 times in the presence of the heavier surfactant in solution at the concentration corresponding to 5 times its critical micelle concentration. Coincidently, the intensity of the background in the vicinity of these lines and its fluctuation were also significantly decreased. Possible changes in sputtering, collisional-recombination and excitation processes that may occur in the near-cathode zone of the discharge are discussed and the phenomenon explained. 1 Introduction Direct current (dc) atmospheric pressure glow discharge (APGD) generated in contact with a owing liquid cathode is now considered to be one of the most promising alternative minia- turized excitation sources that can be applied in process control or environmental monitoring studies for the direct trace element analysis of various liquid samples. 1–6 This is primarily due to the expedient emission characteristic of this new exci- tation source, i.e., relatively simple atomic emission spectra containing the most prominent atomic lines and less common spectral overlaps of these lines. Such a distinctive feature of dc- APGD generated in contact with the liquid cathode makes it highly desirable for direct and on-line optical emission spec- trometric (OES) determinations of trace metal impurities in different sample solutions. 7–11 In addition, the inherent nature of this miniaturized discharge brings power density between electrolyte solutions serving as the cathode and the counter electrode that is about one order of magnitude or more higher than the density power established for commercially available inductively coupled plasma (ICP) sources. 3 As a result, over- whelming in analytical applications of this excitation source, quantitative measurements by OES are possible with reasonably good detectability, commonly sub-mg l À1 range, is attained. Decent precision and the reproducibility of signals is better than several %, while the consumption of discharge gases is incomparably smaller; even no gas supply is needed since the discharge is fully operable in air. 12,13 This in turn means little effort and low operating costs are required to sustain and control the discharge. 1,2,4,9,14 Electrical power consumed by dc- APGD generated in contact with the liquid cathode typically ranges from several to tens Watts and is mostly dissipated in the near-cathode region of the discharge to evaporate the electrolyte solution and sustain important processes and reactions occur- ring at the gas–liquid interface. 1–6 The progress made in the last decade in terms of the design of discharge cells for this type of excitation source has led to an increase in the concentration of atoms in the near-cathode region of the discharge and has strict implications for the improvement of analytical performance of APGD generated in contact with the liquid cathode. 1–6,9,15–21 Correspondingly, the latest modications, consisting changes in the construction and the geometry of capillaries used for the introduction of electrolyte solutions, are reected by enhanced optical thinness of the discharge, its better stability and much greater repro- ducibility of the discharge gap. 1–4,18–20 As a result, improved detection limits of metals, commonly in the range of 0.001– 0.01 mg l À1 , linearity concentration ranges from 2 to at least Wroclaw University of Technology, Faculty of Chemistry, Division of Analytical Chemistry, Wybrzeze Stanislawa Wyspianskiego 27, 50-370 Wroclaw, Poland. E-mail: pawel.pohl@pwr.wroc.pl; Fax: +48-71-320-2494; Tel: +48-71-320-3445 Cite this: J. Anal. At. Spectrom., 2013, 28, 134 Received 1st October 2012 Accepted 9th November 2012 DOI: 10.1039/c2ja30275f www.rsc.org/jaas 134 | J. Anal. At. Spectrom., 2013, 28, 134–141 This journal is ª The Royal Society of Chemistry 2013 JAAS PAPER Published on 12 November 2012. Downloaded on 28/03/2014 19:13:30. View Article Online / Journal Homepage / Table of Contents for this issue