The effect of a miniature argon flow rate on the spectral characteristics of a direct current atmospheric pressure glow micro-discharge between an argon microjet and a small sized flowing liquid cathode Piotr Jamróz ⁎, Wiesław Żyrnicki, Paweł Pohl Wroclaw University of Technology, Faculty of Chemistry, Division of Analytical Chemistry, Wybrzeze Stanislawa Wyspianskiego 27, 50‐370 Wroclaw, Poland abstract article info Article history: Received 16 March 2012 Accepted 15 June 2012 Available online 23 June 2012 Keywords: Atmospheric pressure glow microdischarge Argon microjet Flowing liquid cathode Spectroscopic diagnostics Optical emission spectrometry A stable direct current atmospheric pressure glow microdischarge (dc-μAPGD) was generated between a miniature Ar flow microjet and a small sized flowing liquid cathode. The microdischarge was operated in the open to air atmosphere. High energy species, including OH, NH, NO, N 2 , H, O and Ar were identified in the emission spectra of this microdischarge. Additionally, atomic lines of metals dissolved in water solutions were easily excited. The near cathode and the near anode zones of the microdischarge were investigated as a function of an Ar flow rate up to 300 sccm. The spectroscopic parameters, i.e., the excitation, the vibrational and the rotational temperatures as well as the electron number density, were determined in the near cathode and the near anode regions of the microdischarge. In the near cathode region, the rotational temperatures obtained for OH (2000–2600 K) and N 2 bands (1600–1950 K) were significantly lower than the excitation temperatures of Ar (7400 K–7800 K) and H (11 000–15 500 K) atoms. Vibrational temperatures of N 2 , OH and NO varied from 3400 to 4000 K, from 2900 to 3400 K and from 2700 to 3000 K, respectively. In the near anode region, rotational temperatures of OH (350–1750 K) and N 2 (400–1350 K) and excitation temper- atures of Ar (5200–5500 K) and H (3600–12 600 K) atoms were lower than those measured in the near cath- ode region. The effect of the introduction of a liquid sample on the microdischarge radiation and spectroscopic parameters was also investigated in the near cathode zone. The electron number density was calculated from the Stark broadening of the H β line and equals to (0.25–1.1)×10 15 cm -3 and (0.68– 1.2)×10 15 cm -3 in the near cathode and the near anode zones, respectively. The intensity of the Na I emission line and the signal to background ratio (SBR) of this line were investigated in both zones to evaluate the ex- citation properties of the developed excitation microsource. The limit of detection for Na was determined at the level of 3ngmL -1 . © 2012 Elsevier B.V. All rights reserved. 1. Introduction Studies of the atmospheric pressure glow microdischarge (μAPGD) are of great importance due to its potential application in the analyti- cal atomic spectrometry as well as in material and environmental pro- tection engineering [1]. The μAPGD generated between water and the miniature gas flow microjets could be employed to produce special kinds of materials [2,3] and for the purification and sterilization of water [1,4]. It is also possible to use such microjets as simple and low cost excitation microsources in the optical emission spectrometry (OES) [5–8]. The understanding of the chemistry and physics of processes oc- curring in new excitation microsources demands knowledge about the concentrations of various active species and their energy distribu- tion under various experimental conditions. Additionally, in order to evaluate the analytical performance of such excitation microsources, it is necessary to acquire their different spectroscopic parameters, namely the electron, the excitation, the vibrational, the rotational temperatures and the electron number density. In the overwhelming APGD systems generated in contact with liq- uid, the discharge was operated in the open to air atmosphere between a solid pin anode and a liquid cathode of a different construction [7–17]. These systems were frequently investigated in terms of different plasma spectroscopic parameters [8–12] and analytical applications [13–17].A stable APGD between the solid anode and the liquid cathode was also generated in the atmosphere of noble gases, i.e., Ar or He [11]. In refer- ence to this, dc-APGD systems with Ar or He jets acting as anodes are unusual and worth investigating due to the presence of high energy states of Ar or He, and a wider range of the plasma stability [18]. So far, microjets generated in contact with liquids have been rarely investigated by means of the OES or other methods. There are only a few studies concerning APGDs generated between Ar or He jets and liquids [18–24]. The electrical properties of a direct current (dc) APGD generated between a miniature He flow microjet and a bulk liq- uid anode were investigated by Shirai et al. [19]. The same research Spectrochimica Acta Part B 73 (2012) 26–34 ⁎ Corresponding author. Tel.: +48 71 320 3807; fax: +48 71 320 2494. E-mail address: piotr.jamroz@pwr.wroc.pl (P. Jamróz). 0584-8547/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.sab.2012.06.008 Contents lists available at SciVerse ScienceDirect Spectrochimica Acta Part B journal homepage: www.elsevier.com/locate/sab