Time-resolved measurement of emission proﬁles in pulsed radiofrequency glow discharge optical emission spectroscopy: Investigation of the pre-peak D. Alberts a , P. Horvath b , Th. Nelis c,d , R. Pereiro a , N. Bordel e , J. Michler b , A. Sanz-Medel a, ⁎ a Department of Physical and Analytical Chemistry, Faculty of Chemistry, University of Oviedo, Julian Claveria 8, 33006 Oviedo, Spain b Swiss Federal Laboratories for Materials Testing and Research (EMPA), Feuerwerkerstrasse 39, 3602 Thun, Switzerland c LAPLACE, Université Paul Sabatier, 118 rte de Narbonne, Bat3R2, 31062 Toulouse Cedex, France d CU Jean François Champollion, Place de Verdun 81012 Albi Cedex 9, France e Department of Physics, Faculty of Science, University of Oviedo, Calvo Sotelo, 33007 Oviedo, Spain abstract article info Article history: Received 12 March 2010 Accepted 28 May 2010 Available online 8 June 2010 Keywords: Glow discharge Optical emission spectroscopy Emission proﬁle Pulsed Radiofrequency Pre-peak Radiofrequency glow discharge coupled to optical emission spectroscopy has been used in pulsed mode in order to perform a detailed study of the measured temporal emission proﬁles for a wide range of copper transitions. Special attention has been paid to the early emission peak (or so-called pre-peak), observed at the beginning of the emission pulse proﬁle. The effects of the important pulse parameters such as frequency, duty cycle, pulse width and power-off time, have been studied upon the Cu pulse emission proﬁles. The inﬂuence of discharge parameters, such as pressure and power, was studied as well. Results have shown that the intensity observed in the pre-peak can be 10 times as large as the plateau value for resonant lines and up to 5 times in case of transitions to the metastable levels. Increasing pressure or power increased the pre-peak intensity while its appearance in time changed. The pre-peak decreased when the discharge off-time was shorter than 100 μs. According to such results, the presence of the pre-peak could be probably due to the lack of self-absorption during the ﬁrst 50 μs, and not to the ignition of the plasma. Under the selected operation conditions, the use of the pre-peak emission as analytical signals increases the linearity of calibration curves for resonant lines subjected to self-absorption at high concentrations. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Glow discharges (GD) have been used for decades in analytical spectrometry, mainly for both bulk direct solid analysis and for compositional depth proﬁling [1–3]. Operating GD in pulsed mode can afford interesting advantages including the alleviation of plasma instability arising from overheating of the sample cathode [4]. Such operation of pulsed glow discharge (PGD) sources consists of an applied square wave power pulse followed by a period of power termination [5]. One of the principal potential advantages arises from the creation of time regimes during which the background signal is suppressed while the analyte signal is enhanced. This is particularly true for mass spectrometry, where Penning ionisation of analyte atoms by argon metastable atoms enhances the ionisation efﬁciency in the afterglow by a large factor. To fully exploit this advantage, time-gated detection should be used. A thorough review was published by Winchester and Payling [6] on radiofrequency (rf) GD-spectrometry which includes a small overview on the work done on PGDs. Also, a recent review by Belenguer et al. [7] has been dedicated to the analytical applications of pulsed discharges. PGDs have been investigated in combination with both optical emission [8,9] and mass [10–12] spectrometries. Nevertheless, most of the published work on PGDs was made with direct current (dc) GDs. Pioneering studies on rf-PGDs were made in 1975 by Harrison et al., exploring pulsed operations as an approach that could increase instantaneous applied power without overheating the cathode sample [13]. Pan and King [14] studied a rf-PGD with 50 Hz pulse frequency and 25% duty cycle, showing that pulsing improves thermal stability. The emission characteristics of rf-PGDs were studied by Winchester et al. [15], observing pre- and post-peaks in the time dependent emission proﬁles dependant on the emission line chosen. They attributed the pre- peak to effects linked to sputtering. The post- or after-peak and its processes during the afterglow have already been studied [16,17] and described by models [18]. Later, Vegiotti [19], who observed the same time dependence, studied the link to self-absorption, but did not come to a clear conclusion. In 2003, Lewis et al. [20] observed little difference between the emission characteristics for millisecond pulsed dc- and rf- GD in the afterglow, when comparing them spatially and temporally, using an experimental set-up at 100 Pa. When utilising the rf-excitation, a pre-peak was observed with a width of several ms, which they attributed to a power surge in the ignition process. The effective use of PGDs requires a more complete understanding of the temporal separation of various excitation and ionisation processes. Spectrochimica Acta Part B 65 (2010) 533–541 ⁎ Corresponding author. Tel./fax: +34 985103474. E-mail address: asm@uniovi.es (A. Sanz-Medel). 0584-8547/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.sab.2010.05.011 Contents lists available at ScienceDirect Spectrochimica Acta Part B journal homepage: www.elsevier.com/locate/sab