ORIGINAL PAPER Investigation of plasmas produced by laser ablation using single and double pulses for food analysis demonstrated by probing potato skins S. Beldjilali & W. L. Yip & J. Hermann & T. Baba-Hamed & A. Belasri Received: 19 January 2011 /Revised: 14 March 2011 /Accepted: 16 March 2011 /Published online: 2 April 2011 # Springer-Verlag 2011 Abstract We report on investigations of plasmas produced by laser ablation of fresh potatoes using infrared nanosec- ond laser radiation. A twin laser system consisting of two Nd:YAG oscillators was used to generate single or double pulses of adjustable interpulse delay. The potatoes were irradiated under ambient air with moderate pulse energies of about 10 mJ. The expansion dynamics of the ablation plume was characterized using fast imaging with a gated camera. In addition, time-resolved optical emission spec- troscopy was applied to study the spectral line emission of the various plasma species. The electron density was deduced from Stark broadening, and the plasma tempera- ture was inferred from the relative emission intensities of spectral lines. The relative concentrations of metals were estimated from the comparison of the measured emission spectra to the spectral radiance computed for a plasma in local thermal equilibrium. It is shown that the plasma produced by double pulses has a larger volume and a lower density. These properties lead to an increase of the signal- to-noise ratio by a factor of 2 and thus to an improved measurement sensitivity. Keywords Laser plasma . Plasma modeling . Calibration- free LIBS . Quality control of food Introduction Laser-induced breakdown spectroscopy (LIBS) is an emerging technique for fast multielemental analysis of gaseous, liquid, and solid samples [1–3]. Recently, LIBS was applied to analyses of organic materials. Thus, metal concentrations were measured in potatoes [4–6], or trace elements were measured in sunflower seedling stem [7]. Heavy metals in biological tissues were detected [8], and the concentrations of minerals in pellets of compressed plants were measured [9]. The investigation of carbon and nitrogen contents in soil was also reported [10]. LIBS was also applied to detect lead and other toxic contaminants such as chromium in paint emulsion samples [11]. Ion- exchange polymer membranes and LIBS were used for the speciation of chromium ions Cr 2+ and Cr 3+ [12]. Analysis of copper in aqueous solutions using an ion-exchange concentrator and LIBS was also reported [13]. Compared with the conventional techniques of organic material analyses, such as flame atomic absorption spectrometry [14–16] or graphite furnace atomic absorption spectrometry [17, 18], inductively coupled atomic emission spectroscopy (ICP-AES) [19] and inductively coupled plasma mass spectrometry (ICP-MS) [20, 21], LIBS has several advan- tages. It allows for real-time and stand-off analysis of multielemental samples and does not require any sample preparation. This makes LIBS a promising technique for quality control of food that needs fast analysis of large amounts of samples. Although the capabilities of LIBS have been demonstrated for different types of materials, the analysis of complex organic materials is still a great challenge. The quality control of aliments via LIBS is a particularly difficult task due to the complex composition of this type of heterogeneous materials. Indeed, organic materials are mainly composed of C, H, O, and N atoms S. Beldjilali (*) : W. L. Yip : J. Hermann LP3, CNRS–Université d’Aix Marseille II, 163 Av. de Luminy, 13288 Marseille, France e-mail: beldjilali-s@univ-usto.dz S. Beldjilali : T. Baba-Hamed : A. Belasri LPPMCA, Université des Sciences et de la Technologie d’Oran, BP 1505( El Mnaouer Oran 31000, Algeria Anal Bioanal Chem (2011) 400:2173–2183 DOI 10.1007/s00216-011-4920-8