Application de la spectrographie de masse a sonde laser a l'etude des variations de la composition minerale dans des tissus ligneux

The aim of this research was to show the interest of an original technique of microanalysis : the laser probe mass spectrograph (L.P.M.S.), to study the variations of the mineral content in transverse sections of woody stems. In this technique a mass spectrometer analyses the ions liberated during the bombardment of the sample by a laser beam. It allows analysis in different points of the surface and in depth with a diameter of the beam of 50 to 100 μm. The detection limits may be increased by accumulation of spectra from repetitive shots at the same point. Samples (5 to 10 mm diameter, 1 to 2 mm thickness) cut on young stems of walnut tree (Juglans regia) were analysed after freeze drying, then observed in scanning electron microscopy to correlate the position of the laser craters with the analytical data. The preliminary results presented give a qualitative information about the variations of the relative content of the following elements : C, O, N, P, K, Ca, Mg, S simultaneously detected along diametral lines on the analysed sections.