In-situ analysis of nitrogen in minerals

Three microscopic techniques have been applied to the analysis in situ of N trapped as NH (super +) (sub 4) in muscovite, biotite and feldspar in schists from Jebilet (Morocco) and Cevennes (France). 1) Spectra obtained with FTIR show vibrational nu (sub 1) , nu (sub 2) , nu (sub 3) bands and some overtones and combinations of the ammonium molecule. The quantitative analysis is disturbed by dichroism effects and needs the use of silicate standards. The NH (super +) (sub 4) of the phyllosilicates is not detected by Raman microspectroscopy. 2) The nuclear microprobe was applied to the same mineral separation and N content was measured using the (super 14) N(d,alpha (sub o) ) (super 12) C and (super 14) N(d,rho (sub o) ) (super 15) N reactions with a deuteron energy of 1.8 MeV. TiN is used for calibration; concentrations of 360-2200 ppm were obtained. 3) The ion microprobe was found to be more sensitive to matrix effects. The isotopic composition could not be obtained due to the low (super 15) N content of the minerals (near 1-10 ppm); the detection limit is 10-100 ppm.