Comparabilitatea rezultatelor obţinute la analiza unor parametri ai apelor de precipitaţii [Comparability of the results obtained analysing precipitation samples]

In order to verify the precision of the results obtained for atmospheric deposition and the comparability of the results, 10 precipitation samples collected in Romania, in open field and under the wood canopy were analysed in 3 chemistry laboratories: ICAS Station Campulung Moldovenesc Romania, INRA and CNRS Nancy France. The analytical methods used were different or the same in the 3 laboratories. The concentrations of seven ions were determined: Cl-, NO3 -, SO4 2-, K+, Na+, Mg2+, Ca2+. The results obtained reveale significant differences between concentrations of the same ion analyzed in samples collected with different types of collectors, in the same place at the same moment. These differences were significant in each of the 3 laboratories which performed the analysis. The best results for the intercomparison exercise were obtained for the concentration of K+, for which the deviation between measurements in the 3 laboratories did not exceed 15 %. The concentration of Na+ was sistematic underestimated by ICP spectrometry in INRA laboratory comparative with the results obtained by AAS or AES spectrometry in ICAS or CNRS laboratories. The best correlation was that between the concentrations determined by AAS at ICAS and those determined by AES at CNRS. For the concentrations of Ca2+ and Mg2+, the correlations obtained between the results of the 3 laboratories were good, but high deviations, as normal, were obtained for values close to the detection limits. The concentrations of SO4 2- determined by spectrophotometry at ICAS were well correlated with those obtained by ion chromatography at CNRS. The results obtained by ICP spectrometry at INRA and CNRS were sistematic higher because this method allows the determination of the total sulphur in preciptation samples, not only the SO4 2-. Deviations of the concentrations obtained by spectrofotometry at ICAS comparative with those determined by ion chromatography at CNRS were higher then 20 % at concentrations < 1 mgCl-/l. The tendency of underestimating the results in the ICAS laboratory is determined by the presence of the Cl- ion in the distiled water used to prepare the calibration curve. The sistematic high deviations obtained for the NO3 - ion can be explained by the high period of time between the determination in the 2 laboratories and the fact that the concentration of this ion vary in time. The intercomparison exercise to which the 3 laboratories participated allowed to verify some hypothesis concerning the results obtained in the ICAS laboratory and to compare the performances of the analytical methods used.