Determination of Al, Cu, Li and Mn in spruce seeds and plant reference materials by slurry sampling graphite furnace atomic absorption spectrometry

An ultrasonic slurry sampling graphite furnace AAS method was developed for the determination of Al, Cu, Li and Mn in spruce seeds, NBS SRM 1575 pine needles and GBW CRM 07602 bush branches and leaves. The only sample prepara tion was grinding in a Mixer Mill before preparing a slurry by adding 0.14 mol/L nitric acid to a small sample aliquot. Cryogenic grinding was used fo r the spruce seeds to solve the problem of agglomerating during grinding at room temperature. A modified sample tray was applied allowing the use of b oth the commercial 1.5 mt vials and home-made 15 mt vials. With optimal con ditions for ultrasonic agitation the homogeneity and particle size distribu tions in the slurries prepared in the two different vials were similar. Sev eral aspects of the slurry sampling approach are discussed and data of impo rtant parameters are given, including the total number of particles injecte d into the graphite furnace, densities of the materials and percentage of a nalyte extracted into the liquid phase of the slurry. The density of the ma terials was determined by two methods: by using a Coulter particle analyser and by using a gravimetric method. The two methods gave similar accuracy a nd precision. The concentration ranges of the elements (in mu g g(-1)) were : 80-2100 for AL, 3-15 for Cu, 0.06-2.5 fur Li and 50-700 for Mn. External calibration with aqueous standards was employed. Chemical modifiers were no t found to be necessary. The relative standard deviations were in the range 1.7-7%. Analyses of the two certified plant reference materials confirmed the accuracy of the method. In addition no significant difference was found for analyses of digested and slurried spruce seeds. The detection limit wa s 10 ng g(-1) for Li and 170 ng g(-1) for Cu. The characteristic mass (area measurements) was 4.4 pg for Li and 11 pg for Cu. For Al and Mn less sensi tive wavelengths were used.