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 preparation 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 for the spruce seeds to solve the problem of agglomerating during grinding at room temperature. A modified sample tray was applied allowing the use of both the commercial 1.5 mL vials and home-made 15 mL vials. With optimal conditions for ultrasonic agitation the homogeneity and particle size distributions in the slurries prepared in the two different vials were similar. Several aspects of the slurry sampling approach are discussed and data of important parameters are given, including the total number of particles injected into the graphite furnace, densities of the materials and percentage of analyte extracted into the liquid phase of the slurry. The density of the materials was determined by two methods; by using a Coulter particle analyser and by using a gravimetric method. The two methods gave similar accuracy and precision. The concentration ranges of the elements (in μg g^–1) were: 80–2100 for Al, 3–15 for Cu, 0.06–2.5 for Li and 50–700 for Mn. External calibration with aqueous standards was employed. Chemical modifiers were not 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 was 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 sensitive wavelengths were used.