原子吸收基本原理概述.ppt

* The Lvov platform is a small plate of solid pyrolytic graphite thats inserted into the graphite cuvette. It has a slight depression in the center which can accommodate up to 50uL of solution. The function of the Lvov platform is to isolate the sample from the tube walls to allow more reproducible atomization of the sample through indirect heating. The platform heats primarily by the radiation given off from the tube walls. Sample vaporization and atomization occur after the tube reaches a steady-state temperature. Use of the Lvov platform provides: Vaporization into a higher temperature gas atmosphere producing more free atoms, which reduce interferences and Longer tube life through reduced attack by sample matrix and reagents. The Omega cuvette is a derivation of the original L’vov design. The platform is curved to accommodate the sample more effectively. * The cuvette, of course, is not just ‘heated’ by the furnace power supply, but is subject to a very carefully controlled sequence of time and temperature ‘phases’. The complete sequence is known as the ‘furnace program’, and usually consists of at least four identifiable phases. These have become known as the Dry Phase, during which the liquid is removed from the sample, leaving behind only solid material, the Ash Phase, during which the bulk of the solid material is removed to leave behind only the analyte and other temperature stable material, the Atomise Phase, during which the analyte is atomised and the absorbance signal is measured, and finally the Cuvette Clean phase, in which any remaining material is removed from the cuvette, leaving it ready for the next sample. Each of these phases will now be discussed in more detail, starting with the Dry Phase. * The purpose of the Ash Phase is to remove as much of the liquid from the sample as possible, leaving dry solid material. The temperature is selected so that the sample is held just below the boiling point - typically around 100 oC. It is im