SamplePrep

Sample Preparation

XRF Mill301

In X-ray Florescence spectroscopy the ideal sample is presented as a solid uniform disk. The sample first needs to be ground into a fine powder and then compressed into a sample cup or metal ring. In the toy application that we are focusing on the toy would first need to be disassembled into its respective parts. The parts would then be sorted into different materials;

plastics, metals, woods, and textiles. These material categories are then further sorted into color groupings; this is necessary since even if the same plastic was used throughout the toy product, the dye or paint could hold the specific contaminants we are looking for. These pieces are then ground using a Mixing Mill pictured at upper right. The mixing mill has different griding tools for different mediums, texture or grain size. When we used the term uniform to describe the sample we are talking about the press

grain size of the ground material. If the grain size is large their will be open air space in the sample which can affect the readings. Also if the grain size varies the sample could settle unevenly and also affect the readings. Grain size is mostly a variable when the sample is manually tamped, when the container is tapped to force the powder to settle the finer grains will sometimes settle on the top. If the sample is prepared and then manually compressed this becomes less of an issue since the particles are not given a chance to moved or settle, they are compressed exactly as they fell into the container and the sample remains more uniform even though it may be made of different substances (http://www.jensentechnologiesllc.com/XRF2.html). Automated presses like the one pictured to the lower right are also available, their advantage is that they a programmable and can produce consistent samples which lead to consistent results. Another option are the toy parts have been ground into a fine powder is to fuse them into uniform size beads. The powdered sample is mixed with flux and heated to form uniform glass like beads.

AAS

Atomic Absorption Spectroscopy sample prep requires the sample to be a liquid. Again the toy in question needs to be disassembled and sorted into its respective categories as detailed above. Since most of the material are solids they are ground down using the mills again but instead of the powder being pressed or fused into beads it is dissolved in a appropriate solvent. The AAS method then takes the sample through three steps, (1) Desolvation or drying of the sample, where the solvent is evaporated so just the dry sample remains (2) Vaporization or Ashing, where the solid sample vaporizes into a gas and (3) Atomization, where the compound are broken down into its free atoms (http://www.absoluteastronomy.com/topics/Atomic_absorption_spectroscopy).

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