Desert RATS - Day 12 - Sample preparation

Source:  Desert RATS - Day 12 - Sample preparation    Tag:  sample preparation for xrf analysis
After the cleanly collected samples from the crew reach us, we have to prepare it for analysis. The cartoon below shows how:

First we chip off a fragment with a vice. Technically the vice should be cleaned in between samples, but by brushing it we hope to get at least the mineral cross contamination down. 

The fragments are collected in aluminum foil, to prevent exposure to any organic containing surface. 

Then the sample is transfered to a mortar to be crushed into fine powder. Both the pestle and mortar were ashed (heated to 500°C for 3 hours) to remove organic contaminants, before they were brought out to the field. The reason to powder the sample is to increase the exposed surface, which makes it easier for volatiles to escape.

The Terra instrument (a portable XRF, brought into the field by Jack Farmer/ASU), a terrestrial version of the CheMin instrument of MSL, requires powder with a grain size of <150 micron (um, micrometer) and we try to analyze one sample with both VAPoR and the Terra. Therefore we sieve the sample to the <150 um fraction, keep half or it ourselves and give the other halve to Terra.

VAPoR can't handle large sample sizes, because the RGA (residual gas analyzer, the mass spec) breaks at pressures higher than 5e-4 mbar. The larger the sample the larger the amount of gases that evolves, so we weigh out the sample to about 10 mg.

This 10 mg sample is then loaded in a quartz tube, which is on one side plugged with quartz wool. Quartz withstands temperatures up to at least 1600 °C, and we reach a sample temperature of ~1300 °C, so we won't melt the tubes.

This sample is loaded into the oven. 

Check the video of day 10 to learn how VAPoR operates.