today's short course
Feb. 9th, 2015 09:21 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
kareinaToday's pre-conference short-course was on Laser-Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS).
The first half of the day was done by the guy at UTAS/CODES who has been doing lots of publications on using LA-ICP-MS for geological questions, and has specialized in the kind of projects we want to do at LTU. He focused his talk on the Laser-ablation side of the machine, and pointed out that while there are many manufactures of ICP-MS machines out there, none of them are optimized for use with a Laser-ablation system--they are all designed first and foremost for analyzing solutions, and can be adapted to work with the laser system.
However, as geologists we prefer the advantages the laser-ablation system offers. The biggest of these is the fact that we can do in-situ work--instead of dissolving the entire sample (and then diluting it) before analyzing it, we can just zap a specific point of interest in our rock, and learn the composition of just that bit. This works because of the plasma generated when the laser hits the sample in the presence of a gas flow--the plasma is sent into the ICP-MS unit for analysis.
He talked about the interface between the Laser ablation unit and the ICP-MS unit, about what is actually happening during the ablation process, about how things change if one changes the spot size, or the power of the laser, or the duration of the laser pulse, and what sorts of things to think about when changing any of these settings.
He confirms that for multi-element analysis the instrument of choice is the quadrupole, but points out that the analysis looks at only one element at a time--it is sequential, making it possible that the composition of what is reaching the analyzer during the analysis of one element is not exactly the same as what arrives while it is doing the next.
He also reminds us that not everything that gets zapped goes into the plasma stream--some residue is deposited onto the sample (and clearly shows in photos when the magnification is appropriate), he also pointed out that for many minerals the melting point it low enough that there is also melting happening, and a glassy melted surface is left behind. In some cases the melt has a different composition than the mineral from which it melted--when analyzing pyrite (FeS2) one can get a melt left behind which is only FeS, so the proportion of Fe to S has changed--this may or may not effect the part of the sample that goes into the plasma to be analysed, and it is something to keep in mind.
The first half of the day was done by the guy at UTAS/CODES who has been doing lots of publications on using LA-ICP-MS for geological questions, and has specialized in the kind of projects we want to do at LTU. He focused his talk on the Laser-ablation side of the machine, and pointed out that while there are many manufactures of ICP-MS machines out there, none of them are optimized for use with a Laser-ablation system--they are all designed first and foremost for analyzing solutions, and can be adapted to work with the laser system.
However, as geologists we prefer the advantages the laser-ablation system offers. The biggest of these is the fact that we can do in-situ work--instead of dissolving the entire sample (and then diluting it) before analyzing it, we can just zap a specific point of interest in our rock, and learn the composition of just that bit. This works because of the plasma generated when the laser hits the sample in the presence of a gas flow--the plasma is sent into the ICP-MS unit for analysis.
He talked about the interface between the Laser ablation unit and the ICP-MS unit, about what is actually happening during the ablation process, about how things change if one changes the spot size, or the power of the laser, or the duration of the laser pulse, and what sorts of things to think about when changing any of these settings.
He confirms that for multi-element analysis the instrument of choice is the quadrupole, but points out that the analysis looks at only one element at a time--it is sequential, making it possible that the composition of what is reaching the analyzer during the analysis of one element is not exactly the same as what arrives while it is doing the next.
He also reminds us that not everything that gets zapped goes into the plasma stream--some residue is deposited onto the sample (and clearly shows in photos when the magnification is appropriate), he also pointed out that for many minerals the melting point it low enough that there is also melting happening, and a glassy melted surface is left behind. In some cases the melt has a different composition than the mineral from which it melted--when analyzing pyrite (FeS2) one can get a melt left behind which is only FeS, so the proportion of Fe to S has changed--this may or may not effect the part of the sample that goes into the plasma to be analysed, and it is something to keep in mind.