Hi, you should try plasma cleaning. It is usually available in most SEM and TEM labs (also in stable isotope labs) for removing the organic material before microscopic study and analyses. Plasma cleaning systems use an energetic plasma created from gaseous species (e.g., argon, oxygen, hydrogen/nitrogen, etc.). The plasma is created by using high frequency voltages to ionise the low pressure gas. It works pretty well in most samples. I hope this can be of help, cheers.

You may to wash your samples in concentrated H2O2 (perhydrol). It would be cheap, fast and simply.

Thanks for the helpful answers. The purpose of 'cleaning' the minerals is to spike them with relatively volatile organics that I do wish to detect. Will any of the suggested methods greatly affect my ability to do this?

I have also used hydrogen peroxide to remove organics from small rock samples. They should be rinsed a few times afterwards with distilled water, otherwise the residue might affect your experiment. I have been told that one can also use KOH, but I don't know if this is as effective as H2O2.

Dear Sophie

The traditional method to remove organics from minerals is sinking the specimen into hydrogen peroxide (from the nearest farmacy). To the best of my knowledge X-irradiation, or UV, beta, gamma, etc..., just only could modify the mineral colour and probably a subtle photooxidation of the organic matter. Javier Garcia-Guinea. Madrid

It seems that this is the best method then. Some of the minerals will be clays, is that likely to be a problem?

Dear Sophie, hydrogen peroxide solutions have acid PH so they will dissolve partially or totally carbonatic fraction of your mineral samples. In this case you can use a bath of organic solvents (as ethanol, acetone, toluene) and a sonicator.

Alessandro's comment suggests a motivation for using KOH, which makes alkaline solutions and will not dissolve carbonate.

but KOH solutions are also very aggressive for the silicates. You have to pay attention to the high PHs of these solutions.

My zoologist friends of our Natural History Museum use hot KOH solutions to destroy animal tissues preserving the bonds, obviously composed by hydroxyapatite and collagen

Could you give more details on your samples. Is organic material inside or outside ?

I don't have samples yet as it's for a proposed project, but need to known it's feasible. They are mixtures of minerals to simulate Martian regoliths (see Bottger et al 2012). The organic background may well be very low, but if not I will need to mitigate for this.

Hydrogen peroxide should be ok

Sophie, we have experience of a range of techniques for removal of organic material from carbonate samples prior to stable isotope analysis. These include chemical treatments involving hydrogen peroxide, sodium hypochlorite all of which have been discussed above. One other method that you might consider is low temperature plasma ashing. Here the organic material is oxidised in a low temperature oxygen plasma. One of my former PhD students investigated different techniques and reported on these in her thesis. If you contact me I can forward you the relevant chapter.

Hopefully, we will be allowed to publish a method developed at our labortories using surfactants. It is performed at 50 C, and to date we have found no negative influence on the clay mineralogy, including the smectites. You are asking a long-standing problem that has needed an answer for decades. If we get the OK, I'll make sure I publish a link on ResearchGate.