Powder XRD sample prep question

[xrdquestionperson]

Hello, I have an unusual case in that I am using XRD to study plant skins before and after certain chemical treatments. So the resulting pattern will have a lot of amorphous regions but also some characteristic peaks showing the presence of fatty acids, etc.

Basically I grind everything to a fine powder and pass it through a sieve and use a glass sample holder to run the experiments. However- and this has happened more than once- I get terrible reproducibility; running the same sample under the same conditions gives me wildly different results on different days, some peaks are missing, etc.

I'm new to the technique so maybe there is something I'm missing because I was trained to just put a thin layer of the powder on the sample holder (glass slide, essentially) without anything to hold it in place and to smooth it out with a spatula until it's more or less evenly distributed. I run the tests in ambient conditions if that makes a difference.

 

[SpinFlop]

Perhaps reaction with the environment or maybe the chemical treatment operates over different time scales. Either could result in breaking down or modifying the chemical structure which would result in a different peak structure. Can you leave the sample on the XRD machine and remeasure over multiple time intervals over the course of a day or two? Perhaps you can see a systematic change as a function of time.