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The Corroboree

Sample preparation recommendations

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Having a think....

I have fifty non-homogeonous biological samples I want to send to a NATA accredited lab for analysis.

They contain volatiles, so heating the samples will drive off some of the compounds I want to check the levels off. Heating the samples is part of the standard process of digesting them so they can be analysed.

Freeze drying is an option, but for that number of samples the prep would be expensive and out of my range

The compounds I'm looking at are relatively stable at ambient temperatures, or at least any variations for the more volatile compounds which come off at above 60C aren't compounds of interest.

I was thinking of grinding samples to dryness under liquid nitrogen in a not-fully-sealed stainless lab blender- because I have one here ( or should I seal it? ) but was told that as soon as the liquid nitrogen evaporates , water will rush in and the sample won't be dry any more.

Is this true? How fast does the water rush back in if I quickly place the dried samples into a -20 freezer

I've previously dried and ground biological samples under liquid nitrogen and found that most suitable, but that was for DNA analysis, not chem analysis.

Next option is to grind and dry at 50C under air.

Neither will give me consistent moisture levels for all samples, and it will prolly be up to the NATA lab to standardise these before analysis

Does anyone reckon grinding under liquid nitrogen to be the superior method in this case?

Ta for help, this place is fulla smarties :D

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I assume a vacuum desiccator (with or without absorption media) is not any good or you would have done that right? would keeping the vacuum level low stop anything (under BP60c) boiling off under reduced vacuum? set up like reflux to collect volatiles as they exit under reduced pressure?

As for liquid nitrogen, have you tried letting it evap off through a suitable drying tube outlet? Perhaps even slowing down it's evap rate too? Dont know what the vapor pressure is for that stuff, but assume it's rather high given it's boiling point.

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Perhaps analyse your protein and volatiles separately? I would suggest doing your digestion as planned (enzymatic/protein?) in a distillation flask. Look at the boiling points of your volatiles and collect the relevant fractions as they come off. Depending on what your looking for, water will most likely come of last and can be discarded. If you're concerned your other fractions are too wet, dry chemically.

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Thanks everyone for your input

We're now looking at air drying, and we have been discussing the sampling protocol with the analytical lab for clarity

I'm unable to say much about this for IP reasons, so I'll close the discussion off until results come in and I've clarified an NDA with everyone involved

Chem is not my special subject and I may have stuffed the original question here up due to my woeful understanding of several processes

Wish me luck.

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