[Sin]

I have a vacuum chamber and vacuum capable of reaching up to a 30hg vacuum.

I have a bunch of supplements that are very hygroscopic, and clump up badly, and could possibly mold in long term storage. If I put them under this vacuum, will the moisture effectively be sucked out of the powder? I would assume yes, but I want to be sure before wasting my time. Under a vacuum, how long could it take for the moisture to leave 1kg of powder? I know this depends on a lot of variables of course, but is there some way of calculating it?

[Corribus]

Yes, you can use a vacuum chamber to do this.  A vacuum oven is even better, if you can warm the substance without it decomposing. As to calculating moisture level, you're better off just measuring it.  Do you have access to TGA?

[Sin]

I do not. I do not even know what TGA stands for .

The powders are not extremely moist, just more or less clumping together, and when those clumps are crushed a paste-like residue remains.

In such a vacuum, the moisture can escape from these clumps without them having to be crushed beforehand, right? How long should I expect to leave them in there to start with? I'm not entirely sure how quickly moisture can leave something under a 25hg vacuum.

[Corribus]

Depends on how moist they are to begin with, as well as a host of other factors.  You can monitor it by weight.  Weigh the sample before, leave it in for a day, weigh it again. Keep it under vacuum until there is no more weight loss.  This is the best you will be able to do (or the best your balance can measure). This is essentially what TGA (thermogravimetric analysis) will do, albeit with a much more sophisticated balance.

[Sin]

Thank you for the replies.

We have one concern. Doesn't really pertain to the question, but rather to lab-vac mechanics. We are using an semi-expensive lab vaccum($1000). My friend is concerned leaving it on for extended periods could break it. Is this a valid concern? I figure it is made for lengthy distillations. Though, I am also not an expert on lab vacuums.

[Corribus]

We leave our lab vacuums on for days at a time or even longer.  The vacuums for our glove boxes are on continuously, all the time.  Consult your user manual, of course, but as long as they are properly maintained, you should be able to leave them on for long periods of time I would think.