weighing reagents is difficult due to static, any adivse?

Dr Engelbert Buxbaum via methods%40net.bio.net (by engelbert_buxbaum from hotmail.com)
Sat Mar 24 15:01:23 EST 2007


Anwar Khan wrote:

> Hello everyone, while measuring in sub mg quantities of a precious reagent 
> (dry powder) I could not keep it at one place due to static and the reagent 
> would go everywhere but down on the weighing boat.  is there any way to 
> avoid this.

In such cases I just trust the manufacturers statement of weight and add
water to the vial directly to make a stock solution. That I then
aliquote and snap-freeze. With some substances you can measure the
concentration of the stock solution (i.e. absorbance or fluorescence
measurements), just as a sanity-check.

Note that with most balances you get 0.1 mg precision, so weighing
sub-mg amounts gives you an error of > 10%. On top of that you get the
error from trying to get the weighted substance into solution
completely. Together that's much larger than the error a reputable
manufacturer may have made.


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