By Chris Allen on Tuesday, June 1, 2004 - 01:30 pm:

I am validating a method which involves weighing 0.5g of a premix with an active concentration of 20% into a disposable centrifuge tube to which 25ml of extraction solvent is pipetted. Direct weighing into the tube is a problem as the static causes a slight loss of material. Weighing by difference with a glass weighing boat is not working as the static is being transfered to the weighing boat which in turn is upsetting the balance and causing inaccurate readings. If possible I would like to avoid washing the material into the tube with the extraction solvent as we are tied to adding the extraction solvent by pipette (i.e. not made to a set volume at a later date). Does anyone have any better suggestions for sample weighing or a method for eliminating static from polypropylene tubes.

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By Anonymous on Tuesday, June 1, 2004 - 02:11 pm:

An air ionizer? something like this:

http://www.trinc.org/english/product/e03.html

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By Anonymous on Wednesday, June 2, 2004 - 12:17 am:

You can try washing the tube/glass weighing boat with the dissolving solvent, dry the inner walls with a twisted tissue before weighing. It helps in minimizing static to some extent.

- Fran

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By Chris Allen on Wednesday, June 2, 2004 - 02:35 am:

Thanks-

Can anyone explain why static causes a problem with analytical balances?

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By Anonymous on Wednesday, June 2, 2004 - 04:59 am:

The static has nothing to do with balance but it is the inherent property of some compound to become charged when in dry state and milled.the particles fly out due to repulsion of same type of polarity. best way to treat is use static gun to neutralise the charge before weighing.