General Spectroscopy - Mechanical pipettes and concentrated acids
Could you perhaps tell us what pipettes you use when handling the harsh solvents/acids (HNO3, HF, etc.) used in ICP standards? We know of issues regarding the useful lifetime of pipettes when used with concentrated acids, and would appreciate any suggestions.
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Ward Keeling
Total posts: 1
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admin
Total posts: 529
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We avoid using mechanical pipettes for concentrated acids due to the harmful effects the fumes have on the internal mechanisms, and instead would recommend simple polyethylene transfer pipettes. They are not as accurate as a calibrated mechanical pipette, but are suitable for many purposes. If very accurate amounts of concentrated acids need to be measured, then weighing can be an option, but the same concerns regarding aggressive fumes still apply (must be performed in hood, fumes damage equipment such as balances, how accurate is a balance in a fume hood, etc.). For ICP applications the acid contents are generally low (<10% acid by volume), and pre-mixing a volume of a diluted acid and then using that as the diluent can not only avoid the above concerns, but can also eliminate any potential differences in acid concentrations if each solution is prepared individually using concentrated acids. If concentrated acids have to be used, then acid resistant bottle top dispensers can be an option, and many of these are accurate and reproducible enough that any slight differences in acid contents between different solutions should be negligible for ICP applications.
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