Analytical balances

Jim Sutton sutton.james at epa.gov
Thu Jan 17 11:34:32 EST 2002


Sir:

I am a QA Manager for an EPA research division in Research Triangle
Park NC.  I have a question that was prompted by an audit of our
research documentation practices last September.  Could you please
forward this technical request to an appropriate individual?

One of our investigators was written up as being afoul of normal
practise because he did not have a procedure for leveling the balance
in his laboratory or for verifying that the balance was level although
it was located on a vibration-free table and otherwise properly
calibrated and installed.  He did not change the feet of the device
after it was installed.  Apparently an auditor noticed that the bubble
in the indicator was not exactly centered and wrote it up as an
infraction.

My question is, given the proper calibration and operation of the
instrument, would not the leveling problem be merely background noise
that was compensated for by the fact that its attitude relative to the
table had never been changed and that all measurements were accurate
to the capacity of the instrument?  It seems to me that the principle
of ceteris parabis would apply and produce results within the range of
variability as specified by the manufacturer.  If I am in error, I'd
like to know.

Jim Sutton
US EPA - Neurotoxicology Division
RTP NC




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