From: Jacqueline Day
Date: 12 December 2011 21:24
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From: Edward A. Berry
I suppose you mean the pipetman and similar, and having it calibrated
by a professional rather than pipetting into a weighing boat to see
if it is OK-
Unless i'm missing something, there is very little that can be done in
the way of calibration- the diameter of the stainless steel shaft and
the pitch of the screw can't be changed (and won't get out of
calibration anyway). This leaves only the zero point to adjust,
and that is unlikely to get off either, except by a clumsy attempt
to calibrate it.
What does need attention is the seal, which can get worn and allow
air to leak. This is noticed (in very bad cases) when you fill the pipet,
hold it up, and solution slowly drips out; or if you are pipetting a
viscous solution and the solution stops flowing in long before the
indicated volume has been taken up.
The seals are available from the manufacturer (Rainin) and can be
changed rather easily by yourself. As for testing when the seal needs
changing, the drip test mentioned above works for large volume pipets,
for P2 or p10 you might need to wick the water out of the tip with a
kimwipe- if the seal is good a little will flow and then stop,
if the entire volume flows out into the kimwipe the seal needs
replacing.
To check the zero point, turn the counter toward zero checking the
play (to "first position") as you approach. The play should go to zero
as the counter does. More practically, pipet a volume into a
weighing boat tared on the analytic balance, and see if the correct
volume was delivered. If either of these tests fails, it's time to have
the pipet calibrated. If there is a bent shaft or cracked plastic,
then it needs repair.
Just my opinion,
Ed
Date: 12 December 2011 21:24
All-
We are reevaluating the frequency of our pipette calibrations and were tasked with determining the "norm". How often do you calibrate your pipettes? Do you have different schedules for different purposes (i.e. crystallization pipettes get calibrated every 18 months, while purification pipettes are calibrated every 2 years)? Who do you use for the calubration? Thanks, everyone!
Jackie
----------
From: Edward A. Berry
I suppose you mean the pipetman and similar, and having it calibrated
by a professional rather than pipetting into a weighing boat to see
if it is OK-
Unless i'm missing something, there is very little that can be done in
the way of calibration- the diameter of the stainless steel shaft and
the pitch of the screw can't be changed (and won't get out of
calibration anyway). This leaves only the zero point to adjust,
and that is unlikely to get off either, except by a clumsy attempt
to calibrate it.
What does need attention is the seal, which can get worn and allow
air to leak. This is noticed (in very bad cases) when you fill the pipet,
hold it up, and solution slowly drips out; or if you are pipetting a
viscous solution and the solution stops flowing in long before the
indicated volume has been taken up.
The seals are available from the manufacturer (Rainin) and can be
changed rather easily by yourself. As for testing when the seal needs
changing, the drip test mentioned above works for large volume pipets,
for P2 or p10 you might need to wick the water out of the tip with a
kimwipe- if the seal is good a little will flow and then stop,
if the entire volume flows out into the kimwipe the seal needs
replacing.
To check the zero point, turn the counter toward zero checking the
play (to "first position") as you approach. The play should go to zero
as the counter does. More practically, pipet a volume into a
weighing boat tared on the analytic balance, and see if the correct
volume was delivered. If either of these tests fails, it's time to have
the pipet calibrated. If there is a bent shaft or cracked plastic,
then it needs repair.
Just my opinion,
Ed
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