Anyone got a good way on these. Automatic, manual, single pans??????
've only done them manually useing the gravimetric method but I've found using a scale instead of a mass compartor does speed up the process some. You have to watch your accuracy ratios though...some of those pippets are pretty precise. We typically check 3 points across the range of the pippet. Also I recommend using a weighing container with a smaller surface area to help reduce evaporation. One last tip...make sure the pippet is clean.
Our SOP calls for 4 shots @ 3 volumes for "as found" and 10 shots @ 3 volumes for "as left". Yes, I know that's a poor statistical sample for the "as found", and I'll have to admit it's a short cut. But I still feel it gives a good representation of the "as found" performance though.
Now when you consider the 8 or 12 channel pipettes, you are looking at 336 to 504 shots MINIMUM. Talk about a time hog! And I'm still not convinced there isn't some interaction between channels on the multi-channel pipettes. True, each channel is independent as far as operation and mechanics. But is there some degree of "drag" or "load" on the pipette as a whole when you aspirate or deliver 12 channels instead of the single channel that we do during calibration. Any opinions anyone?
Be sure you correct for evaporation. Allow uniform drain time before the blow-out stroke. Make sure you use a balance with sufficient accuracy and resolution. Practice and get your brush-off stroke consistent. The temperature of the water makes a big difference in your Z factor so make sure you use a precision thermistor in your supply beaker. The tip immersion depth makes a big difference on aspiration.
For something as simple as a pipette is, there is quite a bit to their calibration. And when you get done, you can stop and consider that what you have just done doesn't really mean squat unless the owner plans on delivering triple distilled water @ 20°C. But that's the way both ASTM E1154 and ISO 8655 test them so at least its uniform across the industry.
And then you can talk about the colorimetric method....