Pipet accuracy... (fwd)

[Robert Preston]

Tim Chipman wrote:
> 
> > we just got a new shipment of yellow tips in from fisher, and they 
> > seem AWFUL at first glance... upon expulsion of the tip, it immediately 
> > seems to draw some liquid back up.... does anyone have any recommendations 
> > for what yellow tips they find the best?

Raj Shankarappa replied:
> 
> As many must have noticed, this is a very frequent problem with most of
> the available tips.  To avoid this inaccuracy, I have now made it a
> habbit to draw the fluid and immediately dispense it back, so that
> the inside of the tip is sufficiently wetted.  If you go in the second
> time and draw the liquid and dispense it, although some might be
> retained in the tip, the amount dispensed will be the set amount.
> Does anyone have other ideas?
> 
Here's another idea: in our lab, infested with occasional workers as
well as the motley core crew, for some inexplicable reason the metal
ejectors on the pipetmen are constantly being maladjusted, not fully
seated into the handle.  The result is that, more frequently than I'd
like, I find the ejector prevents a tight seal forming when the tip is
put on.  The ejector should be jammed fully onto its post, to prevent
this, and there should be a visible gap present between the top of the
tip and the bottom of the ejector. 

Rob Preston
rapr at med.pitt.edu