Pipette bulb filler

Mine does this all the time as well. It was doing it from the moment I first connected it to a pipette and it was brand new. I've been using one for well over a decade, so I'm used to the bulbs and behaviors of pipettes on them. The 25ml pipette I use most of the time is an expensive glass one, with an etched scale (I think it's grade A) and heavy walls, so I can stick it right the way into the bulb and it'll seal well.

It either means the seals on the valves aren't working very well or, as you suck up a low viscosity, low boiling point solvent (like DCM), the solvent is likely expanding a little as it warms in the pipette, which will reduce the vacuum above it, causing a little to drip out.

It's just something I've gotten used to. I'll either transfer over surfaces where it doesn't matter if it drips or put my finger over the tip if it's something filthy, like DCM with iodine in it.

We've had those rack and pinion, trigger fillers in some of the labs I've been in, but we almost always got the rubber bulbs. I can't remember if the linear pump ones dripped, as we rarely used the odd solvents I do now, if ever. I also seem to remember that the plunger on those used to 'fall' back down on it's own sometimes as, like with the bulbs, the trigger opens a valve to vent the vacuum above the liquid to atmosphere, it doesn't lock and release the rack and pinion it's self.

I don't have a single bulb pipette, all of mine are volumetric, with 'dead space' below the scale as it goes to the tip. As such, loosing a few drips doesn't equate to any difference in the accuracy of the volumes dispensed. Also, damage to the tip doesn't make any difference to the readings from the scale.

If you think about these volumetric pipettes and the tips not being important, you can then ask, well why would they put so much effort into making the hole so small? Which encourages it to clog and fill / dispense painfully slowly when working with viscous liquids (we had to titrate thick toilet bleach at one point, nightmare...). It suggests that's a factor in the pipette dripping.

Bulb pipettes are good for titrations and other work involving repetitive stock solutions, where it's easier to get a very accurate reading with them because the bulb contains most of the volume and the last few drops are read on the thin 'capillary' section above, reducing the error. There's only one end point as well, the line, not two as there are with scaled pipettes. With a scaled pipette, it can also be easy to mix up the graduations on them as you try to get it horizontal to reduce parallax errors. On the downside (for bulb pipettes), damage to the tip begins ruining the accuracy, as it's effectively part of the scale.

You do need to be careful letting things get into the bulb. A number of solvents will start ruining the seals. Before getting my own pipettes, I tried transferring DCM with the old (shit) turkey baster method. It would pour out of the end, despite there being no valves on the end of the 'pipette' to leak. Once it touched the red rubber bulb, it fell apart in a few minutes.

It's quite easy to accidentally suck solvent back into a genuine bulb when you're dealing with small pipettes and low viscosity solvents. If that happens, take the pipette out, squeeze the fill valve and violently squeeze the bulb for a minute or so, giving it a flick to encourage the drips back out. If it's natural rubber, don't leave it sat on the window ledge either.

If your bulb looks like mine, look down the tubes for the squeezy ports and you should see a tiny, glass BB acting as the stopper in the valve. I doubt it's those that'll be leaking on such a new filler, as they're normally a force fit in there and require a good, hard squeeze to open. A more likely candidate is the plastic bit at the top, which could possibly be improved by taking it apart and adding something to the seat (not tried it myself).

I've had some absolutely horrible 5ml serological pipettes from Volac. The numbers have literally fallen off them, into my solutions, creating an integer number solution and meaning I'll need to start all over again. The glass is laughably, scarily, thin. Every time I use one, I'm worried it's going to shatter and end up in my hand. They're gradually breaking and falling apart (well, quite rapidly actually), so they're going in the bin as they do and I won't be buying anymore.

I have considered getting a repeating pipette, but I haven't seen anywhere doing glass tips for them, so that's out in terms of reactivity & solubility. I doubt the seals on the piston are designed for contact with solvent vapours.

I would like one of these electric glass fillers entropy has, but I'm willing to put up with the squeezing for now and spend the money on other bits that I can't really do without. I expect it'd make the pipettes easier to damage as well, as there's not the same degree of flex between the filler and glass.

You could easily make you own electric filler with an aquarium pump, a bit of tubing and a foot valve (like a dentist uses) or switch for the power. If you use a valve, you could also operate it in reverse, to blow the pipettes out. You could connect multiple pipettes to the same hose, so you don't need to swap them over. And you get back the flexibility. A fridge compressor would also work (for free), but you'd need to limit the positive pressure if using it for blowing out. If the fill / dispense rate is too high, use a proportional valve or pinch the tubing off. The proportional foot valve could be as simple as an old style tredel pedal (like a Wah Wah pedal) with a spring in it to force it back when you take your foot off, so it pinches the tubing closed at the ankle end of the pedal (silicon is very easy to squash shut, neoprene works okay as well, latex may be another or thin walled natural rubber, PVC and similars will be harder to get working as they don't collapse very well). Using wide bore tubing for this valve bit will make it easier to control the flow rate. You could make the foot pedal from two bits of wood and hinge, put the spring near your toes, pushing the pedal back. Put a little block of wood beside or through the spring to limit the excursion to the point where the tubing just about returns to it's normal size, to help your brain gauge the travel and avoid overdoing it.

Personally, I still mouth pipette, which would likely get me thrown out of a normal lab. But it's quick and works and is reasonably safe as long as you're careful and using 10ml+ pipettes.

This is my filler bulb (Now with automatic fill valve! );


[Edited on 12-8-2010 by peach]