Making TLC spotters from Pasteur pipettes is one of those tasks that really isn’t worth the time it takes, but is just too much fun to stop doing. Cheap, reliable spotters can be purchased from your favourite lab supply company for about $0.30 a piece (just look for “micropipets”. The 5μL drummond ones are good), and used nearly indefinitely provided you rinse them three times with methanol or acetone between each use (blot dry on a kimwipe). In my hands they tend to last for several months, until I accidentally snap them in half.
Still, if you’re running a reflux there’s no way you’re sticking one of these little 7cm glass twigs down your condenser. So, enter the home made TLC spotter. The easiest way to make them is with a butane torch, but if you don’t have one handy a Meker-Fisher burner will work wonders (Bunsen burners are trickier, but are manageable if you hold the pipette just above the inner blue flame).
A word of warning. Make sure you’re wearing your lab coat for this, as the heavy cotton is generally non-pyrophoric, unlike whatever polyester blend you might have on underneath. And skip the gloves, latex or otherwise. The only thing worse than a burn on your hand is a burn with plastic melted into it.
Alright, so you’ve located the one place in your lab far from both solvents and fire alarms. Grab a box of Pasteur pipettes and hold one up in the flame, aiming for the region just above the light blue colour (the hottest flame burns in the UV). Rotate the tube constantly, until the bit in the middle takes on the consistency of silly putty and is nearly impossible to keep from sagging. Take a deep breath, remove the glass from the flame and pull in one smooth motion. The speed of your pull will determine the thickness of the glass, so it’s key to pull evenly, unless you actually want a bulbous wreck.
Spotter made, set it down on the counter and move on to the next. Hot glass doesn’t change colour until at least several hundred degrees Celsius, so what looks like perfectly ordinary glass can still leave a painful burn. Give each finished peace three minutes or so to cool down, then snap the ends off to give a nice, uniform tube.
The pull is the tricky part in all this. Wait too long after removing the pipette from the flame and you’ll end up with a stubby tube, useless. Pull while the pipette is still in the flame and the thinner glass will melt, breaking the connection and giving you two melted pipette halves. It’s a delicate balance, and don’t worry if your first few (dozen) attempts don’t end so well. I’ve turned at least a full box of clean pipettes into modern art myself.
Once you’ve got a nice tidy stock built up you can shut everything down. Break the pipettes where the tube starts to widen and toss the fat bits into the glass waste. Like the kind you can buy these spotters can be used near infinitely, provided you clean them properly. I seldom bother. They’re too much fun to make.
If all this is old hat to you, let’s see if you can beat the length record.