Serological pipettes sold unplugged--do I plug it myself?

January 17, 2014 10:19 PM

Does a pipette that is sold unplugged work fine as-is, or do I need to plug it?

I have a couple of plastic pipettes for measuring essential oils. They've been great except for the oils dissolving the plastic (!) so I'm looking at glass pipettes such as the Sibata 25ml serological pipette, which I found for a decent price.

It's not plugged (as in, the length of cord-looking stuff in the narrow bit at the top that my plastic pipettes have). I've researched and found one reference to plugging pipettes as something done in a lab, but no instructions.

I don't actually know what the plug does, will the pipette work fine without a plug? Maybe the plug just protects the pipette suction pump from liquid if I overdo it? If I have to plug it, any advice on what to use and how to do it?

Thanks for any advice you can offer.

posted by Anwan to Science & Nature (10 answers total)

In the last clinical lab I worked at, we used glass pipettes without a plug all the time. I'd imagine that all it does is protect the suction bulb (like you thought), and I guess we never worried about that because we washed our pipette bulbs if someone got a little over-excited while pipetting. I wouldn't worry about plugging them, just get a few bulbs in case you get one dirty and pipette away!
posted by sherber at 10:31 PM on January 17, 2014

Do not plug with nonporous material! You won't be able to create suction.

The plugs are to protect your pipet bulb or pipet-aid from overdraw. In a 25-mL pipette there is usually 8-9 mL extra volume marked off past the 25-mL mark. Make a habit of only drawing up to 25-mL and you will not need the overdraw or plug.

Plastic pipettes are plugged because they are single use. Glass pipettes are unplugged if they are the sort that are intended to be reused- a plug would prevent proper washing before the pipette was autoclaved and reused.
posted by variella at 10:46 PM on January 17, 2014 [2 favorites]

Yeah, all it does is protect the bulb, and if your technique is good enough, you don't need it, but you can stuff the top with loose cotton batting if you want to play it safe. (Replace the cotton when you clean or sterilize the pipette or if you get the cotton damp.) And, yeah, bulbs are usually washable, so it's more important if you're aliquotting something that's prone to aerosolization or really hard to clean up.
posted by gingerest at 1:04 AM on January 18, 2014

When I first started working in labs, it was long enough ago that we didn't use plastic pipettes. We used glass for everything and plugged the pipettes by hand after washing them and before autoclaving them. You use cotton batting - which, if I can remember from close to 30 years ago, is shorter fiber than a regular cotton swab. It takes a bit of practice to get a piece just the right size. You then jammed it into the pipette with a tiny wood dowel - a bit thicker than a toothpick and about five inches long. Any little stick would do. I think you can use regular cotton swabs if you pull apart a smaller amount from the swab. To remove the cotton before washing, you'd use a small wire with a hook at the end. Stick it in the plug end and twist then remove.

A simple way to get a nice piece of cotton to plug your pipet is to remove it from a disposable plastic pipette and put it in the glass pipette. Sometimes they come out easily, other times, not so much.

Above comments, except the wax suggestion, are correct in that the cotton protects your equipment from whatever is being pipetted. Back when I first learned how to pipet, the equipment in question was the person mouth pipetting!

Bulbs are fairly washable, but will be annoying with oils. Electric pipettors usually have some sort of filter in them which is replaceable when you inevitably get it wet/oily. Those filters cost money, so this is something to avoid. Those weird plastic things that scroll to pipet are also annoying to open up and clean.
posted by sciencegeek at 1:46 AM on January 18, 2014

I started out in an old microbial genetics lab that still uses its old glass pippettes, and that is exactly what the plug bits are for.

Glass pippettes will work just fine without a plug of any kind, and are generally used that way, but some people plug them with a bit of cotton. I never did it working with microbes, but I was taught that you take a small bit of the stuff and carefully shove it through the back end of the pippette with a toothpick. Old professors tend to have a giant box of cotton with a texture they like that they bought in bulk thirty to fifty years ago, but you can just grab a bunch of cotton bits from disposable pippettes. The reason people do it is because washing out a fucked up plug is a lot less of a pain in the ass than replacing a fucked up bulb, even though it makes the general pippette washing process even more of a pain in the ass. With essential oils I imagine using cotton could be more useful to you with oil vapors that might be capable of dissolving rubber bulbs, much less contaminating them, than it was to me.

A lot of this though depends on how you plan to clean your equipment and how clean you need it. If your work needs to be sterile you can use an autoclave, which is perfectly compatible with cotton, where you can just stuff it in after cleaning but before sterilizing. However if you plan on using an oven - brought slowly up to 250°C, left there for half a day-ish, and brought slowly down to room temperature - cotton will just ruin your pippettes. In general using an oven, for pippettes anyway, is a lot less of a pain in the ass because you don't need to worry about drying them. I just use my oven to sterilize the pippettes I use to culture beer yeasts at home.

With glass pippettes, depending on the volatility, pleasantness, and hazard of the oils you're using, you may also want to consider learning how to mouth pippette, or if you have access to some cash just using an electric dispenser you can buy a bunch of disposable filters for, both of which would make this question moot. I'm glad that the instructions for how to mouth pippette are as difficult to google as they seem to be, but if you mention what exactly you're working with and its the kind of stuff where fucking up would be hilarious rather than tragic, I'd be happy to memail you with how to do it.
posted by Blasdelb at 2:55 AM on January 18, 2014

Also, as a general tip, if accuracy is important you don't want to rely on the last mL at the bottom for measurement because it won't be nearly as accurate. Thus, if you want to pippette 20 mL, draw up 21 mL, dispense 20, and return the remaining mL to the original container.
posted by Blasdelb at 2:59 AM on January 18, 2014 [1 favorite]

It's just there to prevent backsplash from ruining your pipette bulb or electric pipettor, or contaminating if you are pipetting cultures. You can use glass wool to make your own. I don't user either for pipetting, I attach a syringe with a short piece of clear silicone tubing, silicone is really stretchy and seals very well (the stuff I use almost feels sticky). The syringe has several advantages: 1) it is graduated, so you can use cheap unmarked pipettes to dispense if you are not too worried about accuracy, 2) Syringes are cheap and you can just toss them if they get contaminated or start to leak, 3) You can easily adjust the level in the pipette exactly and it automatically holds the level, 4) They come presterilized, so for sterile work you can just pull it out of the package and then toss it when you are done.
posted by 445supermag at 8:38 AM on January 18, 2014

BTW, if you are still using a rubber bulb, I would highly recommend switching to a hand pump. They're far more precise that a bulb and will hold volume better when transferring. As they are less likely to overdraw, the need for a plug to prevent washing the bulb/pump is much reduced. Safer and more effective.
posted by bonehead at 9:26 AM on January 18, 2014 [1 favorite]

return the remaining mL to the original container.

!?!
posted by bonehead at 9:27 AM on January 18, 2014 [2 favorites]

return the remaining mL to the original container.

!?!

If Blasdelb's experience is anything like mine, you unwrap a pipette tube, use it to transfer material from a stock container, and, when you go to transfer something different, that one goes into your trash and you unwrap a new tube.
posted by Kid Charlemagne at 6:45 PM on January 18, 2014