cleaning pipettes

[Kirk Gittings]

Hey now. This may seem utterly silly to some people but.............what is the best way to clean your pipette when you are basically using it to measure fairly viscous liquids like Pyrocat HD in Glycol?

[Michael Cienfuegos]

I rinse them in hot water, with a final rinse in distilled, then set them aside to drain and dry.

m

[NancyP]

Gravity helps eliminate some excess, stand the pipette on end and let it drip. Back in the day when we used glass pipettes, we had a tall polypropylene tube 6" diameter with inlet and outlet, for soaking and rinsing pipets. Really grimy ones got the potassium permanganate treatment - nasty. You could fit a small diameter latex rubber tube on the top and run water slowly through the single pipet. A plastic syringe without the needle may be the best reusable tool for viscous solutions.

[jp]

I use plastic disposable pipettes. I draw in water, shake it up, drain it, do that 3-4 times, then I have a drying rack for them (sort of like a spice rack but with 1/4" holes instead of 2" holes, labeled so I only use one particular pipette for each chemical I'd dispense. I have pipettes for photoflo, cyanotype A, cyanotype B, cyanotype dispensing, fixer tester, etc...

[jnantz]

hi kirk

if you really want it to be CLEAN get a "line cleaner"
you can probably get one off of amazon, or a beer making
supply shop ... they are like a test tube brush but smaller

[Michael Rosenberg]

Nancy,
I think you meant potassium dichromate, a very caustic acid.

Kirk,
Scientist would wash pipettes in a pipette washer, which fills and then siphons out the water - much like a film washer. I assume they are plastic pipettes?? What I do is keep them separate to avoid potential cross contamination and attach them to my faucet with a hose, and while holding tight I run water through them for 20-30 sec. I have a milliQ system, and I then do a rinse fill 6X.

Mike

[Harold_4074]

I think you meant potassium dichromate, a very caustic acid.

The traditional chem-lab ultimate cleaner was a mixture of chromic and sulfuric acids, made by dissolving sodium or potassium dichromate (or pure chromic acid) in concentrated sulfuric acid. Not, by any means, a material to trifle with, although I remember using it in high school. I suppose that back then glassware was more expensive than liability insurance...

On the original question: unless a deposit of some sort is being formed inside the pipette, a piece of rubber tubing and a connection to a faucet should be all that is needed. The cycling fill-and-empty pipette washers did just that, sometimes overnight, although when I worked in a biochemistry lab one summer the pipettes that had been used for bacterial cultures and such were first soaked in Alconox (a strong detergent) for a few hours before going into the washer.

Photography may actually be more forgiving than biochemistry: anything that doesn't come off during an extended rinse probably isn't going to come off into your next measure of Pyrocat either. :)

[Kirk Gittings]

The ones I have are 10ml and glass.

[Harold_4074]

I routinely use "disposable" plastic syringes to measure PMK for 120 film, so 5 ml of one solution and 10 ml of the other. I rinse the syringe water that becomes part of the developer, about four or five fillings each time.

Consider that the "dead volume" of the syringe or pipette might be as much as 0.1 ml. Mixing this into 10 ml on the first rinse will leave 0.1 ml dead volume of a solution that is 1% of the original concentration. After the second cycle, it will be 0.1 ml of 0.01%, then 0.0001%....you can see where this is going. For something really viscous (HC-110 syrup, for example) one would want to half-fill the pipette and shake vigorously on the first few cycles to be sure that the thick stuff is mixed in.

Incidentally, as a matter of good practice you should be using a pipette bulb, which makes the rinsing almost trivial. "Measure" 50 ml of water into your tank after measuring the developer, and you should be good to go.

[Peter De Smidt]

I use the 10ml glass pipettes. I have one dedicate to each solution. After use I use running water to down the bulb end to rinse the inside and outside, and then I set it to dry. Since they are dedicated, they don't have to be super duper clean.

[Andrew O'Neill]

I use plastic ones ever since I broke my glass pipette. I managed to keep the glass pipette clean and stain-free by rinsing it thoroughly after each use. Maybe I didn't have it long enough for it to get dirty...

[Kirk Gittings]

Incidentally, as a matter of good practice you should be using a pipette bulb, which makes the rinsing almost trivial.

I use this. Is that what you are referring to? 113296

[Michael Cienfuegos]

I use this. Is that what you are referring to? 113296

A pipette pump? That's what I use. I have one for my 5mL Pipettes and a red one (larger) for my 25mL pipettes.

m

[Harold_4074]

That's the contemporary, high-end equivalen.

The original pipette bulbs were probably just like a turkey baster bulb, but by the time I came along they were equipped with squeeze valves so that you can (with one hand and a bit of skill) fill, adjust, and empty the pipette with good control. What you have is probably better. There's a picture of a rubber "pipette filler" here: http://www.crscientific.com/pipettes.html

The real point of my comment was that mouth pipetting is really not a good practice. Folks did it for years, and some of them almost certainly regretted it. Usually a wad of sterile cotton would be placed in the top end, on the principle that if the solution wet it, the flow rate would be reduced enougn to protect the user (sort of).

[Kirk Gittings]

Thanks Harold.

[NancyP]

D'oh. Chromic acid. Shows you how long it has been since I have used glass pipettes (late 1980s).

[NancyP]

Re: the green pipette pump above. Our safety officer more or less banned these once people started using the flimsier disposable borosilicate glass pipettes. People would jam the pipette into the pump too vigorously, and the glass pipette would shear off and people would jam it into their wrist. I stopped using them when I had a near-miss with a Pasteur pipet (flimsy in the extreme). I prefer the old fashioned rubber bulb with valve if I am not using one of the fancy electric pumps.

[Cor]

Dedicated pipettes is indeed the way to go (I use disposable ones, and I removed the cotton on top so I can rinse with a spray bottle filled with distilled water). I now use this:

113503

Well actually it's predecessor the nice ones above got replaced with, ( and I happily could recycle them..:)..) no speed control but a joy for pipetting really viscous stuff like Mytol. We used to have the green ones Kirk posted in the lab, but they proven to be much less reliable and sturdy as the old fashion red balloon:

113504

Best,

Cor

[Stoogley]

How about using pipe cleaners? (ala for tobacco pipes)

[Nathan Potter]

In the semiconductor industry the lab guys would use piranha etch as a glass cleaner. It does not etch glass but viciously attacks organic residue and most chemical stains. It's half sulfuric acid mixed slowly with half hydrogen peroxide by volumes. A short soak is all that is needed. The common sequence follows.

Piranha etch 2 to 5 min.
DI wash 3 min.
Ethanol rinse 1 min.
N2 blow dry maybe 30 sec.

All analytical reagents.

No doubt overkill for what you need.

Nate Potter, Austin TX.

[Harold_4074]

Not that it is particularly relevant to Kirk's original question, but piranha etch is usually equal volumes of 96% sulfuric acid and 30% hydrogen peroxide, so it is actually about a 3:1 sulfuric-peroxide solution. For what it is worth, either of the ingredients alone will also viciously attack organic residue, such as skin, hair, fingernails and most clothing---and if accidentally mixed with certain other things, either one can result in a steam explosion, a fire, or both at once.

Amazing what chemists will do in order to clean things....

[Arne Croell]

Not that it is particularly relevant to Kirk's original question, but piranha etch is usually equal volumes of 96% sulfuric acid and 30% hydrogen peroxide, so it is actually about a 3:1 sulfuric-peroxide solution. For what it is worth, either of the ingredients alone will also viciously attack organic residue, such as skin, hair, fingernails and most clothing---and if accidentally mixed with certain other things, either one can result in a steam explosion, a fire, or both at once.

Amazing what chemists will do in order to clean things....

And the mixing of the two Piranha constituents will of course heat it up to something like 60°-100°C before you even start putting the wafer (or whatever else you want to clean) into it. It is very exothermic. The name says everything, doesn't it?

A milder (relatively) agent for removing organic residue is what is known as SC-1 or RCA-1 solution in the semiconductor community: 1 part Hydrogen peroxide (30%), 1 part ammonia (ca. 30%), 5 parts water. Heat up to 80°C and let it steep for 10 minutes. Probably still overkill for Kirk's needs, but a bit safer to handle. A fume hood is of course needed.

[Peter De Smidt]

These powerful cleaning agents are way overkill, as some have mentioned. Glass pipettes are cheap. Get one for each solution that you use. Label it. Use it. Rinse some water through and over it. Place it vertically in a secure place where it can air dry.

[evan clarke]

Weigh it..