Pipettes

[Chris]

I know this is not directly related to HPLC analysis but I have a question regarding pipette washing.

We have a soaking jar for pipettes and I was wondring what is best to put in it. I thought either a dilute detergent or mild acid (e.g. 0.1M HCl).

Any comments?

[usallevyn]

We have one of those pipet washer receptacle that can be connected to water supply and it cleans the pipes. We use Alconox tablets that we get from VWR. We just drop the tablets in the receptacle and wash it with city water. then we rinse the pipets with DI water and dry before use.

[Cliff Mitchell]

Chromic acid is the best for getting glassware clean, especially if you want to do precision volumetric measurements. If you have spots on you glassware where solution sticks after the pipette has been drained, a chromic acid treatment will clean the surface so it drains smoothly and there is no residual solution in the pipette. Basically, it will oxidize any organics to CO2, and dissolve any inorganics (glass containers only!). You can soak pitettes overnight with a room temp solution, or 5-10 minutes with a hot solution.

You can buy this stuff from VWR and Fisher, or you can make it by adding potassium dichromate to concentrated sulfuric acid. I can post a procedure to make it if you wish.

The down side is that it can be very dangerous, and it's toxic. With proper procedures and saftey equipment it is safe to use. I have wiped up drops of the stuff with kim wipes and seen it rapidly eat through the tissue.

You can keep and re-use the solution you decant out of the cleaning bath, but the stuff that you rinse from the glassware must be collected as waste and segregated from other waste.

[DR]

We use dilute Alconox or Citrinox for soaking them, then Alcotabs & city water for siphon washing them. My only "trick" is to manually fill the siphon washer w/ hot (~60°C) city water and let it sit for a few minutes before doing the normal ~60-90 minute DI cycle (we don't use city water for the siphon washer flushing).

[David Blais]

Just to chime in here, I follow a similar procedure to usallevyn and DR except I don't use city water, always DI water. Necessary? - probably not, as long as the final wash/rinse is with DI water, but management feels better by not introducing city water in the mix anywhere.

[HW Mueller]

Interesting, pipetting HPLC solvents and afterwards shocking these pipets with chromic acid (last time I used that was over 30 years ago when I burned tar into a flask, this stuff is a sledge hammer), detergents, or tap water?
Well, just want to point out that it might be wise to adjust the washing method to what was handled, and what is done subsequently with the pipet. (For instance, detergents have shown up in GC chromatograms).

[DR]

I save the chromic acid for sticky hamilton syringes (well, that's what I did when in an academic setting, now I just order new ones ).

A friendlier alternative to chromic acid (environmentally) is NaOH. A dip in 25-50% caustic will generally knock stubborn stuff loose.