Chromatography Forum

Hey I'm looking for a 'micro'-pipet with a max adjustable volume of 15ml.
Only thing I can find are old-school glass pipettes.

If by "micro" you mean "auto" then I think that you are out of luck. For reagent or solvent dispensing at that volume I would use a bottle top dispenser, for taking a volume of sample you might have to set a 10 ml autopipette to 7.5 ml and have two shots at it.

Peter

Hey I'm looking for a 'micro'-pipet with a max adjustable volume of 15ml.
Only thing I can find are old-school glass pipettes.

You may buy two 10 mL pipettes instead of one 15 mL.
Just kidding
Seems that 10 mL is max volume for such pippetes.

ok thanks a lot.
I have to pipet samples, so using a dispensette is not possible.

2x7.5 will give me twice the pipetting error, but I have no choise I guess.
Only solution would be using e.g. a Multipette plus with a 25ml tip. but that would be to expensive.

You can eliminate the effects of pipetting error completely by weighing how much sample you actually dispense and correcting the results accordingly.

Peter

Or use a Hamilton type dispenser/diluter and set to 15.00 ml ?

Hi

Both Peter and CPG made some pertinent comments - especially about weight checking.

What is your solvent and sample prep requirements and how many dispensings do you have to do per day?

There is nothing wrong with nor more simple than using a grade A 15ml glass bulb pipette ( used correctly - e.g. drainage time, tip touching etc)

Keep it simple

Kind regards

Ralph

I used Class A pipets like 15.00ml all the time. These were considered in calibration and didn't need checking for cGMP. I did not use a squeeze bulb with valves in it either, just the old fashioned red rubber bulb.

I liked to spike placebo product with 4.00ml, 5.00ml, and 6.00ml pipets in accuracy studies to readily get 80, 100, and 120% of target active level.

On the other hand, a younger chemist in the department hated to use manual pipets.

We use the auto pipettes from Rainin in 10ml sizes and do a weight check on them every morning before use. They seem to remain very accurate between servicing which we do every 6 months(send them off for refurb and recalibration). We have a rule to never use a one below 10% of the max volume to help prevent errors, so a 10ml we use down to 1ml and the 1000ul we use down to 100ul. Any smaller volumes we use micro syringes.

We don't use weight simply because it takes longer if you are trying to get an exact volume like 7.5ml several times in a row plus unless you are factoring in changes in density due to acid concentration and temperature and air pressure, the auto pipettes are in the same accuracy class as a tech trying to do such precision weighing on a 3 or 4 place balance in a room with a lot of air movement. When you are measuring out 50-100 samples per hour that just isn't feasible.

We use the auto pipettes from Rainin in 10ml sizes and do a weight check on them every morning before use. They seem to remain very accurate between servicing which we do every 6 months(send them off for refurb and recalibration). We have a rule to never use a one below 10% of the max volume to help prevent errors, so a 10ml we use down to 1ml and the 1000ul we use down to 100ul. Any smaller volumes we use micro syringes.

We don't use weight simply because it takes longer if you are trying to get an exact volume like 7.5ml several times in a row plus unless you are factoring in changes in density due to acid concentration and temperature and air pressure, the auto pipettes are in the same accuracy class as a tech trying to do such precision weighing on a 3 or 4 place balance in a room with a lot of air movement. When you are measuring out 50-100 samples per hour that just isn't feasible.

Hi James

I agree; adjusting to a target weight in order to get a precise target volume is slower than using an autopipette under most circumstances. But in many (most ?) cases you do not need the precision in sample volume that is provided by a 3-figure balance (nominally 1ul of anything aqueous) as long as you know how much sample you dispensed and do a correction in the final calculation. Using a correction for the actual weight dispensed avoids having to dispense an exact volume or weight. It also has the advantage that you have a QC check on actual quantity for every sample.

This does not apply if you are using a reagent that has to be present in an exact quantity, but it does apply to solvents etc used to make extracts and what not.

Peter

I see this has been a busy topic during my week of vacation.

I would use the pipet for water samples, and there would be about 30-50 each batch.
I guess for us the best way would be to just use 2x 7.5ml and check this on a balance to see how much error we introduce this way. If it is accaptable than we just use it this way. if not we will weigh our samples.

thanks

Commercially available pipettors are Class A devices; that is, they will dispense to +/-1% of the nominal volume over their working range. James accurately points out that the working range for most pipettors is 10-100% of the nominal maximum volume.