Chromatography Forum

I've been given a fun brain teaser and can't seem to solve it so any help would be appreciated.

How do you calibrate a flow rate under the following conditions:

1 uL / min

calibration gives the RF

20 minutes or less

4-5 place accuracy

fully automated

Weigh a 2ml septum-capped vial to six figures. Insert the 1/16 inch outlet of the flow system through the septum and run for 20 min. Remove vial from tube. Reweigh. Calculate gain in weight. Correct for density. Repeat N times and take the mean. Send me 10% of your fee .

Peter

Weigh a 2ml septum-capped vial to six figures. Insert the 1/16 inch outlet of the flow system through the septum and run for 20 min. Remove vial from tube. Reweigh. Calculate gain in weight. Correct for density. Repeat N times and take the mean. Send me 10% of your fee .

Peter

lol I wish I was getting paid for this. I also forgot to mention that the process needs to be fully automated. I'll fix the OP to reflect this.

We inject uracil at different flow rates, by plotting flow vs retention time, you can find the bias of the flow.
That's our procedure for HPLC, which uses mL/min instead of uL, so this might not work for you...

Ace

For automation put the 2 ml vials into a fraction collector. I'm sure that you can get robots that will do the weighing - several years ago Zymark had weighing stations in their automated sample prep robots to confirm that additions had been correctly made.

Alternatively; pump water into a Karl Fischer apparatus.

Direct volumetric measurement by pumping into a very thin capillary and tracking the front of the liquid with some fancy optics would also work. For repeat measurements either keep pumping into the same capillary, or have several capillaries connected to an automated selector valve.

Peter

Upchurch sells a flowmeter with RS232 data collection for 1.5 nL/min up to 8 uL/min. Right in the sweet spot for your measurement.

Weigh a 2ml septum-capped vial to six figures. Insert the 1/16 inch outlet of the flow system through the septum and run for 20 min. Remove vial from tube. Reweigh. Calculate gain in weight. Correct for density. Repeat N times and take the mean. Send me 10% of your fee .

Peter

If you go this way, use plastic, low volume vials (that weigh less than 2g) if you want to use a semi-micro balance (many of which will not read beyond 2g, at least not to thousandths of a mg).

Are you serious about 4-5 decimal places on 1uL/min? That means you want to detect 0.1 - 0.01nL changes in flow at 1uL/min?

Of course, at the resolution that you say you need you will have to thermostat everything to the nth degree.

Peter

Or just prolong the collection time to 40 min, or 60 or whatever is doable.

Best Regards

20 minutes or less the man said.

Peter

My point was: Prolonging the collection time is much less complicated as well as cheaper than buying, installing, qualifying etc. a robot for instance

Best Regards