USP Ethanol Impurities by GC.

[James A. Coulter]

Hey Folks. I'm new to the Forum, first time post. Does anyone have experience handling Acetaldehyde for the preparation of standards listed in the USP Monograph Method, USP 36, page 2357?

It boils at 21C, and is a bit difficult to handle in a way reasonable for inclusion into a Pharma QC method.

Also, they treat 10 ug/L as "10 ppm"; it is 10 ppb, wgt/vol. I looked, and previous USP's were vol. /vol., and 10 uL/L was 10 ppm vol/vol, but when they went to 10 ug/L the mistake occurred.

[RogerBardsley]

I have used refrigerator temperature glassware to do this. Typically make a stock by weighing with cold glass dispo pipet, then diluting down to level required.

[dlbenach]

While we do not do this specific method, we do prep acetaldehyde stds and they are difficult. We have had success by putting acetaldehyde in a 2 mL GC vial. We then use a syringe and inject air into the vial to pressurize it a little. Next we fill the syringe with the amout of acetaldehyde needed. We use the density to calculate the volume needed. Before removing the syringe from the vial, we move the syringe tip into the headspace of the vial and withdraw the plunger to add an air slug in the tip of the syringe. This helps prevent the acetaldehyde from shooting out of the syringe when removed from the vial. Hope this helps.

[rb6banjo]

I don't perform this specific method either but when I make AA standards, I choose the volumetric flask, add some solvent to it (I usually use methanol or ethanol because mine don't sit around long and my samples are substantially aqueous) and tare that on my analytical balance. I then drip it in and whatever mass gets caught in the liquid is what I have. I dilute it to volume and then dilute from there if needed.

AA is so soluble in water, you probably use that to make solutions on par with 1,000 ppm. Good luck!

[Arne]

If you have access to a cold room, do the sample prep there. Also, use a refrigerated autosampler tray, of course. We have had good success analyzing acetaldehyde by headspace analysis.