I need to develop a GC FID method (using HP-1701 column) for measuring EtOH in ion-exchange buffers that are >70% water. EtOH in these solutions is from 0.5-15% range, I am thinking of simple solvent extraction into hexane or something. Do I need to desalt? These buffers contain citric acid as well.
Thanks very much.
By Consumer Products Guy on Wednesday, March 24, 2004 - 03:47 pm:
Your samples are approximately the same ethanol range as commercial mouthwashes. I would mix 10.00 ml of your sample with 1.00 ml n-propyl alcohol internal standard and add about 25 ml water, shake, and inject 0.5ul using a polar capillary column such as a PEG-type. I would get a 99.8% ethanol standard and make up my IS mix using that, and calculate as % ethanol v/v (that's how ethanol in finished products is normally determined), but you could also calculate it as weight/weight. Extracting into a nonpolar solvent makes no sense to me, and likely would be poor partitioning. If you are confined to any column and not able to be flexible, that's not always the best science.
By Anonymous on Thursday, March 25, 2004 - 11:30 am:
Thanks, I am using a mid polarity 35% Trifluoropropyl)-methylpolysiloxane DB-200 column. Prepared the stds using 200 proof EtOH, added n-propanol as IS. I also added MeOH and IPA to collect those data as well.
I have reproducible RT, areas and excellent calibration. I am injecting only 0.5 ul to minimize backflash and salting of the inlet. Now to try the extraction you suggest.
By ced on Thursday, April 22, 2004 - 12:15 pm:
You should try head space with isopropanol or n-propanol as IS,and PEG column (wax) or db 624 for ex 30m*0.32*1.8 or 30*0.53*3.