Chromatography Forum

I am a student lab technician at Louisiana Tech University. I have a problem seperating 2 compounds on my Varian Star 3600 GC. We are running our GC at an oven temp of 45 deg C ramping up to 46 deg C at .2 deg/ min oven temp. My injector temp is 125 deg C my detector temp is 220 deg C and I am running a HP-5 30M X .053mm glass column and I keep getting overlapping peaks for ethanol and Isopropanol. I want to have good seperation but I have found nothing that works. I have tried isothermal operation of the column at different temperatures and have not gotten 2 peaks. The samples we are running are not diluted because they are samples from our distillation column to make sure it is working. I am trying to get a volume percent in each sample to make sure we get the seperation we need. Please someone help me get my GC Running

Hi
You won't get separation how ever hard you try on a "5" phase.
Try using something more polar such as a "wax" type column.
Or even a 624 phase.
There are plenty of separations on Agilent,Varian and Supelco websites/catalogues.
Good luck
WK

I have a FFAP column and was wondering if this would be a better column for me to use. I am running a concentration of 50% pure Isopropanol and 50% denatured ethanol which contains 90% ethanol 5% methanol and 5% Isopropanol. This makes my final percentages 52.5% Isopropanol, 45% Ethanol 2.5% Methanol. by weight. Is there any suggestions to improve the sample prep to get a good seperation.

Oh yes, the old ethanol-IPA separation issue, these co-elute on a lot of columns. Personally, I like a packed column of Tenax-GC or Tenax-TA for this. But we've also obtained satisfactory results using a 25 m x 0.20 mm i.d. HP-1 fused silica capillary column with 0.33u film thickness (Agilent #19091Z-102. The column must be installed into a split-type capillary injection port with a split ratio of approximately 120:1 to 200:1; detector make-up gas of about 30 ml/min. should be used. Initial temp. = 35 °C Run time = 5.0 min. Inlet temp. = 275 °C
FID temp. = 280 °C Column head pressure = 10.0 psi

Ethanol elutes at about 2.7 minutes and n-propyl alcohol internal standard elutes at about 3.6 minutes with these conditions Isopropyl alcohol will elute at about 3.0 minutes.

Besides the Texax almost any of the porous polymer columns packed with Hayesep or Porapak polymers will separate these EASILY.

Tenax is not quite as good as the others IMHO.

The Q polymer will work nicely.

Or course, a PLOT capillary will also work.

These are the columns I have on hand. Can any of these work????
Type DIMensions

1 FFAP 30 X .053
2 HP-1 30 X .053
3 HP-5 30 X .053
4 Suple-Q plot 30 X .053
5 Alltech AT-Q 30 X .053

Which one would be best????

Suple-Q plot 30 X .053 would be my choice. The FFAP would also be acceptable. The Alltech is a PLOT column, but they don't specifically recommend it for R-OHs. might work O.K.. The HP-1 and HP-5 are generally for petroleum, semi-volatiles (BNAs) and the like.

I like W.K.s excellent suggestion to check the the various sources that sell G.C. columns as they frequently have sample chromatograms in the catalogs. Great aid for the young chemist, usually specifies columns, flows and even detectors. A great place to start for many projects. Nice separation, C.P. guy. I've done a lot of PorPak Q work on packed columns back in the day, Chromatographer 1. A good choice also.

Anyone here read Separation Times? Sounds more like a divorce manual than chromatograhy information. There are several good free G.C. publications. Read them all.


Regards,

Glenn