Gc. plz help..?
i use semi polar column for other standard (EPA and ALA) with IT= 70 oC and FT=265 oc? i've no idea what to do.. i've check web site and no solution. :"(
Answer:
How long are you running the detector? What is the column length? What type of detector are you using?
DHA methyl ester (C24 O2 H34) is a very polar, very high MW compound. My guess is that you are not running the detector long enough to see it. The retention index should be very high, so with a semi-polar column, I would expect that it should take 4 times as long as, say, octane. Break out the CRC handbook and look for the RI (I don't have mine with me, or I would look it up to be sure). Try running shorter esters and looking for their peaks. If you want it to come out faster, use a non-polar column, increase the ramp temperature speed, increase the final temperature, increase the inlet temperature, or increase the carrier gas flow rate.
If you are running long enough to see it, but still aren't getting a peak, drop the split ratio, inject more, or bump up the detector sensitivity (ie: increase the EV for a MS, clean an FID, etc).
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