Chromatography Forum

I am considering getting into FAMES. My question is can you get an accurate total fat % from it. At a previous position I did good old soxlet extraction with pet ether to get total fat.

I read this article the other day by AOAC
http://www.aoac.org/vmeth/996_01.pdf
stating they are using it also for the total fat number. My concern is some of the fatty acids won't be in the standard mix, some will be to small to detect and intergrate, and some peaks how do you know if it is a fatty acid on the FID?

I am also working on amino acid method that uses a short 1701 column. I am fairly confident I can also use a long 90% cyanopropyl column for it as well as the fatty acids so if I can turn my 5890-FID to a MSG and fat analyzer that would be really great.

I guess it is the same old interference issue - the assumption is that coextractables from the old pet ether method are not significant or may be efficiently removed. A GC-FID method would presumably be more effective at measuring only fatty acids verse a gravimetric method, but it still won't address interferences well enough. Cooler technology though.

My opinion, after 30+ years in consumer products industry, experience with bar soaps and meat products: this idea in the publication is not really new, we used odd-chain internal standards 20 years ago for stuff like this.

My opinion would be to use a modified Soxhlet for total fat content, then saponify/esterify that residue and do FAME composition on that.

It's an estimate at best.

Given that it costs ~$150 to perform one of these analyses, we perform the total fat measurement in the procedure used to obtain the oil to do the GC analysis. There is no need to estimate it from the GC data.

What about if you're doing the analysis on pure fat, and you want to determine the actual fat percentage (ranging from 90-95 per cent) ?

What about if you're doing the analysis on pure fat, and you want to determine the actual fat percentage (ranging from 90-95 per cent) ?

Modified Soxhlet. Also will drive off the moisture.

Do you have a link with such a ready-made product?

Wouldn't an odd number carbon chain internal standard make the determination easier or more cost effective than a soxhlet extraction ?

I am referring to vegetable oils and animal fats as samples.

Normally I wouldn't mind soxlet but my lab is kind of limited with hood space and I have no water plumbing other than one sink and the dishwasher. I operate a small satellite lab and I try to make it into a swiss army knife lab where I can do as much as possible albeit not always the most efficient way. I have low sample load but high variety.

How well it works for you depends on your application and how well you optimize. For low sample load and high variety, it might be a challenge. We're working with algae, whole broth or dried biomass, and spent a good amount of time on method development. We get total derivable FAME and profiles in a single analysis. We currently run about 70,000 samples by direct transesterification per year, with a maximum throughput capacity of 300,000 samples/year. Obviously Soxhlet extraction is not an option for us. The method has proven to be very robust, and for inter-user precision and accuracy, the %CV is typically less than 1%.

It can be done, if you're willing to put the effort in.

... , and spent a good amount of time on method development. We get total derivable FAME and profiles in a single analysis. We currently run about 70,000 samples by direct transesterification per year, with a maximum throughput capacity of 300,000 samples/year. ...

It's very impressive.
70000 samples/year makes 233 samples yearly, assuming 0.5 hour chromatographic run you need 115 hours for chromatography

but day has 24 hours, so 6 GCs work every day all day long

not to mention a good amount of time on method development

very busy lab

Yep method develoment can take a lot of time. I've been working on my amino acid GC method for several months and finally got the proper derivitization reaction mixture today. Now I have to work on sample prep.

Yep method develoment can take a lot of time. I've been working on my amino acid GC method for several months and finally got the proper derivitization reaction mixture today. Now I have to work on sample prep.

Congratulation and good luck.

BTW
It's a pity that Jake's lab utilizes only 1/4 of it's maximum throughput capacity.

300000 samples/year would give ca. 820 samples daily.
Assuming again 30 minutes GC runs for FAME it takes 410 hours daily (not to mention transesterification).

300000 samples/year would give ca. 820 samples daily.

Actually, maximum capacity is about 1000 samples/ 24 hours. As pointed out, we're obviously using more than one GC; our LTM set-up alone handles 330 samples/24 h.

Yes, we're busy.

Normally I wouldn't mind soxlet but my lab is kind of limited with hood space and I have no water plumbing other than one sink and the dishwasher. I operate a small satellite lab and I try to make it into a swiss army knife lab where I can do as much as possible albeit not always the most efficient way. I have low sample load but high variety.

what do you ned the hood for with soxlet?

Just because the petro ether is very flamable and my lab is all one room including the flash point tester on the other side with an open flame.