[yaku]

I have received under recovery of fats (less than target value) using Soxhlet apparatus. What could be the reasons for that?

Method: Ether extraction

Sample: Moist fish based sample

Sample is dried at 100°C for 30 minutes before reflux for 6 hours on a hot plate. Remaining ether in the flask is evaporated and dried in a drying oven for 2 hours at 100°C. Flask is then cooled in desiccator for about 30 minutes and weighed.

[curiouscat]

Malnourished fish?

How much fat were you expecting. How much did you recover.

[yaku]

No, not malnourished fish.

I was expecting 14.11% of fat, but i got 11.70%

What could be the reasons?

[curiouscat]

What's your basis behind expecting 14.11%?

[yaku]

As it was moist sample, I think sample might not have completely dried before reflux, water/moisture content in the sample might have affected the final result.

What are your opinions?

[Arkcon]

What are your opinions?

Just like curiouscat: asked, how does someone standardize a Soxhlet extraction?  How do you know how much fat there should be, and how do you know a given extraction is 100% efficient?

[yaku]

What are your opinions?

Just like curiouscat: asked, how does someone standardize a Soxhlet extraction?  How do you know how much fat there should be, and how do you know a given extraction is 100% efficient?

This sample has known value of fat%. This sample is from an external proficiency scheme, so once we submit our results to their portal we will know how good we did in this tests.

[curiouscat]

Does your mass balance agree? How much fish did you start with? How much ether? And how much was left before you flashed the ether off.

[marquis]

With a soxhlet, the amount extracted depends on the number of cycles
the soxhlet goes through.  If, for some reason, the soxhlet isn't cycling,
you won't get all of the fat extracted.

Reasons for slow cycles can be as easy as the soxhlet isn't level, the
heat level is low, etc.

Suggestion- check how long it takes for your soxhlet to cycle.  Adjust the
parameters (heat, cooling water flow, etc.) to get a reasonable cycle time
(5-10 minutes was common, but longer is possible).

An additional suggestion is to extend the amount of time you are doing the
soxhlet extract.  We used to do ether soxhlet extractions for 24 hours to
 get as much extracted as possible.

You might also make the sample as small in particle size as possible.  Grinding
or cutting will help. 

Good luck.