calculation of triglyceride ammount to fatty acid methyl.est

[leo1352]

I have hydrolyzed and esterified an amount of 260 microgram of C4:0 triglyceride(TAG) to its respective butyric acid mehyl ester. What I am getting in GC by the software is an amount 85 microgram Butyric acid methyl ester. apart from glycerol part the theoretical yield of TAG to C 4:0 butyric acid mehyl ester should be around 87% .
yet the kinetic of TAG transformation to fatty acid methyl ester is not very clear to me.
I wonder how much yield this 85 microgram Butyric acid methyl ester from TAG is returning to me.

thanks for help

[Don_Hilton]

I am not quite sure of your question - first kentics involves reaction rates and you say nothing about time.

I compute the theoretical ratio of triglyderide to mass of generated methyl esters as much higher than 87%, so I don't follow what you are doing with the calculation.

For computing the yeild of methyl butyrate to that expected, you need to compute the correct expeted yield.

This should give you some direction toward looking at your problem.

From the wording of the question, I am not sure if this is a homework/exam question or if you are working with a real lab problem, so I will hold off a few days of giving further clarification.

[Consumer Products Guy]

Same here. I get paid good old USD$$$ for this type of work every week.

[leo1352]

I am not quite sure of your question - first kentics involves reaction rates and you say nothing about time.

I compute the theoretical ratio of triglyderide to mass of generated methyl esters as much higher than 87%, so I don't follow what you are doing with the calculation.

For computing the yeild of methyl butyrate to that expected, you need to compute the correct expeted yield.

This should give you some direction toward looking at your problem.

From the wording of the question, I am not sure if this is a homework/exam question or if you are working with a real lab problem, so I will hold off a few days of giving further clarification.

Hi,
This is a real lab work. I do esterification in 1.5 hours with 6% sulfuric acid /Isopropanol(I should correct my previous mail as I talked about methyl esters). I do appreciate if you show me your computation.

thanks

[leo1352]

I wonder if someone could help about my question?

[leo1352]

I am not quite sure of your question - first kentics involves reaction rates and you say nothing about time.

I compute the theoretical ratio of triglyderide to mass of generated methyl esters as much higher than 87%, so I don't follow what you are doing with the calculation.

For computing the yeild of methyl butyrate to that expected, you need to compute the correct expeted yield.

This should give you some direction toward looking at your problem.

From the wording of the question, I am not sure if this is a homework/exam question or if you are working with a real lab problem, so I will hold off a few days of giving further clarification.

Hi Don,

I wonder if you have any updates about my problem.

[Don_Hilton]

Let's do it this way - You have already computed some values for what you expect as a yield. Write out the steps and show them here. It may be that as you write them out and check to be sure that you are not missing anything, you may answer your own question.

[leo1352]

Let's do it this way - You have already computed some values for what you expect as a yield. Write out the steps and show them here. It may be that as you write them out and check to be sure that you are not missing anything, you may answer your own question.

Tributyrin 268µgr
Concentration of Isopropyl Butyrate that I have got in GC-FID was 169.7131 µgr.
Trimyristin 230 µgr
Concentration of Isopropyl Myristate that I have got in GC-FID was 292.1239 µgr.
Tripalmitin 227 µgr
Concentration of Isopropyl Myristate that I have got in GC-FID was 272.1029 µgr.

gr/mol minus (3*OH) Theoratical yield
Butyric acid 3*88.11= 264.33----> 213.33 0.705549676
Myristic acid 3*228.37= 685.11----> 634.11 0.876859893
Palmitic acid 3*256.42= 769.26----> 718.26 0.889662348



Theoratical yiel has calculated using the 213.33 , 634.11 and 718.26 values divided by molecular weight of their respected Triglyceirids.
Tributyrin 302.36

Trimyristin 723.16

Tripalmitin 807.34


So I wonder if my calculations are correct. I subtract the OH group from each of the free fatty acids as they would generate one molecule of water as they detach from their glycerol backbone.
I would be very glad if you let me know about my approach.

cheers

[Don_Hilton]

One mole of triglyceride will give three moles of fatty acid - and yield three moles of fatty acid ester.

Thus for one mole of tributyrin (MW 302.36) you would expect three moles of isopropyl butyrate (MW 130.18). Or we would expect a ratio of 302.36 g tributyrin/390.54 g isopropyl butyrate

We can calculate the expected return of isoproply butyrate based on the quantity of triglyceride in the sample because the molar ratio (thus the mass ratio) is always the same:

302.26 g tributyrin / 390.52 g isopropyl butyrate = 268 µg tributyrin / X µg isopropyl butyrate. So we expect 346 µg isopropyl butyrate.

There is no need to account for the water involved in hydrolysis. You ratio what you weighed: triglycerides and fatty acid esters.

Your yield was what you found as the fraction of what you expected: 170 µg found/346 µg expected or 49%

And, if you built your calibration curve by weighing out fatty acids and used the weights obtained for building the curve (rather than calculating the corresponding weight for the same number of moles of ester) use the molecular weight of the acid instead. And because you weigh out the entire molecule, you use the entire molecular weight.

[leo1352]

One mole of triglyceride will give three moles of fatty acid - and yield three moles of fatty acid ester.

Thus for one mole of tributyrin (MW 302.36) you would expect three moles of isopropyl butyrate (MW 130.18). Or we would expect a ratio of 302.36 g tributyrin/390.54 g isopropyl butyrate

We can calculate the expected return of isoproply butyrate based on the quantity of triglyceride in the sample because the molar ratio (thus the mass ratio) is always the same:

302.26 g tributyrin / 390.52 g isopropyl butyrate = 268 µg tributyrin / X µg isopropyl butyrate. So we expect 346 µg isopropyl butyrate.

There is no need to account for the water involved in hydrolysis. You ratio what you weighed: triglycerides and fatty acid esters.

Your yield was what you found as the fraction of what you expected: 170 µg found/346 µg expected or 49%

And, if you built your calibration curve by weighing out fatty acids and used the weights obtained for building the curve (rather than calculating the corresponding weight for the same number of moles of ester) use the molecular weight of the acid instead. And because you weigh out the entire molecule, you use the entire molecular weight.

Thanks very much for the clarification of my issue. I am just wondering what the problem might be as the esterification efficieny for respective esters of Trimyristin and Tripalmitin goes beyond 100% according to the calculation.

[Don_Hilton]

Describe how you made standards and samples. What did you weigh, what did you add. What were the weights and volumes used?

Did you use an internal standard? If so, what? Include how that was added in the description of the procedure.

How many levels in calibrtation curves and how did the curves look? Did your analytes fall within the range of the calibration curve?

Did you run blanks in the sequence to ensure you had no caryover from vial to vial? (If you are not careful, fatty acid esters can give a carry over problem.) Did you shoot a calibration standard at the end of the sequence to ensure that nothing had changed in the GC? Did you run all your samples for a given fatty acid on the same day that you calibrated the instrument? If not, did you confirm the calibration before you started?

[leo1352]

Describe how you made standards and samples. What did you weigh, what did you add. What were the weights and volumes used?

Did you use an internal standard? If so, what? Include how that was added in the description of the procedure.

How many levels in calibrtation curves and how did the curves look? Did your analytes fall within the range of the calibration curve?

Did you run blanks in the sequence to ensure you had no caryover from vial to vial? (If you are not careful, fatty acid esters can give a carry over problem.) Did you shoot a calibration standard at the end of the sequence to ensure that nothing had changed in the GC? Did you run all your samples for a given fatty acid on the same day that you calibrated the instrument? If not, did you confirm the calibration before you started?

I have weighed the 3 triglycerides in a 50ml volumetric flask and brought to volume with chloroform. added 1 ml of this cocktail to 5 kimax tubes followed by adding 600ugr of C 23:0 methyl ester as internal standard prior to esterification process with 5% sulfuric acid. the recovery for C 23:0 methyl ester was 81%.
I made a serial dilution of C 23:0 ranging from 25ugr/ml to 1000ugr/ml in at 7 levels. The GC software (Chromaleon) has calculated the amount of Isopropyl esters according to the line equation from the calibration curve r=0.998. I had one blank as well to make sure there no cross contamination.

thanks again

[Don_Hilton]

Did you make the standards in the same way (by weighing and diluting into the same volume of chloroform?) and did you weigh out the free fatty acid or the isopropyl esters?

[leo1352]

Did you make the standards in the same way (by weighing and diluting into the same volume of chloroform?) and did you weigh out the free fatty acid or the isopropyl esters?

Yes , I did. i am getting a bit worried about the weighing process maybe. I am thinking about doing the assay again. But your equation definitely helped a lot. My analysis is stable isotope based (GC-IRMS) so I suppose the esterification yield is not much of an issue to some extent ; but I wonder if you have any idea to increase the esterification yield, e.g. change of reagent or concentration of reagent or temperature profile. Of course there are lot of articles and most of them claim their own method as the best!

[Don_Hilton]

I can not comment on how to improved the yield of your procedure as I do not have the details - all the steps and reagents.