Chromatography Forum

This video provides a key understanding about Relative Response Factor, how to calculate Relative Response Factor, Relative Response Factor calculation example and what can Relative Response Factor be used for when it comes to FID and Mole basis as concentration unit.

https://youtu.be/BOjP5H7Prb8

Peter.

Being in the consumer products business, we did a lot of work on soap bars and fatty acids. These contained C8 to C18 fatty acids or salts, and we would convert to methyl esters and then do GC analysis. In the early days we used theoretical equations to assign response factors. Later on, we purchased reference mixtures of fatty acid methyl esters (FAME) containing equal weights of the C8 to C18 FAMEs and we found that the responses/areas were all extremely similar, making response factors unnecessary in our instances.

Soap manufacturers are concerned about the make-up of the fatty acid mix, as that determines properties such as speed of lather, amount of lather, longevity of the bar, and ease of stamping.

You are very right. As far as my experience goes hydrocarbons from C5 onwards should have very similar response factors that most of the times no individual calibration is necessary. However just a clarification here, that should be correct by weight basic not mole basic. In your case of FAME analysis I believe you are seeing similar response factors when the concentration is expressed in weight. In fact one of the most common methods about FAME is EN14103-2020 and it specifies the FAME's factor in weight. It would be great if you can respond and confirm that. Thanks for your comment.

Peter.

Peter - I've been retired several years, and am not familiar with EN14103-2020, and I'm not going to pay for that.

Our company's goal was not necessarily to be 100% exact, just to ensure that our products were made properly and consistent from batch to batch.

In molecules with a high ratio of carbon to other elements, an FID is quite close to a carbon counter. It turns molecules of any size into their constituent carbon atoms and then detects them. That is why it's response if per mass, not per mole.