Surrogate Recovery Calculation

[jclark]

I am trying to figure out how to calculate "surrogate recovery" for EPA 552.3 (haloacetic acids). The method uses an internal standard AND a surrogate (2-bromobutyric acid). The surrogate should tell us how efficient the extraction and methylation steps are. The EPA method, in Sect. 9.7, gives the formula R = (A/B) x 100%, where A = "calculated surrogate concentration for the Field Sample" and B = "fortified concentration of the surrogate". It seems to me that any % recovery boils down to "what you actually got" divided by "what you should have got", times 100. So the A term would be the area of the surrogate peak I actually got on a sample injection, and the B term would be the area of a completely extracted, completely methylated sample of 2-bromobutyric acid. But the EPA method does not explicitly mention or describe running a premethylated sample.
Am I missing something here? Thanks in advance for any comments!

PS. I love this website! This is my first post.

[jh1]

I am trying to figure out how to calculate "surrogate recovery" for EPA 552.3 (haloacetic acids). The method uses an internal standard AND a surrogate (2-bromobutyric acid). The surrogate should tell us how efficient the extraction and methylation steps are. The EPA method, in Sect. 9.7, gives the formula R = (A/B) x 100%, where A = "calculated surrogate concentration for the Field Sample" and B = "fortified concentration of the surrogate". It seems to me that any % recovery boils down to "what you actually got" divided by "what you should have got", times 100. So the A term would be the area of the surrogate peak I actually got on a sample injection, and the B term would be the area of a completely extracted, completely methylated sample of 2-bromobutyric acid. But the EPA method does not explicitly mention or describe running a premethylated sample.
Am I missing something here? Thanks in advance for any comments!

PS. I love this website! This is my first post.

A should be the actual recovery concentration not peak area, the value obtained when comparing the sample to an appropriate standard and B is the theoretical 100% recovery.
So if you spiked at 5ug/ml and recovered 4.1ug/ml you would have an 82% surrogate recovery.