[mooming]

Hello, I was wondering can someone please help me.

We usually use an internal standard to quantify a compound (eg. steroid) using LC-MS and to minimise errors during the quantification due to loss of samples.

But my question is how exactly do isotope dilution (ID) quantify a compound? 

During ID- we add a known amount of internal standard to an increasing concentration range of of a known steroid- lets say estrogen. ( and a theoretical ratio is calculated) And calibration curve is constructed by measuring the area under the peak (of the ion chromatogram) of the internal standard and the steroid. And a ratio of the area is calculated.


When we want to quantify the amount of estrogen in a given sample, we add a known amount of the same internal standard into the sample, and it's fed to the LC-MS, which gives us the ion chromatogram of both the estrogen and the internal standard....   

My question is what is the next step... ? how do u use the first set of calibration curves to quantify the estrogen present in the sample.

I would really really appreciate it if someone can explain the whole principle to me! Thank you so much!!!