Parameters:
(1) area under the curve for the peak in the patient sample
(2) area under the curve for the compound peak in the internal standard
(3) amount of compound in the internal standard
Usually the compound in the internal sample is similar to the target compound but comes off at a different time so that there are 2 distinct peaks. This allows both to be read off the same run. Since the internal standard can be added to a known volume of the patient sample prior to extraction it is subject to the same variations in processing.
amount of the compound in the patient sample =
= (area under the curve of the patient sample) / (area under curve for the compound in the internal standard) * (amount of the compound for the internal standard)
The area under the curve:
(1) ideally is calculated by the chromatographic instrument
(2) can be estimated by cutting out the curve and weighing the paper
(3) can be estimated by assuming that the peak is a symmetrical triangle
(4) can be estimated by integrating the line curve
For greater accuracy a standard curve can be prepared with different amounts of the compound so that a standard plot of area vs amount can be generated.
