what is %area method and external standard method
Posted: Sun Apr 29, 2007 2:46 am
Please help I have interview on monday ..I really need this job
thanks in advance
thanks in advance
Area% method is just what it sounds like: you assume that all peaks have the same response factor and that the area % = mass %. Not generally a good idea, but often (too often!) done where exact structures are unknown but assumed to be related.
External standard method is what you do most of the time: run a series of calibrators at known concentrations, plot area (or height) vs amount. The slope is the response factor. Run your sample, measure the area (or height), divide by the response factor and get the amount of analyte. Much better if standards are available, and if response can be assumed to be constant from run to run (if not, internal standard is better).
Internal standard method is a variant on the external standard method in which you add a known amount of a known compound (the "internal standard"). You then always work with area ratios (analyte/IS) and concentration ratios. Other than that, the math is the same as external standard. This improves things when there is significant run-to-run variation that affects the analyte and IS in proportion (usually not the case in LC with UV detection).