I am a little bit confused by these two methods, is the IDM best?
What is relationship of these two methods? Is IDM one kind of ISM? In addition to these questions, what about the surrogate standard method?
Generally isotope labeled standards are the best choice of standards to use in internal standard methods. I agree as you suggest that IDM is one type of ISM.
IDM is to use isotopically labelled analogue as internal std to minimize matrix effects, e.g. IBP-d4 for IBP. It is ideal to have isotope standard for each of your target compounds, but they are usually quite expensive. For normal ISM, you can use one single standard (not necessarily isotope) or more to calibrate the quantification. Internal std is commonly added to post-SPE extracts, while surrogate is directly added to pre-SPE samples to calculate the SPE recovery rate. FYI
Isotope Dilution Methods compensate for matrix losses. The only caveat to this technique is extensive dilution of the sample. Like any analyte, the IS can be diluted out. For this reason, you may find that you need an extended calibration range if you anticipate significant concentrations. With an extended calibration range you can meet minimum reporting limits have be able to quantify larger concentrations.
For example of the technique, you may want to see a commercial application that is being currently implemented. I would recommend the ASSET Isocyanate sample developed by IFKAN and made available worldwide by Supelco. The literature in the attached link goes into great detail in the analysis.
Generally single Quad MS is sufficient for this technicque, however, in the above mentioned technique triple quad MS was warranted.
http://www.sigmaaldrich.com/analytical-chromatography/air-monitoring/asset-nco-sampler.html
Isotope dilution method(IDM) is an internal standard method(ISM), the only difference being the internal standard is a stable isotopically labelled analogue. As, the physical and chemical properties are same, they are ideally suited for Mass Spectrometry analysis. The instrument measure the ratio of signals i.e. normal/IS. This method compensates for matrix interferences and give most accurate results
Ramesh is correct. The only drawback here is cost. ISM using isotopically labelled analogues are expensive.
Well, yes. Ramesh is almost correct but I would slightly modify his statement "As, the physical and chemical properties are same". It should read "As, the physical and chemical properties are almost same..."
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