What will cause the internal standard to have a higher peak height than the compound of interest If the compound of interest and internal standard are at the same concentration? The instrument has been optimised to detect the compound of interest.
If you're using mass spec as a detector, and the internal standard is a stable-isotope-labeled isotopomer of your analyte, then you probably don't really have the same concentration for each, i.e.,double-check your procedure. If the standard and analyte are different compounds, then it's not unusual for different compounds to show different responses to the ionization process, especially with respect to electrospray (or to have different extinction coefficients if you're using UV). It would be easier to answer your question if you had given some additional information, e.g., if you're using GC-MS, LC-MS, UV detection; the chemical natures of your analyte and standard, etc. (Check the ResearchGate suggestions for improving your questions: https://www.researchgate.net/topics.TopicGuidelines.html.)
You just look after the volume you have injected are equal or some variation are there
If you're using mass spec as a detector, and the internal standard is a stable-isotope-labeled isotopomer of your analyte, then you probably don't really have the same concentration for each, i.e.,double-check your procedure. If the standard and analyte are different compounds, then it's not unusual for different compounds to show different responses to the ionization process, especially with respect to electrospray (or to have different extinction coefficients if you're using UV). It would be easier to answer your question if you had given some additional information, e.g., if you're using GC-MS, LC-MS, UV detection; the chemical natures of your analyte and standard, etc. (Check the ResearchGate suggestions for improving your questions: https://www.researchgate.net/topics.TopicGuidelines.html.)
If you're working with a 1:1 internal standard:analyte, and the internal standard is the exact same thing as your analyte except for the presence of a stable isotope (deuterium, C13, etc), and you are not getting the same peak height difference, then you need to verify the purity of your internal standard. Once you have done that, you verify that you really have a 1:1 concentration. If that doesn't do it, try different concentrations at 1:1 - you could be saturating the detector or underwhelming it (not likely, but it's worth a shot). If all these things are true, and you've done all these things and still have something different than internal standard/analyte that is off from 1, then and only then see how reproducible the ratio is. Full description can be found in my Clin Chem paper from last month.
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