By Anonymous on Tuesday, November 18, 2003 - 08:33 am:
Is there a "rule" to choose the most suitable concentration of the internal standard (isotope standard) to spike in the sample with an LC/MS method.
Thanks in advance.
Best regards.
Martine
By MG on Tuesday, November 18, 2003 - 09:02 am:
I don't know if there's a rule. We use a level near or at the mid-point of the calibration curve. Too low, and your response will vary too much. Too high, and you'll suppress your analyte signal (if analyte and ISTD coelute).
By Anonymous on Monday, November 24, 2003 - 11:27 pm:
Could you explain the function of INTERFACE in LCMS. Is interface available in GCMS,if it is there what is the difference between the two.
Thanks in advance
By MG on Tuesday, November 25, 2003 - 06:24 am:
The interface is what separates the LC (liquids under high pressure) from the MS (gas phase ions at very low pressure). At least, that's one possible usage of the word. In LC/MS, it is also the ion source. The ion source desolvates and ionizes the sample. Modern LC/MS sources do this at atmospheric pressure. Then the ions are introduced into the high vacuum region for mass analysis. With GC/MS, the sample is first introduced into a low pressure ion source, then ionized.