Chromatography Forum

I use internal standards for an lcms method. Now I want to know the transitions without having to tune them in the LCMS, they are very expensive. And we don't have a lot of volume. I know you can calculate it by knowing the transitions of the normal component. How do you calculate that? For example Aflatoxin B1 313.3 -> 241.1 and 285.1
what is the transition of the internal standard 13C isotope?

I use internal standards for an lcms method. Now I want to know the transitions without having to tune them in the LCMS, they are very expensive. And we don't have a lot of volume. I know you can calculate it by knowing the transitions of the normal component. How do you calculate that? For example Aflatoxin B1 313.3 -> 241.1 and 285.1
what is the transition of the internal standard 13C isotope?

In the case of 13C Aflatoxin B1 transition is 330->301. If you look around you can find application notes, which saves the hassle. Calculating you need to work out a likely composition of the fragment (in this case C-O) and go from there. Obviously as the fragment gets bigger the permutations increase and things get more complicated.

… as a general rule, if you aren't sure of the fragment, and the standard is ludicrously expensive, you still don't have to repeat the tune. There are two cheap and easy alternatives:
(1) do a chromatography run with a little bit of internal standard, and an MS2 method with a scan across the region where you expect the product ions (using the collision energy that you already optimized with the unlabeled analyte). Check what the products are, or...
(2) if the standard is so expensive that you can't inject enough to see in scan mode, set up MRMs. Say your internal standard is mass +5, set up MRMs for the fragment you see from unlabeled analyte, and +1, +2, +3, +4, +5, and see which MRM gives you the biggest peak in a chromatography run of internal standard alone. Then delete the transitions you didn't need.

… as a general rule, if you aren't sure of the fragment, and the standard is ludicrously expensive, you still don't have to repeat the tune. There are two cheap and easy alternatives:
(1) do a chromatography run with a little bit of internal standard, and an MS2 method with a scan across the region where you expect the product ions (using the collision energy that you already optimized with the unlabeled analyte). Check what the products are, or...
(2) if the standard is so expensive that you can't inject enough to see in scan mode, set up MRMs. Say your internal standard is mass +5, set up MRMs for the fragment you see from unlabeled analyte, and +1, +2, +3, +4, +5, and see which MRM gives you the biggest peak in a chromatography run of internal standard alone. Then delete the transitions you didn't need.

This is what I would do. The only time you might have trouble with this is if the precursor is not the molecular ion, which should only happen with very labile molecules(or in GCMSMS). The reason to do the multiple masses for the product ion is when you don't know which part of the C13 remains, the part that fragmented off with low mass or the part that remains with fairly high mass.

All analytical measurements have an inherent uncertainty. Particularly in the case of chromatographic methods for trace organic analytes, this can be significant. It is not unknown for a reported result to have an associated LiteBlue

I use internal standards for an lcms method. Now I want to know the transitions without having to tune them in the LCMS, they are very expensive. And we don't have a lot of volume. I know you can calculate it by knowing the transitions of the normal component. How do you calculate that? For example Aflatoxin B1 313.3 -> 241.1 and 285.1
what is the transition of the internal standard 13C isotope?

I also have same query Mymorri..

I use internal standards for an lcms method. Now I want to know the transitions without having to tune them in the LCMS, they are very expensive. And we don't have a lot of volume. I know you can calculate it by knowing the transitions of the normal component. How do you calculate that? For example Aflatoxin B1 313.3 -> 241.1 and 285.1
what is the transition of the internal standard 13C isotope?

I also have same query Mymorri..

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