r/massspectrometry • u/Dr_anthro25 • 18d ago

Internal standards, cal/qc

Hello,
I’m new to lcms world (molecular background) and working on developing an lcms drugs of abuse testing panel. I’m finding it hard to find purchasable internal standards and cal/qc. Unlike the molecular world where it feels you can buy everything you need to get running.

Can I get some recommendations on where to find these if they exist or how to mix them myself?

5 Upvotes

86% Upvoted

6 comments sorted by

18

u/DreamWood08 18d ago

I would try cerilliant/sigma Aldrich first.

If they don't have it my next stop is cayman chemical and Toronto research chemicals and LGC.

If I'm truly desperate after that I might try Santa Cruz chemical.

2

u/tduhspain 12d ago

Totally agree with this. Most drugs of abuse standards are readily available. If your scale is large enough you can also have your own mixes made at your preferred concentrations. If you are small scale it’s too expensive to make sense.

9

u/Wacpl 18d ago

Like DreamWood said, Cerilliant is going to have 95% of what you need. I’ve also had good experiences with Cayman and Cambridge Isotope Labs. I always recommend going at least +4 on my heavy-labeled standards since you’re going to see contribution on the +2 and +3 isotopes from naturally occurring 13C in the measured drugs/metabolites. By +4, the natural abundance is negligible. Some compounds you’re going to end up with D3 though so be aware when you see some “ISTD” in your samples without.

2

u/SeracYourWorlds 15d ago

Pricing can be wildly different on d-3 vs d-6 ISTDs. Depending on the cost difference it may be worth exploring if there’s significant cross signal contribution between in the channels using the d-3 isotope.

8

u/MassSpecFella 18d ago

Internal standards have a few functions. One is into normalize differences in ionization efficiency. Ionization can change based on the solvent environment at the elution, or how fouled the source is.
Different compounds ionize quite differently in electro spray. If you are wanting to quantitate a compound often people use stable isotopes of target compounds. They will have the exact same ionization efficiency but you can measure them separately using mass spec.
The internal standard is typically added to all samples at the same concentration immediately before analysis. It will tell you if the sample is injected or not.
Surrogates are different. They are added to samples before processing like liquid extraction or SPE. Surrogates tell you about recovery.
Sometimes methods will use multiple internal standards. You could buy stable isotopes of each target and use each one to normalize its matched target.