For retention time locking, can you use your internal standard as a locking compound?

Question

I am setting up a calibration curve for a group of external standards. For this I am using the internal standard calibration method. My internal standard sits nicely in the middle of the spectrum. Can I use this internal standard as my locking compound for retention time locking?

Answer 1

Yes, you can use your internal standard as the locking compound for retention time locking (RTL), provided that it meets the necessary criteria for a good RTL compound.

Considerations:

1. Reproducibility: The internal standard should elute at a consistent retention time across different runs.
2. Peak Shape & Resolution: It should have a well-defined, sharp peak that is easily identifiable and not subject to interference from nearby peaks.
3. Matrix Effects: Ensure that the internal standard is not affected by matrix variability, which could shift its retention time.
4. Stability: The compound should be stable under your analysis conditions to avoid degradation or variability.
5. Instrument Compatibility: Some systems may require specific RTL compounds optimized for the software, so confirm that your method allows for using a custom RTL compound.

Advantages:

1. Since your internal standard is already in every sample and calibration standard, using it for RTL simplifies the method.
2. It ensures retention time consistency without needing an additional compound.

If your internal standard meets the above criteria, it should work well for retention time locking. However, always verify by running test samples to confirm stability and reproducibility.