solution:
) Separate analyte from the matrix.

Lessons Learnt:
) Highering dissolvation temperature and gas flow will help to get a better dissolvation
) Decreasing flow rate (especially on TQD) around 0.4 ml/min will help to get better RSD’s (also linked to dissolvation)
) Lowing capillary voltage may give higher sensitivity but may increase Rsd (consider a test at 3kv and then compare with 1.5 and 1 kv, never go to 0.5kv).

Situation:
I’m wondering what folks here consider to be acceptable limits for accuracy using LCMSMS.

I work in a clinical lab. Historically the limit has been 10%. Most procedures nowadays are performed on automated instruments using few manual steps if any at all. My lab director wants 10% for the LCMSMS as well. I have found this is not so easy. From an article I read from Validation Viewpoint the FDA recommends 15% for four of six points and 20% at the lower limit of quantitation. That seems rather wide for me but I don’t see why there can’t be some compromise between 10 and 15%.

As an example I am working up a Levetiracetam method on a UPLC/TQD. I get an obs error of 6.3% with concentrations 0 to 50 ug/mL. But pushing the upper limit to 75 ug/mL gets me an error up to 11%. He will not accept this. Problem is therapuetic range for this drug is up to 80 ug/mL which means we’ll be diluting quite a few samples.

Solution:
Response #1:
While MRM experiments usually provide sufficient specificity, I have often found that simply separating your analyte of interest from the matrix will vastly improve your RSDs and often increase the sensitivity of the method.

Response #2:
It will not be always easy to reach these 10% all the way in LC-MS/MS. FDA regulation is accepted almost everywhere… A more robust source will help to achieve these limits for a specified assay: to help to stay away from the LOQ for this assay. What MS instrument do you have?

However, here is a possible list from one of our application chemists of things to check for the system as a rough guide.

1. Detuning the Probe adjuster (spraying a little bit more far away from the Cone)

2. Highering dissolvation temperature and gas flow will help to get a better dissolvation

3. Eventually decreasing flow rate (especially on TQD) around 0.4 ml/min will help to get better RSD’s (also linked to dissolvation)

4. Too low capillary voltage may give higher sensitivity but may increase RSD (consider a test at 3kv and then compare with 1.5 and 1 kv, never go to 0.5kv).

5. Internal standard with deuterated compounds should be used.

6. Matrix effect is also something to consider, a very specific and selective sample prep will help to reduce RSDs.

7. In addition to this, Full loop injection will help from the UPLC end.

Reference:
Waters: Accuracy for LC-MS/MS