by
Rndirk » Fri Sep 15, 2017 7:49 am
Hello,
Are the "samples" in this case solvent blanks? It's obvious that they will have no iSTD and an ion ratio of 0 (= no peaks).
If you're looking at samples there are many possibilities:
For internal standard recovery:
- No internal standard, or the wrong amount of internal standard added (check calculations)
- Loss of internal standard during sample prep
- Sensitivity of the instrument changes during the batch
- Higher/lower signal in samples compared to calibration curve (matrix effect in GC, very common and very dependant on the analyte).
-....
For ion ratio:
- There is no analyte present in the sample
- The ion ratio is not set at the right value (define it on a calibration standard)
- The peak is not the analyte peak
- Interference
- For low amounts of analyte: the qualifier ion (typically lower in signal compared to the quantifier) can be below the LOD/LOQ, which can significantly inflate the quantifier/qualifier ratio.
-...