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Internal standard miscible with water?

Question asked by kaitlin.greenfield on Jun 4, 2020
Latest reply on Jun 9, 2020 by james_jenkins

I am trying to quantify ethyl lactate in ethanol 20% (remainder water). When I run multiple injections, the RSD is 6-8% for the ethyl lactate peak. The ethyl lactate standard should be 0.2% v/v.


We typically test samples that are 95-100% ethanol and use an internal standard (cyclohexane), I don’t know if the amount of water is impacting the results or if it’s that we are not using an internal standard (it is not miscible with water).


Any idea on how to improve RSD between replicate injections? Do you know of an internal standard that we could use that is miscible with water?


Instrument Setup:

Agilent 7890, auto-injector, FID, the column DB-624 60m x 0.53mm x 3.00um

Oven Temperature: 60°C for 0.5min, then 20°C/min to 160°C for 0.333min, then 25°C/min to 200°C for 1 min
Injection Volume: 0.5µL
Inlet Split Ratio: 25:1
Inlet Temperature: 250°C
Column Flow: 7.2895mL/min
Total Flow: 192.53mL/min
Hydrogen Flow: 30mL/min
Air Flow : 400mL/min
Helium Flow : 25mL/min
Split Flow: 182.24mL/min
Detector Temperature: 275°C