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- Posts: 2
- Joined: Thu Oct 28, 2021 2:09 am
Long time lurker, new poster.
I have been tasked with developing a new GC/FID method for fatty acid determination in a topical drug product (5% label claim linoleic acid). I have been able to meet LoQ requirements, have good peak shape (tailing factor below 1.3, etc.), and have reproducible results. However, what I also have is a carryover problem. This is my first GC method that is purposefully trying to quantitate and use fatty acids, so maybe I do not have the appropriate method conditions?
Diluent: EtOH (DMSO was assessed, EtOH showed better results)
Internal Standard: Palmitic Acid
Quant. Standard: 1.25 mg/mL linoleic acid and 0.0625 mg/mL palmitic acid
LoQ - 0.1% of nominal
GC: Agilent 7890 with ALS
Column: DB-FFAP (30 m x 0.32 mm x 0.25 µm)
Liner: Agilent 5186-4647 (Low pressure drop, split, deactivated (removed glass wool))
Carrier Gas: He
Injection volume: 0.5 µL
Injection Temp: 230 °C
Mode: Pulsed Split (30 PSI for 0.75 min)
Split: 5:1
Column Flow: 1.5 ml/min
Septum Purge: 3 ml/min
Initial Oven Temp: 120 °C
Ramp: 20 °C/min
Final Oven Temp: 245 °C, hold for 23.75 min (GC run time = 30 min)
FID: 280 °C; 400 ml/min air; 40 ml/min H2; 30 ml/min makeup gas (He))
Anyone have any advise?