Chromatography Forum

Hi everyone,

I have an issue about PEG3350 residual solvents test (Ethylene oxide, 1,4Dioxane). I am using GC/HS-FID method for the analysis. When I tried to do Accuracy test for the analytical method validation my recoveries too low (%30-%10) for both residual solvents. My method is a validated method from manufacturer.

In my opinion this could be related with distrbution of EO and DO in polyethelen glycol. But i can not solve it.

Thank you for answers.

You're going to have to provide a lot more information than that for us to help you. Please describe your method as well as you can (instrument conditions, chromatographic conditions, sampling procedure and conditions, etc.). What is the nature of your sample (solid, liquid)?

My analyte is PEG3350(MP: 56°C) which is solid in room temperature. The limit for ethylene oxide is 1ppm and for dioxane 10ppm so that i have to work on very low concentrations. I am using HS-FID GC method with HS: 30min equilabrating time and 70°C HS oven temperature. My peak shape and resolution for standard is applicable. But, when I work with spiked samples , I faced with very low recoveries. Basically, My problem is to increase recoveries for my Accuracy parameter.

Your analytes are ethylene oxide and dioxane. Your sample is the PEG. So, if I read between the lines a bit, you're using static headspace analysis. Is that correct?

You are above the melting point for the PEG. That's a good thing. When you prepare your fortified samples to determine your recovery, how do you do it? It can be tricky to spike solid samples.

Hi Thank for answering,

I am using a calibration stock solution, then i take it 10uL to my HS vial for standard solution. For spiked sample solution, I weigh 2g of peg3350 then add on 10uL stock solution. In my opinion areas should be close but i could not get it. I even try to add 100uL for both sample and standard but problem continues.

In the time allotted, are you sure your PEG 3350 is all melting? Have you tried dissolving the solid in water and then perform the fortification experiment? I was looking at volatiles in a liquid soap (pretty viscous sample) once and I discovered that the detection limit of one of my analytes improved when I cut the soap with a little water. I'm assuming that even melted PEG 3350 is pretty viscous.

Hi Thank for answering,

I am using a calibration stock solution, then i take it 10uL to my HS vial for standard solution. For spiked sample solution, I weigh 2g of peg3350 then add on 10uL stock solution. In my opinion areas should be close but i could not get it. I even try to add 100uL for both sample and standard but problem continues.

Do you have any PEG in your standard vials ?

Peter