Chromatography Forum

Hello,

I am running EurPharm method 2.4.25, ethylene oxide and dioxan. The method states, "Weigh 1.00 g of cold ethylene oxide stock solution (this is in PEG200) into a cold flask containing 40.0 g of cold polyethylene glycol (PEG) 200". Does anyone have experience with this method or weighing cold reagents into a cold flask? I've always heard you should weigh at room temperature. This is a standard prep so accuracy is critical. Any tips would be appreciated.

I speculate (big word for me) that the reason for the cold is to reduce evaporation of the ethylene oxide and dioxane. So I would follow instructions as written, to be in compliance.

Best practise weighing needs everything at room temp, but the instructions only need a precision of 0.01 g so the adverse effects of cooling (eratic bouyancy and condensation) will not be a practical problem.

Peter

Hi

The only additional comments that I would make from when I used to use a similar prep for this analysis are

1. On removing the flask with solvent and EO (previously dispensed into a septum sealed vial from a lab cylinder) from the fridge I would allow a short time to allow the flask to come above the dew point to avoid condensation problems affecting the weighing. Humidity in the lab could be quite high.

2. After prep I would return the volumetric flask to the fridge but noticed that if I used a plastic stopper it would become loose on cooling but I overcame that by using a ground glass stopper.

3. Later I modified the method to SPME headspace with either single or multiple standard addition, spiking with a pre - prepared standard certified EO solution supplied in sealed ampoules from Sigma. Although multiple standard addition added to the overall analysis time, the savings in the standard prep and removing safety problems associated with dispensing from the EO cylinder balanced out. This method worked really well down to 1ppm. I have the details somewhere

4. Some samples may contain acetaldehyde, also C2H40 (e.g. nonionic detergent alcohol ethoxylates) and you need to ensure that your phase will separate that from EO to avoid getting a false positive result.

Regards

Ralph