toluene works well for most inhibited latex samples. I've seen THF work for some but toluene is better. WARM the samples for 4 hours or more if you can. Use a laser pointer to shine through the solution in a clear vial to see if you have gel floating around -- it usually sparkles or looks hazy through the focused beam. Often seen in old or uninhibited fresh latex samples.
For PE, forget toluene or MEK. You need TCB or maybe ODCB at 120C or higher to dissolve these. Hot toluene will extract the low MW fraction and possibly additives but will not dissolve the polymer.
If you can't get TCB in your area or country, you can forget the sample unless alternate techniques like thermal analysis or pyrolysis GC could tell you what you want to know. Call the suppliers below, see what they say.
Waters and Polymer Labs make GPC systems capable of operation at these temperatures, controlled from injector thru detectors.
