I can’t stand waiting for my primers to thaw when I run a PCR. So when I know I’ll be running the same PCR reaction frequently, I leave a 10 uM working stock of my primers at 4C, particularly for 96-well primer plates (they thaw very slowly). However, the first time a used up an entire 96-well primer plate, I noticed that the edges of the plate (i.e. rows A and H; columns 1 and 12) ran out quite a bit faster than the remaining wells. At the time, I’d been told to use aluminum foil plate seals for my primers. But it was clear that the aluminum seal wasn’t sufficient to prevent evaporation of my primers.
After digging around biosupply websites, I noticed some companies that sold 96-well plates also sold silicon sealing mats for them; the sealing mats looked like the same material IDT used to seal the full concentration primer plates they sent me. The sealing mats were a little pricey, but they did the trick. I can now leave my primer plates in the fridge for long periods of time (a few months) and have little to no evaporation.