I've tried a couple of brands of vial caps and the persistent problem is that if the cap is pierced then the solvent leaches a rubber spectrum out of the vial cap and ruins the detection limit.

I've tried prepping cal curves directly in the A/S vial by adding the appropriate spike through the cap. This makes for spikes ranging from C22 to C36.

Making the standards in glassware and storing them in VOA vials avoids this problem but is not as convenient.

Is this an unavoidable problem or can anybody recommend a favorite brand that is less susceptible to leaching?