Grapefruit seed extract

Evening all.

I am trying to find a supplier of Citricidal Professional Strength. I already have some 'normal strength' but want to use it as a preservative in handmade aromatherapy creams and lotions and the only recepies I can find about how much is needed refers to the professional strength.

Alternatively does anyone know how much of the standard strength is required for what shelf life ?

Last but not least I have some liquid vit E that I want to include for it's antioxidant properties. Again, does anyone know how much is recommended as a percentage ?

I do understand that these methods are not aseffective as Parabens, and therefore much shorter shelf lifes apply but am am wanting to be able to provide an all natural alternative.

Any guidance would be greatly appreciated.

Thanks everso

Louise x