Last update 7 April 2017
A PLC must contain, as an integral part of its composition, at least two of the atomic elements carbon, hydrogen, nitrogen, oxygen, silicon and sulphur.
Excluding impurities, a PLC must only contain the following:
- carbon,hydrogen, nitrogen, oxygen, silicon and sulphur
- sodium,magnesium, aluminium, potassium, calcium, chlorine, bromine and iodine as the monatomic counter-ions Na+, Mg2+, Al3+, K+, Ca2+, Cl-, Br- or I-
- fluorine,chlorine, bromine or iodine covalently bound to carbon
- <0.2%(by weight) of any combination of the atomic elements lithium, boron, phosphorus, titanium, manganese, iron, nickel, copper, zinc, tin and zirconium.
No other elements are allowed, except as impurities. Specifically, the fluoride anion F- is not allowed as it has a high acute toxicity.
This requirement refers to monatomic species only. For example, a polymer containing the ammonium counter ion may be a PLC provided it meets the other PLC criteria.
Regarding the binding of halogens to carbon, it should be noted that the perchlorate anion ClO4- would not be allowed because the chlorine is not covalently bound to carbon, but the trichloroacetate anion CCl3CO2- would be allowed.