This mixture may be a mixture of water and propanol having a concentration of propanol in the range of 1-5% w/w, the concentration being within a tolerance of ???10% relative, preferably less than ???5wt. % relative, such as less than ???2 wt. % relative, preferably less than -1 wt. % relative, such as less than ???0.5 wt. % relative, preferably less than ???0.25 wt. % relative.