By definition , volatility is given as the ratio of the vapor pressure of the substance in question to the vapor pressure of the highly volatile reference substance diethyl ether (this at 20 ° C and 65 ± 5% relative humidity ):
In Germany, the evaporation rate (VD) is determined according to DIN 53170. The time it takes for a substance to completely evaporate (evaporation time = VDZ) is related to the time it takes diethyl ether to evaporate.
A high evaporation rate means relatively slow evaporation, i.e. low volatility. A small evaporation number means faster evaporation, i.e. a relatively high volatility.
Examples of the evaporation rates of solvents (for diethyl ether = 1) solvent Evaporation rate Butyl diglycol > 1200 2-butoxyethyl acetate 250 Butyl glycol 163 N -methyl pyrrolidone water Test petrol 145-200 (K30) Xylene 1-butanol 1-methoxy-2-propanol Butyl acetate (acetic acid n- butyl ester) Ethanol Methyl isobutyl ketone acetone Hexane
In the USA, the evaporation rate (E) is determined over time and in relation to butyl acetate .
with = time, up to 90% of the sample has evaporated.
Examples of the evaporation rates of solvents (for butyl acetate = 1) solvent Evaporation rate Methyl ethyl ketone 3.8 acetone 5.6 Hexane 8.3 Ethanol, 95% 3.8 naphtha 1.4 Xylene 0.6 2-methyl-1-propanol 0.6 water 0.3 White spirit 0.1
Classification of solvents according to volatility
Comparison of different classifications In Germany In the USA Classification Evaporation rate Classification evaporation rate very difficult to volatilize > 50 slow evaporation <0.8 not very volatile 35… 50 medium evaporation 0.8 ... 3.0 medium volatile 10 ... 35 rapid evaporation > 3.0 volatile <10