The invention relates to a standard solution for inverse gas chromatography and/or surface energy analysis; a volumetric container for preparing such a standard solution; a method of preparing such a standard solution for inverse gas chromatography and/or a surface energy analysis and a method of probing a solid sample. The standard solution comprises a series of three or more compounds of increasing carbon chain length of general formula (I): R-X wherein: for the three or more compounds R is a series of alkyl, a series of alkenyl or a series of alkynyl groups of increasing carbon chain length; and for all three or more compounds X is H, OH, CO2H, C(O)H, C(O)CH3, NH2, SH or halogen; and the relationship between carbon chain length and volume of the compounds of increasing carbon chain length of general formula (I) is determined by the following formula.
