The use of liquid scintillation counting as a fundamental radionuclide standardisation method requires a correct description of the physical phenomena induced by the interaction of the ionising radiation with the liquid scintillator. In particular the standardisation of radionuclides decaying by electron capture as 55Fe and other electron-capture nuclides, requires the knowledge of total linear absorption coefficients of the liquid scintillator used for absolute activity measurement. Total linear absorption coefficient measurements have been undertaken using synchrotron radiation. Linear absorption coefficients of two widely used commercial liquid scintillators were measured in the 5.5-23 keV energy range. Small discrepancies were noted between theoretical and measured values of the Ultima-Gold mass attenuation coefficients for low energy photons.