A capillary electrophoresis-electrospray ionisation time-of-flight mass spectrometry (CE-ESI-TOF-MS) method for characterisation of non-covalent protein complexes is described using a coaxial liquid sheath-flow sprayer. The CE capillary was connected to the mass spectrometer using a commercial CE-MS sprayer mounted on a ceramic holder of the ESI interface of the mass spectrometer. Using myoglobin (Mb) as an example of non-covalent protein complex, the effect on complex stability caused by organic modifiers added to the sheath liquid was analysed. Depending on the amount of methanol, either intact Mb or the apoprotein and the prosthetic heme group were detected.