One typical step of early-stage bioactive glass characterisation are in vitro dissolution studies in simulated physiological solutions, which have a pH of around 7.4. The chemical buffer used is typically tris(hydroxymethyl)aminomethane (Tris), and it is used for example in simulated body fluid, which contains several ions known to be present in blood plasma, or on its own, with the pH being adjusted by adding hydrochloric acid (HCl). Tris buffer solution, which does not contain high concentrations of ions involved in apatite formation, is particularly interesting for early stage ion release experiments, kinetic studies and to investigate the influence of glass components only on apatite precipitation. We are showing that chloride ions, which are present in high concentrations (~40 mmol/l) can be incorporated into the apatite formed in vitro (forming a partially substituted chloro apatite) and may thus have an influence on how early apatite forms. To investigate the effect of chloride ions, we compared the performance of the conventionally used Tris-buffered solution with a chloride ion free solution, whose advantage is less participation in the apatite formation. The chloride-free Tris-buffered solution was invented by using acetic acid for pH regulation. The in vitro dissolution behaviour of Bioglass® particles was investigated for 6, 15 and 24 hours in both Tris-buffered solutions and apatite formation was verified via X-ray diffraction and fourier transform infrared spectroscopy. For scanning electron microscopy and energy dispersive X-ray spectroscopy examinations Bioglass® particles were kept for 1, 3 and 7 days in both immersion media. The chloride-free Tris led to a faster apatite formation in comparison to the conventional Tris. The amorphous pre-stage of apatite was observed; a phase consisting of both, calcium phosphate and calcium carbonate. Furthermore, calcite was precipitated whereas in presence of chloride ions the calcite formation was inhibited.