To quantify the amount of Co in LLZO, ICP-OES measurements were performed of small parts of the single crystals. Since single crystals have no grain boundaries, it can be considered that all Co detected is incorporated in the garnet structure. In Table the compositions of differently heat-treated samples are summarized in comparison to the intended stoichiometry of pristine LLZO, given as Li6.4Ga0.2La3Zr2O12. The chemical compositions of the analyzed crystals reveal Co concentration of 0.002 and 0.1 Co pfu for LLZO-o and LLZO-b, respectively. Despite additional slight changes in the Ga content no significant further change has been observed.