Fluorescence quantum yields are measured by comparison to a standard. The quinine salt "quinine sulfate" in a sulfuric acid solution was regarded as the most common fluorescence standard, however, a recent study revealed that the fluorescence quantum yield of this solution is strongly affected by the temperature, and should no longer be used as the standard solution. The quinine in 0.1M perchloric acid (Φ=0.60) shows no temperature dependence up to 45°C, therefore it can be considered as a reliable standard solution.