There are two commonly used methods to replace the Mg 2+ with Na + in the ATP-Mg complex: Chelex 100 sodium ion exchange resin or ethylenediaminetetraacetic acid (EDTA), which functions as a divalent and trivalent metal ion chelator. While, the former would allow to remove interfering Mg 2+ cations without introducing new compounds to the solution, it requires 12 h for the ion exchange complete. It also adds an additional filtering and drying/concentration step to remove the resin and water from the sample. EDTA water solution however can be added to the RBC or plasma extracts directly when reconstituting the dried samples. Both methods were tested to replace ATP-Mg with ATP-Na in RBC extract (See SI, Figure ).