Fig. 5. (A) CE-MS analysis of a human colon tissue biopsy (18 mg) enables the identification of several important inositol phosphate (InsP₆ and InsP₅) and pyrophosphate (5-PP-InsP₅) isomers. (B) 4/6-PP-InsP₅ is identified in PBMCs by CE-MS analysis. The electropherograms are representative of independent biological triplicates giving comparable results. (C) 4/6-PP-InsP₅ is enriched in a CD8⁺ T-cell preparation and is also present in the CD8⁺ depleted PBMC pool (D). It is assigned by its exact same migration time as [¹⁸O₂] 4-PP-InsP₅. PP-InsP₅ (filled red plot) isomer identification is achieved with the aid of [¹³C₆]5-PP-InsP₅, [¹³C₆]1-PP-InsP₅ (black plot) and [¹⁸O₂] 4-PP-InsP₅ (blue plot).