Despite having only one reactive P-unit per molecule, sodium pyrophosphate is a useful phosphate source due to its highly selective and efficient conversion to phosphite. Therefore, we carried out phosphite isolation studies using Na4P2O7 as starting material. Isolation of phosphite from phosphates in the crude mixture was achieved through precipitating orthophosphate as struvite (NH4MgPO4 • 6H2O), taking advantage of the low solubility of this mineral. This method led to a 34% isolated yield of phosphite (67% based on reactive P) in the form of a barium phosphite salt BaHPO3•H2O (see SI). Phosphorous acid solutions can be prepared by treatment of the barium phosphite salt with sulfuric acid, and protocols for separation of phosphorous acid from phosphoric acid on an industrial scale are well established. In biological systems, long-chain polyphosphate (polyP) is involved in ATP synthesis catalyzed by polyP kinases in which polyP is the source of a third PO3 -group leading to ATP. Inspired by the biochemical reactivity of polyP, we turned our attention to the application of bioproduced polyP as a source of PO3 -. A recent protocol of polyP accumulation using Saccharomyces cerevisiae (baker's yeast) followed by isolation allowed us to obtain bioproduced polyP (bio-polyP, Figure ) in multigram quantities. The composition and structure of the isolated bio-polyP was analyzed by P NMR spectroscopy in conjunction with several elemental analytical methods. Linear phosphates (with Na + , Mg 2+ , K + , and Ca 2+ as counterions) constitute 77.8 wt.% of bio-polyP with an average degree of polymerization of 37, whereas residual orthophosphate and trimetaphosphate are <1.5 wt.%. The measured metal composition and average chain length of the isolated bio-polyP are similar to those of intracellular polyphosphates in bacteria in EBPR systems. Major impurities include residual organic substances (protein and nucleic acid), water, and NaCl.