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What it is. This sodium phosphate, dibasic (disodium hydrogen phosphate), is ACS reagent grade, supplied in a 100 g size. It is a white, water-soluble salt used mainly to prepare phosphate buffers for biological and analytical work.
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What ACS grade guarantees. ACS reagent anhydrous disodium phosphate assays at a minimum of 99.0%, with limits of 0.01% insoluble matter, 0.2% loss on drying at 105 °C, 0.002% chloride, 0.005% sulfate, 0.001% heavy metals, and 0.002% iron. A 5% solution has a pH of 8.7 to 9.3.
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Chemical identity. Anhydrous disodium phosphate (CAS 7558-79-4, Na2HPO4, 141.96 g/mol) is the most common dibasic phosphate salt. It is also sold as the dihydrate, heptahydrate, and dodecahydrate, each with a different formula weight, so check the form before weighing.
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Phosphate buffers. Combined with monobasic sodium phosphate, disodium phosphate forms buffers effective around pH 6.2 to 8.2, centered on phosphoric acid's second pKa of about 7.2. Phosphate buffers are among the most widely used in biology, chromatography, and analytical chemistry.
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Phosphate-buffered saline. Disodium phosphate is a key component of phosphate-buffered saline (PBS), together with sodium chloride, potassium chloride, and potassium dihydrogen phosphate. PBS keeps cells and proteins at a stable, physiological pH and tonicity.
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Other uses. Disodium phosphate is used in HPLC mobile phases, culture media, protein purification, as a water-softening and anti-caking agent in industry, and as an emulsifier and buffering agent in food applications.
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Storage. The anhydrous salt can absorb moisture from the air. Keep the container tightly closed and dry, and dry the salt before weighing if exact concentrations are required.
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Preparing PBS. A common 1X PBS recipe dissolves sodium chloride, potassium chloride, disodium phosphate, and potassium dihydrogen phosphate in water and adjusts the pH to about 7.4. Use the formula weight that matches the hydrate form of each phosphate salt.
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Buffer capacity. Phosphate buffers have their greatest buffering capacity near pH 7.2. Concentrations from about 10 to 100 mM are common, chosen to balance buffering strength against effects on ionic strength and downstream steps.
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Related products. For saline component work, see Lab Pro's Sodium Chloride, ACS Reagent Grade, Crystal, 2.5 kg. For acid adjustment of phosphate buffers, see Phosphoric Acid 85%, ACS Grade (100 mL, 1 Pint).
Technical Specifications
| Chemical Name |
Sodium phosphate, dibasic, anhydrous |
| CAS Number |
7558-79-4 |
| EC Number |
231-448-7 |
| Synonyms |
Disodium hydrogen phosphate, disodium phosphate, sec-sodium phosphate |
| Formula |
Na2HPO4 |
| Molecular Weight |
141.96 g/mol |
| Grade |
ACS reagent |
| Assay (by acidimetry) |
99.0% min |
| pH (5% solution, 25 °C) |
8.7 to 9.3 |
| Insoluble Matter |
0.01% max |
| Loss on Drying (105 °C) |
0.2% max |
| Chloride (Cl) |
0.002% max |
| Sulfate (SO4) |
0.005% max |
| Heavy Metals (as Pb) |
0.001% max |
| Iron (Fe) |
0.002% max |
| Melting Point |
About 250 °C (decomposes) |
| Buffer Range (with NaH2PO4) |
About pH 6.2 to 8.2 |
| Form |
White powder or crystals |
| Hazard Profile |
Low hazard; may irritate eyes |
| Package Size |
100 g |
Applications / Common Uses
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Phosphate buffers: Prepares buffers around pH 7.
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PBS preparation: Supplies the dibasic phosphate in PBS.
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HPLC mobile phases: Buffers aqueous mobile phases.
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Culture media: Provides phosphate and buffering.
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Protein purification: Buffers chromatography and dialysis solutions.
Storage, Handling & Shipping
Store tightly closed in a cool, dry place at room temperature. Anhydrous disodium phosphate can absorb moisture, so reseal the container promptly and dry the salt before weighing for exact work.
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Incompatible materials: Strong acids and strong oxidizers.
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Personal protection: Safety glasses, gloves, and dust control.
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Spill response: Sweep up without raising dust and place in a closed container.
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First aid: Eyes: rinse with water for several minutes.
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