Preparation Monosodium phosphate Stock Solution

This guide describes the preparation of Monosodium phosphate Stock Solution at a defined molarity for laboratory use.

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Stock Solution Preparation Guide – Monosodium Phosphate (NaH₂PO₄)

Monosodium phosphate (also called Sodium dihydrogen phosphate) can be used to prepare sodium phosphate buffers or other phosphate-based solutions. A 1 M stock solution is frequently used as a component when preparing phosphate buffers of desired pH by mixing with dibasic sodium phosphate.

Chemical Information

NameMolecular FormulaMolecular WeightCAS
Monosodium phosphate, anhydrousNaH₂PO₄119.98 g/mol7558-80-7
Monosodium phosphate monohydrateNaH₂PO₄·H₂O137.99 g/mol10049-21-5
Monosodium phosphate dihydrateNaH₂PO₄·2H₂O156.01 g/mol13472-35-0

Preparation of 1 M Monosodium Phosphate

To prepare 1 L of 1 M sodium phosphate monobasic solution:

  1. Weigh 119.98 g of anhydrous monosodium phosphate (NaH₂PO₄).
  2. Transfer to a 2 L beaker or flask.
  3. Add ~800 mL of deionized or distilled water and stir until fully dissolved.
  4. Adjust the volume to 1000 mL with deionized water and mix thoroughly.
  5. Solution should be clear and colorless.
  6. Optionally, transfer to an autoclavable bottle and autoclave (20 min at 121–124 °C) for sterilization.

Notes and Precautions

  • Anhydrous monosodium phosphate is hygroscopic and may absorb water; adjust calculations accordingly.
  • Do not dissolve directly into final volume water; additions will increase solution volume.
  • Use appropriate personal protective equipment.

Storage and Usage

  • Store at room temperature when not in use.
  • Use this stock solution directly or mix with sodium phosphate dibasic to prepare buffers of desired pH.
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