Sodium orthovanadate Stock Solution

Stock Solution Preparation Guide – 0.2 M Sodium Orthovanadate (Na₃VO₄) Solution

Sodium orthovanadate (Na₃VO₄) is widely used in biochemical experiments as a **phosphatase inhibitor** and is typically prepared as a **200 mM (0.2 M) stock solution**. To maximize inhibitory activity, the solution must be activated (depolymerized) by repeated pH adjustment and boiling so that it remains colorless and stable at pH 10.

Objective

Preparation of **20 mL of 0.2 M sodium orthovanadate stock solution** for use in cell lysis buffers or enzymatic assays.

Composition

• Sodium orthovanadate (Na₃VO₄) in deionized/Milli‑Q water at 0.2 M (200 mM)

Required Materials

• Sodium orthovanadate (Na₃VO₄) solid
• 6 M Hydrochloric acid (HCl) or 1 M HCl
• Deionized / Milli‑Q water
• 50 mL screw-cap tube for dissolution and mixing; a vented, heat-resistant vessel approved by its manufacturer for the selected heating method
• Microwave or boiling water bath
• pH meter or pH strips capable of pH 10 measurement
• Volumetric pipettes/micronipettes
• PPE (gloves, goggles, lab coat)

Procedure

• Step 1
  Weigh **0.736 g** of sodium orthovanadate (MW = 183.91) into a 50 mL screw‑cap tube. Add **15 mL** of deionized/Milli‑Q water and mix by inversion until dissolved (≈ 5 min).
• Step 2
  Adjust the pH of the solution to **10.0** using 6 M HCl (add dropwise ~10 µL at a time while mixing). The pH before adjustment may be ~13.5 and the solution may turn yellow upon acid addition.
• Step 3
  Before heating, ensure that the vessel is suitable for the selected heating method and that its closure is removed or loosened to allow pressure to escape; transfer the solution to a suitable vessel if necessary. Do not heat a tightly capped tube. Heat in a boiling water bath until the solution becomes colorless, then cool to room temperature. Use microwave heating only with a vessel explicitly approved for that use and a validated laboratory procedure.
• Step 4
  After cooling, readjust the pH to **10.0** and repeat the boiling/cooling cycle. Perform this **2–3 cycles** until the solution remains colorless and stable at pH 10 upon cooling.
• Step 5
  Adjust the final volume to **20 mL** with deionized/Milli‑Q water and mix by inversion.

Note: The repeated pH adjustment and boiling cycles eliminate polymeric vanadate species, resulting in an active, colorless orthovanadate stock. Label aliquots with concentration, activation date, and store at **–20 °C** in small volumes (e.g., 0.5–1 mL). Discard if color returns or pH changes.

Available Reagents