Sorensen’s Phosphate Buffer

Description

Sorensen’s Phosphate Buffer

Sorensen’s phosphate buffer is also known as a mixture of sodium salts and phosphate. The osmolarity of a 0.1 M solution at pH 7.2 is 226 mosmols; adding 0.18 M sucrose to the solution increases the osmolarity to 425 mosmols. The pH can be specified at the time of order. The maximum shelf life after receipt is 3 months.

Characteristics

• All products used are selected for their purity.
• Storage: 4-8°C
• Available in different pH ranges: 5.8 – 8

Advantages and Disadvantages

👍 Advantages

• The most physiological of all common buffers.
• Mimics some components of extracellular fluids.
• Non-toxic to cells.
• pH varies little with temperature.
• Stable for several weeks at 4°C.

⚠️ Disadvantages

• Precipitation is more likely to occur during fixation.
• Tends to form precipitates in the presence of calcium ions.
• Precipitates uranyl acetate and tends to react with lead salts.
• Slowly contaminates with microorganisms.

Preparation of Solutions

Stock Solutions

• 0.2 M Dibasic Sodium Phosphate 1 liter:
  • Na2HPO4 * 2H2O (MW = 178.05) 35.61 g
  • or Na2HPO4 * 7H2O (MW = 268.07) 53.65 g
  • or Na2HPO4 * 12H2O (MW = 358.14) 71.64 g
  • ddH2O to make 1 liter
• 0.2 M Monobasic Sodium Phosphate 1 liter:
  • NaH2PO4 * H2O (MW = 138.01) 27.6 g
  • or NaH2PO4 * 2H2O (MW = 156.03) 31.21 g
  • ddH2O to make 1 liter

Working Buffer

• 0.1 M 100 ml: Mix X ml of 0.2 M dibasic sodium phosphate with Y ml of 0.2 M monobasic sodium phosphate. Dilute to 100 ml with ddH2O or dilute 1:1 with fixative.

pH Table

Osmolarity

• The osmolarity is adjusted by varying the molarity of the phosphates or by adding sucrose, glucose, or sodium chloride.
• pH 7.2:
  • 0.10 M = 226 mOs (milliosmoles)
  • 0.05 M = 118 mOs
  • 0.075 M = 180 mOs
  • 0.15 M = 350 mOs