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PREPARING LABORATORY SOLUTIONS AND REAGENTS II

PREPARING LABORATORY SOLUTIONS AND REAGENTS II. Solutions With More Than One Solute. RECIPE I Na 2 HPO 4 6 g KH 2 PO 4 3 g 0.4% glycerol 10 mL Dissolve in water. Bring to a volume of 1 liter. Recipe lists amounts of solutes. This is easy to follow.

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PREPARING LABORATORY SOLUTIONS AND REAGENTS II

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  1. PREPARING LABORATORYSOLUTIONS AND REAGENTS II

  2. Solutions WithMore Than One Solute RECIPE I • Na2HPO4 6 g • KH2PO4 3 g • 0.4% glycerol 10 mL • Dissolve in water. • Bring to a volume of 1 liter. • Recipe lists amounts of solutes. • This is easy to follow

  3. Solutions WithMore Than One Solute Cont… RECIPE II • 1 M MgCl2 • 0.1 M Tris • Gives the final concentration of each solute. • You must calculate the amount of each to use. • This is harder to interpret

  4. A Recipe WithMultiple Solutes, SM Buffer SM BUFFER 0.1 M NaCl 1 mM MgSO4 0.2 M Tris, pH 7.5 0.01% gelatin • This might be whole recipe as given in a manual

  5. Strategy 1: PREPARING SM BUFFER WITHOUT STOCK SOLUTIONS, OVERVIEW: • Prepare a solution of 0.2 M Tris, pH 7.5. • Calculate grams of each of the other solutes required. • Weigh out solutes and dissolve directly in Tris buffer.

  6. Strategy 1 • Decide how much buffer to make, for example, 1 liter. • 1 liter of 0.2 M Tris requires 24.2 g of Tris base. (MW = 121.1 g/mole.) • Dissolve Tris in about 700 mL of water and bring pH to 7.5. • Do not bring Tris to volume.

  7. 4. 1 liter of 0.1 M NaCl requires 5.84 g of NaCl. Add this to Tris buffer. • 5. 1 liter of 1 mM MgSO4 requires 1/1000 of its MW. • MgSO4 comes in more than one hydrated form; read • container to determine MW. • Weigh out correct amount. • Add it to Tris buffer.

  8. 0.01% gelatin is 0.1 g in 1 L. Weigh out and add to Tris buffer. • Stir to dissolve • BTV 1 L • Check and record pH.

  9. Strategy 2: PREPARING SM BUFFER WITH STOCK SOLUTIONS • In overview: • Four solutes are each prepared separately as concentrated stock solutions.

  10. When the four stocks are combined, they dilute one another to the proper final concentrations

  11. Steps Are: • Prepare a stock solution of Tris buffer at pH 7.5. a. No set rule as to what should be concentration of stock. b. Example: To make 1 L of 1 M stock, dissolve 121.1 g of Tris base in about 900 mL of water.

  12. c. Bring pH to 7.5. d. BTV 1L. 2. Prepare a stock solution of magnesium sulfate, for example, 1 M. a. To make 100 mL, dissolve 0.1 MW of MgSO4 in water, bring to a volume of 100 mL.

  13. 3. Prepare a stock solution of NaCl, for example,1 M. a. To make 100 mL of stock, dissolve 5.84 grams in water and BTV 100 mL.

  14. Prepare a stock solution of gelatin, for example, 1%. a. Dissolve 1 g in a final volume of 100 mL of water.

  15. 5. To make the final solution, combine the right amounts of each stock. a. Since this is a situation where stocks are diluted, use the C1V1 = C2V2 equation four times, once for each solute.

  16. For example, to calculate how much Tris stock is required: C1 V1 = C2 V2 (1 M) (?) (0.2 M) (1000 mL) ? = 200 mL

  17. Summary To make 1000 mL of SM buffer, combine: 200 mL Tris stock 1 mL MgSO4 stock 100 mL NaCl stock 10 mL Gelatin stock BTV 1L; check and record pH.

  18. Which Strategy? • Both strategy 1 and 2 are correct. • Generally efficient to make stock solutions of frequently used solutes because weighing out chemicals is time-consuming.

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