Safety and Patient Selection
Table 4. Calculations for Making Extract Dilutionsa All dilutions can be calculated by using the following formula:
V1 x C1 = V2 x C2, where V1 = Final volume you want to prepare C1 = Concentration (wt/vol or protein nitrogen units) of extract you want to prepare V2 = Volume of extract you will need for dilution C2 = Concentration of extract you will use.
Example: Solve for V2; (V1 x C1)/C2 = V2. To determine the concentration of an item in a mixture: 1. determine which formula you need to use; 2. choose the numbers/fractions that will be inserted into the formula for V1, C1, V2, and C2;
3. change all wt/vol fractions to a decimal number and insert into the formula (see below); and
4. multiply first and then divide to get the answer. To express concentration as a percentage:
1:10 wt/vol 1/10 = 0.1 x 100 = 10% solution 1:20 wt/vol 1/20 = 0.05 x 100 = 5% solution 1:40 wt/vol 1/40 = 0.025 x 100 = 2.5% solution
Example: V1 = 5 mL C1 = 1:200
V2 = Unknown
Add values into formula: V1 x C1 = V2 x C2
V2 (V1 x C1)/C2
Final volume you want to prepare Concentration you want to prepare
Volume of extract you will need for dilution
5 x (1/200) = V2 x (1/10) 5 x (0.005) = V2 x (0.1) V2 = 0.025/0.1 = 0.25
To determine amount of diluent needed: V1-V2
5-0.25 = 4.75 mL
a Adapted from the Greer Allergy Compendium. Lenoir (NC): Greer Laboratories; 2005. p. 71. Permission provided by Robert Esch, PhD.
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