Scientific investigators and technicians need to be adept at calculating the amounts of stock materials needed to give the desired concentrations in the final reagent. Because a small error in calculation can result in an experiment's failure, or worse: unreproducible data, verification of such calculations is often sought. Recipe Maker was intended to fill the role of the guy at the next bench when he/she is too busy to check your calculations.Index
I) The Use of Recipe Maker II) A Note on Density and Volume III) A note on mixtures (ie dNTPs) IV) Conversions NOT attempted by program V) Calculations I) The Use of Recipe Maker
II) A Note On Density and Volume 
When a pure substance is measured by mass, Recipe Maker calculates its volume based on its density. If the user does not enter a value for
density the program will assume a density of 1.0 g/ml. This is the density of water and will be too small for most crystalline substances. If the
user does not enter a value for density, the calculated volume of solvent may be incorrect. There may also be a small change of combined volume
upon solution. If the amount of pure substance is relatively small, the error will be insignificant. However, if a relatively large amount of
pure substance is used in a solution, the value given by Recipe Maker for the volume of solvent should be used only as a rough guide. The author
recommends the use of a volumetric cylinder to measure the final volume as the last of the solvent is added. The addition of acids and/or bases
to adjust the solution's pH will also demand the use of volumetric cylinder to adjust the final volume.
III) A Note On Mixtures (ie: dNTPs)
At this time, Recipe Maker has no elegant way of treating mixtures. Except when the individual components all have the same concentration (ie:
10mM dNTPs), it might be best to designate mixtures in terms of X (as in 10X MOPS buffer).
IV) Conversions NOT attempted by Recipe-Maker:
| FROM | TO |
|---|---|
| percentage | molarity |
| percentage | activity (U/vol, U/mass) |
| molarity | percentage |
| molarity | activity (U/vol, U/mass) |
| mass/volume | percentage |
| mass/volume | activity (U/vol, U/mass) |
| activity (U/vol, U/mass) | percentage |
| activity (U/vol, U/mass) | molarity |
| activity (U/vol, U/mass) | mass/vol |
V) Calculations
| To | From | Calculation | Note |
|---|---|---|---|
| x(%) | y(%) | vol*(x/y) liters | see below |
| x(%) | y(g/l) | vol*(x*10)/y liters | 1%=1g/100ml |
| x(%) | pure | vol*(x*10) grams | 1%=1g/100ml |
| x(M) | y(M) | vol*(x/y) liters | |
| x(M) | y(g/l);z(MW) | vol*(x*z)/y liters | |
| x(M) | pure;z(MW) | vol*(x*z) grams | |
| x(g/l) | y(M) | vol*x/(z*y) liters | |
| x(g/l) | y(g/l) | vol*(x/y) liters | |
| x(g/l) | pure | vol*x grams | |
| x(U/l) | y(U/g) | vol*(x/y) grams | |
| x(U/l) | y(U/l) | vol*(x/y) liters |
Note that the meaning of % has been inferred from the context. Thus if x% is desired and the stock is a pure substance or a solution with concentration expressed in g/l, Recipe Maker infers the user wants x grams/100 ml.
The calculations are based on stoichiometric multiplication: Determine what you want, then multiply it by one until it is expressed in terms of
what you have. For example, if I want 500 ml of a 4 M solution of NaCl and I have a pure crystalline salt: Therefore I want: 0.5 liters * 4
moles/liter = 2 moles. Since I know that: 1 mole of NaCl = 58.44 grams, I can multiply 2 moles by 1: 2 moles * (58.44 grams/1 mole) to
get 116.88 grams. The trick is to express 1 so that when you multiply, the units cancel each other:
For example, the factor 10 in entries 2 and 3 above derive from the conversion:
1% = 1g/100ml = (1g/100ml) * (10/10) * (1000 ml/1liter) = 10g/liter
Therefore: (10g/liter)/1% = 10g/%liter = 1