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 VolumeWhen 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.

NOTE: If the user enters a value for density but not for its units, g/ml is assumed.

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 |

M = moles per liter.

MW = molecular weight in grams/mole.

pure = a pure substance.

U/l = units per liter.

vol = desired volume in 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