MadSci Network: Biochemistry
Query:

Re: Axis for standard curves

Date: Wed Mar 5 00:43:54 2008
Posted By: Neil Saunders, Computational biologist
Area of science: Biochemistry
ID: 1204616144.Bc
Message:

Dear Alle,

Thanks for your question. When plotting graphs, the convention is that you plot the independent variable: the variable over which you have control, on the x-axis (also called the abscissa). The dependent variable - the variable which you are measuring as a function of your known, controlled variable - is plotted on the y-axis (also called the ordinate).

In the case of a standard curve, the standards are known protein concentrations upon which the absorbance is dependent. So your initial idea was the correct one. Ideally, you will obtain a best-fit straight line through your points and be able to use the equation y = mx + c to obtain the concentration of the unknown sample from its absorbance.

In practice, switching the axes will make no difference to the calculation provided that you remember which is x and which is y. However, the convention is as I described and best followed to avoid confusion.

Hope that helps,
Neil

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