Page 57 - Quality control of pharmaceuticals (07-PA 704)

4. Linearity and range:

The linearity of an analytical method is its ability to elicit test results that are
directly or by a well-defined mathematical transformation, proportional to the
concentration of analyte in samples within a given range.
The correlation coefficient, r, y- intercept, slope of the regression line, should be
submitted.
At least five points are needed for regression analysis.

y = a +b x
Where (b) is the slope of the line and (a) it's intercept on the y-axis. The individual
points on the line will be referred to as (xi, yi) – normally the blank reading, (x2, y2),
(x3, y3) ……(xi, yi)……. (xn, yn), i.e. there are n points altogether.
The mean of the x-values is, as usual, called ̅, and the mean of the y-values is ̅ .
The point ( ̅, ̅ ) is then known as the centroid of all the points.