spline curve - (Apr/16/2013 )

I am using graphpad and and working on elisa data for my protein of interest.In graphpad i used spline curve as a standard curve and to detect my sample concnetration and when done with elisa reader i find most of the samples at a very low concentartion below then that of least standard value.
The question is does any one know how to caluculate those low concentration samples using the spline curve equation manually.
Can anyone plesase tell the spline curve equation and an example how to use it.

Thanks in advance

Putting aside that you should not be doing it (the error may be huge).
A spline curve is not the best formula to extrapolate with. It is used as a way of smoothing disjointed curves/data. Better instead to try one of the binding equations, I’m not sure what graphpad calls them, maybe Hill-equation? These at least will asymptote to your blank levels.