log plot calculation - (Sep/30/2009 )
Hi,
I wonder if a maths whizz can help me out.. I'm stumped on an equation.
Basically I'm trying to calculate unknown concentrations of samples from a standard curve, in log format.
I performed a standard curve with a tenfold serial dilution of my 'Standard' compound, and also have my sample measurements (luminescence).
The compound was diluted in concentrations ranging from1^-10 tp 1^-16 moles (as per manufacturers instructions).
When I plot this on Excel, luminescence is on the Y axis (Log scale), and compound concentration is on X scale (Log).
I add a trendline to get the equation, and get y=4E + 3x 0.8406
In order to get my x concentration I'm not sure what to do. (I normally work it through using y=mx +c)
Can anyone help me out? thanks
OKSO on Oct 1 2009, 12:05 AM said:
I add a trendline to get the equation, and get y=4E + 3x 0.8406
I think you should be reading this as: y = (4E3) x0.8406
which makes x = (y/(4E3))^(1/0.8)
Thanks for that help
Yes, I've worked out some y values from this and they correlate with my standard curve.
So briefly if my y value (luminescence) was 1500 then x turns out to be
x=<(1500)/4E3>^(1/0.8)
x=<(0.375)^(1.25)>
x=0.29
Does this tally up with your thoughts?
thanks again
Looks good. Just don’t get caught with my crude rounding (^(1/0.8) is different to (^(1/0.8406)