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log plot calculation


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#1 OKSO

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Posted 30 September 2009 - 06:05 AM

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 :huh:

#2 DRT

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Posted 30 September 2009 - 04:08 PM

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


I think you should be reading this as: y = (4E3) x0.8406
which makes x = (y/(4E3))^(1/0.8)

#3 OKSO

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Posted 01 October 2009 - 01:55 AM

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

#4 DRT

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Posted 01 October 2009 - 03:33 PM

Looks good. Just donít get caught with my crude rounding (^(1/0.8) is different to (^(1/0.8406)




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