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# Help please - molar extinction coefficient Watch

1. Hi, im having loads of difficulties trying to calculate the molar extinction coffient for phosphate at 670nm.

I currently have a stand curve, with the x-axis in micro grams of phosphate and the y-axis with absorbance at 670nm.

could someone explain how to do it i know i have to use the formula e=A/CxL (L is 1cm) but im not sure how to convert the micrograms of phosphate and use it to get the coefficient :-S
2. I would first convert the micro grams into a concentration value i.e. mM or M then at each molarity do absorbance/ concentration * pathlength and average the values to get an extinction coefficient.

Hope that helps, quote me if you have any more questions.
3. (Original post by joshed)
I would first convert the micro grams into a concentration value i.e. mM or M then at each molarity do absorbance/ concentration * pathlength and average the values to get an extinction coefficient.

Hope that helps, quote me if you have any more questions.
hey thanks for the reply, once tried to convert them into mM, but once i do that do you think i should re draw the graph with the new x values and take the gradient of the line?
4. (Original post by swift464)
hey thanks for the reply, once tried to convert them into mM, but once i do that do you think i should re draw the graph with the new x values and take the gradient of the line?
Yes, that is a far better and more accurate way than I described

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Updated: December 4, 2010
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