Question

An internal standard calibration curve was generated for the determination of ethyl acetate by gas chromatography, using butyl acetate as an internal standard. The equation of the best-fit line was y = 0.0588x (-0.0172). When an unknown was injected, peak areas of 82 and 9.0 × 101 were obtained for ethyl acetate and butyl acetate, respectively. Determine the concentration of ethyl acetate (%v/v) in the unknown.

Answer 1

We already have the calibration fit line:

y = 0.0588x - 0.0172

For a peak area of 82:

82 = 0.0588x - 0.0172

82 - 0.0172 / 0.0588 = x

x = 1394.27

For a peak area of 90:

90 - 0.0172 / 0.0588 = x

x = 1530.32

Now, in which units do you have this? you are not indicating that, however, The correct answer could be calculated like this:

% = 1394.27 / 1530.32 * 100 = 91.11 %

This could be the %v/v however, I need you to tell me the units you are working for, in that way I can know if the primary units are M (mol/L) or ppm.

Hope this helps