You wish to measure the concentration of methyl benzoate in a plant stream by ga

Question

You wish to measure the concentration of methyl benzoate in a plant stream by gas chromatography. You prepare a sample of butyl benzoate to use as an internal standard. A preliminary run, shown at the right involved a solution containing 1.45 mg/mL of methyl benzoate (peak A) and 1.60 mg/mL of butyl benzoate (peak B). The area of peak A was determined to be 325 and of peak B to be 394 (measured in arbitrary units by the computer). To measure the sample, 1.00 mL of a standard sample of butyl benzoate containing 2.57 mg/mL was mixed with 1.00 mL of the plant stream material, and analysis of the mixture gave a peak area of 477 for peak A and 423 for peak B. What is the concentration of the methyl benzoate in the plant stream? Conc_methyl benoate =

Explanation / Answer

To determine the concentration of methyl benzoate in plant

preliminary run: conc. of methyl benzoate (specific compound of interest) = 1.45 mg/mL ; peak area = 325

conc. of butyl benzoate (internal standard)= 1.60 mg/mL; peak area= 394

response factor = area of internal standard * amount of specific compound of interest / (amount of internal standard * area of specific compound of interest )

response factor = 394 * 1.45 mg/mL / (1.60 mg/mL * 325) = 1.0986

To measure the sample:

conc. of butyl benzoate = 2.57 mg/mL peak area = 423

conc of methyl benzoate in sample = ? peak area = 477

amount of specific compound (methyl benzoate) =( amount of Internal standard butyl benzoate * area of specific comound methyl benzoate * response factor) / area of internal standard butyl benzoate

= 2.57 mg/mL * 477 * 1.0986 / 423

= 3.18 mg/mL

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