wish to measure the concentration of methyl benzoate in a plant stream by gas ch
ID: 525269 • Letter: W
Question
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 1.39 mg/mL of methyl benzoate (peak A) and 1.53 mg/mL of butyl benzoate (peak B). The area of peak A was determined to be 362 and of peak B to be 411 (measured in arbitrary units by the computer). To measure the sample, 1.00 mL of a standard sample of butyl benzoate containing 2.35 mg/mL was mixed with 1.00 mL of the plant stream material, and analysis of the mixture gave a peak area of 451 for peak A and 395 for peak B. What is the concentration of the methyl benzoate in the plant stream? conc_methyl benzoate = Number mg/mLExplanation / Answer
We can use the concept of response factor. The ratio of the response factor of the analyte fi and the response factor of the standard, fst must stay constant for a particular combination of analyte/internal standard. The response factor is defined as the ratio of the peak of a substance to the concentration of the substance.
fi = 362/( 1.39 mg/mL) = 260.432 mL/mg
fst = 411/(1.53 mg/mL) = 268.627 mL/mg.
Therefore, fi/fst = (260.432 mL/mg)/(268.627 mL/mg) = 0.969 ……(1)
Let the concentration of methyl benzoate in the second run be c mg/mL. We know that
fi = 451/(c mg/mL)
and fst = 395/(2.35 mg/mL) = 168.085 mL/mg.
Therefore, fi/fst = (451/c) mL/mg/(168.085 mL/mg)
===> 0.969*168.085 mL/mg = (451/c) mL/mg
===> c = 451/(0.969*168.085) = 2.769 2.77
The concentration of methyl benzoate in the second sample is 2.77 mg/mL (ans).
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.