Question

A scientist wishes to measure the concentration of methyl benzoate in a plant stream by gas chromatography. He prepares a sample of butyl benzoate to use as an internal standard. The results of a preliminary run, which used a solution known to contain 1.11 mg/mL of methyl benzoate (peak A) and 1.22 mg/mL of butyl benzoate (peak B), are shown. The area of peak A is determined to be 342 and the area of peak B is determined to be 413 measured in arbitrary units by the computer. To measure the sample, 1.00 mL of a standard sample of butyl benzoate containing 2.25 mg/mL is mixed with 1.00 mL of the plant stream material. Analysis of the mixture gave a peak area of 493 for peak A and 417 for peak B. Detector Response 15 Time (min) What is the concentration of methyl benzoate in the plant stream?

Answer 1

The concentration of methyl benzoate in the plant stream is approximately 1.44 mg/mL, calculated by comparing peak areas from gas chromatography using a known internal standard.

Step-by-step explanation:

The concentration of methyl benzoate in the plant stream is determined by comparing the peak areas of the known concentrations (the preliminary run) to the peak areas of the sample mixture using gas chromatography. To find the concentration in the sample, a ratio of the peak areas for both the internal standard and the methyl benzoate is used.

From the preliminary run, we have the ratio of the peak areas which is:

Peak A / Peak B = 342 / 413 = 0.8278

Now, analyze the actual sample:

Peak A / Peak B = 493 / 417 ≈ 1.1823

We can set up a proportion using these ratios:

1.11 mg/mL / 1.22 mg/mL = 493 area units / 417 area units

Solving for the concentration of methyl benzoate in the plant stream:

(493 area units / 417 area units) × (1.22 mg/mL) = 1.11 mg/mL

(1.1823) × (1.22 mg/mL) = 1.44 mg/mL

Therefore, the concentration of methyl benzoate in the plant stream is approximately 1.44 mg/mL.