A researcher was attemping to quantify the amount of DDT (dichlorodiphenyltrichl

Question

A researcher was attemping to quantify the amount of DDT (dichlorodiphenyltrichloroethane) in spinach with gas chromotography using a chloroform internal standard. To begin, the researcher examined a sample containing 9.23 mg/L DDT standard and 3.50 mg/L chloroform as the internal standard, producing peak areas of 2535 and 10115, respectively.

Then, the researcher collected 14.37 g of spinach, homogenized the sample, and extracted the DDT using an established method (assume 100% extraction), producing a 2.74 mL volume of unknown sample. The researcher then prepared a sample that contained 0.500 mL of the unknown sample and 1.50 mL of 11.79 mg/L chloroform, which was diluted to a final volume of 25.00 mL. The sample was analzed using GCMS, producing peak areas of 7205 and 12341 for the unknown and chloroform, respectively.

Calculate the DDT concentration in the spinach sample. Express the final answer as milligrams DDT per gram of spinach.

HINT:Begin by determining the response factor, F, of this separation method. Use the following equation, where Ax and [X] are the analye instrument response and concentration, respectively, and As and [S] are the internal standard instrument response and signal, respectively.

Explanation / Answer

The equation for F is missing!

The response factor F = (2335/9.23)/(10115/3.50) = 0.0875

Assume the spinach sample (14.37 g) contains X mg DDT then:

X mg DDT are in 2.74 mL volume of unknown/extracted sample.

The researcher has taken

X

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