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.

Explanation / Answer

Relative Response factor =response factor DDT/ response factor chloroform = (2535/9.23)/(10115/3.50)=0.095

we know Mstd1Vstd1 = Mstd2Vstd2

so, after dilution conc of Chloroform = 11.79*1.50/25= 0.7074mg/L

so this smaple has conc = (peak area DDT/peak area chloroform)/(RRF) * conc of chloroform

conc of DDT in diluted sample = ((7205/12341)/0.095) * 0.7074 = 4.3467 mg/L

again 0.5mL of solution contains 4.3467 mg/L DDT, so 2.74mL contains 23.82 mg/L DDT.

For per gram= 23.82/14.37 =1.6576 mg/g of spinach

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