Question

A researcher was attempting to quantify the amount of dichlorodiphenyltrichloroethane (DDT) in spinach using gas chromatography mass spectrometry (GCMS). First attempts using external calibration proved difficult, as reproducibility and external standard agreement were poor. To overcome these problems, the researcher used the internal standard calibration method with chloroform as the internal standard. To begin, the researcher analyzed a sample containing 7.24 mg/L DDT standard and 3.12 mg/L chloroform as the internal standard, which produced peak areas of 3447 and 9165 for the DDT and chloroform, respectively. Determine the response factor (F). After establishing the response factor of the instrument, the researcher collected 7.57 g of spinach, homogenized the sample, and extracted the DDT using an established method, producing a 3.98 ml solution containing an unknown amount of extracted DDT. The researcher then prepared a sample for analysis that contained 1.00 mL of the unknown DDT solution and 1.75 mL of 12.60 mg/L. chloroform, which was diluted to a final volume of 25.00 mL. The sample was analyzed using GCMS, producing peak areas of 7731 and 11985 for the DDT and chloroform, respectively. Calculate the amount of DDT in the spinach sample. Express the final answer as milligrams of DDT per gram of spinach. amount of DDT mg DDT /g spinach

Answer 1

An aiven tthat Conotaon 0 Standasd = 3.12ng/L Concomtsation % aralyte = 724 mg lL uo kmow thot FX ea of standasd Sigral Aa o amalyte sigral Contombsahon of sarhy cenonteatoton o aralyt 9165 3u7 -F X 312 724 476.104 FY 2437 5 F-0.162 n Sample mixtue dha concentration o Stands Cs(2.60) lsm2 2S mL 0.882 mglL Foon anmnample AC 0.162 1l98S () Cx3-51 mgl L 131 0-88 2mgl

The cooentation m 00m as lolloos Cx)= = 3.51 X 25 875 malaL 0 879 mg mL O,877S 3.98 Mass n 3,9g mL 3.4 g DDT eu bhE 759 cononbation DDT o.46 mg ODT9 spirach.