The concentration of pesticide residues on agricultural products, such as oranges, may be determined by GC-MS.25 Pesticide residues are extracted from the sample using methylene chloride, and the...

The concentration of pesticide residues on agricultural products, such as oranges, may be determined by GC-MS.25 Pesticide residues are extracted from the sample using methylene chloride, and the concentrations of the extracted pesticides are concentrated by evaporating the methylene chloride to a smaller volume. Calibration is accomplished using anthracene-d10 as an internal standard. In a study to determine the parts per billion of heptachlor epoxide on oranges, a 50.0-g sample of orange rinds was chopped and extracted with 50.00 mL of methylene chloride. After removing any insoluble material by filtration, the methylene chloride was reduced in volume, spiked with a known amount of the internal standard, and diluted to 10 mL in a volumetric flask. Analysis of the sample gives a peak–area ratio (A_anal/ A_{int stan}) of 0.108. A series of calibration standards, each containing the same amount of anthracene-d10 as the sample, give the following results.

Report the concentration of heptachlor epoxide residue (in nanograms per gram) on the oranges.