GC-MS Analysis of Environmental Pollutants

You are tasked with analyzing trace levels of polychlorinated biphenyls (PCBs) in river water using GC-MS. (a) Describe the sample preparation procedure (extraction and cleanup). (b) Why is GC-MS preferred over GC-FID for PCB analysis? (c) Explain the difference between EI (electron ionization) and CI (chemical ionization) and which is better for PCB identification. (d) How would you use Selected Ion Monitoring (SIM) mode to improve sensitivity? (e) Calculate the detection limit if the signal-to-noise ratio is 3:1 at 0.5 ppb and the calibration slope is 1500 ppb⁻¹.