PIDs are commonly used for the detection of what substances?

Answer: B — Organic vapors and gases

Photoionization Detectors (PIDs) are primarily employed for detecting organic vapors and gases due to their sensitivity to ionizing wavelengths of light that cause many organic compounds to ionize. These detectors work by utilizing ultraviolet light to excite molecules in the sample, allowing them to release electrons. Organic compounds tend to have lower ionization potentials compared to inorganic materials, making PIDs particularly effective for identifying a wide range of volatile organic compounds (VOCs), solvents, and other hydrocarbon-related substances. While PIDs can detect some types of inorganic vapors and gases, their primary application and effectiveness are with organic species. Heavy metals cannot be detected by PIDs as they do not present a vapor phase that can be ionized for detection in the same way that organic chemicals can. Therefore, the use-case of PIDs aligns closely with the detection of organic vapors and gases.