Answer :
Final answer:
The thermal conductivity detector is universal because it detects any analyte that changes the conductivity of the mobile phase, except the carrier gas. The flame ionization detector is not universal because it is largely sensitive only to hydrocarbons.
Explanation:
Because each solute modifies the thermal conductivity of the mobile phase, the thermal conductivity detector (TCD) reacts to all analytes with the exception of the carrier gas.
TCD is considered a universal detector due to this property and has the advantage of a linear response over a vast concentration range, is non-destructive, and allows for analyte recovery. However, its major disadvantage is a poor detection limit for most analytes.
On the other hand, the flame ionization detector (FID) is not universal because it is primarily sensitive to hydrocarbons and cannot detect non-hydrocarbon compounds such as water. It exhibits selectivity rather than universality, making it advantageous for detecting specific types of analytes with greater sensitivity.
