Chromatographic Methods for Environmental Analysis - Fundamentals of Environmental Sampling and Analysis - page 271

Table 10.5 Comparison of major GC detectors

Sensitivity

Detector Principles Applications range Linearity

TCD Conduct away heat Universal Fair Good

FID Burn in H 2 O 2 flame Universal for Very good Excellent

and ionize hydrocarbons

ECD Electronegative Selective for Excellent Poor

compounds capture halogens; No

electron (e ) response to

from 63 Ni hydrocarbons

PID Analyte ionized Selective for Excellent Excellent

by UV light aromatics

NPD Ionization at the Selective for N, Excellent Excellent

alkali metal anode P containing

compounds

FPD Flame and then Selective for S, Very good Excellent

chemiluminescene P containing

measurement compounds

Hall Catalytic conversion Selective for Excellent Excellent

to ions, then halogens, S,

measured by N containing

conductivity compounds

MS Electron impact or Universal; Provide Excellent Excellent

chemical ionization structural

information

EXAMPLE 10.3. Five U.S. EPA priority pollutants have been identified from a
Superfund site and are being considered for a larger scale investigation using GC methods.
Available GC detectors proposed for initial screening are TCD, FID, ECD, PID, NPD, Hall,
and MS. The five priority pollutants include benzene, DDT, a-BHC (hexachlorocyclohex-
ane), chlordane, and trichloethylene (TCE). In a tabulated form, summarize the
applicability of various GC detectors to each of these five compounds. Briefly explain
why or why not they are applicable.

SOLUTION: The structure of these compounds can be found in Appendix B. Note that
benzene is the only hydrocarbon, whereas all others are chlorinated (halogenated). TCE is a
chlorinated aliphatic compound with 2 C and 3 Cl (C 2 Cl 3 H), and DDT is a chlorinated
aromatic pesticide with two benzene rings. a-BHC has a 6-carbon ring structure, but it is not
aromatic. Chlordane is a highly chlorinated pesticide with 6 Cl in its molecule. The
applicability of various GC detectors is summarized in Table 10.6 on the basis of what we
have discussed in this Chapter.

Since TCD and MS are universal detectors, in theory, both detectors should be
admissible for these five compounds. NPD will only respond to N and P containing
compounds, so it does not respond to any compound listed. The sensitivity of FID