| Thermal conductivity detector (TCD, katharometer) | 1 × 10–10 g propane (in helium carrier gas) | 1 × 106 | Universal response, concentration detector | Ultimate sensitivity depends on analyte thermal conductivity difference with carrier gas
Because thermal conductivity is temperature dependent, response depends on cell temperature
Wire selection depends on chemical nature of analyte
Helium is recommended as carrier and make-up gas; when analyzing mixtures containing hydrogen, one can use a mixture of 8.5% (mass/mass) hydrogen in helium |
| Gas density balance detector (GADE) | 1 × 10–9 g: H2 with SF6 as carrier gas | 1 × 106 | Universal response, concentration detector | Response and sensitivity are based on difference in relative molecular mass of analyte with that of the carrier gas; approximate calibration can be done on the basis of relative density
The sensing elements (hot wires) never touch sample, thus making GADE suitable for the analysis of corrosive analytes such as gaseous acids; gold-sheathed tungsten wires are most common
Best used with SF6 as a carrier gas, switched with nitrogen when analyses are required
Detector can be sensitive to vibrations and should be isolated on a cushioned base |
| Flame ionization detector (FID) | 1 × 10–11 g to 1 × 10–10 g | 1 × 107 | Organic compounds with C–H bonds | Ultimate sensitivity depends on the number of C–H bonds on analyte
Nitrogen is recommended as carrier gas and make-up gas to enhance sensitivity
Sensitivity depends on carrier make-up, and jet gas flow rates
Column must be positioned 1 mm to 2 mm below the base of the flame tip
Jet gases must be of high purity |
| Nitrogen-phosphorus detector (NPD, thermionic detector, alkali flame ionization detector) | 4 × 10–13 g to 1 × 10–11 g of nitrogen compounds
1 × 10–13 g to 1 × 10–12 g of phosphorus compounds | 1 × 104 | 105 to 106 by mass selectivity of N or P over carbon | Does not respond to inorganic nitrogen such as N2 or NH3
Jet gas flow rates are critical to optimization
Response is temperature dependent
Used for trace analysis only, and is very sensitive to contamination
Avoid use of phosphate detergents or leak detectors
Avoid tobacco use nearby
Solvent-quenching is often a problem |
| Electron capture detector (ECD) | 5 × 10–14 g to 1 × 10–12 g | 1 × 104 | Selective for compounds with high electron affinity, such as chlorinated organics; concentration detector | Sensitivity depends on number of halogen atoms on analyte
Used with nitrogen or argon/methane (95/5, mass/mass) carrier and make-up gases
Carrier and make-up gases must be pure and dry
The radioactive 63Ni source is subject to regulation and periodic inspection |
| Flame photometric detector (FPD) | 2 × 10–11 g of sulfur compounds
9 × 10–13 g of phosphorus compounds | 1 × 103 for sulfur compounds 1 × 104 for phosphorus compounds | 105 to 1 by mass selectivity of S or P over carbon | Hydrocarbon quenching can result from high levels of CO2 in the flame
Self-quenching of S and P analytes can occur with large samples
Gas flows are critical to optimization
Response is temperature dependent
Condensed water can be a source of window fogging and corrosion |
| Photoionization detector (PID) | 1 × 10–12 g to 1 × 10–11 g | 1 × 107 | Depends on ionization potentials of analytes | Used with lamps with energies of 10.0 eV to 10.2 eV
Detector will have response to ionizable compounds such as aromatics and unsaturated organics, some carboxylic acids, aldehydes, esters, ketones, silanes, iodo- and bromoalkanes, alkylamines and amides, and some thiocyanates |
| Sulfur chemiluminescence detector (SCD) | 1 × 10–12 g of sulfur in sulfur compounds | 1 × 104 | 107 by mass selectivity of S over carbon | Equimolar response to all sulfur compounds to within 10%
Requires pure hydrogen and oxygen combustion gases
Instrument generates ozone in situ, which must be catalytically destroyed at detector outlet
Catalyst operates at 950 °C to 975 °C
Detector operated at reduced pressure (10–3 Pa) |
| Electrolytic conductivity detector (ECD, Hall detector) | 1 × 10–13 g to 1 × 10–12 g of chlorinated compounds
2 × 10–12 g of sulfur compounds
4 × 10–12 g of nitrogen compounds | 1 × 106 for chlorinated compounds, 104 for sulfur and nitrogen compounds | 106 by mass selectivity of Cl over carbon, 105 to 106 by mass selectivity of S and N over carbon | Only high-purity solvents should be used
Carbon particles in conductivity chamber can be problematic
Frequent cleaning and maintenance is required
Often used in conjunction with a photoionization detector
For chlorine, use hydrogen as the reactant gas and 1-propanol as the electrolyte
For nitrogen or sulfur, hydrogen or oxygen can be used as reactant gas, and water or methanol as the electrolyte
Ultrahigh purity reactant gases are required |
| Ion mobility detector (IMD) | 1 × 10–12 g | 1 × 103 to 1 × 104 | 103 | Amenable to use in handheld instruments
Linear dynamic range of 103 for radioactive sources and 105 for photoionization sources
Selectivity depends on mobility differences of ions
Has been used for a wide variety of compounds including amino acids, halogenated organics, explosives
The radioactive 63Ni source is subject to regulation and periodic inspection |
| Mass selective detector (MSD, mass spectrometer, MS) | 1 × 10–11 g (single ion monitoring); 1 × 10–8 g (scan mode) | 1 × 105 | Universal | Single quadrupole, multiple quadrupole, ion trap, time-of-flight and magnetic sector instruments available (see separate table entitled: “Varieties of Hyphenated Gas Chromatography with Mass Spectrometry” in this section)
Must operate under moderate vacuum (1 × 10‑4 Pa)
Requires a molecular jet separator to operate with packed columns
Amenable to library searching for qualitative identification
Requires tuning of electronic optics over the entire m/e range of interest |
| Infrared detector (IRD) | 1 × 10–9 g of a strong infrared absorber | 1 × 103 | Universal for compounds with mid-infrared active functionality | A costly and temperamental instrument that requires high purity carrier gas, a nitrogen purge of optical components (purified air will, in general, not be adequate)
Must be isolated from vibrations
Presence of carbon dioxide is a typical impurity band at 2200 cm–1 to 2300 cm–1
Requires frequent cleaning and optics maintenance
Amenable to library searching for qualitative identification |
| Atomic emission detector (AED) | 1 × 10–13 g to 2 × 10–11 g of each element | 1 × 103 to 1 × 104 | 103 to 105, element to element | Requires the use of ultrahigh-purity carrier and plasma gases
Plasma produced in a microwave cavity operated at 2450 MHz
Scavenger gases (H2, O2) are used as dopants
Photodiode array is used to detect emitted radiation |
| Vacuum ultraviolet absorption detector (VUV) | 1 × 10–11 to 1 × 10–9 g | 1 × 103 to 1 × 104 | Universal except for He, H2, Ar, N2 | Wavelength range of 120 to 430 nm, filter selectable
Operable to 430 °C to prevent condensation of low volatility compounds
Amenable to library search, though current libraries are limited
Software can deconvolute multiple overlapping peaks
Requires a ≈ 2 mL/min make-up gas of Ar, He, H2, or N2, which maintains constant pressure in flow cell |
