Gas Chromatography Detectors

Gas Chromatography Detectors
Introduction
Classification of Detectors
General-Purpose Detectors
Selective, High-Sensitivity Detectors
Flame Ionization Detector
Nitrogen Phosphorus Detector
Electron Capture Detector
Thermal Conductivity Detector
Flame Photometric Detector
Photoionization Detector
Mass Spectrometer
Conclusion
References

1. Prepared by: Aditya Sharma M.S. (Pharm) Pharmaceutical Analysis NIPER Guwahati 1 GAS CHROMATOGRAPHY DETECTORS

2. CONTENTS Introduction Flame Ionization Detector Nitrogen Phosphorus Detector Electron Capture Detector Thermal Conductivity Detector Flame Photometric Detector Photoionization Detector Mass Spectrometer Conclusion References 2

3. INTRODUCTION As solutes elute from the column, they interact with the detector. The detector converts this interaction into an electronic signal that is sent to the data system. The magnitude of the signal is plotted versus time (from the time of injection) and a chromatogram is generated. 3 Figure 1: Classification of Detectors

4. FLAME IONIZATION DETECTOR (FID): Compounds are burned in a hydrogen-air flame. Carbon containing compounds produce ions that are attracted to the collector. The number of ions hitting the collector is measured and a signal is generated.  Selectivity: Compounds with C-H bonds. A poor response for some non-hydrogen containing organics (e.g., hexachlorobenzene ). Figure 2: Flame Ionization Detector Reference:https://www.shimadzu.com/an/service-support/technical-support/analysis basics/fundamentals/detector.html. Accessed on 21/02/2021. 4

5. NITROGEN PHOSPHORUS DETECTOR (NPD ): Compounds are burned in a plasma surrounding a rubidium bead supplied with hydrogen and air. Nitrogen and phosphorous containing compounds produce ions that are attracted to the collector. The number of ions hitting the collector is measured and a signal is generated. Selectivity: Nitrogen and phosphorous containing compounds. Figure 3: Nitrogen Phosphorus Detector Reference:https://www.shimadzu.com/an/service-support/technical-support/analysis basics/fundamentals/detector.html. Accessed on 21/02/2021. 5

6. ELECTRON CAPTURE DETECTOR (ECD ): Electrons are supplied from a 63Ni foil lining the detector cell. A current is generated in the cell. Electronegative compounds capture electrons resulting in a reduction in the current. The amount of current loss is indirectly measured and a signal is generated .  Selectivity: Halogens, nitrates and conjugated carbonyls . Figure 4: Electron Capture Detector Reference:https://www.shimadzu.com/an/service-support/technical-support/analysis basics/fundamentals/detector.html. Accessed on 21/02/2021. 6

7. THERMAL CONDUCTIVITY DETECTOR (TCD ): A detector cell contains a heated filament with an applied current. As carrier gas containing solutes passes through the cell, a change in the filament current occurs. The current change is compared against the current in a reference cell. The difference is measured and a signal is generated. Selectivity: All compounds except for the carrier gas . Figure 5: Thermal Conductivity Detector Reference:https://www.shimadzu.com/an/service-support/technical-support/analysis basics/fundamentals/detector.html. Accessed on 21/02/2021. 7

8. FLAME PHOTOMETRIC DETECTOR (FPD):  Compounds are burned in a hydrogen-air flame. Sulfur and phosphorous containing compounds produce light emitting species (sulfur at 394 nm and phosphorous at 526 nm). A monochromatic filter allows only one of the wavelengths to pass. A photomultiplier tube is used to measure the amount of light and a signal is generated. A different filter is required for each detection mode . Selectivity: Sulfur or phosphorous containing compounds. Only one at a time . Figure 6: Flame Photometric Detector Reference:https://www.shimadzu.com/an/service-support/technical-support/analysis basics/fundamentals/detector.html. Accessed on 21/02/2021. 8

9. PHOTOIONIZATION DETECTOR (PID):  Compounds eluting into a cell are bombarded with high energy photons emitted from a lamp. Compounds with ionization potentials below the photon energy are ionized. The resulting ions are attracted to an electrode, measured, and a signal is generated . Selectivity: Depends on lamp energy. Usually used for aromatics and olefins (10 eV lamp).   Figure 7: Photoionization Detector Reference:https://www.shimadzu.com/an/service-support/technical-support/analysis basics/fundamentals/detector.html. Accessed on 21/02/2021. 9

10. MASS SPECTROMETER (MS ): The detector is maintained under vacuum. Compounds are bombarded with electrons or gas molecules. Compounds fragment into characteristic charged ions or fragments. The resulting ions are focused and accelerated into a mass filter which selectively allows detection of all ions of a specific mass to pass through to the electron multiplier. The mass filter then allows the next mass to pass through while excluding all others. The total number of ions are counted for each scan. The abundance or number of ions per scan is plotted versus time to obtain the chromatogram. A mass spectrum is obtained for each scan which plots the various ion masses versus their abundance or number. 10

11. CONCLUSION Detector  Type Support Gases Selectivity Detectability Dynamic range Flame Ionization Detector Mass Flow Hydrogen and air Most organic compounds 100 pg 10 7 Thermal Conductivity Detector Concentration Reference Universal 1 ng 10 7 Electron Capture Detector Concentration Make-up Halides, nitrates, nitriles, peroxides, anhydrides, organometallics 50 fg 10 5 Nitrogen Phosphorus Detector Mass Flow Hydrogen and air Nitrogen, phosphorus  10 pg 10 6 Flame Photometric Detector Mass Flow Hydrogen and air possibly oxygen Sulphur, phosphorus, tin, boron, arsenic, germanium, selenium, chromium 100 pg 10 3 Photoionization Detector Concentration Make-up Aliphatics, aromatics, ketones, esters, aldehydes, amines, heterocyclics, organosulphurs, some organometallics 2 pg 10 7 11

12. REFERENCES Poole, C., 2015. Ionization-based detectors for gas chromatography. Journal of Chromatography A, 15(8), 1421, pp.137-153 . Eiceman, G., Gardea-Torresdey, J., Overton, E., Carney, K. and Dorman, F., 2002. Gas Chromatography. Analytical Chemistry, 74(12), pp.2771-2780 . Selucky, M., 1971. Specific gas chromatography detectors. Chromatographia, 4(9), pp.425-434 . Adlard, E. and Juvet, R., 1975. A Review of Detectors for Gas Chromatography Part I: Universal Detectors. C R C Critical Reviews in Analytical Chemistry, 5(1), pp.03-13 . Guiochon, G. and Guillemin, C., 1990. Gas chromatography. Review of Scientific Instruments, 61(11), pp.3317-3339. 12