How to Choose a Gas Chromatographic Detector for my Analysis?

In Gas Chromatography detection is based on a property of the eluting compound which is different from the carrier gas. It is necessary to have a clear understanding of your analysis requirements in advance before you can decide on the suitability of the detector. Important considerations are:

  • Is the detector Destructive or Nondestructive. Nondestructive detectors are concentration sensitive and can be used in series before destructive detectors. On the other hand destructive detectors are mass sensing and cannot be used in conjunction with other detectors.
  • Sensitivity requirements in terms of lowest detectable quantity and large linear dynamic range.
  • Selectivity refers to what type of compounds a detector will respond to falls into two categories
  • Universal detectors respond to all compounds reaching them from the column
  • Selective or specific detectors respond only to a class of compounds containing a particular functional group (selective) or only to a particular compound (specific)

Once you have the clarity on the requirements of your analysis the next stage is selection of your Gas Chromatographic detector from the available options.

We shall consider some common detection options available:

Flame Ionization detector

Flame ionization detector is the most commonly used detector as it responds to most organic compounds that can ionize in the hydrogen – air flame. It has a vast linear dynamic range of 10^ 7.

It is not suitable for inorganic gases such as CO, O_2, CS_2, N_2, CO_2, H_2O and NO_x and inert gases.

Thermal Conductivity detector

Thermal Conductivity detector is nondestructive and universal. It responds to compounds which have thermal conductivites different from the carrier gas. Inorganic gases which cannot be detected on FID can be analysed with the TCD. Its linear dynamic range is 10^6. It has useful applications in analysis of natural and refinery gases.

Electron capture detector

Electron detector is nondestructive and selective to compounds with electro negative substituents such as halogens, nitriles, nitrates, conjugated carbonyls, organometallics and oxygenated components. Linearity is 10^5 and applications include chlorinated pesticides, polyfluorinated biphenyls and herbicides.

Nitrogen phosphorus detector

Nitrogen phosphorus detector responds selectively to most compounds that contain nitrogen or phosphorus. Linear dynamic range is 10^6. Widely used for drugs of abuse and pesticides containing nitrogen or phosphorus.

Flame Photometric detector

Flame Photometric Gas Chromatographicdetector is destructive and selective. It is sensitive to compounds containing phosphorus or sulphur. Linear dynamic ranges from 10^3 for S to 10^4 for P. It is useful for analysis of organophosphorus pesticides, sulphurf in petroleum products and pulp milling process studies.

Photo Ionization detector

Photo Ionization Gas Chromatographic detector is a nondestructive and selective detector. It responds to compounds ionized by UV light such as aromatic and unsaturated compounds in drinking water, wastewater and sludge. Benzene, toluene, xylene and PAH’s in petroleum products. Linear dynamic range is 10^7.

Electrolytic Conductivity detector or Hall detector

Electro Conductive the Gas Chromatographic detector is sensitive to halogens, sulphur and nitrogen compounds, PCB’s, volatile organic compounds, sulphur compounds such as petroleum products and pesticides. Linear dynamic range is 10^6 for chlorine.

Mass Selective detectors

These Gas Chromatographic detectors are destructive and are based on the fragmentation of molecules by electron bombardment and separation based on mass to charge ratio. Linear dynamic range is 10^5. Applications include pharmaceuticals, environmental monitoring and pesticide residue analysis.

Please do leave your comments on analysis using such Gas Chromatographic detectors.

About Dr. Deepak Bhanot

Dr Deepak Bhanot is a seasoned professional having nearly 30 years expertise beginning from sales and product support of analytical instruments. After completing his graduation and post graduation from Delhi University and IIT Delhi he went on to Loughborough University of Technology, UK for doctorate research in analytical chemistry. His mission is to develop training programs on analytical techniques and share his experiences with broad spectrum of users ranging from professionals engaged in analytical development and research as well as young enthusiasts fresh from academics who wish to embark upon a career in analytical industry.

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