Chromatography detector

A chromatography detector is a device used in gas chromatography (GC) or liquid chromatography (LC) to visualize components of the mixture being eluted off the chromatography column. There are two general types of detectors: destructive and non-destructive. The destructive detectors perform continuous transformation of the column effluent (burning, evaporation or mixing with reagents) with subsequent measurement of some physical property of the resulting material (plasma, aerosol or reaction mixture). The non-destructive detectors are directly measuring some property of the column effluent (for example UV absorption) and thus affords for the further analyte recovery.

Destructive detectors:

• Flame ionization detector. The column effluent is injected into hydrogen flame and the flame conductivity is measured. Only used in GC.
• Aerosol-based detector [NQAD]. The column effluent is nebulized, the mobile phase evaporated, a water shell condensed on it and then it is detected. Very sensitive detection for reverse phase applications.
• Flame photometric detector, FPD. Column eluate is burned in hydrogen flame. The light of the flame is filtered through an optical filter. Allows the detection of sulfur and phosphorus.
• Atomic-emission detector (AED).^[1] The column effluent is injected into plasma and the plasma spectrum is recorded. This detector allows for immediate determination of the elements present in the analyte.
• MS detector. The column effluent is continuously injected into mass spectrometer. This detector allows for immediate determination of the molecular weight of analyte and/or fragmentation pattern thus providing a significant amount of information about analyte.
• Nitrogen Phosphorus Detector, used only in GC.
• Evaporative light scattering detector (ELD).^[2] The column effluent is continuously evaporated and the light scattering of the resulting aerosol is measured. Only used in LC.

Non-destructive detectors:

• UV detectors, fixed or variable wavelength, which includes diode array detector (DAD or PDA). The UV absorption of the effluent is continuously measured at single or multiple wavelength. These are by far most popular detectors for LC.^[3]
• Thermal conductivity detector, (TCD). Measures the thermal conductivity of the effluent. Only used in GC.
• Fluorescence detector. Irradiates the effluent with a light of set wavelength and measure the fluorescence of the effluent at a single or multiple wavelength. Used only in LC
• Electron Capture Detector, ECD. The most sensitive detector known. Allows for the detection of organic molecules containing halogen, nitro groups etc.
• Conductivity monitor.^[4] Continuously measures the conductivity of the effluent. Used only in LC when conductive eluents (water or alcohols) are used.
• Refractive index detector (RI or RID). Continuously measures the refractive index of the effluent. Used only in LC. The lowest sensitivity of all detectors. Useful when nothing else works and at high analyte concentrations.
• Radio flow detector. Measures radioactivity of the effluent. This detector can be destructive if a scintillation cocktail is continuously added to the effluent.
• Chiral detector. Continuously measures the optical angle of rotation of the elutant. Used only in LC when chiral compounds are being analyzed.

References