High-Performance Liquid Chromatography (HPLC) detectors are crucial for identifying and quantifying compounds as they elute from the chromatographic column. Different detectors are chosen based on the nature of the analyte and the sensitivity required. Here’s a detailed explanation of the different types of HPLC detectors:

1. UV-Visible (UV-Vis) Detector

• Principle: Measures the absorbance of UV or visible light by analytes.

• Types:

  • Fixed-wavelength UV detector: Detects absorbance at a single wavelength.

  • Variable-wavelength UV detector: Allows selection of different wavelengths.

  • Diode Array Detector (DAD): Measures absorbance across a range of wavelengths simultaneously.

• Applications: Widely used for compounds with chromophores (aromatic rings, double bonds).

2. Fluorescence Detector (FLD)

• Principle: Measures emitted light from a compound after excitation by a specific wavelength.

• Advantages: Highly sensitive and selective.

• Applications: Useful for detecting naturally fluorescent compounds or those that can be derivatized (e.g., proteins, polyaromatic hydrocarbons).

3. Refractive Index Detector (RID)

• Principle: Measures the change in refractive index between the mobile phase and the sample.

• Advantages: Universal (detects almost all compounds).

• Limitations: Less sensitive; not compatible with gradient elution.

• Applications: Sugars, lipids, polymers, and other non-UV-absorbing compounds.

4. Evaporative Light Scattering Detector (ELSD)

• Principle: Nebulizes the eluent, evaporates the solvent, and scatters light off the remaining analyte particles.

• Advantages: Can detect non-volatile and semi-volatile compounds.

• Applications: Lipids, surfactants, and other non-UV-active analytes.

5. Mass Spectrometric Detector (MS)

• Principle: Ionizes compounds and measures mass-to-charge ratios of analyte ions.

• Advantages: Extremely sensitive and provides structural information.

• Applications: Complex mixtures, trace analysis, and molecular identification.

6. Conductivity Detector

• Principle: Measures the ability of ions to conduct electricity in solution.

• Applications: Ion chromatography (a subset of HPLC), especially for inorganic ions.

7. Electrochemical Detector

• Principle: Measures current resulting from oxidation or reduction of analytes at an electrode.

• Advantages: Highly sensitive for redox-active compounds.

• Applications: Neurotransmitters, vitamins, and drugs.

8. Charged Aerosol Detector (CAD)

• Principle: Similar to ELSD but uses a corona discharge to charge aerosol particles before detection.

• Advantages: Universal, more sensitive and consistent than RID or ELSD.

• Applications: Pharmaceuticals, lipids, carbohydrates.

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