Decoding Chromatography: A Comprehensive Guide to Different Types of HPLC Detectors

• by Rahul Ramakrishna
• 01 Apr 2011
• HPLC

High-Performance Liquid Chromatography (HPLC) is a cornerstone in analytical chemistry, and the detector plays a pivotal role in the precision of analyses. This article explores the diverse landscape of HPLC detectors, shedding light on various types and their unique functionalities. From UV-Vis detectors to fluorescence and mass spectrometry, delve into the intricacies of each, providing insights for researchers, analysts, and enthusiasts in the field.

High-Performance Liquid Chromatography (HPLC) detectors are crucial components used to detect and quantify solutes within the eluent coming from the HPLC column. These detectors are capable of identifying and measuring the concentration of compounds in the mobile phase. There are specific detectors that respond to particular compounds independently of the mobile phase composition, and there are bulk property detectors whose response depends on collective changes in both the mobile phase and the sample. Important features of HPLC detectors include sensitivity, a linear response, and either a universal or selective response.

Here are some desirable features of HPLC detectors:

1. Specific or General Response: Detectors should have either specific or general responses to compounds in a mixture.
2. Sensitivity: They should be more sensitive to solutes than to the mobile phase.
3. No Response to Mobile Phase: Detectors should respond to solutes and not to the mobile phase.
4. Low Cell Volume: A low cell volume helps minimize memory effects.
5. Linear Response: Detectors should respond linearly to changes in solute concentration.
6. Low Noise and Detection Limits: Minimal detector noise and low detection limits are essential for accurate analysis.
7. No Contribution to Zone Spreading: Detectors should not contribute to the spreading of chromatographic peaks.
8. Temperature and Flow Rate Insensitivity: Detectors should not be significantly affected by temperature variations or changes in flow rate.

HPLC detectors can be categorized into two main types:

A) Specific HPLC Detectors:

1. Mass Spectroscopic HPLC Detectors: These detectors offer high selectivity and sensitivity. They work based on molecular fragmentation and the mass-to-charge ratio of fragmented molecules.
2. UV/VIS HPLC Detectors: This category includes fixed wavelength detectors, variable wavelength detectors, and diode array detectors. UV-VIS detectors are widely used and respond to compounds with light-absorbing functional groups.
3. Photo Diode Array (PDA) HPLC Detectors: PDA detectors allow simultaneous monitoring of multiple components at different wavelengths, reducing analysis time and solvent use.
4. Fluorescence HPLC Detectors: Fluorescence detectors are highly specific, sensitive, and selective, particularly useful for naturally fluorescent compounds. They include single-wavelength, multi-wavelength, and laser-induced fluorescent detectors.

B) Bulk Property HPLC Detectors:

1. Electrical Conductivity HPLC Detectors: These detectors provide universal and high-sensitivity detection of charged species and surfactants by measuring the conductivity of the mobile phase.
2. Refractive Index HPLC Detectors: Various types of RI detectors are available, based on changes in the refractive index of eluting molecules in the mobile phase. They are used for detecting non-ionic compounds.
3. Electrochemical HPLC Detectors: Electrochemical detectors respond to oxidizable or reducible substances and are sensitive to changes in flow rate or mobile phase composition.
4. Light Scattering HPLC Detectors: Light scattering detectors measure scattered light and are useful for detecting large molecular weight molecules. They come in low-angle and multiple-angle laser light scattering types.

In addition to these, there are other HPLC detectors, such as evaporative light scattering detectors, IR detectors, transport detectors, aerosol-based detectors, chiral detectors, and pulsed amperometric detectors. The choice of detector depends on the specific requirements of the analysis and the nature of the compounds being studied.