When it comes to liquid chromatography there are numerous choices available for the detection of your analyte, but which of these offers the greatest sensitivity, is most suitable for your particular application(s) and most affordable? In this article I will briefly outline the choices of (U)HPLC detectors available, their pros and cons, and provide some sources for further information.
UV-Vis Absorption Detectors – These are the most commonly used detectors in liquid chromatography and can be used to detect a broad range of analytes across many application areas. There are also different types of UV-Vis absorption detectors: Diode Array Detectors (DAD) offer high levels of sensitivity and a near-uniform response whilst Variable Wavelength Detectors (VWD) deliver great linearity and robustness for routine use. For example, if you are analyzing trace impurities I would suggest a DAD, whilst for routine QC procedures a VWD would potentially be a better option.
This application note is a good example of the sensitivity afforded by a DAD using LightPipe™ technology to further enhance sensitivity.
Flourescence Detection – Such detectors are one of the most sensitive, offering sensitivities three to six orders of magnitude higher than UV-Vis. Modern fluorescent detectors also allow the monitoring of multiple excitation/emission wavelength pairs simultaneously.
You can watch an overview of fluorescence detection for HPLC in this whiteboard video.
Electrochemical Detectors – These detectors are typically used for the sensitive and selective detection of compounds in complex matrices that undergo oxidation or reduction, such as neurotransmitters. Used with amperometric cells for high sensitivity, low sample volumes, and coulometric sensors to maximize both selectivity and sensitivity.
Refractive Index Detectors – The often forgotten detector! It works by measuring the difference between the refractive index of the mobile phase and the deflection of the sample using Snell’s Law. Its application areas include where compounds lack chromophores and in sugar and polymer detection.
Charged Aerosol Detection – This detector, frequently abbreviated to CAD, offers universal detection with a near-uniform response, meaning that it can be used for a wide range of analytes that do not contain a chromophore or fluorophore, and can be used for relative quantitation without the use of reference standards.
Mass Spectrometry – Not always considered a detector but more of a separate instrument, the mass spectrometer offers both detection and identification with the ability to use different liquid chromatography flow rates (nano, micro, capillary and analytical).
Pros: High sensitivity, wide compound detection range and identification
Cons: Expensive and generally not as intuitive as other detectors
Conductivity and pH Monitors – These are not for the detection of analytes but for monitoring pH and conductivity as the name suggests. These are useful for monitoring salt and pH gradients and are mostly used in biopharmaceutical separations.
As you can see, there are many options when it comes to (U)HPLC detectors, with each having its unique capabilities and applications. Which one is most suited to your needs is dependent on a number of factors such as application, analyte(s), budget, and ease of use. In many instances, it may be appropriate to combine different detectors to get a comprehensive understanding of the sample.
HDI section image for Vanquish Flex UHPLC System, 230×195
We recently conducted a five-part webinar series dedicated to HPLC detectors, overviewing the various types of detectors, mechanisms of operation, which detector to choose for particular applications and tips and tricks. Please visit thermofisher.com/lc-webinars to view these on-demand.
Learn more about the various types of detectors on this informative webpage, with links to the specific detector types.
Dr. Timothy Cross is a Senior Manager of Regional Marketing in EMEA for the Chromatography and Mass Spectrometry division at Thermo Fisher Scientific. He holds a Ph.D. and M.Sc. in Immunology and a B.Sc. in Biological Sciences, with professional experience in proteomics R&D before embarking on a career in marketing. He has over 20 years’ experience in both life and analytical science marketing management across a broad range of channels. He is passionate with writing about science to make it accessible to all and offering educational content to help scientists make informed decisions. In his spare time, Tim is a (very) keen runner and with a background in immunology is fascinated with how exercise impacts the immune system.
