44
May/June 2011
Water Condensation Nucleation … a Universal detection technique opening up new HPLC applications
Eddie Goodall, Dorton Analytical Limited • Tel: (0)7872 520670 •
www.dortonanalytical.co.uk Introduction
Water Condensation Nucleation (or Water Condensation Particle Counting) is a technology originally developed to detect aerosol particles in the application field of environmental monitoring. Using this technique air was drawn through an instrument and any particles counted to produce a global particle count for the environment.
By introducing a liquid stream rather than a gas flow the technology has been now been refined for use in Liquid Chromatography. Since Water Condensation Nucleation requires no knowledge of chemical structure to detect compounds it has found use in the area of universal detection. This article was written to demonstrate how the Water Condensation Nucleation technique has been developed into a LC detector with the ability to detect sub-nanogram levels that operates with a superior linear response over a wide dynamic range (3-4 orders of magnitude) and offers near universal detection for compounds that are less volatile than the mobile phase.
What is universal detection? ‘Universal detection in Liquid Chromatography’ is the ability to detect compounds eluting through an LC system without the need to use any of the chemical structure of a molecule for detection – typical of these types of detector are UV, fluorescence, mass spectroscopy and electrochemical.
The ‘original’ universal detector was refractive index, although used in many applications its limitations were lack of sensitivity and could only be used with isocratic mobile phases.
The need to enhance sensitivity of universal detection lead first to the development of the evaporative light scattering detector (ELSD), then the charged aerosol detector (CAD) and now the Water Condensation Particle Counter (WCPC).
Water Condensation Nucleation Water condensation nucleation is a technique where particles are grown to a size in which they can be individually detected and counted. Particles are grown by exposing them to a chamber of water saturated air. This causes water to condense on the surface of the particle much like water will condense on a cold drinks can sitting outside on a hot day. The result is a dry particle with a shell of water around it. This particle is much larger than the
Figure 1: CPC Efficiency Detection Curve
Figure 2: WCPC Particle Counting
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