Charged Aerosol DetectionI recently received a notification on a recently released poster note (presented at the 2014 AOAC Conference) exploring the fundamental differences between Charged Aerosol Detection (CAD) and Evaporative Light Scattering Detection (ELSD) (link to article) and thought it would make an excellent read for those chromatographers wishing to learn more about these two detection techniques.

As stated in the email, both detection techniques share some similarities in that mobile phase exiting the column is first nebulized and then dried to form analyte particles, the mechanism by which these techniques measure analyte mass differ markedly and this has major impact on analytical performance. Poster Note, Charged Aerosol Detection and Evaporative Light Scattering Detection – Fundamental Differences Affecting Analytical Performance, (downloadable PDF) explores these differences and, using comparative data, explains why CAD shows superior analytical performance when compared to ELSD including lower limits of detection, wider linear dynamic range, decreased inter-analyte response variability, and better precision.

Scientists from our Chelmsford Center of Excellence (USA) used several different isocratic and gradient HPLC methods to evaluate the two detectors; they also used one of our rapid-separation HPLC systems (Thermo Scientific Dionex UltiMate 3000 RSLC system) equipped with our latest Charged Aerosol Detector (Thermo Scientific Dionex Corona Veo Charged Aerosol Detector) and an ELSD (Sedex 90LT Evaporative Light Scattering Detector). One of our reversed-phase HPLC columns (Thermo Scientific Acclaim 120 C18 column) was used in the experiment.

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As per their conclusions:

  • Both CAD and ELSD are non-linear. The limits of detection cannot be extrapolated from the response of high levels of analyte but can only be determined through the generation of calibration curves.
  • The sigmoidal response of ELSD results in a small dynamic range. The analytesignal rapidly decreases and completely disappears as the amount of analyte decreases.
  • CAD performs better for the measurement of low levels of analytes, and has a wide dynamic range of four orders of magnitude. Furthermore, CAD is affected much less by an analyte’s physicochemical properties.
  • CAD uses a single nebulizer to address a wide flow rate range while ELSD requires multiple nebulizers adding to expense and downtime.

Additional Resources

  • Our Chromatography Solution Online Center features many useful and complimentary chromatography tools which can help speed up your analysis. The site is updated on a monthly basis; therefore, do check out the Archives section to see what was previously featured.

Let us know if you have any questions on the expertiment featured in this post using the Comments box below. We look forward to hearing from you.