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Sedex Vs CoronaTM Discharge detectors technology comparison

 

A novel detection technique for HPLC has just appeared on the market: forgetting all marketing statements, what can we expect from such device?

Trying to competing ELSD or CLND, even Mass spectrometry, CoronaTM discharge detector is promoted to be a "revolution" in HPLC detection systems. This device is well described in some patents, and some preliminary results are extensively shown in marketing materials.
This new technology uses a five step process:

  • A nebulization
  • An evaporation
  • A Corona discharge
  • A charge "filtration"
  • A detection

    What about Sensitivity?
    The first example shown is a carbohydrate separation. The conditions are not described so that it is difficult to do a real comparison between detectors.
    However, in the particular case of carbohydrates,

  • CLND is not the detector of choice since only nitrogen-containing compounds can be detected.
  • Mass Spectrometry may allow the detection of such compound with a fairly good sensitivity (below 1 ng).
  • RID may be a good alternative, if the system is not based on a gradient elution. In addition, the sensitivity may appear poor.
  • LT-ELSD is still the best choice for this application : a comparable system has been set up, and using a gradient system, the LOD (Signal to Noise ratio = 3) was found to be barely 2.5 ng on column.
    Comparing LT-ELSD and the CoronaTM discharge detector: we observe that the sensitivity is quite close. Looking to the performance/price ratio, the corona detector is about 2 times more expensive than the most performing LT-ELSD.

    What about the Applicability?
    The example of the applicability is shown in the marketing material: it is clearly shown that semi volatile solutes (i.e Natphtol) can't be detected. This phenomenon is common with high Temperature ELSDs. With LT-ELSD from SEDERE, even semi volatile compounds are detected: ethylene glycol (ebullition point 182°C - commonly analyzed by gas chromatography) detection has been reported to be approximatively 13ng (LC-GC North America, Application Note September 2004 Issue).

    Dynamic range of Sedex Model 85 ELS detector

    Dynamic Range
    An indication is shown about the dynamic range of CoronaTM discharge detectors. The value of dynamic range appears really high: about 10000, or 4 orders of magnitude (104).
    SEDEX detectors provide a gain control which is a very convenient way to manage higher dynamic range: if the dynamic range at one value of gain is about 2500, using the gain switching (for example with our software, or manually), you can increase the dynamic range up to 30000 (3.104) In addition, with SEDEX LT-ELSD, within one or two decades, fairly acceptable (r> 0.999) linear correlation coefficients can be observed (LC-GC International, March 1996 Issue).

    Reproducibility
    The reproducibility of CoronaTM discharge detector is claimed to be 2% : this is also true for SEDEX LT-ELSD 85

    Conclusion
    This new detector is available at a relative high price compares to LT-ELSD. Considering the poor performances and the non universal detection type, users may not shift to such a detection.

    "Corona" is trademarked by ESA Biosciences, Inc.