By pierre on Monday, June 7, 2004 - 08:45 am:

Hello,
I would like to know the reason why the electrospray mass spectrometer is a concentration sensible and not a mass sensible detector.
Thanks in advance

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By RH on Thursday, June 10, 2004 - 10:34 am:

This is due to the mechanism by which ions are
formed. But this mechanism is not yet clear.
There are two main models that describe the
actual ion formation from primary and secondary
droplets, the ion emission model and the charged
residue model. But one things seems to be clear:
The dimension of the primary droplets is
dependent on the concentration of analyte in the
spray solution.

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By A.Mouse on Thursday, June 10, 2004 - 07:26 pm:

RH: Many thanks, this is one of the best answers I heard on this. Are there any publications to read that support this?

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By Anonymous on Friday, June 11, 2004 - 12:29 am:

There is also another theory that says that the ion formation is a redox process that happens in the capillary tip (and redox processes are concentration depedent). This is off course an explanation for the ESI technique. APCI is amount dependent.
literature:

on spray mass spectrometric detection for liquid chromatography: a concentration- or a mass-flow-sensitive device? Hopfgartner, Gerard; Bean, Karen; Henion, Jack; Henry, Richard. Drug Testing and Toxicology, New York State College of Veterinary Medicine, Cornell University, 925 Warren Drive, Ithaca, NY, USA. Journal of Chromatography (1993), 647(1), 51-61. CODEN: JOCRAM ISSN: 0021-9673. Journal written in English. CAN 119:285520 AN 1993:685520 CAPLUS

Abstract

As the mass spectrometer becomes more accepted as a detector for HPLC, its characteristics should become better understood by those performing routine LC-MS expts. In particular, the ion current response for quant. anal. studies involving significant dynamic range in concn. for target analytes must be detd. as well as other factors that affect MS response. This work describes the concn.-sensitive response for the ion spray (pneumatically-assisted electrospray) LC-MS interface from the chromatographer's perspective. A comparison of LC-MS ion current response in the isocratic mode resulting from studies of a synthetic mixt. contg. alkyl benzoates is presented. LC-MS total ion current chromatograms from three different column sizes (1 mm internal diam., 2.1 mm internal diam. and 4.6 mm internal diam.) with and without a post-column split, and high-flow ion spray LC-MS without a post-column split illustrates that the former behaves as a concn.-sensitive detector whereas the latter behaves as a mass-flow-sensitive detector. The flexibility of ion spray to high-flow applications allows the use of HPLC eluent flow ranging from 0.001-2.0 mL/min. The use of solvent-buffer post-column addn. also allows optimization for improved analyte ion current response.

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By A.Mouse on Friday, June 11, 2004 - 02:19 pm:

Thank you

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By RH on Friday, June 25, 2004 - 12:29 pm:

Sorry, a little late, I was a little busy.....

A.P. Bruins, Mechanistic aspects of electrospray
ionization, J. Chromatogr. A. [794] (1998)
345-357.
P. Kerbarle, L.Tang, From ions in solution to
ions in the gas phase, Anal. Chem. [65] (1993)
972A-986A.
S.J. Gaskell, Electrospray: Principles and
Practice, J. Mass Spectrom. [32] (1997) 677-688.