Thermo Scientific HESI-II Probe, Руководство пользователя

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1
Introduction
Thermo Scientific HESI-II Probe User Guide 3
Figure 2. H-ESI process in the positive ion polarity mode
You can use the HESI-II probe in either positive or negative ion polarity mode. The ion
polarity mode of choice is determined by the polarity of the preformed ions in solution:
Acidic molecules form negative ions in solution, and basic molecules form positive ions.
Because the ejection of sample ions from droplets is facilitated when the ionic charge and
surface charge of the droplet have the same polarity, use the positive ion polarity mode to
analyze positive ions and the negative ion polarity mode to analyze negative ions.
Sample ions can carry a single charge or multiple charges. The number of charges carried by
the sample ion depends on the structure of the analyte of interest and the carrier solvent.
(In H-ESI, the buffer and the buffer strength both have a noticeable effect on sensitivity, so it
is important to choose these variables correctly.) In the case of higher molecular weight
proteins or peptides, the resulting mass spectrum consists typically of a series of peaks
corresponding to a distribution of multiply charged analyte ions.
Droplet size, surface charge, liquid surface tension, solvent volatility, and ion solvation
strength are factors that affect the H-ESI process. Large droplets with high surface tension,
low volatility, strong ion solvation, low surface charge, and high conductivity prevent good
electrospray.
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Charged
droplet
Solvent
evaporates
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Ejected
positive ions
Ion transfer
tube
HESI-II probe
nozzle