Introducing the MSQ
_______________________________________________ The Source–An Introduction to API Techniques
Source fragmentation is used in both APCI and electrospray to give
structural information.
In general, increasing the voltage applied to the source block (the cone
voltage) yields increasing amounts of fragmentation, depending on the
nature of the compound. The optimum source voltage required to give
the maximum intensity of the protonated or deprotonated molecule is
compound-dependent, as is the source voltage required for
fragmentation. The energies involved in source fragmentation are low,
so usually only weaker bonds such as C-N and C-O are broken.
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Since there are many similarities between electrospray and APCI, there are
many applications common to both.
Compounds suitable for analysis by electrospray are polar and of molecular
weight less than 100,000 amu. The higher molecular weight compounds,
such as proteins, can produce multiply charged ions. As it is the mass-to-
charge ratio (m/z) that is measured by the MS detector, these can often be
seen at lower masses. For example, if the molecular weight is 10,000, a
doubly charged ion (2+ in +ve ion) would be seen at m/z 5001, 10+ at m/z
1001, etc.
Typical electrospray applications are: peptides, proteins, oligonucleotides,
sugars, drugs, steroids, and pesticides.
Compounds suitable for analysis by APCI are generally polar (although less
polar than electrospray) and of molecular weight <1000 amu.
Typical APCI applications are: pesticides, drugs, azo dyes, and steroids.
A summary comparing electrospray and APCI is shown in Table 1-2.
___________________________MSQ Hardware Manual ___________________________
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