LC/MS and the Cone Wash
____________________________________________________________________LC/MS Considerations
Other Additives
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Trifluoroacetic acid (TFA)
This is frequently used for peptide and protein analysis. High levels,
>0.1% v/v, can cause suppression of sensitivity in positive ion mode. TFA
may completely suppress ionization in negative ion mode.
Triethylamine (TEA)
This may suppress the ionization of less basic compounds in positive ion
mode (as it also is readily ionized to give a [M+H]
+
ion at m/z 102). TEA
enhances ionization of other compounds in negative ion mode because it is
basic. This is a particularly useful additive for the analysis of nucleic acids.
Tetrahydrofuran (THF)
In ESI, use of THF can reduce sensitivity. This effect can be counteracted
by post-column addition of ammonium acetate. It has no effect in APCI.
Caution.
Do not use a concentration of THF greater than 5% with PEEK
tubing. THF causes swelling in the PEEK tubing and consequently presents
a risk of the LC tubing bursting.
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Inorganic acids
Inorganic acids (for example, sulfuric acid or phosphoric acid) can be used.
Check the suitability of the LC column to low pHs.
Caution.
After using phosphoric acid, thoroughly clean the source, source
enclosure, and hexapole RF lens to minimize the physical damage.
____________________________MSQ Hardware Manual ____________________________
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