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Which type of electron can be removed most easily from a molecule? Least easily? (Rank them)
- Non bonding (n) electrons are easiest
- pi bonding electrons are middle
- sigma electrons are hardest (highest ionization energy)
Is EI operated at low or high temperatures?
High (150-250C), therefore analyte must be thermally stable
Why does an EI source require regular cleaning?
Low volatility by products may not be removed by the vacuum system, and contaminate the focusing lenses
For CI is there more reagent gas or more analyte gas in the chamber?
Large amount of reagent gas mixed with small amount of sample
Name three common reagent gases for CI
- Methane (for organics, lots of fragmentation)
- isobutane (less common)
- ammonia (for polar and basic compounds, less fragmentation)
Can EI and CI be used for insoluble samples?
Can ESI and APCI be used for thermally unstable (thermally labile) compounds?
Yes, that is an advantage
Is ESI best for polar or non polar compounds?
Polar (must be soluble in polar molecules)
Glycerol, thioglycerol, and nitrobenzylalcohol (NBA) are common matrices for what technique?
FAB fast atom bombardment
Are FAB and MALDI good for quantitation?
No, varies based on sample prep
Which techniques are typically used for huge molecules such as proteins?
FAB and MALDI
Can you use MALDI for low molecular weight samples?
No, there's too much background interferences from the matrix