Instrumental Analysis ACS Exam 2023

Instrumental Analysis ACS Exam 2023

1). How to calculate signal to noise

 Ans: S/N = mean/STDEV

-inverse of RSD
-STDEV: 5 (#STDEV gaussian curve)
-STDEV: peak-to-peak noise/5


2). S/n relationships

 Ans: -increase S/N, increase run time
-decrease noise, increase S/N


3). Beer's law

 Ans:


4). Beer's law calculations

 Ans:


5). Hard ionization vs soft ionization

 Ans: -hard: no M+ peak (or small)
-soft: M+ peak is visible


6). Ms: hard ionization sources

 Ans: -impart high quantities of residual energy in the subject molecule invoking large
degrees of fragmentation


7). Ms: hard ionization sources examples

 Ans: -electron impact



Electron impact (ei)


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, 8).
 Ans: -Uses electron impact to ionize a molecule
-gas phase
-energetic electrons
-possibility of over fragmentation
-hard
-most common


9). Ei advantages

 Ans: -good stability
-universal ionization
-reproducible spectra


10). Ei disadvantages

 Ans: -MW can be hard to determine
-compatible only with volatiles (GCMS)
-Hard to make negative ions


11). Ms: soft ionization sources

 Ans: -processes which impart little residual energy onto the subject molecule and as
such result in little fragmentation


12). Ms: soft ionization sources examples

 Ans: -CI
-ESI
-MALDI


13). Chemical ionization (ci)

 Ans: -First ionizes a molecular gas which in turn ionizes the molecule of interest. A
"gentler" method of ionization.
-soft
-electron beam creates ions
-proton transfer between reagent gas and the analyte
-gives MW and MW+1 or MW-1


14). Fragmentation in ci




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