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Instrumental Analysis ACS Exam Questions and Answers 100% Correct
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Instrumental Analysis ACS Exam Questions and Answers 100% CorrectInstrumental Analysis ACS Exam Questions and Answers 100% CorrectInstrumental Analysis ACS Exam Questions and Answers 100% CorrectInstrumental Analysis ACS Exam Questions and Answers 100% Correct How to calculate signal to noise - AN...

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  • November 15, 2024
  • 5
  • 2024/2025
  • Exam (elaborations)
  • Questions & answers

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  • instrumental analysis acs exam questions and answe
  • instrumental analysis acs exam answers
  • how to calculate signal to noise answer sn me

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Instrumental Analysis ACS Exam
Questions and Answers 100% Correct
How to calculate signal to noise - ANSWER-S/N = mean/STDEV

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

S/N relationships - ANSWER--increase S/N, increase run time
-decrease noise, increase S/N

Beer's Law - ANSWER-

Beer's Law Calculations - ANSWER-

Potentiometry - ANSWER-the use of electrodes to measure voltages that provide
chemical information

Coulometry - ANSWER-a technique in which the quantity of analyte is determined by
measuring the number of coulombs needed for complete electrolysis

Voltammetry - ANSWER-an analytical method in which the relation between current and
voltage is observed during an electrochemical reaction

How does changing flow rate affect retention time? (HPLC) - ANSWER--a high flow rate
reduces retention times

Hard ionization vs soft ionization - ANSWER--hard: no M+ peak (or small)
-soft: M+ peak is visible

MS: hard ionization sources - ANSWER--impart high quantities of residual energy in the
subject molecule invoking large degrees of fragmentation

MS: hard ionization sources examples - ANSWER--electron impact

Electron Impact (EI) - ANSWER--Uses electron impact to ionize a molecule
-gas phase
-energetic electrons
-possibility of over fragmentation
-hard
-most common

, EI advantages - ANSWER--good stability
-universal ionization
-reproducible spectra

EI disadvantages - ANSWER--MW can be hard to determine
-compatible only with volatiles (GCMS)
-Hard to make negative ions

MS: soft ionization sources - ANSWER--processes which impart little residual energy
onto the subject molecule and as such result in little fragmentation

MS: soft ionization sources examples - ANSWER--CI
-ESI
-MALDI

Chemical ionization (CI) - ANSWER--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

fragmentation in CI - ANSWER--occurs if enough excess energy after the ionization of
the analyte

CI advantages - ANSWER--MW info more readily available
-fewer fragments
-control specificity

CI disadvantages - ANSWER--fragments not very reproducible
-compatible only with volatiles (GCMS)

Electrospray ionization (ESI) - ANSWER--multiple charged ions
-can make positive or negative ions by taking on hydrogens or removing hydrogens

MALDI abreviation - ANSWER-Matrix assisted-laser desorption ionization

MALDI Theory - ANSWER--non-volatile ionization
-don't want fragmentation
-TOF
-absorption of laser beam by matrix
-transfer energy form matrix to analyte
-desorption of both matrix and analyte
-transfer of proton to analyte from matrix
-large MW

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