Practice Exam - Separations Flashcards
What is a suitable solute for determining void volume in reversed-phase HPLC with UV detection?
A solute with ๐พโ0 and strong absorptivity.
Why is Electron Ionisation (EI) preferred for MS libraries?
EI provides structural-specific fragmentation, aiding compound identification.
Why should MS library matches be used with caution?
Library matches may suggest structures, but spectra arenโt always unique, especially for isomers.
How does using retention indices improve GC-MS analysis?
Retention indices filter possible compounds by retention time, confirming compound identity with MS library.
What are the four main components of an HPLC system?
Pump, injector, column, and detector.
What is the advantage of eluent gradient in HPLC?
It improves resolution, reduces retention time, and speeds up analysis.
Name four ideal characteristics of a detector.
High sensitivity, stability, linear response, short response time.
What is NP-HPLC, and give an example compound analyzed this way.
Non-polar eluent with a polar stationary phase; example: alkylphenylpolyethoxylates.
Why do GC methods have many stationary phase options but limited mobile phase choices?
GC relies on stationary phase variation for selectivity, as the mobile phase remains inert (non-interacting).
Why is formic acid often added before ESI in MS?
It encourages protonation, aiding ionization in positive mode.
What is hard ionisation?
Hard ionization techniques, such as electron ionization (EI), typically result in extensive fragmentation of the analyte molecules, often leading to the absence of intact molecular ions in the mass spectrum. This fragmentation can provide valuable structural information but complicates the interpretation of complex mixtures
What is soft ionisation?
soft ionization methods are designed to minimize fragmentation, allowing for the preservation of molecular ions. These techniques facilitate the identification of a broader range of compounds, particularly those sensitive to fragmentation, by producing fewer fragments and retaining the molecular ion
Choices between hard and soft ionisation?
Soft ionization being preferable for applications requiring molecular integrity and detailed compound identification. For hard, aids in the structural elucidation of complex molecules, high sensitivity and reproducibility, making them suitable for quantitative analyses
