Final for che 215

20

What is a Mass spectrometry?

A technique for studying the masses of atoms or molecules or fragments of molecules

What does a mass spectrometer measure in units?

It measures the mass‑to‑charge ratio (m/z) of ions.

What are two major uses of mass spectrometry?

Identifying unknown compounds and obtaining structural/isotopic information.

What are the main components of a mass spectrometer?

Ion source > mass analyzer > ion detector> data analysis

How Does Mass Spectrometry Work?

1. Sample in → gas phase

   1. The analyte must enter the instrument (the vacuum) in the gas phase

   2. for HPLC

2. Ionization → molecules become charged\

3. Mass analyzer → ions separated by m/z

   1. Once ions are formed, they are sorted by their mass‑to‑charge ratio (m/z).

4. Detector → ions counted

   1. Separated ions hit a detector that converts ion impacts into an electrical signal.

5. Spectrum → m/z vs. abundance

   1. Spectral output = ion abundance vs. mass to charge ratio

What does an MS spectrum plot?

Ion abundance vs. m/z.

Why can MS analyze chemically complex samples?

Because ions are separated by m/z, allowing mixtures to be resolved

What are isobaric molecules?

Different structures that have the same mass

What is tandem MS (MS/MS)?

Multiple stages of ion fragmentation and mass analysis for structural information

What does high‑resolution MS allow you to do?

Distinguish molecules with very similar masses by providing accurate m/z values.

Which atomic analysis method has the lowest detection limits?

ICP‑MS (Inductively Coupled Plasma Mass Spectrometry).

What is the linear range of ICP‑MS?

Up to 10⁸

What ionization method is used in GC‑MS?

Electron Ionization (EI).

What ionization method is commonly used in LC‑MS or CE‑MS?

Electrospray Ionization (ESI)

What is the Taylor cone?

The charged droplet formation point in ESI.

Is ESI a soft or hard ionization method?

Soft — produces little fragmentation.

What is DESI used for?

Ambient ionization directly from surfaces with no sample prep

What is the main advantage of ambient ionization methods like DESI and PSI?

They allow rapid, direct analysis with minimal preparation.

What does ICP‑MS analyze?

Elements with extremely low detection limits

Why is high‑resolution MS needed for molecules like C₆H₁₂, C₅H₈O, and C₄H₄N₂?

They have nearly identical masses, so only high‑accuracy m/z can differentiate them.

What does EI typically produce?

Fragmented ions, because it is a hard ionization method.

What does ESI allow you to analyze that EI cannot?

Large, non‑volatile, thermally sensitive biomolecules in solution.

How do you ionize analytes in solution?

Module 1