ChemistryChapter 12: Analytical Chemistry
Mass Spectrometry
Mass spectrometry (MS) ionises sample molecules, accelerates ions, separates them by mass-to-charge (m/z) in electric/magnetic fields, and d
Learning objectives
- Explain mass spectrometry in clear and easy chemistry language.
- Use the important definitions, equations, examples, and conditions correctly.
- Apply the idea in an FBISE-style question and avoid the common exam mistake.
Definition
Mass spectrometry (MS) ionises sample molecules, accelerates ions, separates them by mass-to-charge (mz) in electric/magnetic fields, and detects the pattern. School steps often listed: vaporisation, ionisation (positive ions), acceleration, deflection/separation, detection. The spectrum gives the molecular ion (related to molecular mass) and fragment ions that help structure. MS also determines relative isotopic masses and isotopic abundances because isotopes appear at different mz with intensity ratios. Forensic and research labs rely on MS with other methods for unknown identification.
Important terms
- MASS SPECTROMETRY
- Mass spectrometry (MS) ionises sample molecules, accelerates ions, separates them by mass-to-charge (m/z) in electric/magnetic fields, and detects the pattern.
- HOW AN MS WORKS
- Vacuum system; ion source; analyser; detector.
- INFORMATION FROM MS
- Relative molecular mass, fragment pattern, isotope ratios.
Overview
Instrument path, then uses:
How An Ms Works
Vacuum system; ion source; analyser; detector. Figure 24.12 style block diagram is common in exams. Only ions are steered by fields.
Examples Electron ionisation idea · Magnetic sector deflection · Detector current vs m/z · Molecular ion peak
Information From Ms
Relative molecular mass, fragment pattern, isotope ratios. Combine with IR/NMR for full structure.
Examples Isotopic mass determination · Abundance percentages · Forensic unknown · Purity / formula support
Core idea — MASS SPECTROMETRY
Mass spectrometry (MS) ionises sample molecules, accelerates ions, separates them by mass-to-charge (mz) in electric/magnetic fields, and detects the pattern. School steps often listed: vaporisation, ionisation (positive ions), acceleration, deflection/separation, detection. The spectrum gives the molecular ion (related to molecular mass) and fragment ions that help structure. MS also determines relative isotopic masses and isotopic abundances because isotopes appear at different mz with intensity ratios. Forensic and research labs rely on MS with other methods for unknown identification.
1. How An Ms Works
Vacuum system; ion source; analyser; detector. Figure 24.12 style block diagram is common in exams. Only ions are steered by fields. Examples: Electron ionisation idea; Magnetic sector deflection; Detector current vs mz; Molecular ion peak.
2. Information From Ms
Relative molecular mass, fragment pattern, isotope ratios. Combine with IR/NMR for full structure. Examples: Isotopic mass determination; Abundance percentages; Forensic unknown; Purity / formula support.
Worked method and exam use
MS pathway: vaporise → ionise → accelerate → separate by mz → detect. Gives mass, fragments, isotope info.
Explanation
MS pathway: vaporise → ionise → accelerate → separate by mz → detect. Gives mass, fragments, isotope info.
In simple words
List the MS stages in order for process marks.
Key points
- ionise · accelerate · separate · detect
- mz spectrum
- isotopes and fragments
- four process words
- ions not neutrals
Exam preparation
Exam Focus
Quick revision
Revision Zone
Review the key facts, formulas and checks before you move on.Mass Spectrometry
Sticky Notes · Quick Revision
Core idea
- Mass spectrometry (MS) ionises sample molecules, accelerates ions, separates them by mass-to-charge (mz) in electric/magnetic fields, and detects the pattern. School steps often listed: vaporisation, ionisation (positive ions), acceleration, deflection/separation, detection. The spectrum gives the molecular ion (related to molecular mass) and fragment ions that help structure. MS also determines relative isotopic masses and isotopic abundances because isotopes appear at different mz with intensity ratios. Forensic and research labs rely on MS with other methods for unknown identification.
How An Ms Works
- Vacuum system; ion source; analyser; detector. Figure 24.12 style block diagram is common in exams. Only ions are steered by fields.
Information From Ms
- Relative molecular mass, fragment pattern, isotope ratios. Combine with IR/NMR for full structure.
Worked method
- MS pathway: vaporise → ionise → accelerate → separate by mz → detect.
- Gives mass, fragments, isotope info.
Common misconception
- List the MS stages in order for process marks.
FBISE exam check
- In an exam answer, include these key points: ionise · accelerate · separate · detect; mz spectrum.
- Check: mz meaning.
60-second revision
- Mass spectrometry (MS) ionises sample molecules, accelerates ions, separates them by mass-to-charge (mz) in electric/magnetic fields, and detects the pattern.
- How An Ms Works: Vacuum system; ion source; analyser; detector.
- Information From Ms: Relative molecular mass, fragment pattern, isotope ratios.
- Exam reminder: List the MS stages in order for process marks.
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