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VICChemistryQuick questions
Unit 1: How can the diversity of materials be explained?
Quick questions on Mass spectrometry as an analytical technique: VCE Chemistry Unit 1
9short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.
What is why mass spectrometry matters?Show answer
Mass spectrometry (MS) is one of the most powerful tools in analytical chemistry. It can:
What is inside the instrument?Show answer
1. Ionisation. A gaseous sample is bombarded with high-energy electrons (electron impact). Each collision knocks an electron off a sample molecule, producing a positive ion (the molecular ion $M^{+}$) and sometimes splitting it into smaller cations and neutral fragments. 2.
What is isotope patterns to know?Show answer
These patterns are diagnostic. Seeing a 3:1 doublet of peaks two units apart almost certainly means a chlorine atom is in the molecule.
What is fragmentation?Show answer
When a molecule is ionised, the molecular ion is excited and often falls apart along its weakest bond. The pieces include:
What is calling the y-axis the mass?Show answer
The y-axis is relative abundance. The mass-to-charge ratio is the x-axis.
What is assuming the base peak is always $M^{+}$?Show answer
It often is not. The base peak is just the most abundant ion. For propan-1-ol the base peak is $C_3H_7^{+}$ at 43, not $M^{+}$ at 60.
What is forgetting that neutral fragments are invisible?Show answer
A fragment of mass 17 lost as a neutral $OH$ does not appear on the spectrum; only the surviving cation at $M - 17$ shows up.
What is counting carbon atoms by the absolute height of $M+1$?Show answer
Use the ratio $M+1 / M$, not the raw height.
What is confusing m/z with mass for multiply charged ions?Show answer
At Unit 1 level almost all ions are +1, so m/z equals the mass; for +2 ions m/z would be half the mass. Worth noting but rare.