# Introduction to analytical chemistry

> CIE A-Level Chemistry · 9701
> Source: https://www.owlsprep.com/study/cie-9701-u16-overview/
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This unit introduces core analytical techniques used to separate mixtures, identify unknown compounds, and determine molecular structure. These methods are foundational for modern chemistry, from synthesis to environmental testing.

**Prerequisites:** Understanding of atomic structure and chemical bonding; Knowledge of common organic functional groups

## Learning objectives

- Understand the underlying principles of three core analytical chemistry techniques: mass spectrometry, infrared spectroscopy, and chromatography
- Interpret data from each technique to identify compounds, molecular formulas, and functional groups
- Calculate standard values from raw analytical experimental data

## Unit at a glance

This unit moves beyond traditional physical property testing to the instrumental and experimental analytical methods used in modern chemistry. You will learn three core techniques in sequence, each building on your understanding of molecular properties to solve compound identification problems.

All sub-topics in this unit are listed below:
- [Mass spectrometry](https://www.owlsprep.com/study/cie-9701-u16-mass-spectrometry/) — Learn how mass spectrometry calculates molecular mass and identifies molecular formulas of compounds.
- [Infra-red spectroscopy](https://www.owlsprep.com/study/cie-9701-u16-infra-red-spectroscopy/) — Understand how IR absorption is used to identify common functional groups in organic molecules.
- [Chromatography basics](https://www.owlsprep.com/study/cie-9701-u16-chromatography-basics/) — Explore mixture separation principles and calculate Rf values to identify mixture components.

## Common pitfalls

- **Wrong:** Confusing the molecular ion peak with the base peak in mass spectrometry.
  - Why it fails: The highest intensity peak is not always the peak corresponding to the full molecule's mass.
  - Correct: The molecular ion peak is the peak with the highest significant m/z value (ignoring small isotope peaks).
- **Wrong:** Assigning any IR absorption to a functional group without checking the wavenumber range.
  - Why it fails: All bonds absorb IR, but only specific ranges correspond to characteristic functional group absorptions.
  - Correct: Always cross-reference your observed peak against the standard wavenumber table for assignments.

## Cheatsheet

| Key Concept / Formula | Summary |
| --- | --- |
| Molecular ion peak ($M^+$) | Gives the relative molecular mass of the analyte compound |
| Base peak (mass spectrometry) | The peak with 100% relative intensity, the most abundant fragment ion |
| IR absorption principle | Bond vibration absorbs specific IR wavenumbers unique to each bond type |
| $R_f$ value (chromatography) | $R_f = \frac{\text{distance moved by solute}}{\text{distance moved by solvent front}}$ |
| Stationary phase | Retains solutes via adsorption or partitioning, enabling mixture separation |

## What's next

Begin this unit by studying the first core technique, mass spectrometry, to learn how it is used to find molecular mass. Once you complete all three sub-topics in this unit, you can move on to the next unit covering organic synthesis.

- [Mass spectrometry](https://www.owlsprep.com/study/cie-9701-u16-mass-spectrometry/)
- [Infra-red Spectroscopy](https://www.owlsprep.com/study/cie-9701-u16-infra-red-spectroscopy/)
- [Chromatography basics](https://www.owlsprep.com/study/cie-9701-u16-chromatography-basics/)

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