Quick questions on Analytical techniques: TCE Chemistry (Tasmania)

Mass spectrometry measures the mass-to-charge ratio ($m/z$) of ions. A sample is vaporised and ionised, often breaking into fragments, and the ions are separated by mass. The peak at the highest $m/z$, the molecular ion peak, gives the molar mass of the original molecule. The pattern of smaller fragment peaks gives structural clues, since particular fragments correspond to particular groups.

Infrared (IR) spectroscopy identifies functional groups. Bonds absorb infrared radiation at characteristic frequencies that make them vibrate, so the wavenumbers at which absorptions occur reveal which bonds are present. A broad absorption around $3200$ to $3550\ \text{cm}^{-1}$ suggests an $\text{O}-\text{H}$ group, while a strong absorption near $1700\ \text{cm}^{-1}$ indicates a carbonyl ($\text{C}=\text{O}$) group. The complex fingerprint region is unique to each compound and confirms identity by comparison with reference spectra.

UV-visible spectroscopy is mainly used for quantitative analysis of coloured solutions. The absorbance at a particular wavelength is proportional to concentration (the Beer-Lambert relationship). By measuring the absorbance of standards of known concentration, you build a calibration curve and read off the concentration of an unknown.

Chromatography separates the components of a mixture by their different affinities for a stationary phase and a mobile phase; components that interact more strongly with the stationary phase move more slowly. In thin-layer and paper chromatography, the retention factor $R_f = \dfrac{\text{distance moved by spot}}{\text{distance moved by solvent front}}$ helps identify components by comparison with standards. High-performance liquid chromatography and gas chromatography give precise separations and can be coupled to a mass spectrometer for both separation and identification.