Brief description of MSD

Mass spectrometry (MS) – which may be coupled to both GC and HPLC – is an extensively used technique in environmental analysis of organics. The widespread use of this technique arises from its unique capability to provide qualitative and quantitative information on the

1. chemical structures,
2. the relative and absolute concentrations, and, in the case of isotope selective instruments,
3. the isotopic compositions of organic compounds in environmental sample.
   MS is hence both highly sensitive and selective.

Detection by MS does not rely on the absorption or release of electromagnetic radiation. MS is hence, strictly speaking, not a 'true' spectroscopic technique. The name originates from times in which MS data were collected photometrically, which resulted in 'lines' resembling lines in optical spectra. So how are analytes detected in a MS?

In brief, organic analytes are converted into ions, which are detected after being separated according to their mass-to-charge ratio in an electromagnetic field (i.e., ions of identical charge but different atomic masses may be differentiated and vice versa). Standard MS instruments used in organic trace analysis contain the following sequentially operating components (see Figure 63 in the script):

1. An inlet system for the analytes,
2. an ionization unit that forms ions from the analyte molecules − typically by bombarding them with electrons, photons, ions, or molecules − ,
3. a mass analyzer in which the ions are accelerated and dispersed according to their mass-to-charge ratio by an electric and/or magnetic field, and
4. an ion detector that records the relative abundance of ions.

Components (2) to (4) are operated under vacuum (i.e., 10 ^-4 to 10 ^-8 Torr). For more details, please refer to chapter XI.3.6 in the script.