Ethanol, contracted spectrum

Figure 7. Absolute abundances of ethanol contracted spectrum reduced so that no ions are greater than the lowest relative abundance ion in contracted spectrum of mixture. Contaminated ions are identified as those ions of the mixture that exceed the relative intensities of the attenuated ethanol pattern (plus the prescribed window tolerance).

If the abundances of the entire ethanol contracted spectrum are lowered — keeping their relative heights the same as in the reference spectrum — a point is reached where none of the unknown ions is of lower abundance than the corresponding ethanol peaks. In the example shown in Figure 7, this occurs when the mass 46 ions become the same height. If a measurement reproducibility of 20% is assumed, two other ions (m/e 43 and 45) are found to agree with the abundances required by the ethanol reference spectrum because they fall within the prescribed tolerance window. In this example, the mixture was about 50% ethanol the excess intensities at m/e 31 and 32 were due to methanol and the excess intensity at m/e 44 was due to the additional presence of CO2. 

Figure 6. Same six-ion contracted spectrum as Figure 5 for unknown mixture (solid lines) superimposed on ethanol spectrum (bars)...

PBM analysis may be clarified by a simple example. Figure 5 shows the values of m/e and the relative abundances found when a 6-ion contracted spectrum of pure ethanol is scanned. In Figure 6, the same contracted spectrum of an unknown mixture (solid vertical lines) has been measured, and is compared with the... 

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