Topic 7 - Modern Analytical Techniques

• Mass spectrometry is an analytical technique used to identify different isotopes and find the overall relative atomic mass of an element.
• The mass spectrum of an element is a graph with a small number of vertical 'peaks', each which represents a different isotope.
• The molecular ion peak is the peak furthest to the right on a mass spectrum (has the highest m/z value).
• The m/z value of the molecular ion peak indicates the relative molecular mass of the compound.
• The M+1 peak is illustrated as a small vertical line to the right of the molecular ion peak, and represents the natural presence of a carbon-13 isotope.
• Peaks with smaller m/z values than the molecular ion peak result from fragmentation in the mass spectrometer. Fragmentation can explain why there are such large numbers of peaks in some mass spectra.
• The tallest peak on a mass spectrum is known as the base peak, and represents the ion of an element with the highest natural abundance.
• The relative atomic mass (Ar) of an element can be calculated by multiplying each m/z by its abundance, then dividing by the total abundance of all species present.
• A mass spectrum is measured via relative intensity (y axis) against m/z ratio (x axis).