Mass spectrometry — Chemistry, 14–17
Mass spectrometry identifies particles by measuring their mass-to-charge ratio. A spectrum can reveal isotopes, molecular masses and fragments, giving evidence about what a sample contains.
A weighing machine for ions
In a mass spectrometer, particles are turned into ions and moved through electric or magnetic fields. The instrument separates them according to mass-to-charge ratio, written m/z. The result is a spectrum: peaks show which ion values were detected and how abundant they were.
Why use mass spectra?
A clear liquid or powder may contain several substances that look alike. Chemists needed a sensitive way to identify tiny amounts and distinguish isotopes or related molecules. A mass spectrum provides a pattern of measured evidence, rather than relying only on colour, smell or a label.
Reading the spectrum of chlorine
Chlorine has two common isotopes: chlorine-35 and chlorine-37. A mass spectrum therefore shows peaks at m/z 35 and 37. If the peak at 35 is about three times as high as the peak at 37, that matches their natural abundances and supports the identification of chlorine atoms.
m/z is not always the mass
It is natural to read m/z as simply the mass, because many ions have a charge of +1. But the instrument measures mass divided by charge. An ion with mass 40 and charge +2 appears at m/z 20, so check the charge before naming the particle.
Finding substances in real samples
Forensic scientists can compare a sample’s mass spectrum with reference spectra to identify drugs, poisons or explosive residues. Environmental laboratories use the same principle to detect pollutants in water or air, often after separating a complex mixture first.
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