Chemical Ionisation:

In a mass spectrometer the sample is loaded into the ionisation chamber using a direct insertion probe for solid samples or by controlled flow devices for the gases and heat volatile liquids. Within gas phase ion sources such as electron impact ionisation and chemical Ionisation the sample is first vaporised and then ionised. In the former a high energy beam of electrons passes through the sample and generates a positively charged ion by knocking off an electron from it whereas in the later ion-molecule reactions are used to produce (M+1)⁺  and (M-1)⁺  ions. In fast atom bombardment method - a desorption ion source, the analyte is dissolved in a liquid matrix and bombarded with a beam of fast atoms to generate ions.

The molecular ion and the fragment ions produced from it are directed towards the analyser where these are sorted out on the basis of their m/ z ratio. In magnetic sector analyser which consists of an evacuated curved metallic tube, an electromagnet mounted perpendicular to the tube is used to separate the fragment ions. The separation is achieved by continuously varying the field strength of the electromagnet. In double focussing instruments, an electrostatic area is applied prior to the magnetic sector to achieve better resolution. The ions after being divided according to their m/z ratios are sent to the detector where these generate electrical signal which are digitalised, processed and recorded by the processing and output device. These devices use a number of microprocessors and microcomputers as a large amount of data needs to be handled to generate a mass spectrum. These data systems also involve softwares for quantification, interpretation or identification of the molecules using on-line spectral libraries.

Mass spectrometry finds extensive applications in diverse areas like chemical analysis, biochemistry, environmental pollution monitoring, clinical chemistry, food adulteration, doping in sports, archaeology, many more. The determination of molar mass, molecular formula and structure of the analyte and the identification of the analyte, alone or in a mixture are the most common qualitative applications of the mass spectrometry.