Electro-spray ionisation (ESI) source can be coupled to HPLC, immediately after the stationary phase of the LC column, to detect compounds as they elute from the column.
MS-ESI spectrometer signal is highly specific.
The sample solution is sprayed across a high potential difference from a needle into an orifice in the interface. Heat and gas flows are used to desolvate the ions existing in the sample solution. The ions are transfered into the mass analyser and separated according to their specific mass/charge ratio (m/z).
The presence of an analyte gives a response assumed to be proportional to the concentration. The instrument’s response to the analyte in the unknown should be compared with the response to a standard.