Explain what is displayed in a reconstructed total ion chromatogram, in selected ion monitoring, and in selected reaction monitoring. Which technique is most selective and which is least selective and why?

Throughout a chromatography experiment a reconstructed total ion chromatogram which is above a standard value of m/z is developed by addition of all ion intensities in each mass spectrum at each time interval. This process does not have any selectivity and responds to everything eluted from the column.

In case of selected ion monitoring intensities (one or a few m/z values) are plotted versus elution time. The species with ion at which m/z values are detected, therefore the selectivity is much higher than that of reconstructured total ion chromatogram. If the entire spectrum were scanned, ions are collected at every m/z for a longer time than it is actually allowed. As a result, the signal to noise ratio increases.

For selected reaction monitoring from the first mass separator one ion is passed through a collision cell. There it breaks into different products which are separated by a second mass separator. The intensities of the generated products are a function of time.

The selected reaction monitoring is the most selective whereas a reconstructed total ion chromatogram is the least selective. This technique is too selective that it can change a poor chromatographic separation into a highly specific determination of one compound with no interference