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Dushyant Patel LC-MS/MS Method

S.K.P.C.P.E.R., Kherva 27 M .Pharm. Thesis

Selected ion monitoring:

¾ Selected ion monitoring (SIM) is a technique in which a particular ion or set of ions is

monitored. SIM experiments are useful in detecting small quantities of a target

compound in a complex mixture when the mass spectrum of the target compound is

known. Thus, SIM is useful in trace analysis and in the rapid screening of a large number

of samples for a target compound.

¾ Because only a few ions are monitored, SIM can provide lower detection limits and

greater speed than the full scan modes. Lower detection limits are achieved because

more time is spent monitoring significant ions that are known to occur in the mass

spectrum of the target analyte. Greater speed is achieved because only a few ions of

interest are monitored; regions of the spectrum that are empty or have no ions of interest

are not monitored.

¾ SIM can improve the detection limit and decrease analysis time, but it can also reduce

specificity. In SIM, only specific ions are monitored. Therefore, any compound that

fragments to produce those ions will appear to be the target compound. Thus, a false

positive result could be obtained.

Selected reaction monitoring:

¾ In selected reaction monitoring (SRM), a particular reaction or set of reactions, such as

the fragmentation of an ion or the loss of a neutral moiety, is monitored.

¾ In SRM, a limited number of parent / product-ion pairs are monitored. In Product-type

experiments, a parent ion is selected as usual, but generally only one product ion is

monitored. SRM experiments are normally conducted with the product scan mode.

¾ Like SIM, SRM allows for the very rapid analysis of trace components in complex

mixtures. However, because two sets of ions are being selected, the specificity obtained

in SRM can be much greater than that obtained in SIM. Any interfering compound

would not only have to form an ion source product (parent ion) of the same mass-to-

charge ratio as the selected parent ion from the target compound, but that parent ion

would also have to fragment to form a product ion of the same mass-to-charge ratio as

the selected product ion from the target compound.

Data types:

¾ You can acquire and display mass spectral data (intensity versus mass-to charge ratio)

with the mass spectrometer in one of two data types: Profile data type & Centroid data

type

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