Mass chromatogram
Encyclopedia
A mass chromatogram is a representation of mass spectrometry
data as a chromatogram, where the x-axis represents time
and the y-axis represents signal intensity. The source data contains mass information; however, it is not graphically represented in a mass chromatogram in favor of visualizing signal intensity versus time. The most common use of this data representation is when mass spectrometry is used in conjunction with some form of chromatography
, such as in liquid chromatography-mass spectrometry
or gas chromatography-mass spectrometry
. In this case, the x-axis represents retention time, analogous to any other chromatogram. The y-axis represents signal intensity or relative signal intensity. There are many different types of metrics that this intensity may represent, depending on what information is extracted from each mass spectrum.
of the instrument collecting the data. This is useful for re-examining data to detect previously-unsuspected analytes, to highlight potential isomers, resolve suspected co-eluting substances, or to provide clean chromatograms of compounds of interest. Extracted-ion chromatograms are created via a data-mining or data-analysis process; selected-ion chromatograms, discussed below, arise from a completely different type of experiment, i.e., one in which data is collected only for specific m/z values representing compounds or compound types of interest.
(SIM) chromatogram is similar to an XIC, with the exception that the mass spectrometer is operated in SIM mode, such that only a selected m/z value (or more) is/are detected in the analysis. SIM experiments can be performed using mass spectrometry (MS) or tandem mass spectrometry (MS/MS) instruments. They are more common on MS instruments. This differs significantly from the Extracted Ion Chromatogram mentioned above in that only data for the ion(s) of interest are collected in a SIM experiment; for extracted-ion chromatograms, data for an entire mass range are collected during the run and then examined for analytes of interest after the completion of the run.
(SRM) experiment is very similar to the SIM
experiment except that tandem mass spectrometry
is used and a specific product ion of a specific parent ion is detected. The mass of the parent analyte is first selected while other ions are filtered away. The parent analyte ion is then fragmented in the gas phase and a specific fragment ion is monitored. This experiment has very high specificity because the SRM chromatogram represents only ions of a particular mass that fragment in a manner that produce a very specific product mass. This type of experiment can only be performed using tandem mass spectrometry.
Mass spectrometry
Mass spectrometry is an analytical technique that measures the mass-to-charge ratio of charged particles.It is used for determining masses of particles, for determining the elemental composition of a sample or molecule, and for elucidating the chemical structures of molecules, such as peptides and...
data as a chromatogram, where the x-axis represents time
Time domain
Time domain is a term used to describe the analysis of mathematical functions, physical signals or time series of economic or environmental data, with respect to time. In the time domain, the signal or function's value is known for all real numbers, for the case of continuous time, or at various...
and the y-axis represents signal intensity. The source data contains mass information; however, it is not graphically represented in a mass chromatogram in favor of visualizing signal intensity versus time. The most common use of this data representation is when mass spectrometry is used in conjunction with some form of chromatography
Chromatography
Chromatography is the collective term for a set of laboratory techniques for the separation of mixtures....
, such as in liquid chromatography-mass spectrometry
Liquid chromatography-mass spectrometry
Liquid chromatography–mass spectrometry is an analytical chemistry technique that combines the physical separation capabilities of liquid chromatography with the mass analysis capabilities of mass spectrometry. LC-MS is a powerful technique used for many applications which has very high...
or gas chromatography-mass spectrometry
Gas chromatography-mass spectrometry
Gas chromatography–mass spectrometry is a method that combines the features of gas-liquid chromatography and mass spectrometry to identify different substances within a test sample. Applications of GC-MS include drug detection, fire investigation, environmental analysis, explosives investigation,...
. In this case, the x-axis represents retention time, analogous to any other chromatogram. The y-axis represents signal intensity or relative signal intensity. There are many different types of metrics that this intensity may represent, depending on what information is extracted from each mass spectrum.
Total ion current (TIC) chromatogram
The total ion current (TIC) chromatogram represents the summed intensity across the entire range of masses being detected at every point in the analysis. The range is typically several hundred mass-to-charge units or more. In complex samples, the TIC chromatogram often provides limited information as multiple analytes elute simultaneously, obscuring individual species.Base peak chromatogram
The base peak chromatogram is similar to the TIC chromatogram, however it monitors only the most intense peak in each spectrum. This means that the base peak chromatogram represents the intensity of the most intense peak at every point in the analysis. Base peak chromatograms often have a cleaner look and thus are more informative than TIC chromatograms because the background is reduced by focusing on a single analyte at every point.Extracted ion chromatogram (XIC)
In an extracted ion chromatogram (XIC or EIC), also called a reconstructed ion chromatogram (RIC), one or more m/z values representing one or more analytes of interest are recovered ('extracted') from the entire data set for a chromatographic run. The total intensity or base peak intensity within a mass tolerance window around a particular analyte's mass-to-charge ratio is plotted at every point in the analysis. The size of the mass tolerance window typically depends on the mass accuracy and mass resolutionResolution (mass spectrometry)
In mass spectrometry, resolution measures of the ability to distinguish two peaks of slightly different mass-to-charge ratios ΔM, in a mass spectrum.- Resolution and Resolving Power :...
of the instrument collecting the data. This is useful for re-examining data to detect previously-unsuspected analytes, to highlight potential isomers, resolve suspected co-eluting substances, or to provide clean chromatograms of compounds of interest. Extracted-ion chromatograms are created via a data-mining or data-analysis process; selected-ion chromatograms, discussed below, arise from a completely different type of experiment, i.e., one in which data is collected only for specific m/z values representing compounds or compound types of interest.
Selected ion monitoring chromatogram
A selected ion monitoringSelected ion monitoring
Selected ion monitoring is a mass spectrometry scanning mode in which only a limited mass-to-charge ratio range is transmitted and/or detected by the instrument, as opposed to the full spectrum range. This mode of operation typically results in significantly increased sensitivity...
(SIM) chromatogram is similar to an XIC, with the exception that the mass spectrometer is operated in SIM mode, such that only a selected m/z value (or more) is/are detected in the analysis. SIM experiments can be performed using mass spectrometry (MS) or tandem mass spectrometry (MS/MS) instruments. They are more common on MS instruments. This differs significantly from the Extracted Ion Chromatogram mentioned above in that only data for the ion(s) of interest are collected in a SIM experiment; for extracted-ion chromatograms, data for an entire mass range are collected during the run and then examined for analytes of interest after the completion of the run.
Selected reaction monitoring chromatogram
The selected reaction monitoringSelected reaction monitoring
Selected reaction monitoring is a method used in tandem mass spectrometry in which an ion of a particular mass is selected in the first stage of a tandem mass spectrometer and an ion product of a fragmentation reaction of the precursor ion is selected in the second mass spectrometer stage for...
(SRM) experiment is very similar to the SIM
Selected ion monitoring
Selected ion monitoring is a mass spectrometry scanning mode in which only a limited mass-to-charge ratio range is transmitted and/or detected by the instrument, as opposed to the full spectrum range. This mode of operation typically results in significantly increased sensitivity...
experiment except that tandem mass spectrometry
Tandem mass spectrometry
Tandem mass spectrometry, also known as MS/MS or MS2, involves multiple steps of mass spectrometry selection, with some form of fragmentation occurring in between the stages.-Tandem MS instruments:...
is used and a specific product ion of a specific parent ion is detected. The mass of the parent analyte is first selected while other ions are filtered away. The parent analyte ion is then fragmented in the gas phase and a specific fragment ion is monitored. This experiment has very high specificity because the SRM chromatogram represents only ions of a particular mass that fragment in a manner that produce a very specific product mass. This type of experiment can only be performed using tandem mass spectrometry.