science

Mass chromatogram

Mass chromatogram is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Mass chromatogram rather than just read about it. In short: 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.

Key takeaways

Mass chromatogram belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Mass chromatogram to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Mass chromatogram from memory before moving on to harder problems.

Reference excerpt

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.

Total ion current chromatogram (TICC)

The total ion current chromatogram (TICC) 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 TICC often provides limited information as multiple analytes elute simultaneously, obscuring individual species.

Base peak chromatogram

The base peak chromatogram is similar to the TICC, 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 (EIC or XIC)

In an extracted-ion chromatogram (EIC or XIC), 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 resolution 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. An extracted-ion chromatogram is generated by separating the ions of interest from a data file containing the full mass spectrum over time after the fact; this is different from selected-ion chromatograms, discussed below, in which data is collected only for specific m/z values. A closely related term is extracted-compound chromatogram (ECC).

Selected-ion monitoring chromatogram (SIM) A selected-ion monitoring (SIM) chromatogram is similar to an EIC/XIC, with the exception that the mass spectrometer is operated in SIM mode, such that only preselected m/z values 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 (EIC or XIC), 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 (SRM, MRM) The selected-reaction monitoring (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. The technology progress in the MS/MS area lead to the development of MRM, Multiple Reaction Monitoring, which allows simultaneous detection of several coeluting analytes with different parent and/or product ions.

Illustrations

Worked examples

Example 1 — a first encounter with Mass chromatogram

Start with the simplest possible case. Write down what Mass chromatogram claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Mass chromatogram before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Mass chromatogram ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Mass chromatogram

In research: Mass chromatogram appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Mass chromatogram in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Mass chromatogram is common in secondary-school and first-year university syllabi. It links to neighbouring topics Mass spectrometry, so understanding it makes those chapters shorter.
In everyday life: Look for Mass chromatogram outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Mass chromatogram in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Mass chromatogram means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Mass chromatogram out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Mass chromatogram in simple terms?

Why does Mass chromatogram matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Mass chromatogram?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Mass chromatogram.