Linear Dynamic Range of Quantification

Dynamic range is one of the critic factors to be dealt with for quantitative analysis by any method. In the modern era, the detectors used in mass spectrometers generally possess a very wide dynamic range although some types of mass detectors (e.g., the detector with multiple-channel plates commonly used in time-of-flight mass spectrometers) have dynamic ranges that are relatively smaller than others. Therefore, the detectors are usually not a factor to limit the dynamic range of a method for quantitative analysis of lipids. 

For both shotgun lipidomics and LC-MS-based approaches, the dynamic range should be examined in the presence of sample matrices instead of using a pure standard. Under such conditions, the matrix effects (e.g., ion suppression) that become more severe in analysis of minor species (or classes) in the presence of abundant species (or classes) can be eliminated for sample analysis. 

There are many other ways to test the linear dynamic range. One is to perform linear least-square regression to fit a line 

4 NUTS AND BOLTS OF TANDEM MASS SPECTROMETRY FOR QUANTIFICATION OF LIPIDS 

it is always better to optimize the collision energy that can balance the fragment intensities of all the ions of the entire class of interest for quantification of lipid species by tandem MS in shotgun lipidomics even more than one internal standards are employed in the method. Similarly, optimization of the SRM/MRM conditions for individual species in an LC-MS/MS method is not recommended when interest is to quantify all the species of a class, unless a calibration curve for each individual species is established under the identical conditions, since optimization of MRM conditions for individual lipid species leads to an incomparable response factor of the species of interest to that of the selected internal standard. In both cases of shotgun lipidomics and LC-MS/MS analyses, different collision energies applied for different species could lead to substantial errors in quantitative analysis, as discussed previously [22]. Careful attention to CID energy must be exercised if accurate quantification is a goal. 

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The compound and its isotopologue should be within a linear dynamic range of quantification. 

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