MS sample purity calculation
The MS sample purity calculation assesses whether a sample is pure or contains impurities. This assessment is based on the comparison of responses. On the one hand, there is the response of all compounds and fragments in a sample. On the other hand, there is the response caused by specific target ions. The sample purity is calculated as the ratio of both responses.
The application performs different steps to calculate the MS sample purity, depending on the selected base signal and calculation:
Target found?
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Get the target masses given in the Target columns of the Injection List (for example, 270). If a formula is entered, calculate the molecular weight from the formula.
Apply the adducts specified in the processing method (for example, +H and +Na and a target mass of 270 would result in the targets 271 and 293).
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Extract EICs for all targets, and sum these EICs to a single EIC.
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Determine the retention time of the peak in that single summed EIC.
Locate the matching peak in the chromatogram of the base signal.
If a matching peak can be located, the target is marked as found.
Base signal is from an MS detector
With calculation TIC %
With calculation EIC/TIC %:
When MS is chosen as the base signal (in the processing method under MS Sample Purity > Properties), and there are multiple TIC signals, each TIC signal will be shown as a base signal on the left side table in the Sample Purity Results window. |
Base signal is from another detector (non-MS)
Assumptions
MS sample purity is calculated under the following assumptions:
The MS sample purity calculation is intended as a rough approximation only.
For EIC/TIC % calculations: MS data is acquired such that most ion abundance is in the molecular ion cluster. There is only a small degree of in-source dissociation.
For base signals from non-MS detectors: The other detector is more uniform and universal in its response than the MS detector.
All compounds in the sample have uniform response factors.