Utilizing the Ion Ratio as a Criterion for the Identification of Analytes in Mass Spectrometry
The ion ratio is the ratio of the areas of the quantitative ion and qualitative ion obtained from a mass spectrometer. While a triple quadrupole mass spectrometer offers excellent selectivity, there remains a possibility of a compound other than the target analyte to produce a signal with a similar m/z value to the qualifying or quantifying ion at the same retention time. Consequently, this can result in a significant deviation in the expected ion ratio for the monitored fragment ions during the two SRM (selected reaction monitoring) transitions. This makes the ion ratio an excellent indicator of a false detection of an analyte and serves as a supplementary criterion to enhance confidence in confirming the compound's presence.
Taking the ion ratio into account as an additional criterion requires extra effort. However, our template will alleviate the workload associated with conducting this supplementary validation. Below, you will find comprehensive instructions on how to effectively utilize this template.
The yellow fields in the figure below represent input fields.
Follow the steps below to utilize the ion ratio template:
Add the name of your analytes.
Input the areas of the quantitative and qualitative ions for each of your samples.
Enter the areas of the quantitative and qualitative ions for the standard.
Set up the tolerance level.
Choose your baseline.
Reference standard
Recommended when you have already established an ion ratio criterion for your analytes.
Sample average.
Recommended for establishing an ion ratio criterion. You can employ this feature when spiking standards into your samples to determine the variability of the ion ratio. For more information, refer to this helpful publication on establishing ion ratio criteria (link here).
Choose your tolerance unit.
Percentage of the baseline ion ratio
Number of standard deviations*
Confidence level*
*It is advisable to use these options when establishing an ion ratio criterion. The standard deviation and confidence level values are calculated based on the sample ion ratios. Therefore, it is recommended to use these values in conjunction with the "sample average" as your baseline.
The summary of the results will be displayed in a separate table as shown below:
The ion ratios are displayed for each analyte in every sample. The template can accommodate up to 5 analytes and 10 samples. The upper and lower limits of the specified tolerance are shown. The final table at the bottom highlights the number of samples with ion ratios that fall outside the tolerance range, and these samples are flagged in red.
Be sure to download the ion ratio template to streamline the calculation process for this important criterion in enhancing confidence in detecting analytes in mass spectrometry!
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