Automated expected retention time and optimal expected retention time window detection
Systems and methods are disclosed for identifying actual XIC peaks of compounds of interest from samples so that more accurate expected retention times and more accurate expected retention time windows can be calculated. In one system, an actual XIC peak is identified using standard samples. The ratio of the quantity of the compound of interest in any two different samples is known, so this ratios is compared to the intensities of the XIC peak calculated in the two samples to identify an actual XIC peak. In another system, an actual XIC peak is identified using information about other compounds of interest in a plurality of samples. It is known that the XIC peaks of compounds of interest in the same samples have a similar distribution of retention times across those samples, so the distributions of retention times of XIC peaks are compared to identify actual XIC peaks.
1. A system for identifying an extracted ion chromatogram (XIC) peak of a compound of interest using a plurality of samples that include a plurality of other compounds of interest, comprising:
a separation device that separates a plurality of compounds of interest over time from each sample of a plurality of samples;
an ion source device that ionizes and transforms the separated compounds of interest of the plurality of compounds of interest for each sample of the plurality of samples into an ion beam;
a mass spectrometer receives the ion beam for each sample of the plurality of samples and mass analyzes the ion beam for at least one ion of each compound of interest of the plurality of compounds of interest, producing a plurality of intensity measurements at a plurality of different acquisition times for the at least one ion of each compound of interest of the plurality of compounds of interest for each sample of the plurality of samples;
a processor in communication with the mass spectrometer that
receives the plurality of intensity measurements for the at least one ion of each compound of interest of the plurality of compounds of interest for each sample of the plurality of sample from the mass spectrometer and a known retention time for each compound of interest of the plurality of compounds of interest from a user,
calculates an XIC for the at least one ion of each compound of interest of the plurality of compounds of interest for each sample of the plurality of samples from the plurality of intensity measurements, producing an XIC for the at least one ion of each compound of interest of the plurality of compounds of interest for each sample of the plurality of samples,
finds one or more XIC peaks in each XIC for the at least one ion of each compound of interest of the plurality of compounds of interest for each sample of the plurality of samples,
calculates for a first XIC peak of an ion of a first compound of interest of the plurality of compounds of interest a retention time for each sample of the plurality of samples and a first distribution function that describes the distribution of the retention times of the first XIC peak across the plurality of samples,
calculates for a second XIC peak of an ion of a first compound of interest of the plurality of compounds of interest a retention time for each sample of the plurality of samples and a second distribution function that describes the distribution of the retention times of the second XIC peak across the plurality of samples, and
identifies the first XIC peak as an actual peak of the first compound of interest, if the first distribution function and the second distribution function have the same width and a first difference between the mean of the first distribution function and the known retention time of the first compound of interest and a second difference between the mean of the second distribution function and the known retention time of the second compound of interest are described by a monotonic function of the plurality of acquisition times.
2. The system of claim 1 , wherein the processor
calculates for one or more other XIC peaks of ions of one or more other compounds of interest of the plurality of compounds of interest a retention time for each sample of the plurality of samples and a distribution function that describes the distribution of the retention times of the one or more other XIC peaks across the plurality of samples and
identifies the first XIC peak as an actual peak of the first compound of interest, if the first distribution function and the distribution functions of the one or more other XIC peaks have the same width and a first difference between the mean of the first distribution function and the known retention time of the first compound of interest and the differences between the means of the distribution functions of the one or more other XIC peaks and the known retention times of the one or more other compounds of interest are described by a monotonic function of the plurality of acquisition times.
3. The system of claim 1 , wherein the processor calculates an expected retention time and an expected retention time window from the first distribution function.
4. The system of claim 3 , wherein the processor calculates an expected retention time as the mean of the first distribution function.
5. The system of claim 3 , wherein the processor calculates the width of the expected retention time window as the width of the first distribution function.
6. The system of claim 3 , wherein the processor calculates the width of the expected retention time window as a multiple of the width of the first distribution function.