Dynamic multiplexed analysis method using ion mobility spectrometer
A method for multiplexed analysis using ion mobility spectrometer in which the effectiveness and efficiency of the multiplexed method is optimized by automatically adjusting rates of passage of analyte materials through an IMS drift tube during operation of the system. This automatic adjustment is performed by the IMS instrument itself after determining the appropriate levels of adjustment according to the method of the present invention. In one example, the adjustment of the rates of passage for these materials is determined by quantifying the total number of analyte molecules delivered to the ion trap in a preselected period of time, comparing this number to the charge capacity of the ion trap, selecting a gate opening sequence; and implementing the selected gate opening sequence to obtain a preselected rate of analytes within said IMS drift tube.
1. A method for increasing the dynamic range of a multidimensional IMS-TOF system comprises the steps of automatically adjusting rates of passage of analyte materials through an IMS drift tube during operation of said system; an ion trap to which a total number of analyte molecules are delivered; quantifying the said total number of analyte molecules delivered to said ion trap in a preselected period of time; comparing this number to the charge capacity of the ion trap; selecting a gate opening sequence; and implementing the selected gate opening sequence to obtain a preselected rate of analytes within said IMS drift tube.
2. The method of claim 1 wherein said quantifying step is comprised of: performing an initial short IMS-TOF pre-scan to determine an experimental sequence, said pre-scan conducted in a signal averaging mode using constant short accumulation times (<1 ms), and comprising several IMS-TOF separations
creating an IMS-TOF vector from data obtained in said pre-scan; and
folding and summing said vector to obtain the total number of ions accumulated in the ion trap during the pre-scan.
3. The method of claim 2 wherein said selecting step comprises:
matching a predesignated pseudo random sequence in a preselected range with the total number of ions accumulated in the ion trap during the pre-scan according to a preselected criteria.
4. The method of claim 3 wherein the pseudo random sequence range extends from 1-bit extended pseudo random sequence (1 ion packet release per IMS separation) to 7-bit extended pseudo-random sequence (64 ion packet releases per IMS separation).
5. The method of claim 3 further comprising the step of conducting a targeted MS/MS experiment by fragmenting precursor ions of interest in an RF ion guide downstream of an IMS drift tube using the same pseudo random sequence as that employed for precursor signal encoding but delayed by the drift time of the species of interest.