System and process for pulsed multiple reaction monitoring
A new pulsed multiple reaction monitoring process and system are disclosed that uses a pulsed ion injection mode for use in conjunction with triple-quadrupole instruments. The pulsed injection mode approach reduces background ion noise at the detector, increases amplitude of the ion signal, and includes a unity duty cycle that provides a significant sensitivity increase for reliable quantitation of proteins/peptides present at attomole levels in highly complex biological mixtures.
1. A pulsed multiple reaction monitoring method characterized by the steps of:
accumulating preselected precursor ions in a trapping device at a pressure of at least about 1 Torr to compress same therein; and
transmitting the accumulated precursor ions from the trapping device as a compressed ion packet into a quadrupole that is synchronized with the onset of an ion scan within the quadrupole.
2. The method of claim 1 , further including the steps of:
transmitting the accumulated precursor ions in the compressed ion packet through a first resolving quadrupole to select precursor ions therein; and
collisionally activating the selected precursor ions in a collision cell to generate fragment ion transitions for same therein.
3. The method of claim 2 , further including transmitting selected fragment ion transitions as compressed ion packets through a second resolving quadrupole for analysis therein.
4. The method of claim 1 , wherein the accumulating and transmitting steps are interspersed between continuous ion flow.
5. The method of claim 1 , wherein the accumulating step utilizes a radio trapping device operating in a range between about m/z 50 to about m/z 10,000.
6. The method of claim 1 , wherein the accumulation step is performed in a time of from about 2 milliseconds to about 50 milliseconds.
7. The method of claim 1 , wherein the step of transmitting accumulated precursor ions includes using a trigger (release) pulse tied with a release time from about 100 μsec to about 500 μsec.
8. The method of claim 1 , wherein the accumulated packet of preselected precursor ions is in a narrow mass range selected from about 1 mDa to about 2 mDa.
9. The method of claim 1 , wherein the transmitting step includes transmitting at a range defined by a mass-to-charge (m/z) ratio of less than 1 Da.
10. The method of claim 1 , wherein the quadrupole is a second resolving quadrupole and the ion scan employs a scan width of about 2 mDa and a scan time of less than 10 msec.
11. The method of claim 1 , wherein the rate of ion packet transmission is determined by DC-potentials applied to electrodes of the trapping portion of the trapping device and pulsed potentials applied to an entrance grid and a trapping grid that introduce and release ions from the trapping device, respectively.
12. The method of claim 1 , wherein the quadrupole is a second resolving quadrupole and the transmitting includes transmitting a single fragment ion (ion transition) as an ion packet while synchronizing release to coincide with the onset of the ion scan in the second resolving quadrupole.
13. A pulsed multiple reaction monitoring method, comprising the steps of:
accumulating preselected precursor ions in a trapping device at a pressure of at least about 1 Torr to form a compressed ion packet therein; and
transmitting the compressed ion packet from the trapping device into a quadrupole that is synchronized with the onset of the ion scan in the quadrupole;
wherein the synchronization employs a delay time with a duration equal to the sum of the dead time between ion transitions and a half width of the ion scan time in the quadrupole.