Considerations of the use of Triple Quadrupoles or Ion Traps in Quantitative Applications

Size: px

Start display at page:

Download "Considerations of the use of Triple Quadrupoles or Ion Traps in Quantitative Applications"

Everett Robinson
6 years ago
Views:

1 Considerations of the use of Triple Quadrupoles or Ion Traps in Quantitative Applications

2 Triple Stage Quadrupole API MS / MS Full Scan Products / - IONS AND NEUTRALS FORMED IN API SOURCE Q0 LENS TRANSPORTS / - IONS TO Q1 PARENT MASS ANALYZER Q1 PARENT MASS ANALYZER IS PARKED, PASSING ONLY PARENT IONS OF A SINGLE M / Z TO Q2 COLLISION CELL Energy PARENT IONS ENTER Q2 COLLISION CELL COLLIDE WITH Ar GAS AND DISASSOCIATE Q3 PRODUCT MASS ANALYZER IS SCANNED, PASSING FULL SCAN PRODUCT ION SPECTRA TO THE DETECTOR ION SOURCE Q0 Q1 Q2 Q3 Ar DETECTOR

3 Triple Stage Quadrupole API MS / MS SRM Products / - IONS AND NEUTRALS FORMED IN API SOURCE Q0 LENS TRANSPORTS / - IONS TO Q1 PARENT MASS ANALYZER Q1 PARENT MASS ANALYZER IS PARKED, PASSING ONLY PARENT IONS OF A SINGLE M / Z TO Q2 COLLISION CELL PARENT IONS ENTER Q2 COLLISION CELL & COLLIDE WITH Ar GAS THEN DISASSOCIATE Q3 PRODUCT MASS ANALYZER IS PARKED, PASSING ONLY PRODUCT IONS OF A SINGLE M / Z TO THE DETECTOR Energy ION SOURCE Q0 Q1 Q2 Q3 Ar DETECTOR

4 Trapology Column Effluent Ion Gate Ion Injection Scanned RF Ion Source Charge Helium Bath Gas Waveforms Ion Trap Mass Analyzer Computer Ion Current Detector

5 An ion trap holds a fixed maximum number of ions and so can be filled and emptied a certain number of times during the evolution of a chromatographic peak.

6 The length of time that the trap stays open to collect ions is determined by a pre-scan which measures total ion current (prevents space charging ) Pre-scan 5 sec.

7 Across a peak 5 sec. wide the trap might fill and empty 5 times. So, a group of ions are collected ca. every 1 sec - each group is then ejected to the detector, smaller ions first. 1 sec 1 sec 1 sec 1 sec 1 sec 5 sec.

8 Quadrupole MS scanning A quadrupole mass analyzer scans by ramping the DC/RF voltage in time across the quadrupoles. So, in any given time, ions of one m/z only are present and pass through to the detector - all others are rejected.

9 Quadrupole MS scanning If one MS/MS scan between m/z 100 and m/z 500 is completed in one second, then each m/z will be allowed to pass for 2.5 ms.

10 For the same peak, the quadrupole performs 5 complete scans from m/z each taking 1 sec m/z m/z m/z m/z m/z 5 sec.

11 Quad and trap full scan summary For the quadrupole, each m/z is scanned (sequentially) to the detector for 2.5 ms For a trap, each m/z (and all m/z at the same time) is/are collected for ca. 750 ms (taking pre-scan and interscan times into account) and then scanned to the detector.

12 Ion traps have the edge over quads in full scan MS/MS For full scan MS/MS, a trap will give better sensitivity - because there are more ions representing each m/z arriving at the detector for each scan.

13 How much more sensitive is the ion trap for full scan MS/MS? Accounting for pre-scan/interscan timing, the trap produces ca. 300 times (750 ms/2.5 ms) for the collection of each m/z compared to a quadrupole with the same ion source emittance (i.e. 2 orders of magnitude.)

14 But wait there s more! What if I wanted to pass (filter) only one m/z ion to the detector (i.e. SRM) - then I could spend more time on that ion...

15 Duty cycle considerations On a quadrupole, interscan times are relatively small and so the quadrupole remains fixed on that one ion - a duty cycle of close to 100%. A trap will still only collect ions in batches - and prescan/interscan times afford a duty cycle of about 75%.

16 The chromatographic time scale While the beam instrument is continuously detecting one particular m/z - a trap builds a curve from an average over each collection time - and the points are least frequent at the most important region for quantitation (the take-off.)

17 In general When comparing a triple quad and an ion trap with identical ion source emittances, the triple quadrupole device provides ~ an order of magnitude better LOQ (from better RSDs) for quantitation experiments than a trap, primarily due to integration effects.

18 SRM 5pg Alprazolam with LCQ DECA Relative Abundance %RSD 6.11 RT: 4.26 SN: SRM 750fg Alprazolam with TSQ %RSD 1.87 RT: 4.41 SN: Time (min)

19 Conclusions Both traps and triple quads can be used very effectively in qualitative and quantitative applications Making a decision on which to use should involve careful consideration of the application as well as budget In general: Traps offer better sensitivity than triple quadrupoles in full scan product ion MS/MS mode (e.g., many qualitative applications, peptide sequencing) Triple quads offer better performance for SRM experiments (e.g., in target compound quantitation) It is important to also consider the ion source emittance and other factors that effect performance. These may not be equivalent across various vendor product lines, which could affect the accuracy of the broad generalizations stated above.

Quadrupole and Ion Trap Mass Analysers and an introduction to Resolution

Quadrupole and Ion Trap Mass Analysers and an introduction to Resolution A simple definition of a Mass Spectrometer A Mass Spectrometer is an analytical instrument that can separate charged molecules according