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Gas chromatography triple quadrupole mass spectrometry (GC-MS TQ) operated using multiple reaction monitoring (MRM) mode has been widely used for multi-residue analysis applications. Fast scan speed in conjunction with good sensitivity, precision, reproducibility and no ‘cross-talk’ is critical when developing a multi-residue MRM method with overlaid transition windows. A Bruker SCION™ TQ GC-MS/MS system recently introduced with a newly designed collision cell for a high speed quantitative MRM acquisition. The collision cell features a lens-free interface, as well as a 180° tight turn (Figure 2a), resulting in the smallest footprint of a TQ MS system on the market (Figure 1). This study evaluates the performance of the new collision cell in terms of scan speed effect on MRM signal precision, as well as ‘cross-talk’. Real world tests using pesticide samples were also carried out to verify the system performance .
The Bruker SCION triple quadrupole mass spectrometer (TQ MS) coupled to a Bruker 451-GC and CP-8400 Auto sampler (see Figure 1).
Figure 1. Bruker SCION TQ MS system with the Bruker 451-GC and a CP 8400 Auto sampler. Dimensions of the SCION TQ MS are shown.
- Injection mode: Splitless, 1mL
- Column: Bruker Br-5ms column (15m×0.25mm×0.25mm)
- Oven Temp: Programmed temperature run
- EI: 70 eV, 250°C, 80 mA
- Transfer line Temp: 280°C
- Emission Current: 80 mA
- Q2 Collision Gas: Ar, 1.5 mTorr
A fast scan test was first carried out, followed by a ‘cross-talk’ evaluation. Conditions for each are outlined in Table 1.
Table 1. Conditions for a fast scan test and cross-talk evaluation on a SCION TQ MS.
|Fast Scan Test
- MRM mode: OFN 1 pg/ml, 1ml splitless injection
- Scan time: 1ms, 2ms, 5ms, 10ms, 20ms, 100ms
- 6 replicates, compare MRM signal precision
- MRM mode: OFN 100 pg/µl, 1µl splitless injection
- OFN MRM transition: 272>222, 1ms scan time
- Dummy MRM transition: 500>222, 1ms scan time
|B. Pesticide Sample
- Propyzamide 100 ppb, 2 µl splitless injection
- MRM transition: 173>145, 20 eV collision energy
- Scan time: 1ms, 2ms, 3ms, 5ms, 10ms
- 10 replicates, compare MRM signal precision
|B. Pesticide Sample|
- 1 ppm mixture of 50 pesticides,
- 1µl splitless injection (1 ng on-column)
- Two pesticides sharing the same m/z product ion are monitored under MRM mode
- Methoxchlor, 12.38min, 227>212, 10ms scan time
- Vinclozolin, 8.85min, 285>212, 10ms scan time
Standard samples of Octafluoronaphthalene (OFN) were prepared at 0.1, 1 and 100pg/ml, in addition to three pesticides at various concentrations: Methoxchlor 1ppm, Vinclozolin 1ppm, Propyzamide 100ppb.
5 scan times were recorded from 10ms to 1ms. As Figure 3 shows in both cases, signal intensities remained unchanged at fast MRM modes even down to 1ms scan time, also obtained excellent precision.
Figure 2. a) SCION TQ Q2: a 180° curved collision cell with a lens-free interface with Q1 and Q3;
b) In Q2, ion stabilization completes within 0.25ms (shown with a calibration gas ion MRM).
Figure 3. Fast scan test on:
3a) Fast MRM scan of OFN (1 pg), 6 scan times from 100ms to 1ms;
3b) Fast MRM scan of propyzamide (200 pg).
Figure 4. Cross-talk’ evaluation on 4a) OFN, two MRM transitions with the same m/z product ion (real vs. dummy). At 1ms scan time, no “cross-talk” presents in the dummy transition; 4b) Methoxchlor and Vinclozolin in mixture with two MRM transitions sharing the same product ion (m/z 212). 1 ng injected at a 10ms scan time yields zero ‘cross-talk’ in the MRM profiles of either compound.
The results generated illustrate the fast ion stabilization of the collision cell in the Bruker SCION TQ MS, enabling rapid MRM scans, whilst retaining both ion intensity and excellent precision. Zero ‘cross-talk’ is achieved at fast MRM scans down to 1 ms. The combination of high quality signals and zero “cross-talk” at high speed MRM acquisition makes the SCION TQ MS an ideal platform for MRM-based multi-residue analysis.
Helen (Qingyu) Sun, Felician Muntean, Zicheng Yang and Kefei Wang, Bruker Chemical & Applied Markets (CAM) division, Fremont, CA.
 Evaluation of high speed MRM data acquisition for GC-MS/MS use in multi-residue analysis. Poster at ASMS 2012, ThP-604.
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