Jianru Stahl-Zeng
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Quantify more than 700 pesticides in 10 different food matrices

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A recent webinar from SCIEX and New Food, presented by Jianru Stahl-Zeng of SCIEX, outlined some of the capabilities of the new SCIEX Triple Quad™ 7500 LC-MS/MS System – QTRAP® Ready. In particular, it highlighted the ability of the SCIEX 7500 System to accurately quantify 700 pesticide residues across 10 different food matrices at ultra-low trace levels. During the webinar, attendees posed various questions. Here, we share the top 5 of these questions, along with their answers.

1. How did you set up the OptiFlow® Pro Ion Source for the assay? Is it any different from the Turbo V™ Ion Source? The OptiFlow Pro Ion Source typically requires lower carrier gas (Gas 1) pressure and ion spray voltage than the Turbo V Ion Source. This assay uses 1500 V for the ion spray and Gas 1 at 35.

2. What is the dynamic range of the SCIEX 7500 System? The SCIEX 7500 System offers a linear dynamic range spanning up to 6 orders of magnitude.

3. How are data points related to cycle time and dwell time? How does this affect the peak shape? You will get sufficient data points to ensure your quantification quality when your instrument is fast enough and the cycle time is not too long. A shorter cycle time and dwell time equals more data points. Enough data points are essential for reproducible peak shape.

4. How long does it take to switch polarity from positive to negative mode? How does this impact my assay? And what is the dwell time for each multiple reaction monitoring (MRM) transition in the positive and negative modes? The SCIEX 7500 System can switch polarity in as little as 5 ms. In our screening assay, where we strive to get a large number of data points, we used 5 ms. In the quantitative assay, where reproducibility and consistent peak integration are important, we used 15 ms. Given the target cycle time of 350 ms, the longer polarity switching time had minimal impact on the number of points across each peak. Dwell time for each transition is calculated by SCIEX OS Software and depends on factors such as your liquid-chromatography (LC) separation, the number of coeluting peaks and the predefined cycle time. This is the same for both positive and negative modes.

5. Along with signal increase, does the larger orifice also affect noise in the system? With a larger orifice, the background noise will increase for some of the analyte signals as you are sampling more ions from the source stream. However, the analyte-specific signal increases will outpace the background noise and deliver meaningful signal-to-noise gains from the SCIEX 7500 System.

For more information on the capabilities of the SCIEX 7500 System, and to access related content, catch the webinar on demand.


Jianru Stahl-Zeng
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Jianru Stahl-Zeng
Global Technical Leader for Food and Environmental Applications, SCIEX

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