Precise testing of pesticides in food using the SCIEX 7500 System

Jianru Stahl-Zeng of SCIEX recently presented a webinar to showcase the capabilities and potential of the new SCIEX Triple Quad™ 7500 LC-MS/MS System – QTRAP® Ready, to accurately quantify 700 pesticide residues across 10 different food matrices at ultra-low trace levels. Here, we revisit the live Q&A session and address some of your queries…

How did you set up the OptiFlow® Pro Ion Source for the assay? Is it any different from Turbo V™ Ion Source?

When running Optiflow® Pro Ion Source, you typically have to use lower Gas 1 and Ion Spray voltages than you would for a Turbo V™ Ion Source. For this assay, you can use 1,500 V and Gas 1 at 35.

What is the dynamic range of the SCIEX 7500 System?

The SCIEX 7500 System offers a linear dynamic range spanning up to six orders of magnitude.

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 quantification quality when your instrument is fast enough and the cycle time is not too long. That means shorter cycle time/dwell time, more data points. Sufficient data points are essential for a reproducible peak shape.

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) in the positive and negative modes?

The SCIEX 7500 System can switch polarity as fast a 5ms. In our screening assay, where we strive to get many data points, we used 5ms for our assay. In the quantitative assay where reproducibility and consistent peak integration are important, we used 15ms for quantification. Given the target cycle time of 350ms, 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 your liquid‑chromatography (LC) separation, number of co-elute peaks, predefined cycle time, etc. This is the same for both positive and negative modes.

Along with signal increase, does the larger orifice also impact noise in the system?

With a larger orifice, the background 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.

Missed the webinar? Don’t worry, you can catch the whole session on-demand.