Using EZLC to adapt an LC pesticide method for lower pressure

 

Our most popular and successful LC column for the broadest range of pesticides is the Raptor ARC-18 column. We are able to retain, provide good separation and peak shape even for many of the more polar pesticides. Whether your matrix is a food, agriculture crop or a cannabis product, the Raptor ARC-18 will probably meet most of your needs for LC analysis of pesticides. Here is a link to the product listing for Raptor ARC-18 columns on our website:

https://www.restek.com/catalog/view/41315

 

The application from Restek that contains the most complete list of pesticides, using the Raptor ARC-18 column, is the following:

Optimizing a 190+ Pesticides Multiresidue Screening Workflow for the Preparation and Analysis of Produce by LC-MS_MS_

Please click the links to see the list of analytes- they are omitted here due to limited space. The featured chromatogram from the above poster is this one from an extraction of brown rice flour (Chromatogram ID LC_FS0521):

We also have example chromatograms for a couple of other sample matrix types, as well as for specific standard mix solutions that we sell. They can all be seen at this link:
https://www.restek.com/chromatogram/search?s=pesticides::type:LC::Raptor%20ARC-18

Please note that all of the examples were using catalog # 9314A12, which is a 100 mm x 2.1 mm, 2.7 um Raptor ARC-18 column.  These dimensions will work best with an LC system that can handle up to 600 bar of pressure. If you are using an LC instrument with a 400 bar pressure limit, you probably need to run the application at a slower flow rate to keep within the desired pressure range.  HPLC models with a 400 bar max pressure also tend to have a larger dwell volume, so it is a good idea also to use a larger ID (3.0 or 4.6 mm) column if you can to minimize these effects.  To make adjustments to your method accordingly, you can use our Pro EZLC method translator here.   https://www.restek.com/Pages/Pro-EZLC-Method-Translator  I recommend to go ahead and download the translator and save on your computer to make things easier. When switching to a larger ID, you might notice that Pro-EZLC will tell you an Isocratic hold at the beginning of the gradient is needed. Also, you might need to take into account your LC system dwell time, which you can obtain from your instrument manual or the instrument manufacturer. Here is what I came up with, translating the chromatogram above from a 100 x 2.1 mm column to a 3.0 mm ID, using the default value of 0.25 mL for the dwell time:

 

(If interested in estimating the dwell time or extra column volume, please see the advice found in the glossary for Pro-EZLC at this link: https://www.restek.com/ProEZLC-MT-Help  If using the downloaded version of Pro-EZLC, the same information can be obtained by clicking on the “?” in the top right-hand corner of the tool.)

You might notice in the above example, under the “Results’ section, that the backpressure remains the about the same. This is because the method is translated to maintain the same linear velocity through the column. However, in this case you need to lower the linear velocity a bit to reduce the overall pressure. So, instead of using the recommended value of 0.82 mL/min, you can manually change the flow to 0.6 mL/min, you can see the pressure is about 73% of what it was originally with the other column. In most cases, that should be enough to reach a comfortable level of backpressure for a 400 bar system.

 

So now you have it- the method translated from a 100 x 2.1 mm column to a 100 x 3.0 with pressure reduced for a 400 bar system.

For additional information about using EZLC, please refer to this page on our website:

Frequently Asked Questions: Pro EZLC Method Translator

 

I hope you find this post useful and thank you for reading.

 

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