2 Replies Latest reply on Mar 15, 2019 3:18 PM by elirodrigues

    integrating a peak

    elirodrigues

      Hi guys,

       

      Trying to integrate the peak for Ethylene in my GC.

       

      I was told that to be accurate I should use different concentrations of calibration gas for that, but I only have one concentration (100ppb).

       

      Is that a way to integrate accurately using only one concentration?

       

      Also, does anyone have a very didactic material showing how to integrate a peak on openlab??

       

      Please help,

       

      Thanks.

        • Re: integrating a peak
          msanders

          By "integrate accurately using only one concentration," I assume you mean 'accurately calculate' using one concentration.  Most USP methods use one external standard for calculation, and the method is generally validated for accuracy between 80 - 120%.  Other organizations use calibration curves for low concentration contaminants.

           

          I successfully validated methods for low concentrations using a single external standard formulated at the top of the analyte specification limit.  Results accuracy depends upon methodology, analyte, and matrix.

           

          For Oxygen determination in a Nitrogen filled container, I use a certified 0.2% Oxygen in Nitrogen gas cylinder to calibrate our MicroGC and calculate results.  The 0.2% is the upper specification limit.

           

          What OpenLab software do you have; e.g., CDS, Chemstation, EZchrom?

           

          For OpenLab CDS EZchrom software, there are ways to use sequence calculation. Here is a link to the concepts and workflow manual:

          (Links removed by moderator as security cannot be verified)

           

          I use "Single Run" option.  Using this way, input a Calibration Factor in the method for automated calculations.

          • Program a method with data collection parameters.
          • Collect multiple standard injections.  Adjust integration parameters and reanalyze injections.  Calculate average analyte peak area.  Input a Calibration Factor in the method for automated calculations.  Reanalyze standard injections to make sure concentration calculated correctly.  Click on Reports>View>External Standard to view results.
            • Calibration Factor (ppb) = 100ppb / Average Standard Peak
          • Analyze the sample using the method containing the Calibration Factor.
            • Analyte in Sample (ppb) = Peak Area of Sample x Calibration Factor (ppb)
          • After data collection is complete, click on Reports>View>External Standard to view results.

           

          For OpenLab CDS Chemstation, here is a link to the concepts and workflow manual:

          https://www.agilent.com/cs/library/usermanuals/public/CDS_CS-concepts.pdf

          (Link removed by moderator as security cannot be verified)

           

          • There are many ways to go about the standard and sample input and calculation scheme; e.g., analyze single or multiple standards and samples.
          • Program and save a Method:
            • Collection Parameters:  As per analytical method
            • Calibration Table:  Input the standard name, retention time, and concentration (ppb) in the Calibration Table.  For now, enter 1.0 as the standard peak area and 1 as the level
            • Select the option to have a copy of the method saved in the sequence file.
          • Program and save a Sequence:
            • Input Sequence Lines:  for equilibration, blank, standard, and sample injections
            • Method Column:  Select correct method for each line.
            • Sample Dilution Factor Column: calculate any dilution due to standard and sample dilutions
            • Sample Multiplication Factor Column: standard weight (g) divided by the sample weight (g); or, 1 if both are gases and same amount analyzed; or, 1 divided by sample weight if sample is solid or liquid;
            • Type Column:  Designate “Sample” for samples and equilibration injections; “Calibration” for calculation standards; and "Blank" for diluent or blank
            • First Calculation Standard:  Select "Replace RF” and “Replace RT”
            • Subsequent Calculation Standards:  Select “Average RF” and “Average RT"
            • Select the option to have a copy of the method saved in the sequence file.
          • Use "Queue Sequence" to collect data.
          • After data collection is complete, use the Offline software and select the Sequence with results.  Use the "Auto Integration" option to help determine the best integration parameters.  Use "Manual Integration" for individual chromatograms if peaks do not integrate consistently.  Apply the manual integration to the data file by right clicking on the sequence line and selecting that option.  Once suitable integration parameters are found, right click and select "Update Master Method."  Reprocess the sequence.
          • If the same standard calibration is to be used over multiple days (Sequence files).  Then, for subsequent sequences do not select "Replace RF,” “Replace RT,” "Average RF,” and “Average RT."  Selecting "Update Master Method" in the original data analysis above transferred the calibration table information to the master method.  The standard can be run as a sample to determine if the result changed significantly / instrument condition changed.
          • Use Print Preview to determine if results calculated correctly.  Update sequence method or sequence table, then reprocess the sequence if necessary.

           

          I hope I answered your questions.  The above brief sketch works for my lab.  The manuals give much more detail, print screens, and possibly better options for your lab.

           

          Good Luck and Chromatograph On! 

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