EPA Method 541 on the Stabilwax Column

EPA Method 541 UCMR4 Standard Chromatogram at 10x the Method Reporting Limit on a 30m x 0.25 mm ID x 0.50 µm Stabilwax (cat# 12039).

I recently posted some chromatograms for our new EPA Method 541 UCMR4 Standards, and wanted to focus on the column in a separate post. EPA Method 541 was developed on a 30m x 0.25 mm ID x 0.50 µm wax column from another manufacturer. I used the Stabilwax because it is a relatively low bleed wax column and has similar selectivity to the column used by the EPA. My chromatogram is shown above, while a calibration standard chromatogram taken directly from the method documentation is shown below.

EPA METHOD 541 FIGURE 2 – Reconstructed ion chromatogram (RIC), SIM mode, for calibration standard on a 30m x 0.25 mm ID x 0.50 µm wax column.

There are 2 major differences I wanted to point out:

  1. The Stabilwax column has the same elution profile but it is less retentive at the same phase ratio. The last target compound (chlorobenzene-D5) elutes on the Stabilwax at 8.66 minutes, which is BEFORE the 1st target compound (1,4-Dioxane) elutes on the column used in the EPA Method (10.3 minutes). UCMR4 does not include 1,4-dioxane, so it is not included in the Stabilwax chromatogram. The GC acquisition parameters were the same for both columns, though the detector settings were different because of the SIM window start times. All peaks had eluted on the Stabilwax before the method recommended solvent delay ended.
  2. The bleed is significantly lower on the Stabilwax compared to the calibration standard chromatogram from the EPA method.

3 Responses to “EPA Method 541 on the Stabilwax Column”

  1. James Ball says:

    I know the method lists the pressure pulse at injection as 10psi, but the required pressure for 0.9ml/min at 30C starting temperature is 16.7psi. Is this method actually using a negative pressure pulse to slow column flow at injection, or should it be interpreted as 10psi above the 16.7psi normal non pulsed flow?

  2. The correct way writing the pressure would be 10 psig, so 10 psi on a gauge zeroed at 1 atmosphere (or 14.7 psi). The absolute pressure (psia) would be 24.7 psi.

    My GC-MS software calculated 5.48 psi(g) required for the 0.9 mL/min flow at 30 C – I’ve included the relevant section from my GC method below:

    Mode: Pulsed Splitless
    Initial temp: 200 ‘C (On)
    Pressure: 5.47 psi (On)
    Pulse pressure: 10.0 psi
    Pulse time: 0.55 min
    Purge flow: 100.0 mL/min
    Purge time: 0.50 min
    Total flow: 103.5 mL/min
    Gas saver: On
    Saver flow: 20.0 mL/min
    Saver time: 3.00 min
    Gas type: Helium

  3. James Ball says:

    Correction to last post, my instrument was calculating the head pressure wrong, it is actually about 6psi at non pulsed flow of 0.9ml/min, so the 10psi pulse makes more sense now.

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