RSD% failure - PAHs

   I please ask if you can verify what I am doing wrong. My analysis is 8270 PAHs using a 7890A/5975C inert XL MSD. I currently use 30m x 0.250mm x 1.00µm DB-5MSUI (Part # 122-5533UI) Agilent column. The attachment below shows my RSD% for three of my four groups of analytes over 15% with noticeable peak deviation in the final CC concentrations. I have made the calibration curve with the desired concentrations more than once with the same instrument results. I will greatly appreciate your help.


Current column settings:

1) 50°C (1min)

2) 15 °C/min to 300° - hold 4.5min

3) 25 °C/min to 320° - hold 12.5

Total time 35.467min


Current GC settings:

MS Source 230°C, MS Quad 150°C, Aux Temp 310°C, HiVac 1.14e-05

Inlet:  Temp=280°C, Pressure=10.052psi, Flow=24.20mL/min, Constant Flow

Splitless injection at 50mL/min at 1min

  • Just noticed that your curve is forcing through 0.

    Remove this and have it fall naturally. Because it's forcing through 0 its taking it a true definative point, you may find that at the lower levels anyway that the graphs are not striaght line linear but in fact polynomial once noise effect the signal.

  • I apologize for not being able to answer before. I can now and this is what I have.  Combining trifecta, Ron and timstrutt's suggestions the result was a method with acquiring settings that have been most successful in run time, peak resolution and calibration curve stability. My RSDs are now all below 15% and I am not using linear or quadratic regressions anymore. The curve looks great and my Proficiency Tests results are perfect. I am sharing my current GC settings below. Thank you all for it has been caring teamwork that made this possible.


    Warmest regards,




    Current column settings:

    1) 40°C (1min)

    2) 25 °C/min to 280° - hold 0 min

    3) 5 °C/min to 320° - hold 3.4

    Total time 22 min


    Current GC settings:

    MS Source 350°C, MS Quad 180°C, Aux Temp 310°C, HiVac 9.62e-06

    Inlet:  Temp=280°C, Pressure=9.432psi, Flow=1.2mL/min, Constant Flow

    9mm drawout lens, part# G3440-20022, MMI Pulsed Split injection at 5:1

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