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

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  • After cutting 10 inches from my previous column and after changing to a new column I still have a upward curved in both procedures. My MMI inlet is untouched since I lack the abrasive brush which I will need to order. Only the glass-wool liner and o-ring has been changed. I have only to re-clean my ion source and rerun my CC. If this doesn't work I would only be able to use quadratic regression to have an acceptable r² coefficient.

  • There are 2 things you may try.

    1. Turn your splitless time down to .5 min or less.

    2. Try using a 6mm drawout lens part number G2589-20045. Assuming you have an inert source. If stainless steel source the part number is G3163-20530.

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