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- Location: Western Colorado
[1] Hold flow constant for width of solvent peak
[2] Hold oven temp below solvent B.P. for splitless interval
[3a] At end of splitless interval, ramp Temp to 10C over solvent B.P.
[3b] Hold Temp 10C over solvent B.P. for solvent peak interval
[4] Ramp Temp and Flow for normal program from that point onward
I did a few calculations and for the column the article is using, the injection pressure is around 36 psi. This means that the calculated B.P. for MeCl is actually not 40C but closer to 65C (using this quick online calculator. So, the 50C cited in the method above is actually not sufficient to boil off the solvent.
I have done this with my GC-FID system for DRO.
analytical column: HP-5 50m x 0.20um x 0.33um column
pre-column: 5m of 0.53 deactivated silica Rxi guard column
Flow Program: 5.4mL/min (hold 2.40min) to 5.0 mL/min at 10 mL/min
Oven Temperature 60C (hold 1.0 min) to 80C at 60C/min (hold 1.1 min) 2.40min total
Program: to 320 @ 20C/min (hold 3 min) total time 18.60 min
Carrier Gas Hydrogen, constant flow 5mL/min
Inlet Mode: Splitless for 1.0 min then split at 100 mL/min
Inlet Temperature: 280C
FID Temp: 350C
Samples are in n-hexane B.P. 69C
For my program and hardware; the B.P. is predicted to be 100C at 60psi which is rather higher than the 80C I have set up. But 100C seems a bit high. So, in light of the referenced link, I'm thinking 80C is OK for my system just like 50C is OK for the MeCl. The solvent peak comes on at 1.35 min and is back to baseline at 2.40 min. And that has guided my settings. I am getting my 1000 ppm reference spike back just fine using 1uL injections and with 5uL injections, the same standard is giving me 5000 ppm with surrogates to match. DRO (C10-C28) runs between 3.4 min and 13.3 min. In the same way, my 10,000 ppm standard at 1uL is giving me 50,000 ppm with 5uL. Even my 100,000 ppm at 1uL is giving me 500,000 ppm at 5uL.
I have a 50uL gastight SGE syringe on backorder and plan to go on up to a 20uL injection at the end of the month when it finally ships.
Does anyone have something to say about the boiling point discrepancy? Am I thinking about this wrong?
P.S. I realize that column is a bit long but it was free. I've been running for some time routinely with it with just the DB-5 column, 1uL injections, the 60psi pulsed split, splitless for 1 minute then 5mL/min flow for a 21.2 min run.