Retention Time/Index Compression??

Discussions about GC and other "gas phase" separation techniques.

3 posts Page 1 of 1
I'm running an isothermal method looking at crude oil from C6-C20 on a ZB1-inferno (30x0.25x0.25), 150 split ratio. Identifying the n-alkanes is easy. They're obviously visible. But consistent ID of inter-alkane peaks becomes difficult, particularly after system maintenance. I've tried calculating retention indeces. I say plural because I've done Kovats, Linear, Linear interpolation, cubic spline, bessel spline, etc. When I calculate them for the same peaks on a run of the same sample after inlet maintenance (column clip included), the indeces for most peaks is fine, (+/- 0-2 points). But for the heavier inter-alkanes, the indeces shift upwards of 8 points. Is this a "normal" phenomena? Does this mean there is something "wrong" with my system? Do I need to change a setting in my method? Being able to consistently id these smaller peaks from one sample set to the next is critical to my experiments and any assistance would be GREATLY appreciated!
sarakuhl wrote:
I'm running an isothermal method looking at crude oil from C6-C20 on a ZB1-inferno (30x0.25x0.25), 150 split ratio. Identifying the n-alkanes is easy. They're obviously visible. But consistent ID of inter-alkane peaks becomes difficult, particularly after system maintenance. I've tried calculating retention indeces. I say plural because I've done Kovats, Linear, Linear interpolation, cubic spline, bessel spline, etc. When I calculate them for the same peaks on a run of the same sample after inlet maintenance (column clip included), the indeces for most peaks is fine, (+/- 0-2 points). But for the heavier inter-alkanes, the indeces shift upwards of 8 points. Is this a "normal" phenomena? Does this mean there is something "wrong" with my system? Do I need to change a setting in my method? Being able to consistently id these smaller peaks from one sample set to the next is critical to my experiments and any assistance would be GREATLY appreciated!


When you clip the column are you adjusting the head pressure lower to account for the shorter length so you have the same linear velocity through the column?
The past is there to guide us into the future, not to dwell in.
I am curious, and it really is none of my business, but why are you doing isothermal between C6 and C20??

Best regards,

AICMM
3 posts Page 1 of 1

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