Column Bleed & Decreased Sensitivity

[m.finnBMBM]

I had an Rxt-1 60 m column that worked great for a while then I started having some serious column bleed issues. I replaced the column with a new one with the same specs, but I am still seeing column bleed. Is it possible that both columns are bad, or is something contaminated with the stationary phase from the first column? The sensitivity also decreased in tandem with the increase in column bleed with the first column and I continue to have reduced sensitivity with this new column. Is this another symptom of the same problem or is this completely separate? I really appreciate any and all help. Thank you.

[carls]

Check your oxygen trap. Oxygen in the carrier will accelerate degradation of the phase and give higher column bleed.

Is the column bleed high throughout the temperaure program or only at high temp?

What detector are you using?

If using MS detection take a look at the spectrum of the bleed at different temperatures. 73, 207, 281 are some of the common PDMS phase bleed ions (from memory). If the major ions are different than these then the bleed is coming from something else.

[Peter Apps]

Very often column bleed is blamed for baseline drift that is really due to dirty inlets and contaminated carrier gas.

Peter

[m.finnBMBM]

I am using a mass spec. The bleed only occurs at higher temps near the end of runs, and the main peak is a 207 with a smaller one at 281.

[carls]

These ions are typical of polydimethylsiloxane (PDMS) column bleed. Bleed always increases at higher temperatures. If the bleed is higher than normal check your oxygen trap as oxygen in your carrier gas increases column bleed. What GC column are you using?

[m.finnBMBM]

I'm using an Rtx-1 column.