I analysed reactive species on a 5% phenyl capillary column. Now, at any temperature program ,I get 'ghost' peaks
Is it possible to repair the column?
By Anonymous on Friday, March 23, 2001 - 11:41 am:
Most modern columns of this type are bonded, and can be rinsed with methylene chloride using helium pressure.
By Jason Ellis on Monday, March 26, 2001 - 08:44 am:
Stationary phases cannot generate peaks by themselves. For peaks to be generated something must be introduced and focused on the front of the column. The peaks you are seeing are not phase eluting from the column (the good news), but they are probably an indication of inlet or carrier gas contamination (the bad news). You can easily clean your inlet out by cooling it down and doing a solvent rinse of the metal body. Also change your glass liner and other inlet consumables (such as gold inlet seal if instrument is an Agilent or HP). If you have any questions about how to do this please feel free to contact me directly.
By Anonymous on Tuesday, May 15, 2001 - 10:56 am:
To avoid wasting time, I recommend cutting 2 feet off the front of the column, replacing the liner and liner seal (if it is Agilent). Rincing the column with solvent seldom works. Most prolbems occur with damaged stationary phase due to injection of a trace amount of acid. 2 feet of column seems like a lot but it only represents 2% of a 30m column and it will only change your retention times by ~0.3min. You can take off less, but if the problem persists, you'll be wondering if you took off enough. Take 2' and be done with it!
A stationary phase that has been severly damaged (i.e. heated to a high temp. with no carrier flow) CAN produce peaks on its own. Thermal degradation (will continue with each oven cycle producing a "picket fence" pattern of peaks.
If the ghost peaks do not appear like this, you probably have contamination in one of the three areas: carrier gas, carrier gas line (injection flash back into the cool, carrier inlet line can condense and slowly bleed into the carrier gas), or the split vent line (spltless injection especially, can allow backward migration of contaminents.
Try this test. Run the oven temp upto between 250 to 290C and let it sit for 15min. Cool it down to 40C and let it sit for 15 min. Run the oven temp. up without injecting anything (not even solvent) and record the chromatogram. Cool the oven to 40 and let it sit for 45min. and run the oven temp program the same as before. If the ghost peaks appear quite a bit larger on the second run, you are definetly trapping contmainents on the head of the column at the low initial oven temp.
If the peaks only occur injection of solvent, and you are positive the solvent is clean (i.e.injection on another clean system), you probably are flashing solvent into the carrier gas line that contains condensed organics. This can be cleaned out by heating the carrier gas line with a heat gun while maintaining a high carrier gas flow rate (turn the split vent up to 150mL/min.) Good luck. I'll check back to see how you make out.
By Jason Ellis on Tuesday, May 15, 2001 - 12:47 pm:
Anonymous, I must respectfully disagree with the statement about phases generating peaks on their own. Thermal degradation of the phase polymer is always occuring, obviously increasing as temperature increases. This is an equilibrium process that occurs at the same rate throughout the column at a given oven temperature. Since it is an equilibrium process there is no way the phase in the column can generate distinct peaks upon breakdown. Instead, a stable baseline is generated as bleed fragments from throughout the column elute into the detection zone.
The phenomenon you describe ("picket fence" peak distribution) is something we often see with polymer degradation (in pyrolysis applications, for example). However, this degradation material must be focused on the phase of the column in order to produce distinct, sharp peaks in the chromatogram. If the degradation material is not focused, then we end up with a series of various sized fragments eluting into the detector at the same time -- hence the baseline elevation during column heating.
Frequently, people using MS detectors will see this phenomenon and scan on the peaks to find that the spectrum matches a siloxane compound. Certainly, the stationary phases of most columns are siloxane in nature, however the inlet septum is also made of a silicone material. "Picket fence" peak distribution patterns in blank runs are frequently derived from septum bleed rather than column bleed. Septum bleed fragments can be nicely focused on the front of the analytical column and chromatographed once the oven is temperature programmed.
Columns sometimes may produce "peaks" per se, however it would not be from the stationary phase material but rather from sample material introduced at some time previously. Sometimes we can see contaminated columns elute broad peaks due to semivolatile contamination. These peaks are usually easy to pick out in a chromatogram as their peak widths do not match those of the compounds injected for that run. These are compounds that were injected some time ago and did not elute during the course of their run due to poor volatility.
Contaminant peaks are contaminant peaks, and regardless of their source they must be removed. However, if we realize where they are coming from it helps in efficiently troubleshooting the system and getting everything back up-and-running again.
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