Chromatography Forum

I'm struggling with finding the best method to do this...

Currently using Agilent zero dead volume 1/16" to 1/16" bulkhead unions (0100-1515) mounted on the side of the oven to join 0.53 mm PLOT columns to 1/16" lines. The unions come with steel ferrules.

Evidently, the way this has been being done is by using a 1/16" polyimide ferrule (0100-1512) with a polyimide sleeve (0100-1513) for the 0.53 mm column. There must be a trick to doing this as described in this document via an insertion tool to hold the sleeve in the proper position in the ferrule during installation. I don't have the insertion tool and find it very hit or miss to get the installation right and I'm never sure if it really is or not.

My question is...isn't there a alternative choice of ferrule? Why can't I use a reducing ferrule with a 0.8 mm hole that works with these 1/16" compression fittings and avoid using the sleeve? Anyone with experience using ferrules such as the CapSeal Bullet long ferrules in this application?

Note a few hard learned lessons...

- You cannot use the steel ferrule that comes with the union with the polyimide sleeve. It'll never tighten.

- If you try and use a short graphite or Vespel ferrule in these 1/16" fittings, you can't get them tightened because the threading for the counter-bored nut in only so deep into fitting. It bottoms out before the ferrule is compressed and further tightening of the nut in an attempt to compress the ferrule damages the threads on the nut. If you then use this damaged nut on another union, the damaged threads of the nut will gall and damage the threads on the union. I destroyed a few unions before I realized what was happening.

Ordinary 0.8 mm bore 1/16 inch ferrules are profiled to fit Swageloks rather than Agilent connectors. They will seal, but might (depending on what the sleeve you are using is actually doing) leave more of a dead volume. Depending on flow rates this volume may or may or may not be significant.

Peter

Thanks. My flow rate will be about 12 ml/min.

I noticed I can actually thread the end of the column past the bottom of the union. I'm hoping if I can get the ferrule tightened with the column threaded past the bottom of the seat of the union by a few millimeters, and the difference in dead volume wouldn't be significant.

Excessive dead volume is evidenced by peak fronting and broadening right? I have before chromatograms using the old ferrule/sleeve connections. I'll compare what I get with that.

Threading the column past the tip of the ferrule as you plan to do will give you the dead volume that you are trying to avoid - a place where the gas does not sweep cleanly through the connector. Keep in mind that some compounds will adsorb / absorb onto / into the ferrule, but if it worked with a ferrule and sleeve it should be OK with just a ferrule.

Dead volumes cause symmetrical broadening and tailing. Fronting (peaks rising slowly and dropping quickly) is caused by concentration overloading i.e. peaks that are way too big or analytes that are a poor match to the column stationary phase.

Peter

One piece Valco ferrule available from Restek 20144. Should work well in your fitting since you are using (as far as I can tell) a Valco bulkhead union. Doesn't solve your "where does the column end" problem since the only real answer to that is to look at the column in the union and just barely stick it below the hole. Your other option is to lightly seat the column in a fitting outside the oven where you can peak down the top and then liquid paper mark the spot for when you install it in your GC.

Best regards,

AICMM