Chromatography Forum

What are the pros/cons of screw vs crimp caps?

What benefit do you see from either?

With electronic tools that crimp and decap for you I wonder who would want to screw all those lids on by hand? Are there benefits I don't know about?

As long as they are crimped properly there is no real difference.

I have crimped literally thousands of vials and never had the electronic crimpers. At Pittcon this year they had the Lab Gauntlet challenge and one of the tasks was to crimp and decrimp 6 vials using the electronic tools. Honestly I could have crimped them 3x faster using hand crimping tools.

The only advantage screw caps would have over crimp ones would be if you have to replace caps multiple times on the same vial. We can use our standards for months and recapping every day you eventually end up with a vial with a broken top from the decrimper. That would be the biggest advantage I could think of. A minor one would be not having to adjust the crimping tool to always give a flat top crimp on the caps, since the central adjustable piece always seems to unscrew over time and give caps with a hump.

I prefer replacing the cap on each vial I plan on injecting a second time, typically handling relatively volatile samples. It is much easier to replace a screw cap than a crimp cap.

I agree that when only crimping/decapping a few at a time the manual tools are a little faster/not as heavy to use.. but I will say the electronic tool is really nice to have when I have to do a whole rack of vials...especially when decapping..wrist just gets tired towards the end and the electronic tool really helps.

As for screw vials, the sealing can be a problem depending on the cap/vial combo, if you twist to far it can ruin the whole seal, same if you don't twist far enough.

Interesting discussion

I have found that using screw caps is far easier and just as fast in terms of capping, uncapping and recapping for both 2ml vials and 22ml SPME headspace vials..

Unlike crimp caps I have never had a problem with screw caps

I found that efficacy is just as good providing that you use the correct septa and certainly overcomes potential errors introduced by incorrect crimping.

Although screw caps are slightly more expensive, how many vials do you actually need to cap/uncap per day? What is the actual time difference between the two methods? Also weigh in the cost of crimpers and potential cost losses from using badly adjusted crimpers.

With crimped vials I would always have to check anyway with an extra slight hand/fingers twist to ensure that each cap was tight. So little or no advantage in time over using a screw cap

I was converted after having had so many problems decrimping and with continually adjusting the crimper with constant use - and other labs "borrowing" my best crimpers

I never had a problem. I consider them equivalent and never affect my results.

Depends on the person doing the capping. If I am using screw caps or crimp caps, it does not matter. If I am leaving the re-capping to someone else, I want properly trained (cannot twist the cap) crimp tops every time. In my opinion, anything in screw tops accessible to the "public" is disposable. That being said, if the sample is running once and then disposed, screw tops are way easier to throw on from the drawer.

Best regards,

AICMM

Interesting conversation so far...
With screw caps, if you had to unscrew them and recap them and say you had a whole tray of vials and maybe you had to do it several times in a given period of time...(these are the unknowns to me)...how much of a hassle is this? Would there be any use for handheld tools that could unscrew and recap them automatically? I am not sure there would be much room for improvement on the time it takes to do the actions, but maybe simply the ergonomics involved in the manual repetition of it all?

I just saw this topic. I find crimps seal better especially after repeated punctures. Most people tend to over-torque the screw caps but are more consistent with the crimping.

I had an HPLC assay where the check standard is injected every 10 samples from the same vial. I noticed the standards were degrading with the screw caps but when I switched to crimp or pre-punched snap it held up.