The pros and cons of crimp vs screw top vials

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

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Obviously Crimp vials are cheaper. They could seal better? The screw top vials are easier to use.

What are other pros and cons of each? What do you use each for?
Naturally, choice is up to the end user and instrument requirements. Some instruments require magnetic seals, and unless there has been a recent introduction of a magnetic screw cap vial in a 1-2mL volume, crimp vials would be required.

As for sealing properties, if sealed properly, I see no advantage of one over the other.

One disadvantage of crimp seal vials is the variation in the depth of the vial opening lip, which is the location of the seal. Septa thickness varies as well; therefore, to reduce or eliminate problems with making a proper seal, use an adjustable crimper.

Screw cap vial are easier to use; however, if the cap is screwed on too tight, the septa stretches creating resistance to the needle, possibly bending the needle. If the threading tool used during manufacturing of the vial has worn down and not noticed right away, threads are distorted, resulting in the cap not fitting properly. If caps are washed and dried at high temperature for reuse, they eventually dry out. This can be dangerous when screwing the cap onto the vial. The cap may break, possibly breaking the vial neck, resulting in the possibility of a hand injury.

If one wants to store samples and have better protection against degradation, and/or loss of sample due to pierced septa, use of a Mininert Valve has two lines of defense. It has an open/close valve and septa in the cap. This valve is very useful when storing standards. When searching for vial valves, such as the Mininert type, pay close attention to the thread type. Not all vials of the same volume, such as 2mL Micro Reaction vials, have the same thread size as standard vials. Match the thread size, not vial volume.

Linda
lkochraney wrote:
Naturally, choice is up to the end user and instrument requirements. Some instruments require magnetic seals, and unless there has been a recent introduction of a magnetic screw cap vial in a 1-2mL volume, crimp vials would be required.

As for sealing properties, if sealed properly, I see no advantage of one over the other.

One disadvantage of crimp seal vials is the variation in the depth of the vial opening lip, which is the location of the seal. Septa thickness varies as well; therefore, to reduce or eliminate problems with making a proper seal, use an adjustable crimper.

Screw cap vial are easier to use; however, if the cap is screwed on too tight, the septa stretches creating resistance to the needle, possibly bending the needle. If the threading tool used during manufacturing of the vial has worn down and not noticed right away, threads are distorted, resulting in the cap not fitting properly. If caps are washed and dried at high temperature for reuse, they eventually dry out. This can be dangerous when screwing the cap onto the vial. The cap may break, possibly breaking the vial neck, resulting in the possibility of a hand injury.

If one wants to store samples and have better protection against degradation, and/or loss of sample due to pierced septa, use of a Mininert Valve has two lines of defense. It has an open/close valve and septa in the cap. This valve is very useful when storing standards. When searching for vial valves, such as the Mininert type, pay close attention to the thread type. Not all vials of the same volume, such as 2mL Micro Reaction vials, have the same thread size as standard vials. Match the thread size, not vial volume.

Linda


A quick trick I learned on the Mininert caps for changing the septa. Someone lost our tool for inserting the septa but I found that "Pin Pusher" the same size used to push the heater pins out on the connectors in a 5890 will accept the cylindrical septa and you can use it to push them into the cap in a pinch.
The past is there to guide us into the future, not to dwell in.
This is good information to have. Thank you for sharing.
mariosapm wrote:
... The screw top vials are easier to use.
...


Oh yes. Especially easier to open.
Why not use something in the middle between crimp and screw, I mean snap on type ?
My understanding is the Mininerts were not designed to seal well in the freezer. They are great for a working standard for daily usage.

For long term, I would not trust any vial with an open cap and septum, crimped or not. Solid screw on cap with little or no headspace has been the most trustworthy in my experience.
In my experience crim is far superior for both HPLC and GC unless you need to open them again for some reason.

I was doing an analysis with screw caps on the HPLC and watched my check standard mysteriously degrade during the course of the sequence. I switched to crimp and that stopped. The septa on the screw vials don't seal as well.

I also see that on the GC with volatile solvents like Methylene chloride hexane and isopentane. The screw cap ones are frequently evaporated off after injection by the next day. The crimp cap ones often hold their seal much longer.

Finally I had an HPLC that about 1 out of 20 injections with a screw cap vial the septa would get pulled and crumpled by the needle into the sample rather than just nicely puncture it. We stopped that by switching to a higher quality cap. We were using a generic and we switched to Agilent caps and vials.

On the other hand I am using up our crimp cap 22ml headspace vials for SPME and I hate using the decapping pliers to open them up after I'm done to retrieve the stir bar.
Yama001 wrote:
My understanding is the Mininerts were not designed to seal well in the freezer. They are great for a working standard for daily usage.

For long term, I would not trust any vial with an open cap and septum, crimped or not. Solid screw on cap with little or no headspace has been the most trustworthy in my experience.


I have always used the Mininerts for my working standards for Volatiles analysis which are stored at -18C and have had no problems as long as I don't forget to close the slide. Biggest problem is when using larger needles on the 100 -250ul syringes it cores out the septa bad and you have to replace often. I definitely would not store standards for months or years in them, but our volatiles standards do last for a month at a time, which is their working expiration date per methods.

As above I have also had the problem with the septa being pushed down into the vial when using screw cap vials. It happened when using the ones where the septa come separate from the caps, and not already seated in them.

I prefer the crimp type for most applications. I did have a former colleague who was afraid to use them because he had cut his hand with one when it broke many years ago. After observing him crimping caps on the vials I understood why it happened. He would hold the crimper in one hand and the vial in the other hand in what looked like a savage death grip and his arms would be shaking from squeezing so hard on the crimper. I finally showed him that if you just slide the vial and cap up into the crimper and put a little pressure on it with your pinky and squeeze the crimper gently you never have to worry about the vial breaking because you are no longer torquing the vial while it is held in the crimper. :)
The past is there to guide us into the future, not to dwell in.
They have crimp and decap tools out there that really make crimp vials a lot easier. Most of the cons for crimp vials are having to manually crimp them and then not being able to get them back off but they now have tools to remove the crimped cap too!! Super Cool!

https://www.youtube.com/watch?v=qjyLDGyrpwM&t=9s
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