Screw thread vials and caps provide low evaporation, reusability, less hand injury during manipulation than crimp seals and require no special tools. All screw threads vials and caps are differentiated by their thread finish as defined by the Glass Packaging Institute, GPI.
For screw thread vials, a two part number is assigned. For example, 8-425 neck finish represents a vial with a diameter of 8 mm across the outside of the threads and a thread style of 425.
Caps for screw thread vials are available with either an open hole for autosampler use and standard addition or with a solid top for sample storage. One piece polypropylene cap and membrane are also available. These pierceable screw thread caps are designed for one time use and reduce sample preparation time as there is no cap and seal to assemble.
Crimp top vials require lacquered aluminum crimp seals which are relatively inexpensive and, when properly assembled, provide the best seal for long term storage. Crimp seals are not reusuable.
Snap seal vials are less prone to breakage during decapping because more glass is used in the neck of the vial. The snap seal neck finish is compatible with either crimp and/or snap seals and no special tools are required to remove the cap. These vials are recommended for short term sample storage and non-volatile samples because the seal is not as secure as a crimp or screw thread seal.
Shell Vials are an economical alternative to screw thread vials for Water's HPLC autosamplers or any other autosampler that doesn’t use a robotic arm to move the vials. Most shells vials are sold with a polyethylene cap that has a starburst design for easy needle penetration.
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