Different caps

There are three types of caps available for sample vials: crimp caps, bayonet caps, and screw caps. Each sealing method has its own advantages.

1. Crimp cap

The crimp cap squeezes the septum between the rim of the glass vial and the crimped aluminum cap. The sealing effect is very good and effectively prevents sample evaporation. The position of the septum remains unchanged when the autosampler needle pierces the sample. Sealing crimp cap vials requires the use of a capper. For a small number of samples, a manual capper is the best choice. For large quantities of samples, an automatic capper can be used.​

2. Snap cap

The bayonet cover is an extension of the crimp cover sealing method. A plastic cap that fits over the rim of the vial creates a seal by squeezing the septum between the glass and the stretched plastic cap. The tension in the plastic cover is caused by its attempt to return to its original size. This tension creates a seal between the glass, cap and septum. The plastic bayonet cap snaps on without any tools.

The sealing effect of the bayonet cover is not as good as the other two sealing methods.

If the fit of the cap is very tight, the cap will be difficult to close and may break.

If it’s too loose, the seal won’t be as effective and the septum may move out of place.

3. Screw cap

Screw caps are universal. Tightening the cap exerts a mechanical force that squeezes the spacer between the glass rim and the aluminum cap. During the puncture sampling process, the screw cap has an excellent sealing effect and mechanically holds against the septum. No tools are required for assembly. The screw cap’s PTFE/silicone septum is secured to the polypropylene cap using a solvent-free bonding process. This bonding technology is designed to keep the septum and cap together during shipping and when the cap is attached to the vial. This bonding helps prevent the septum from dislodging during use, but the primary sealing mechanism remains the mechanical force exerted when tightening the cap onto the vial. The mechanism of the cap tightening is to create a seal and hold the septum in the correct position during insertion of the sampling needle. There is no need to tighten the bottle cap too tightly, otherwise it will affect the seal and cause the septum to fall off and become dislocated. If the cap is tightened too tightly, the septum will cup or become indented.

The material of the sample bottle itself

1. Type I, 33-expanded borosilicate glass is currently the most chemically inert glass and is commonly used in analytical laboratories to obtain high-quality experimental results. It is mainly composed of silicon oxygen and also contains trace amounts of boron and sodium.​

2. Type I, 51-expanded glass is more alkaline than 33-expanded glass and can be used for a variety of laboratory purposes. It is mainly composed of silicon and oxygen, and also contains trace amounts of boron.

3. Deactivated glass (DV) For analytes that are highly polar and can bind to the polar glass surface of the glass, deactivated vials may be a good choice. Glass vials are treated with glass-phase reactive organosilane, creating a hydrophobic glass surface. Deactivated vials can be stored dry indefinitely.

4. Polypropylene plastic Polypropylene (PP) is a non-reactive plastic that can be used in places where glass is not suitable. Polypropylene vials retain their seal when exposed to fire, minimizing exposure to potentially hazardous substances. The maximum operating temperature is 135 ℃.