2.2 Bayonet cap
A plastic cap over the edge of the sample vial forms a seal by pressing the pad between the glass and the stretched plastic cap. The tension is formed due to its attempt to restore its original size, which creates a seal between the glass, the cap and the pad. The plastic bayonet cap can be covered without any tools.
The sealing effect is not as good as the other two sealing methods. Too tight, the cap is difficult to cover and may break. Too loose, the sealing effect will be poor and the pad may leave the original position.
2.3 Screw cap
The screw cap is universal. Tightening the cap will apply a mechanical force to squeeze the pad between the edge of the glass and the aluminum cap.
The screw cap has an excellent sealing effect and mechanically resists the pad, during the piercing sampling process. Moreover, there is no tool needed.
The screw cap PTFE/silica pad is attached to the polypropylene cap by a non-solvent bonding process. The bonding technique is designed to ensure that the pad is always with the cap during transport and when the cap is placed on the vial.
This bonding helps prevent the pad from escaping during use, but the primary sealing mechanism is still the mechanical force applied when the cap is screwed onto the vial.
The mechanism by which the cap is tightened is to form a seal and hold the pad in the correct position during the insertion of the needle. It is not necessary to screw the cap too tightly, otherwise, it will affect the seal and cause the pad to escape. If the cap is screwed too tight, the cap will become cup-shaped or dent.
3. Choice of the material of sample vial
Type I, 33-expanded borosilicate glass
It is currently the most chemically inert glass and is commonly used in analytical laboratories to provide high-quality results. Its expansion coefficient is about 33×10^(-7) °C, mainly composed of silicon oxide, and also contains trace amounts of boron and sodium.
Type I, 51-expanded glass
It is more alkaline than 33-expanded glass and can be used in a variety of laboratory applications.
Its expansion coefficient is about 51x 10^(-7) °C, mainly composed of silicon and oxygen, and also contains trace amounts of boron.
For analytes with strong polarity and binding to the polar glass surface of the glass, deactivation of the vial may be a good choice. The glass vials are treated with a glass phase reactive organosilane to produce a hydrophobic glass surface. Deactivated vials can be stored dry indefinitely.
Polypropylene (PP) is a non-reactive plastic that can be used where it is not suitable for glass selection. PP vials maintain a good seal when fired, minimizing the potential for exposure to potentially hazardous materials. The maximum operating temperature is 135℃.