How To Choose A Sample Vial When Doing An Experiment?
When there is a problem with our experimental results, we always think of the sample vial in the end, but it is what we should consider first. When choosing the right vial for your application, you need to make three decisions: the capping pad, the cap, and the vial itself.
1. About the choice of Inner cap pad
PTFE
Recommended for a single injection
Excellent solvent resistance and chemical compatibility
Will not reseal after piercing
Long-term sample storage is not recommended
PTFE/silica gel
Recommended for multiple injections and sample storage
Excellent resealing characteristics
Chemical resistance to PTFE prior to piercing. After piercing, the capping pad will have chemical compatibility with silicone
Working temperature: -40 °C to 200 °C
Pre-cut PTFE/silica gel
Provides good ventilation to prevent vacuum in the sample vial for excellent sample reproducibility
Eliminate clogging of the bottom needle after sampling
Good resealability
Recommended for multiple injections
Operating temperature is the same as PTFE/silica gel
PE without cap pad
With the same advantages as PTFE
2. About the choice of cap
There are three types of caps for the vial: the jaw cap, the bayonet cap, and the screw cap. Each type of sealing has its own advantages.
2.1 Jaw cap
The jaw cover squeezes the pad between the bottle edge of the glass sample vial and the flanged aluminum cap.
It has an excellent sealing effect and can effectively prevent the sample from evaporating.
When the syringe of the autosampler is pierced, the position of the pad remains the same.
A capper is required to seal the jaw cap vial.
For a small number of samples, a manual crimper is the best choice. For a large number of samples, an automatic capper can be used.
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.
Deactivated glass
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 plastic
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℃.
