How to choose a chromatography sample vial
2024.09.12
A. Selection of the material of vial
1. Type I, 33-expanded borosilicate glass
It is the most chemically inert glass available and is commonly used in analytical laboratories to obtain high-quality experimental results. Its expansion coefficient is about 33x10^(-7) ℃, mainly composed of silicon and oxygen, and also contains trace amounts of boron and sodium.
2. Type I, 51-expansion glass
More alkaline than 33-expanded glass and can be used for a variety of laboratory purposes. Its expansion coefficient is about 51x 10^(-7) ℃, 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, deactivating 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 where glass is not an appropriate option. Polypropylene vials retain their seal when exposed to fire, minimizing exposure to potentially hazardous substances. The maximum operating temperature is 135 ℃.
B. Selection of caps
There are three types of caps available for sample vials: crimp caps, snap caps, and screw caps. Each sealing method has its own advantages.
1.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 septa. No tools are required for assembly.
The screw cap's PTFE/silicone septa is secured to the polypropylene cap using a solvent-free bonding process. This bonding technology is designed to keep the septa and cap together during shipping and when the cap is attached to the vial. This bonding helps prevent the septa from becoming dislodged 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 septa 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 septa to fall off and become dislocated. If the cap is tightened too tightly, the septa will cup or become indented.
2. Crimp cap
The crimp cap squeezes the septa 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 septa 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.
3. Snap cap
The snap cap is an extension of the crimp cap sealing method. A plastic cap that fits over the rim of the vial creates a seal by squeezing the septa between the glass and the stretched plastic cap. The tension in the plastic cap is caused by its attempt to return to its original size. This tension creates a seal between the glass, cap and septa. The plastic snap cap snaps on without any tools.
The sealing effect of the snap cap 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 septa may move out of place.
C. Selection of sample vial septa
1. PTFE
Recommended for single injection, excellent solvent resistance and chemical compatibility, will not reseal after piercing, but long term sample storage is not recommended.
2. PTFE/silicone
Used for multiple injections and sample storage, has excellent reseal characteristics, has the chemical resistance of PTFE before piercing, and has the chemical compatibility of silicone after piercing, operating temperature range is -40 ℃ to 200 ℃ .
3. Pre-cut PTFE/silicone
Provides good ventilation to prevent vacuum from forming in the vial, resulting in excellent sampling reproducibility, eliminates bottom needle clogging after sampling, good resealability, recommended for multiple injections, operating temperature range -40 ℃ to 200 ℃.
4. PE without septa
Has the same advantages as PTFE.
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