How can we select a suitable vial?

**Original from Internet

Vials may be small, but there is a "great deal" to consider. When selecting the right sample vial for a particular application, three decisions must be made: septa, cap and the vial itself.

1.PTFE is recommended for single-use sampling; it offers excellent solvent resistance and chemical compatibility; it does not reseal after puncture; it is not recommended for long-term sample storage.

2. PTFE/silicone is recommended for multiple injections and sample storage; offers excellent resealing properties; exhibits the chemical resistance of PTFE prior to puncture, whilst the septum displays the chemical compatibility of silicone after puncture; operating temperature range: -40 °C to 200 °C.

3. Pre-cut PTFE/silicone provides good venting to prevent vacuum formation within the sample vial, thereby ensuring excellent sampling reproducibility; eliminates needle blockage at the bottom after sampling; offers good resealing capability; recommended for multiple injections; operating temperature range: -40 °C to 200 °C.

4. Diaphragm-free PE offers the same advantages as PTFE

Caps have there styles:Crimp cap/Snap cap/ screw caps. Each sealing method has its own advantages.

These caps compress the septum between the rim of the glass sample vial and the flanged aluminium cap. They provide an excellent seal, effectively preventing sample evaporation. The position of the septum remains unchanged when the autosampler’s needle pierces it during sampling. A capping machine is required to seal vials fitted with clamp caps. For small numbers of samples, a manual capping machine is the best option. For large volumes of samples, an automatic capping machine may be used.

Snap-on caps are an extension of the clamp-on sealing method. A plastic cap fitted over the rim of the sample bottle forms a seal by compressing the septum between the glass and the expanded plastic cap. The tension in the plastic cap is generated by its attempt to return to its original size. This tension creates a seal between the glass, the cap and the septum. Plastic snap-on caps can be fitted without the need for any tools.

Screw cap is universal. Tightening the cap applies mechanical force, compressing the gasket between the rim of the glass vial and the aluminium cap. During the piercing sampling process, the screw cap provides an excellent seal by mechanically holding the gasket in place. No tools are required for assembly. The PTFE/silicone gasket of the screw cap is secured to the polypropylene cap using a solvent-free bonding process. This bonding technology is designed to ensure that the gasket remains firmly attached to the cap throughout transport and when the cap is fitted to the sample vial.

The mechanism of tightening the cap serves to form the seal and to hold the gasket in the correct position during the insertion of the sampling needle. It is not necessary to overtighten the cap, as this may compromise the seal and cause the gasket to detach or become displaced. If the cap is overtightened, the gasket may become cupped or develop indentations.

1. Type I, 33-expansion borosilicate glass is currently the most chemically inert glass available. It is commonly used in analytical laboratories to ensure high-quality experimental results. Its coefficient of thermal expansion is approximately 33 × 10⁻⁷ °C. It is primarily composed of silicon and oxygen, and also contains trace amounts of boron and sodium.

2. Type I, 51-expansion glass is more alkaline than 33-expansion glass and can be used for a wide range of laboratory applications. Its coefficient of thermal expansion is approximately 51 × 10⁻⁷ °C. It consists mainly of silicon and oxygen, and also contains trace amounts of boron.

3. Deactivated Glass (DV) For analytes with strong polarity that may bind to the polar surface of the glass, deactivated sample vials may be a suitable choice. The glass sample vials are treated with organosilane compounds that react with the glass phase, creating a hydrophobic surface. Deactivated sample vials can be stored in a dry environment indefinitely.

4. Polypropylene (PP) is a non-reactive plastic that can be used where glass is not suitable. Polypropylene sample vials maintain a good seal even when exposed to fire, thereby minimising the risk of exposure to potentially hazardous substances. The maximum operating temperature is 135 °C.