Sample vial major components with cap, septa, and vial body. Let us know the detail about these components. 1. Sample vial material 1.1 Borosilicate glass The Borosilicate glass can be divided into Grade A(33) and Grade B(55) and silanized or deactivated glass. Each has its unique features. As a chemically inert glass, Grade A is widely used in laboratories, especially in chromatographic analysis applications. Grade B contains trace amounts of boron, sodium, and more alkali metals than Grade A glass, but it can still meet laboratory use. Silanized or deactivated glass is suitable for pH-sensitive compounds, trace analysis, and long-term sample storage.
1.2 PP and TPX Polypropylene (PP) is suitable for short-term storage of most laboratory chemicals and it is frequently used in ion chromatography. Because PP sample vials can be directly incinerated after being sealed, the exposure of harmful substances is also reduced. While the polymethylpentene (TPX) vials are usually used in situations that require visual inspection of samples or high-temperature use. TPX vials are brittle at room temperature.
2. Cap 2.1 Crimp cap The crimp cap has an excellent sealing effect without evaporating. Cap squeezes the septum between the rim of the glass vial and the folded aluminum cap. Please note the crimped cap bottles are cheap but need to be equipped with crimp tools, and the caps cannot be reused
2.2 Snap Top cap The snap top cap is an extension caused by its attempt to restore its original size of the sealing method of the crimp cap. By the tension, it forms a seal among the glass, bottle cap, and septum. The plastic bayonet cap can be closed without any tools. Compared with the other two sealing methods, the bayonet cap sealing effect is not that good. Too tight, it would be difficult to close the bottle cap and may break. If it is too loose, the sealing effect will be poor and the septum may leave its original position.
2.3 Screw thread cap The screw cap is universal. Tightening the cap will exert a mechanical force, squeezing the septum between the rim of the glass bottle and the aluminum cap. In the process of piercing and sampling, the screw cap has an excellent sealing effect, and mechanically resists the septum. No tools are required for assembly.
3. Septa Septa is one of the key components for sample introduction into the chromatographic column. All columns must have a high enough air carrier column head pressure to allow airflow through the column. The role of the septa is to keep the chromatographic system sealed and prevent air from entering the system. Septa of different sizes and types of materials are available for injector type and analysis requirements. Do not screw the septa too tightly when replacing it. Generally, the septa are changed at room temperature, which will become tighter after the temperature rises. If the septa are screwed too tightly, it will be difficult to inject samples and easy to bend the syringe needle.
Septa are usually chosen according to the recommended upper limit temperature. The low-temperature cushion is soft, good sealing performance. Compared with the high-temperature septa, the puncture resistance is better. However, if the use temperature of the septa is higher than the recommended temperature, leakage or decomposition may occur, which will lead to sample loss, column carrier gas flow decline, column life is short, ghost peak, etc. The septa separate the sample flow path from the outside and its blocking effect. When the injection needle is inserted, the pressure inside the system can be maintained to prevent leakage and prevent external air from infiltrating and polluting the system. Septa are generally made of silicone rubber with high-temperature resistance and good airtightness.