What are the Materials of the Sample Vials, Cap, and Septa?

The sample vial is a must for pollution detection. It is a special appliance qualified for cleaning according to the international standard: ISO3722 “Appraisal of Cleaning Methods for Hydraulic Drives and Sampling Containers”. It is different from other liquid samplers, not just a bottle of beverage can be used.

Sample vial material
The glass sample vials are most frequently seen. When talking about the material, we must first talk about the linear expansion coefficient, which refers to the change in glass length every time the temperature changes. The lower the linear expansion coefficient, the greater the temperature change the glass can withstand. The classification of laboratory glass is formulated by the USP (United States Pharmacopeia) based on its water resistance.

2ml Screw Thread Top Sample Vials

USP Type 1, Class A, 33 Borosilicate glass is the most chemically inert glass, widely used in laboratories, especially chromatographic analysis applications. Class I glass is mainly composed of silicon and oxygen, and contains trace amounts of boron and sodium. It has the lowest dissolution and a linear expansion coefficient of 33.

USP Type 1, Class B, 51 borosilicate glass is mainly composed of silicon and oxygen. It contains trace amounts of boron, sodium, and alkali metal more than Class A glass, but it can still meet laboratory use, with a linear expansion coefficient of 51(all brown glass).

Silanized or deactivated glass is a borosilicate glass that is deactivated by organosiliconizing the surface of the glass. Its glass surface has strong hydrophobicity and inertness. It is suitable for pH-sensitive compounds, trace analysis, and long-term sample storage.

In addition to glass materials, there are some other materials. As a hard material, Polypropylene (PP) can be processed into a variety of colors, with good chemical resistance, suitable for short-term storage of most laboratory chemicals. The ion content is low and can be washed with dilute acid and deionized water for the aromatic hydrocarbons or halogenated hydrocarbons whose tolerance decreases over time. PP sample vials are often used for ion chromatography. It can be directly incinerated after sealing, and the PP sample vial also reduces exposure to harmful substances.

polymethylpentene (TPX) is a hard, transparent material with a high melting point and with a use range of 0°-170°C. Due to its high transparency, TPX sample vials can replace opaque PP. Its chemical resistance is similar to PP. TPX vials are usually used in cases where visual samples or high-temperature use are required. TPX vials are relatively brittle at room temperature.

Sample vial cap
In general, it is recommended to use a solid cap for storing samples, because the hollow evaporation rate will be higher, but as mentioned earlier, even if solid, evaporation is inevitable, depending on whether this level is acceptable. Generally speaking, it is a little volatile.

However, there is one problem, that is, sometimes we worry that it will evaporate if we don’t tighten it, so we tighten it tightly, and then find that it is more volatile and sometimes the septa will swell after a long time this is because the tightening is too tight and the PTFE layer is twisted and deformed. At this time, it is easy to cause the organic solvent to penetrate the PTFE layer and cause the silicone to swell; in fact, as long as it is usually used, it only needs to be slightly tightened, because the silicone is elastic enough to ensure sealing.

Sample vial septa
Regarding the septa, the two layers are PTFE/silicone or PTFE/rubber, but the color is not a standard for distinguishing materials, because both silicone and PTFE have different colors, this should depend on the thickness: the thinner one is the PTFE layer, which should face the inside of the contact solution.