How Much Do You Know About the Correct Capping of a Sample Vial?

Sample vials are common chromatographic consumables in laboratories. Due to their tightness, they are very suitable for transportation and long-term storage of samples. When analyzing samples in chromatograms, have you encountered bad data parallelism and miscellaneous peaks in data analysis?

When encountering this situation, many will first analyze whether the experimental process and experimental method are correct, but in fact, the first step should be to see whether the cap of the sample vial is screwed correctly. Because incorrect capping or pressing (for crimp sample vial) will also interfere with the chromatographic analysis. Seeing this, I believe you must be a question mark. Don’t believe it, because the experimental test results show that over-tightening the cap of the sample vial will increase the risk of peaks.

Let us take a look at the risks of incorrectly tightening/pressing the cap, and how to judge the correct tightening/pressing state of the cap. (Only take a 9mm threaded 2mL sample vial, PP cap, and PTFE/silicone gasket as an example. The same applies to the clamp cap gasket.)

The wrong situation
1. The cap is too tight
When the cap is tightened too tightly, the septum is likely to be visibly recessed. The tighter the screw, the more severe the recession of the septum will be. At this time, the septum is in a very tight state. This tight state may lead to the increased probability of septal debris when the chromatographic needle is injected into the sample, which will lead to inaccurate chromatographic analysis and poor sample parallelism.

2. The cap is too loose
When the cap is not screwed tight enough, the septum is not well fixed between the cap and the vial mouth at this time, which will cause:
1) The tightness of the sample vial is not enough, the sample in the sample vial is easier to volatilize and lose, causing problems such as inaccurate sample concentration;
2) During chromatographic injection, the septum is more likely to be punctured.

The right situation
When the cap is tightened correctly, the septum appears flat to a slightly concave state. By observing the status of the septum, you can judge whether the lid is tightened correctly, and adjust the tightness of the lid. For those with stronger hands, the lid may be too tight with a slight twist, so you need to pay special attention.

For crimping vials, if you want to cap properly, you need to adjust the capper. The following is how to adjust the capper:

First, adjust the positioning screw: first, loosen the lock nut, and then determine the height of the positioning screw according to the required tightness (if the actual gland is loose, lower the screw height; if the actual pressure is too tight, then the screw height adjustment), and finally screw the lock nut to the bottom locking position.

Secondly, in the case that the gland can’t be adjusted well only by the positioning screw, an Allen wrench needs to be used to adjust the screw in the middle of the gland. If the pressure is too loose, turn the Allen key counterclockwise, if it is too tight, turn it clockwise.

So, after learning the importance of capping, you can check it before the experiment. The HAWACH sample vial is made of high-quality silicate glass to ensure that the sample is free from contamination. At the same time, the septum is made of a non-adhesive process, which not only ensures the purity of the sample but also retains the high resilience of the septum, which protects the sample needle. HAWACH provides various colors and specifications of sample vials and matching cover pads to customers.