Preparation of headspace vials and samples

Headspace vial

The most commonly used headspace vial specifications on the market are 20ml, in addition to 10ml, 6ml and other headspace vials.

The headspace sampler is recommended to use a new headspace vial for each sample preparation. The headspace vial can be reused after cleaning and drying, but repeated use of the headspace vial may cause defects due to multiple compression, high and low temperature cycles, cleaning collisions, and other factors. There is a risk of cracking during the heating and pressurization process. It is recommended not to reuse the headspace vial more than 5 times.

Only when the user's headspace vial specifications, including outer diameter, height, or volume, comply with the manufacturer's regulations (consistent with the headspace vial size provided at the factory), can the normal use of the headspace sampler be guaranteed

Sample placement

Sample Volume: Usually, the sample loading in the headspace vial does not exceed 50% of the vial volume, and it is prohibited to exceed 80%. Usually, the Sample volume is 2-10ml. In theory, increasing the sample loading is beneficial for substance detection. However, there is no linear correlation between the Sample volume and the detection limit of related substances. Substances with different properties are affected to varying degrees by the Sample volume, which is related to the distribution coefficient of related substances in the sample system. Increasing the Sample volume of benzene derivatives can significantly increase the concentration of the gas phase in the headspace vial, thereby improving the detection ability; For ethanol, the effect of Sample volume is relatively small. (The sample volume here refers to the sample volume)

In addition to paying attention to the Sample volume, it is also important to note that if the sample is a volatile substance, it needs to be transferred and sealed as soon as possible.

When conducting repetitive experiments, it is necessary to ensure that the Sample volume, and remaining space in the vial are the same.

Sealing of headspace vial

The sealing gasket of the headspace vial comes in various materials, corresponding to different application scenarios. When the equilibrium temperature is low, conventional silicone pads can be chosen; For high temperature or low content analysis, it is recommended to use PTFE spacers (silicone pads with polytetrafluoroethylene film). There are also various options for sealing aluminum caps. For example, when the equilibrium temperature is low, a conventional aluminum cap can be chosen. For higher temperature analysis, a thickened sealing aluminum cap or a bimetallic aluminum cap (mixed with Fe) can be chosen. For higher temperature analysis, such as near 300 ℃, a steel clamp vial cap can be chosen.

Poor sealing of the sample vial cap can lead to air leakage, poor repeatability, and inaccurate analysis results. After pressing the headspace vial tightly with a capping pliers, you can rotate the headspace vial cap slightly with one hand to see if it is tightened. If it is easier to twist, press it again. The sealing gasket and aluminum cover are both disposable products and cannot be reused.