Tips for using glass sample vials with chromatographs
Author:Orgianl from Internet
Glass sample vials are commonly used consumables in gas and liquid chromatography systems; their selection, sealing method and cleanliness directly affect injection accuracy, peak shape and detection repeatability. Mastering the techniques for their proper use can effectively prevent issues such as leakage, contamination, needle blockage and baseline drift, thereby ensuring the accuracy of chromatographic analysis data.
I. Tips for Selecting the Right Specifications
Ensure that the specifications of the chromatograph’s autosampler are met; standard 2 mL glass vials are commonly used. Check that the mouth diameter, threading and height of the vial are compatible with the instrument’s tray slots to prevent vials from becoming stuck or falling out
For small sample volumes, use micro-vials; for high-concentration or volatile samples, use thick-walled, pressure-resistant glass vials to prevent evaporation, leakage or breakage.
Distinguish between screw-top and clamp-top vials; for automatic samplers, clamp-top vials are preferred as they provide a better seal; for manual sampling, screw-top vials may be used as they are easier to open and close repeatedly.
II. Key Considerations for Vial Cap Septa Compatibility
Select the septum according to the injection needle: for gas chromatography, choose a high-temperature-resistant silicone rubber septum; for liquid chromatography, choose a solvent-resistant septum to prevent contamination of the sample by leachables.
The septum should not be punctured too frequently, as repeated punctures can cause flaking and leakage, leading to blockages in the injection needle and baseline noise. It is recommended that the septum be replaced after each test.
The cap should be tightened to the correct degree; if it is too loose, the contents may evaporate or leak; if it is too tight, it may compress the septum and cause it to deform, resulting in difficulty in piercing the septum with the injection needle.
III. Sample Preparation and Injection Guidelines
The sample volume should be between one-third and two-thirds of the vial’s capacity; it must not be overfilled, to prevent spillage and contamination of the instrument during injection, nor should it be too small, to prevent the injection needle from drawing air.
The sample volume should be between one-third and two-thirds of the vial’s capacity; it must not be overfilled, to prevent spillage and contamination of the instrument during injection, nor should it be too small, to prevent the injection needle from drawing air.
Volatile samples should be sealed immediately after preparation and stored in a cool place away from light; ensure that the samples do not come into contact with air, as this may cause oxidation or moisture absorption.
Particulate matter in the sample must be filtered out in advance to prevent impurities from settling at the bottom of the vial and blocking the injection needle and tubing.
IV. Tips for Cleaning and Reusing Adapters
Reusable glass sample vials must be ultrasonically cleaned sequentially with solvent and pure water, then dried and cooled before use. It is strictly forbidden for any residue from the previous sample to remain.
Do not use sample vials that are scratched or cracked, to prevent them from shattering during high-pressure injection and damaging the chromatography injection module.
Cleaned sample vials must be fitted with brand-new septa to prevent contamination caused by the ageing of old septa.
V. Key points to avoid pitfalls in everyday use
Wipe the outside of the sample vial clean to prevent sample residues from contaminating the tray and sensor.
When using the automatic sampler, ensure the vial is positioned upright, as tilting it may result in the sampling needle failing to align correctly.
Ensure that empty bottles that are not in use for long periods are kept dust-free to prevent dust from settling inside and affecting subsequent testing.