In High Performance Liquid Chromatography (HPLC) analysis, the choice of autosampler vial material can have a significant impact on the integrity and reliability of your analytical results. The composition of the vial can influence the interactions between the sample and the container, leading to undesirable effects that can affect the accuracy and reproducibility of your measurements.
The chemical compatibility between the vial material and the sample components is a critical consideration. Certain materials, such as borosilicate glass or high quality polymers such as polypropylene, are generally inert and will not interact with a wide range of analytes. However, some plastics or other materials may leach additives or contaminants that can interfere with the analytes of interest, leading to inaccurate quantification or the presence of extraneous peaks in the HPLC chromatogram. For example, some plastics may contain plasticisers or other additives that can be extracted by the sample, causing unwanted interference. In contrast, borosilicate glass is known for its excellent chemical resistance and inertness, making it a preferred choice for HPLC applications where sample purity is paramount.
The propensity of the vial material to adsorb or desorb sample components is another critical factor. Some materials, such as certain types of plastic, may have a higher affinity for certain analytes, causing them to be retained on the vial walls. This can lead to sample loss, reduced sensitivity and poor reproducibility. Conversely, desorption of previously adsorbed compounds can lead to carryover and cross-contamination between samples. Glass and certain polymers, such as polypropylene, generally have lower adsorption characteristics than some other plastic materials, making them more suitable for minimising sample loss and ensuring consistent results.
The potential for the vial material to release extractables or leachables is another important consideration. Extractables are compounds that can be released from the vial material itself, while leachables are compounds that can migrate from the vial closure system, such as the septum or cap. These contaminants can interfere with the analytes of interest, leading to false positive results or baseline interference. Vial materials should be thoroughly evaluated for their ability to minimise the release of extractables and leachables to ensure that the sample composition remains unchanged during storage and analysis.
For volatile analytes, vial material can also affect the ability to retain sample components during storage and analysis. Materials with high gas permeability, such as certain polymers, can allow increased sample evaporation, resulting in analyte loss and inaccurate quantification. Glass and some specialised polymer vials, such as those with low adsorption coatings, are generally better at maintaining the integrity of volatile samples by minimising evaporation losses.
The thermal stability of the vial material is particularly important when HPLC analyses involve elevated temperatures, such as in the case of reversed-phase liquid chromatography (RPLC) or high-temperature liquid chromatography (HTLC). Some materials can degrade or undergo structural changes at higher temperatures, potentially affecting sample integrity or introducing interfering compounds. Borosilicate glass and certain high performance polymers have excellent thermal stability, making them suitable for HPLC applications that require elevated temperatures.
By carefully considering the vial material and its compatibility with your specific HPLC application, you can minimise the impact on sample integrity and ensure the reliability of your analytical results. Choosing the right vial material, in combination with other best practices for HPLC sample handling and preparation, can contribute significantly to the overall success of your HPLC analyses.