How to Choose the Right Vial for Chromatography Applications By Scott Adams
For many users of chromatography vials, the vial is nothing more than a temporary container to hold a sample until it can be analyzed by gas chromatography (GC) or liquid chromatography (LC). However, choosing the correct vial, and using it properly, will go a long way toward ensuring that the results from your sample analyses are as accurate as possible. Here are a few tips for choosing the best vial for your chromatography needs.
Identify Vial Types
Many vial types are available, and it is important to be able to distinguish them based on size and closure. Vials come in various sizes, with the most common for liquid injections being 12 x 32 mm vials and 15 x 45 mm vials. Depending upon the vial manufacturer, a 12 x 32 mm vial may also be referred to as a 1.5 mL vial, a 1.8 mL vial, or a 2.0 mL vial. Vials also have different closures, including crimp/snap or screw-type closures. Screw-type closures also come in different sizes identified by the outer diameter of the mouth of the vial. The screw-type closures used on chromatography vials are either 8 mm, 9 mm, or 10 mm, with 9 mm being the most popular size.
Select the Right Vial
If using an autosampler, make sure you choose a vial that is designed to work for your specific instrument brand. For example, 11 mm crimp and 9 mm screw-cap vials will work with an Agilent® autosampler, but 10 mm and 8 mm screw caps will not. This is because the space between the cap and the shoulder of the vial needed for the autosampler to operate properly differs by instrument.
In addition to instrument requirements, you should also consider how vial color and material may affect your sample. If your sample is sensitive to light, use amber vials. If you need to view a color change (e.g., for a QuEChERS cleanup) then a clear vial is the best choice. Finally, if your analysis involves IC or the chromatography of ions, avoid glass vials/vial inserts and choose a vial made of polymeric material to avoid ions leaching out of the glass.
Choose the Correct Closure
The vial closure consists of a cap and cap liner. The cap is typically made of either aluminum for crimp seals or plastic (polyethylene, polypropylene, or a phenolic resin), for non-crimp seals. The cap liner is the septum material that is pierced by the syringe needle to extract the sample from the vial. Cap liners come in a variety of different configurations and are also made of various materials. Cap liners are typically made of rubber (natural or synthetic) or silicone. They can also be faced with PTFE on one or both sides. Make sure to choose a cap liner that is compatible with your solvent. In most cases, vial cap liners that are lined with PTFE on the side facing the sample are the best option. Vial cap liners can also come pre-slit, as either a single slit, cross-slit, or starburst. Pre-slitting the vial cap liner allows for easier needle penetration, especially for the larger needles typically used in LC autosamplers. Once the vial closure has been selected, using crimpers to secure the closure and decappers to remove it is recommended. These useful tools are specifically designed for the job and make capping and decapping a much simpler task. Crimpers and decappers are available in both electronic and manual styles.
Preserve Valuable Samples
If you have a limited amount of sample, consider using inserts for your chromatography vials. Vial inserts come in a variety of shapes and sizes. A conical insert with a plastic spring on the bottom is preferred because the spring assures a seal with the vial cap liner. In addition, it will accommodate the autosampler syringe needle and will automatically adjust to different sampling depths. Inserts typically have an outer diameter of 5 or 6 mm, so make sure to choose a vial size that will accommodate the insert. Vials with an 11 mm, 10 mm, or 9 mm outer diameter will accommodate either size insert, but vials with an 8 mm outer diameter can only use inserts that have a 5 mm outer diameter. Another option is to use vials that already have the inserts fused into them. This convenience eliminates the need for assembling the vials and inserts prior to use.