Choosing Autosampler Vials and Caps for HPLC & GC Analysis

In HPLC and GC, the choice of vials and caps is critical to ensure accurate and reliable results. The vial is the container for the sample injected into the chromatograph, and its design has a significant impact on the analysis. This discussion will cover the various types of HPLC and GC vials and caps, their materials, features, and selection considerations. Aijiren autosampler vials are suitable for HPLC, LC/MS, GC, and GC/MS instruments and applications.

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HPLC & GC Autosampler Vial Types

1. Screw Cap Vials

Screw cap vials are one of the most commonly used vials in HPLC applications. They have a threaded neck that can be easily sealed with a screw cap. They can be easily opened and closed, which is convenient for sample preparation. Compatible with most autosamplers, it increases the degree of automation in the laboratory. It is very suitable for routine analysis that requires rapid access to samples. The working temperature of the bottle is below 100℃ and the cap is below 90℃.

2. Crimp Top Vial

Crimp top vials are sealed with a crimp cap to ensure a secure closure. The position of the septum remains unchanged when the autosampler's injection needle pierces the sample. The crimping process of the crimp top vial produces a tighter seal, which is critical for volatile samples that may evaporate. Crimp top vials are better suited for high-pressure applications because they minimize the risk of leaks under pressure. It is often used in applications that require high sensitivity or when handling volatile compounds.

3. Snap Top Vial

Snap-on vials are equipped with a snap-on cap for quick and secure closure without crimping or tightening. Snap-on vials are easy to open and close, making them user-friendly. It is usually cheaper than crimp top vials.

Snap top vials are suitable for general laboratory use where sample volatility is not a major issue.

4. Micro Vial

Micro vials are smaller sample vials designed for very low volume samples (usually less than 1 ml). Micro inserts can be used with screw cap, crimp cap, or snap cap vials. Different bottom shapes are available, including flat bottom, conical bottom, and conical bottom with poly spring.

Micro inserts maximize sample recovery and make sample removal easier when used with autosampler vials because the conical shape reduces the surface area inside the vial.

For more information on Autosampler Vials for Gas Chromatography, refer to this article: 2 mL Autosampler Vials for Gas Chromatography

Materials used for HPLC and GC Vials

1. Borosilicate glass Vial

Borosilicate glass is widely used due to its chemical resistance and low reactivity. The inertness minimizes sample contamination. The transparent properties allow visual inspection of the contents. Amber glass is mainly used for light-sensitive samples to protect the contents from UV degradation.

2. Plastic Vial

Polypropylene or polyethylene vials are an alternative to glass. Polypropylene, PP is a non-reactive plastic that can be used where glass is not an option. Polypropylene vials can maintain a good seal when burned with fire, thereby minimizing exposure to potentially hazardous substances. The maximum operating temperature is 135 °C. Polypropylene vials are lightweight and shatterproof, making them safer to use.

Choice of Septa type

PTFE/silicone septa are suitable for multiple injections and sample storage. Widely used due to its chemical resistance and ability to withstand multiple punctures. Before puncture, it has the chemical resistance of PTFE, and after puncture, the septum will have the chemical compatibility of silicone. The most versatile multifunctional septum material, which can be customized in a variety of hardnesses to meet the requirements of different needles, is the first choice for most GC/HPLC applications.

Pre-cut PTFE/silicone provides good ventilation to prevent vacuum formation in the sample bottle, thereby achieving excellent sampling reproducibility. Avoid the problem of difficult puncture, and after continuous injection, the pressure inside and outside the vial can be balanced without negative pressure.

Considerations for Selecting Autosampler Sample Vials and Caps

When selecting HPLC & GC autosampler vials and caps, the following factors should be considered:

1. The nature of the sample (volatile vs. non-volatile) will affect the choice of sample bottle type. For volatile compounds, it is recommended to use a crimp sample bottle with a secure seal to prevent evaporation.

2. Choose the sample vial size according to the amount of sample you usually analyze. The larger the sample volume, the larger the sample volume may require.

3. Make sure the selected vial is compatible with your specific autosampler model to avoid problems during automatic sample handling.

4. When choosing the vial material and septum type, consider the chemical properties of the sample to avoid reactions that may affect the results.

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How to choose the injection volume for a 2ml autosampler vial?

The lower end of the injection needle should be 2~3mm from the bottom of the autosampler vial; if the sample is too little, it is recommended to use micro insert in the autosampler vial. 

If there are many samples, 1mL is enough. Too much may easily cause other unnecessary troubles. The sample volume is small, generally around 0.3mL. If the sample volume is less than 0.3mL, it is recommended to add micro insert. It is recommended to keep the height of the injection needle as it is. It is not recommended to adjust the needle height at will. If the height of some brands of injection needles is adjusted incorrectly, the needle may skip and fail to inject the sample.

In summary, choosing the right HPLC GC vials and closures is critical to achieving reliable analytical results. The choice between screw caps, crimp caps, snap caps, or micro vials depends on specific laboratory needs, including sample type, volume requirements, and compatibility with autosamplers. Additionally, careful consideration of the material (whether glass or plastic) and closure type will further improve sample integrity during analysis. By understanding these factors, laboratories can optimize their chromatography workflows and improve the overall efficiency of the analytical process.