5 Points Need to Consider When Choosing An Autosampler Vial
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5 Points Need to Consider When Choosing An Autosampler Vial

Dec. 9th, 2022
There are many factors to consider when choosing a chromatography vial. Choosing the best vial for your needs will not only improve the ROI of your process, but also protect the viability of your samples. There is also a risk of sample degradation if samples are not collected and stored properly.

1. Autosampler Compatibility

Not all autosamplers are the same. Some use a robotic arm to pick up sample vials. Some use tray rotation, while others move the sampling needle to the respective vial coordinates. Autosampler vial dimensions vary. Most autosamplers are equipped with trays that use a 12x32 mm vial configuration, while some autosamplers, such as Waters Wisp, require a 15x45 mm configuration. Consult the autosampler's operating manual or the manufacturer to determine the required vial dimensions.

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2. Check the Quality of the Vials

In many cases, you are dealing with trace amounts of sample that need to be measured as accurately as possible. In addition, there may be strict requirements for inertness and cleanliness.
In any case, it is important to minimise the risk of contaminating or comprising samples. Ensure that the product you are buying has a quality certification, such as ISO 9001:2015, and verify the process by which the vials and associated accessories such as septums and inserts are manufactured.
Ensure that the vial manufacturer has a policy of clean room production and R&D/quality control measures. Experienced technicians should audit the product to ensure the highest possible quality.

3. Determine the Vial Material

Glass autosampler vials:

The most common type of autosampler vial is Type 1 borosilicate glass, which is the least reactive glass. Type 1 glass has the lowest pH shift (lowest leaching properties) and a coefficient of expansion = 33 for transparent and 51 for amber.

Plastic autosampler vials:

Plastic vials are an economical option when small volumes of vials are required. Plastic vials are mostly polypropylene (PP). Polypropylene vials are compatible with acetone, ethyl acetate, methanol, isobutyl alcohol, methanol, and methyl ethyl ketone. Incompatible with cyclohexane, ether, dichlorobenzene, pentane, methylene chloride and trichlorobenzene. 

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4. Sample Volume

The amount of sample available for analysis is important in selecting a suitable vial. If the sample volume is limitedeither regular autosampler vials, inserts for microbiological or high recovery vials should be selected.
Note: Most 12x32 mm autosampler vials hold between 1.5 mL and 2.0 mL of liquid, depending on where the manufacturer measures.Vials are full. The dimensions of the 12x32 mm vials are standard between manufacturers, but the neck length and the width/shape of the vial may vary.

Vial shoulders may vary. 12x32 mm micro vials have the same external dimensions, but the inside of the vial may be tapered.Volume or fusion inserts are included. 12x32 mm high recovery vials have an internal conical bottom allowing for maximum sample recovery.

5. Crimp Vials vs. Snap Vials vs. Screw Cap Vials, how to Choose?

Autosampler vials are available in a variety of neck finishes and apertures. The mouth opening of large or wide ID vials is approximately 40% wider than that of standard aperture vials. The larger opening reduces the risk of the autosampler needle bending during sampling.
The crimped vial compresses the septum between the rim of the glass vial and the crimped aluminium cap. This creates an excellent seal that prevents evaporation. The septum remains in place during puncturing with the autosampler needle. Crimp Cap vials require a crimping tool to carry out the sealing process. For low-volume settings, a manual crimp tool is the best choice. For larger volume settings, automatic crimpers are available.
Snap cap vials are an extension of the sealing crimp cap system. By squeezing the septum between the glass and the stretched plastic cap, the plastic cap is extended around the rim of the vial to form a seal. The plastic has a memory and wants to return to its original dimension. This tension, which causes the cap to return to its original size, is the force that forms a seal between the glass, cap and septum. The advantage of plastic snap caps is that no tools are required for assembly. Snap-top caps are a compromise sealing system.
Screw cap vials are universal. When the cap is screwed on, mechanical force is applied, squeezing the septum between the glass rim and the cap. The screw cap forms an excellent seal and mechanically holds the septum in place during drilling. No tools are required for assembly.