Vials with small volume internal ID are designed to allow the user to use most of the sample which may be too low for the injection needle to reach with standard, flat-bottom vials. One drawback, is that filling microvials can lead to bubble formation in some cases requiring the user to physically shake the bubble loose for proper injection. See example of bubble in a microvial belows.
If you’re concerned about bubble formation using limited volume, consider low-volume inserts with wider, conical, internal bottoms instead. These inserts have a more narrow opening than the microvial but the bottom itself is wider. This makes the inserts less prone to bubble formation which is handy when filling many at one time.
Low volume inserts
Use these inserts with standard 9mm screw top or 12x32mm snap top autosampler vials.