Overview

Autosampler vials used in HPLC, UHPLC, LC-MS, and GC applications are commonly manufactured from high-quality borosilicate glass. MICROSOLV™ autosampler vials are produced using First Hydrolytic Class borosilicate glass, providing excellent chemical resistance, dimensional stability, and compatibility with analytical workflows.

Two common expansion classes used in analytical vial manufacturing are:

• 33 Expansion Glass
• 51 Expansion Glass

Both materials meet the performance requirements of chromatographic applications, but there are differences in their physical characteristics and manufacturing processes.

What Is Expansion Glass?

The expansion number refers to the coefficient of thermal expansion of the glass.  Thermal expansion describes how much the glass changes dimension when exposed to temperature changes.

Lower expansion values generally indicate:

• Greater thermal stability
• Improved resistance to thermal shock
• Higher processing temperatures during manufacturing

Higher expansion values generally indicate:

• Slightly greater dimensional response to temperature change
• Lower manufacturing temperatures
• Different glass formulations for specific applications

Characteristics of 33 Expansion Glass

33 expansion borosilicate glass is commonly classified as:  Type I, Class A Borosilicate Glass

Characteristics include:

• Low thermal expansion coefficient
• Excellent thermal stability
• High mechanical hardness
• Strong chemical resistance
• Excellent dimensional consistency

Because of its lower expansion coefficient, 33 expansion glass typically requires higher forming temperatures during manufacturing.

Typical processing temperatures may approach:  Approximately 1200°C

MICROSOLV clear RSA™ autosampler vials utilize this glass type.

Characteristics of 51 Expansion Glass

51 expansion borosilicate glass is commonly classified as:  Type I, Class B Borosilicate Glass

Characteristics include:

• Slightly higher thermal expansion coefficient
• Excellent chemical resistance
• Suitable thermal stability for analytical applications
• Efficient manufacturing characteristics

Because it can be formed at somewhat lower temperatures, manufacturing may occur near:  Approximately 1000°C

MICROSOLV amber RSA™ vials commonly utilize 51 expansion glass.

Chemical Resistance and Analytical Performance

Both 33 and 51 expansion glass are considered First Hydrolytic Class borosilicate materials.

This provides:

• Resistance to aqueous solutions
• Resistance to acidic solutions
• Resistance to neutral solvents
• Compatibility with most chromatographic solvents
• Low extractables under normal analytical conditions

For routine chromatography applications, both glass types provide excellent analytical performance.

Manufacturing Considerations

During vial production, temperature variations can occur between different portions of the vial, including:

• The vial body
• The neck
• Closure threads
• Base geometry

These temperature differences may influence surface properties during manufacturing.

MICROSOLV controls these variables through precision manufacturing processes designed to maintain:

• Consistent dimensions
• Proper autosampler compatibility
• Surface quality
• Manufacturing repeatability

Which Glass Should You Choose?

For most analytical laboratories, the choice is typically determined by application requirements rather than performance limitations.

Consider 33 Expansion Glass When:

• Maximum thermal stability is desired.
• Clear glass is preferred.
• High mechanical hardness is important.

Consider 51 Expansion Glass When:

• Amber glass protection is required.
• Light-sensitive samples are being analyzed.
• Standard analytical performance requirements apply.

Both materials are suitable for demanding chromatography environments.

Key Takeaways

• Both 33 and 51 expansion glass are First Hydrolytic Class borosilicate materials.
• 33 expansion glass has a lower thermal expansion coefficient and greater thermal stability.
• 51 expansion glass has a slightly higher expansion coefficient and is commonly used in amber vials.
• Both glass types provide excellent chemical resistance for chromatographic applications.
• MICROSOLV™ vials are manufactured to precise dimensional standards regardless of expansion class.
• The choice is often driven by application requirements such as light protection and thermal performance.

Additional Resources

For autosampler vial specifications, glass options, closure configurations, product images, and ordering information, view:  Autosampler Vial Specifications, Borosilicate Glass Options, Closure Systems, and Ordering Information