Formic acid is one of the most commonly used additives in HPLC, UHPLC, and LC-MS mobile phases due to its volatility, strong buffering characteristics, and compatibility with mass spectrometry. Because it is frequently used in sample preparation and storage, analysts often ask whether formic acid solutions can be safely stored in borosilicate glass autosampler vials or glass inserts.

In general, formic acid is considered compatible with borosilicate glass. However, there are several factors to consider when storing formic acid-containing solutions for extended periods.

Is Formic Acid Compatible with Borosilicate Glass?

Yes.

Borosilicate glass is widely used throughout analytical laboratories because it offers:

• Excellent chemical resistance
• Low reactivity
• Good thermal stability
• Compatibility with many acids and solvents

For typical chromatography applications, formic acid solutions can be stored in borosilicate glass autosampler vials and inserts without significant compatibility concerns.

Formic Acid Decomposition During Storage

One consideration when storing formic acid solutions is that formic acid can slowly decompose over time.

Decomposition may produce:

• Carbon monoxide (CO)
• Water

The rate of decomposition increases as temperature increases. For this reason, formic acid is often supplied in:

• Plastic containers
• Vent-cap containers when appropriate
• Refrigerated storage conditions

When storing formic acid-containing samples, minimizing heat exposure can help maintain solution stability and reduce pressure buildup within closed containers.

Potential Pressure Buildup

As decomposition occurs, gas formation may result in gradual pressure increases within tightly sealed containers.

Although this effect is generally minimal under normal laboratory storage conditions, it becomes more important when:

• Solutions are stored for extended periods
• Elevated temperatures are encountered
• Highly concentrated formic acid solutions are involved

Proper storage conditions help minimize these effects.

Trace Element Leaching from Glass

Another consideration applies not only to formic acid, but to virtually all solutions stored in glass containers.

Over time, glass surfaces may contribute trace amounts of materials to stored solutions, including:

• Sodium
• Boron-containing species
• Silicic acid derivatives

This phenomenon is commonly referred to as glass leaching.

The amount of leaching depends on factors such as:

• Storage duration
• Solution composition
• Temperature
• Glass quality
• Surface area-to-volume ratio

Why Glass Quality Matters

Higher-quality laboratory glass, such as First Hydrolytic Class Borosilicate Glass, is specifically designed to minimize chemical interaction with stored solutions.

Benefits include:

• Lower extractables
• Reduced ionic contamination
• Improved analytical reproducibility
• Enhanced sample integrity

These characteristics are important for trace-level chromatography and LC-MS applications.

Considerations for LC-MS Applications

LC-MS analyses may be sensitive to even very low levels of contamination.

When working with trace-level analytes:

• Use high-quality borosilicate glass vials.
• Minimize unnecessary storage times.
• Prepare fresh standards when possible.
• Evaluate storage stability as part of method development.

These practices can help reduce potential variability associated with long-term storage.

Best Practices for Formic Acid Storage

For optimal analytical performance:

• Store formic acid solutions at appropriate temperatures.
• Use high-quality borosilicate glass vials or inserts.
• Avoid prolonged storage when freshly prepared solutions are practical.
• Monitor sample stability when conducting validated studies.
• Ensure vial caps and septa are compatible with the storage conditions.

These precautions can help maintain sample integrity and analytical reliability.

Conclusion

Formic acid is generally compatible with borosilicate glass autosampler vials and inserts and is routinely used in chromatography laboratories worldwide. The primary considerations for storage are the gradual decomposition of formic acid, which can generate carbon monoxide and water over time, and the possibility of trace elemental leaching from the glass surface. Using high-quality borosilicate glass and appropriate storage conditions helps ensure reliable performance for HPLC, UHPLC, and LC-MS applications.