What Is Endcapping in HPLC Columns

Endcapping the bonded phase of an HPLC column reduces silanol interactions and protects the silica support from dissolution. Modern HPLC columns use various endcapping techniques. Endcapping replaces free silanol groups on the bonded stationary phase with trimethylsilyl (TMS) groups, improving column performance and stability.

What Is Double Endcapping?

Double endcapping refers to endcapping the column twice (or even triple). This process further minimizes silanol interactions and enhances stability in the mid pH range.

For methods developed in the mid pH range, using an endcapped column is recommended. Endcapping also reduces silica dissolution as pH increases, extending column life.

When to Use a Non-Endcapped HPLC Phase

Non-endcapped phases are ideal for low pH methods. Agilent Zorbax StableBond bonding, for example, is a non-endcapped bonded phase that performs well at low pH down to pH 1. It is designed for selectivity and long lifetime under acidic conditions. This patented sterically protected bonding is available in five selectivities: C18, C8, CN, Phenyl, or C3.

Agilent StableBond Sterically Protected Surface Reaction

HPLC Columns for LC/MS

When selecting HPLC columns for LC/MS, chromatographers consider factors such as resolution, flow rate, and stationary phase choice. Shorter, high-resolution columns are often preferred for simple analytes, offering high throughput while maintaining separation efficiency.

Many LC/MS analyses run at lower flow rates, typically from µL/min up to 1 mL/min. Narrow bore columns (e.g., 2.1 mm id) reduce solvent usage and provide higher resolution and sensitivity than larger columns. For most LC/MS methods, an endcapped C18 phase is recommended. For fast, high-throughput separations, the Agilent Poroshell 120 EC-C18 column is ideal. Its larger frit accommodates dirtier samples, such as blood plasma, which may otherwise clog columns with smaller frits.

Conclusion

To extend column lifetime, ensure the method pH is within the recommended bonded phase range. Endcapped columns are ideal for mid-range pH methods, while non-endcapped columns excel in low pH applications.

Additional protection can be achieved using HPLC syringe filters, inline filters, and HPLC guard columns. For recommendations on HPLC columns or consumables, including Idex fittings and in-line filters, please contact Chrom Tech.