When an HPLC separation produces poor peak shape or insufficient resolution, analysts often begin by adjusting the stationary phase, particle size, mobile phase, temperature, or flow rate. However, the column hardware itself can also affect chromatographic performance.
Polar and metal-sensitive analytes can interact with stainless steel surfaces within the flow path. These interactions may contribute to analyte adsorption, peak tailing, band broadening, reduced recovery, and lower resolution.
A 2026 study published in the Journal of Chromatography Open examined whether Dursan®-coated stainless steel column hardware could improve the enantioselective separation of these challenging analytes. The results demonstrate how replacing a reactive metal surface with an inert barrier coating can produce sharper peaks and better resolution without sacrificing the strength and pressure capability of stainless steel.
Stainless steel is commonly used for HPLC column hardware because it is durable and capable of withstanding high operating pressures. However, the metal surface may interact with certain analytes through adsorption, electrostatic interactions, and metal chelation.
Compounds that are particularly susceptible to these interactions include:
When these compounds interact with the column hardware, adsorption and desorption processes can introduce additional dispersion into the separation. The result may be broader or asymmetrical peaks, reduced analyte recovery, and insufficient resolution between enantiomers.
Analysts sometimes address these problems through acid passivation or by adding metal-chelating compounds such as EDTA or citric acid to the mobile phase. However, passivation may provide only temporary benefits, while mobile phase additives can create complications for LC-MS analysis, including ion suppression and source contamination.
Instead of repeatedly treating the surface or modifying the mobile phase, an inert coating can address the source of the interaction directly.
Dursan is a functionalized, amorphous silicon oxide-like coating applied to stainless steel through a thermal chemical vapor deposition process. The coating creates a bioinert, iron-free barrier between the analyte and the underlying metal surface.
Dursan coatings are typically 400 to 1,600 nm thick, hydrophobic, and stable across a pH range of 0 to 14. Because the coating is applied directly to stainless steel hardware, analysts can retain the mechanical strength and pressure capabilities of the original component while reducing opportunities for analyte-metal interactions.
This approach allows laboratories to preserve their existing analytical workflows without relying on polymer-lined column hardware or introducing additional chelating compounds into the mobile phase.
The researchers compared conventional stainless steel column hardware with Dursan-coated hardware using two chiral stationary phases:
Similarly packed coated and uncoated columns demonstrated comparable quality-control performance, helping the researchers isolate the effect of the column hardware.
The ZWIX(+) columns were used to evaluate the enantiomer separation of amino acids and related compounds. The QN-AX columns were used to examine hydroxy carboxylic acids with varying levels of hydrophilicity and susceptibility to metal interactions.
For many of the amino acids analyzed using ZWIX(+), the Dursan-coated hardware improved peak symmetry, reduced plate height, and increased chromatographic resolution.
Two notable examples were glutamic acid and aspartic acid:
| Analyte | Performance improvement with Dursan-coated hardware |
|---|---|
| Glutamic acid | 28% higher resolution |
| Aspartic acid | 36% higher resolution |
Highly metal-sensitive amino phosphonic acids also demonstrated pronounced improvements. Because these compounds have strong metal-binding properties, they are particularly susceptible to adsorption on stainless steel surfaces. Covering the available metal-binding sites improved peak symmetry, reduced plate height, and enhanced resolution.
The study also evaluated hydroxy carboxylic acids using QN-AX columns. Dursan-coated hardware produced measurable improvements for two particularly hydrophilic analytes:
| Analyte | Metric | Performance improvement |
|---|---|---|
| 2-Hydroxyglutarate | Reduced plate height | 22% lower |
| 2-Hydroxyglutarate | Resolution | 10% higher |
| Lactate | Reduced plate height | 35% lower |
| Lactate | Resolution | 17% higher |
Less hydrophilic hydroxy carboxylic acids showed little improvement when analyzed using coated hardware. This finding reinforces an important point: the value of an inert column surface depends on the analyte’s susceptibility to surface interactions.
Analytes with a stronger affinity for stainless steel have more potential to benefit from Dursan-coated hardware. Compounds that interact minimally with the metal surface may demonstrate little difference between coated and uncoated columns.
Chromatograms of 2-hydroxycarboxylic acids. (a) 2-Hydroxyglutarate (with MP-6), (b) lactate (with MP-5), (c) 2-hydroxy-3methylbutyrate (with MP-5) and (d) 2-hydroxy-3-methylpentanoate (with MP-5), tested on coated (shown in red) vs uncoated (shown in black) QN-AX column.
Metal-analyte interactions can also affect mass spectrometry. Metal-sensitive analytes may form adducts that distribute the analyte signal across multiple ion species, potentially reducing effective MS sensitivity.
The study notes that Dursan-coated column hardware and tubing can reduce metal leaching and associated adduct formation for polar, chelating analytes. This can be particularly valuable when mobile phase chelators would otherwise introduce ion suppression, contamination, or additional method complexity.
As column efficiency improves, extra-column contributions become increasingly important. Stainless steel connecting tubing, fittings, valves, and other components can still contribute to analyte adsorption and band broadening, even when an inert column is used.
Extending Dursan-coated surfaces throughout the analytical flow path may offer additional performance gains by reducing the number of reactive metal sites the sample encounters. A consistently inert flow path can help analysts address adsorption at its source instead of troubleshooting individual symptoms throughout the system.
For laboratories working with metal-sensitive analytes, the effects of uncoated stainless steel can extend beyond chromatographic performance. Poor peak shape, analyte loss, and inadequate resolution may lead to repeated analyses, additional method development, wasted samples, and lost analyst time.
The study demonstrates that Dursan-coated HPLC column hardware can provide meaningful improvements for analytes that are particularly susceptible to metal-surface interactions. Potential benefits include:
By creating an inert barrier over stainless steel, Dursan can help laboratories obtain more reliable results while reducing the inefficiencies associated with difficult, metal-sensitive separations.
SilcoTek can apply Dursan to stainless steel HPLC columns, tubing, fittings, valves, and other components within the analytical flow path. Contact our coating experts to discuss your analytes, equipment, and performance challenges.
Maalouf, M.; Janek, M.; Friedrich, S.; Hausser, N.; Bischof, J.; Lämmerhofer, M. “Bioinert Chiral Columns with Dursan-Coated Stainless-Steel Hardware for Enantioselective Liquid Chromatography of Polar Analytes.” Journal of Chromatography Open, 2026, 9, 100347. https://doi.org/10.1016/j.jcoa.2026.100347.