The Promise and Challenges of Capillary LC: Lessons From Pittcon 2026 Networking Session

Capillary liquid chromatography (CapLC), broadly encompassing microflow and capillary‑scale separations, has been discussed, developed, and periodically rediscovered for more than three decades. Theoretical advantages, higher separation efficiency, improved mass sensitivity, reduced solvent consumption, and enhanced compatibility with mass spectrometry are well documented. Yet, despite these benefits, CapLC has not achieved widespread adoption as a routine analytical technique outside specialized domains.

At Pittcon 2026, a diverse group of scientists from academia, instrument manufacturing, column production, and industrial laboratories convened for an open networking session titled “CapLC Conversations: Expert Insights on Small‑Scale, Yet Big‑Impact Chromatography.” ¹ Rather than presenting polished success stories, the session focused on candid discussion: Why CapLC remains niche, which barriers are real vs. perceived, and what conditions might finally allow the technique to cross from early adoption into mainstream practice.

Although not well-defined by the industry (see discussions below), the group established a rough framework for the discussion on capillary chromatography as packed columns with 0.75 mm to 300 mm inner diameters (i.d.).

This synopsis distills those discussions into several core themes: education and perception, instrumentation and detection, column manufacturing and materials, robustness and usability, economic and regulatory drivers, and emerging application spaces. Together, they provide a realistic assessment of where CapLC stands today—and where it may be headed.

Education, Familiarity, and the Persistence of Perception

One of the most consistently cited barriers to CapLC adoption is lack of education and familiarity. Many participants noted that capillary‑scale separations are rarely covered in undergraduate curricula and only sporadically addressed in graduate training. As a result, even experienced chromatographers often encounter CapLC as an unknown technology rather than a natural extension of analytical LC.

This educational gap has practical consequences. Users accustomed to conventional 4.6 mm i.d. or 2.1 mm i.d. columns may underestimate the importance of extra‑column effects, flow‑path volumes, and fittings when working at the capillary scale. When early attempts produce distorted peak shapes or unstable baselines, users may conclude that CapLC is inherently fragile or unreliable, reinforcing longstanding perceptions formed during earlier generations of instrumentation.

Several panelists emphasized that many of these issues are not unique to CapLC but become more visible as column diameters shrink. The transition from 4.6 mm to 2.1 mm columns already forces analysts to consider tubing lengths, detector volumes, and system dispersion. CapLC simply pushes this awareness further. In this sense, CapLC is less a radical departure than a continuation of trends already familiar to users of modern ultrahigh-pressure liquid chromatography systems.

Instrumentation: Progress, Limitations, and Mismatched Expectations

Instrumentation emerged as a central theme throughout the discussion. While most major LC manufacturers now offer systems capable of low‑flow operation, many of these platforms are adaptations of analytical‑scale instruments rather than systems designed from the ground up for capillary workflows.

Two dominant approaches were discussed:

1. Metered‑down analytical pumps, often using flow splitting; and
2. Dedicated low‑flow or syringe‑based pumping systems.

Each approach carries trade‑offs. Split‑flow systems can provide continuous operation and leverage robust analytical pumps, but they sacrifice solvent efficiency and require careful plumbing to minimize dispersion. Syringe‑based systems offer precise low‑flow delivery but suffer from interruptions during refilling and sensitivity to pressure fluctuations.

Participants noted that pump performance typically degrades below tens of microliters per minute for conventional reciprocating designs, creating a practical lower limit for many “standard” LC systems. Below this range, flow stability and gradient accuracy become increasingly difficult to maintain.

Importantly, several contributors emphasized that CapLC instrumentation has historically been marketed primarily as front ends for mass spectrometry, rather than as general‑purpose chromatographic systems. This positioning reinforces the perception that CapLC is a specialized tool rather than a broadly applicable analytical technique.

Detection Challenges Beyond Mass Spectrometry

While mass spectrometry pairs naturally with capillary‑scale separations, detection remains a major challenge for applications relying on optical detectors, particularly ultraviolet (UV) absorbance.

Beer–Lambert law imposes a fundamental constraint: as column diameters shrink, optical path lengths decrease, reducing the absorbance signal. Increasing path length often increases detector volume, introducing peak broadening that negates chromatographic gains. Achieving the optimal balance—sometimes described as a “Goldilocks zone”—remains a technical challenge

On‑column detection and fluorescence detection were discussed as potential solutions, particularly where derivatization is acceptable. However, many routine HPLC users are reluctant to add derivatization steps, limiting the adoption of fluorescence‑based approaches in industrial workflows.

Although commercial low‑volume UV flow cells have improved in recent years, panelists agreed that detection remains one of the least mature aspects of CapLC outside mass spectrometry (MS)‑based applications. Furthermore, alternative detection techniques, including refractive index, charged aerosol, evaporative light scattering, and circular dichroism detectors, are scarce or unavailable for use at the capillary scale.

Column Manufacturing: Materials, Packing, and Supply‑Chain Constraints

Column manufacturing at the capillary scale presents challenges that are often invisible to end users. While capillary columns require less stationary‑phase material, they demand greater labor, tighter tolerances, specialized packing procedures, and more rigorous quality control. These factors largely offset material savings, resulting in prices comparable to analytical columns.

Participants described several technical hurdles:

• Packing efficiency, especially for superficially porous particles, becomes increasingly difficult as column diameters shrink.
• Wall effects and surface roughness play a larger role at small diameters, motivating the use of glass‑lined or polymer‑based column bodies.
• Frit technology remains a persistent bottleneck, with limited material options below 0.5 mm i.d. and trade‑offs between strength, permeability, and chemical compatibility.

The discussion highlighted that capillary columns rely on a narrow materials ecosystem, often dominated by poly(ether ether ketone). (PEEK), PEEK-coated silica tubing (PEEKsil), polyimide-coated fused silica, and glass‑lined stainless steel. Advancing beyond current pressure and durability limits would require coordinated changes across suppliers of tubing, fittings, frits, and column hardware—a nontrivial supply‑chain challenge given the relatively small market size. A discussion of the frit construction and composition (stainless steel, silica) was particularly illuminating, highlighting the manufacturing challenges presented by packed column CapLC.

Robustness, Durability, and the Reality of Use

Perhaps the most sobering conclusion of the session was that capillary columns are inherently less forgiving than analytical columns. Even under ideal conditions, smaller columns typically support fewer injections before performance degrades. This limitation becomes especially pronounced for complex matrices such as proteomics samples, biological fluids, or environmental extracts.

Two dominant failure modes were discussed:

1. Chemical and physical degradation of the stationary phase, often due to overload or matrix components.
2. Emitter or frit failure, particularly for columns with integrated electrospray emitters.

While these issues are well understood in specialized communities such as proteomics, they pose a significant barrier for routine analytical labs accustomed to thousands of injections from a single analytical column.

Some participants proposed rethinking column formats altogether—multi‑column cartridges, replaceable modules, or application‑specific “black box” systems—to shift expectations away from long column lifetimes and toward predictable, managed replacement.

Method Development: Familiar in Theory, Subtle in Practice

From a theoretical standpoint, method development at capillary scale closely parallels analytical LC. Scaling relationships based on column diameter allow straightforward translation of flow rates, gradients, and injection volumes.

In practice, however, gradient delay volume and system dwell volume become much more significant at low flow rates. Differences between mixing strategies, pump architectures, and system layouts can dramatically affect gradient reproducibility.

While method‑translation calculators and modeling tools exist, participants noted that many analysts underestimate the impact of “everything between the pump and the column head.” This gap reinforces the perception that CapLC is difficult, even when the underlying separation science is familiar.

Green Chemistry: Benefit or Secondary Consideration?

CapLC is often promoted as a green technology due to dramatic reductions in solvent consumption. Session participants acknowledged these benefits but offered a nuanced perspective.

For fee‑for‑service laboratories, such as drug‑testing facilities, solvent savings translate directly into cost reductions and can be a meaningful driver of adoption. In contrast, for large pharmaceutical organizations, solvent costs in analytical laboratories are often dwarfed by synthetic operations, for example, making green arguments less compelling on their own.

Nevertheless, environmental, social, and governance (ESG) considerations are becoming increasingly important, particularly in regulated industries. CapLC, and other potentially “greener” techniques such as SFC, may gain greater traction when solvent reduction aligns with regulatory pressure, as illustrated by successful applications in oligonucleotide analysis where restrictions on certain mobile‑phase additives created a strong incentive to adopt lower‑flow methods.

Defining Microflow and Capillary: A Terminology Problem

A recurring challenge highlighted in the discussion is a lack of consensus on terminology. Definitions of microflow, capillary LC, and nano‑LC vary widely across vendors and users, with flow‑rate ranges and column diameters often overlapping.

This ambiguity complicates communication, marketing, and education. Several participants suggested that clearer, community‑driven definitions—based on column diameter, flow rate, or application context—could help normalize expectations and reduce confusion among potential adopters.

It was suggested by one participant that "IUPAC defines a capillary column qualitatively as a chromatography column of small diameter and notes that the term is ambiguous unless it is qualified as packed or open tubular. For liquid chromatography, it is therefore preferable to use the term packed capillary LC column and to state the internal diameter explicitly. In practical LC usage, [at least one] major vendor considers capillary columns as having an internal diameter of less than 0.5 mm. [In contrast,] modern hardware commonly uses columns with internal diameters in the range of 75 micrometers, to 300 micrometers, although this diameter range will continue to evolve with technology." This highlights the need for improved definition within the community.

Applications Where CapLC Already Delivers

Despite its challenges, CapLC is far from a failed technology. Participants highlighted several application areas where it already provides clear, demonstrable value:

• Proteomics, particularly at capillary (rather than nano) flow rates, where modern mass spectrometers no longer require extreme miniaturization.
• Oligonucleotide analysis, driven by regulatory pressure to reduce problematic mobile‑phase additives.
• High‑throughput and fast separations, where compatibility with electrospray ionization at moderate flow rates offers both speed and sensitivity.
• Targeted analyses where sample amounts are limited, or sensitivity is paramount, or, as in the case of studies using radio chemistry, for example, the high cost of solvent and solvent disposal.

These successes suggest that CapLC adoption is most likely to expand through specific, high‑value workflows, rather than as a universal replacement for analytical LC.

Regulation, Standardization, and the Cost of Change

Regulatory inertia remains one of the strongest barriers to adoption. Many validated methods—particularly pharmacopeial assays—rely on decades‑old column formats and operating conditions. Even modest changes, such as reducing column diameter from 4.6 mm to 2.1 mm, can trigger extensive revalidation.

Participants emphasized that simplicity often outweighs performance in regulated environments. A method that works with minimal training and intervention is difficult to displace, regardless of theoretical advantages.

Some contributors envisioned future systems where validated methods are embedded within application‑specific instruments, reducing user discretion and lowering barriers to regulatory acceptance.

Rethinking the Path Forward

Rather than asking how CapLC can replace analytical LC, many participants argued that the more productive question is where does CapLC fit best. The consensus view was that CapLC is unlikely to become a universal solution but can thrive in well‑defined niches where its advantages are decisive.

Several strategies emerged:

• Focus on fit‑for‑purpose instruments rather than general‑purpose platforms.
• Embrace modularity and disposability to manage durability limitations.
• Improve education and messaging, particularly around modern instrumentation improvements.
• Align CapLC adoption with regulatory, economic, or performance drivers, not abstract advantages.

Conclusion: From Promise to Practical Impact

The Pittcon 2026 CapLC networking session made clear that the science behind capillary liquid chromatography is sound—but science alone is not enough to drive adoption. Education, perception, instrumentation design, supply‑chain coordination, and regulatory realities all play decisive roles.

CapLC is neither a failed idea nor an inevitable replacement for analytical LC. Instead, it represents a powerful, specialized tool whose impact depends on thoughtful application and realistic expectations. By focusing on workflows where its strengths matter most—and by addressing practical barriers rather than theoretical ones—the community may finally enable CapLC to deliver on its long‑recognized promise.

Acknowledgments

Thank you to the participants in the networking session for a lively and frank discussion. Secondly, a huge thank you to Axcend for sponsoring the session and aiding in its organization and promotion. A special thank you to James Grinias, M. Farooq Wahab, Samuel Foster, and Fabrice Gritti for their incredible insight and assistance in preparing for the session.

Reference
1. CapLC Conversations: Expert Insights on Small‑Scale, yet Big‑Impact Chromatography. Presented at Pittcon 2026, San Antonio, TX, March 10, 2026.