Why Capillary LC Is the Future of LC-MS Sensitivity

What makes capillary LC so powerful—and why are more scientists paying attention to it?

In this episode of ‪ChromatographyTalk‬, David sits down with Samuel Foster of Axcend to discuss how capillary liquid chromatography is changing the conversation around LC-MS sensitivity, solvent consumption, instrument footprint, and chromatographic efficiency.

Sam explains how lower flow rates can dramatically improve electrospray ionization performance, why capillary LC can reduce solvent usage by orders of magnitude, and where the technology is already making an impact in pharmaceutical, environmental, and radiopharmaceutical workflows.

They also discuss common misconceptions about capillary LC, why older systems gave the technology a mixed reputation, and why modern advances may make now the right time for labs to take another look.

Topics Covered:

• What capillary LC is and how it differs from traditional HPLC
• Why lower flow rates improve LC-MS sensitivity
• Solvent savings and sustainability benefits
• Extra-column effects and hidden performance killers
• Applications in pharma, biologics, drugs of abuse, and radiopharmaceuticals
• Is capillary LC ready for routine lab adoption?
• The future of liquid chromatography

Video Transcription

Capillary liquid chromatography has existed for decades, but improvements in pumps, fittings, system design, and LC–MS interfaces are giving the technique renewed relevance. In an interview for Concentrating on Chromatography, Samuel Foster discussed how capillary LC differs from conventional analytical-scale HPLC, why lower flow rates can improve electrospray ionization sensitivity, and where miniaturized LC systems could have the greatest practical impact.

Foster also explained the engineering challenges associated with operating at microliter-per-minute flow rates, the importance of controlling extra-column volume, and why applications ranging from radiopharmaceuticals to pharmaceutical analysis could benefit from dramatically lower solvent consumption.

From Undergraduate Research to Capillary Chromatography

Foster’s interest in chromatography began during his first year of university, when he joined the research group of Jim Grinias at Rowan University. What started as an undergraduate research opportunity gradually developed into a long-term focus on separation science.

According to Foster, Grinias became an important influence on his scientific career and introduced him to many aspects of chromatography, including capillary-scale separations.

That early exposure eventually shaped Foster’s doctoral research and his current work at Excend, where capillary LC plays a central role.

What Is Capillary LC?

The primary difference between conventional analytical-scale HPLC and capillary LC is the internal diameter of the chromatographic column.

Typical analytical-scale HPLC commonly uses columns with internal diameters between approximately 2.1 and 4.6 mm. Capillary LC moves to substantially smaller dimensions, typically around 0.1 to 0.3 mm internal diameter.

Reducing column diameter also requires a major reduction in mobile-phase flow.

An analytical-scale separation that might operate at approximately 1 mL/min on a 4.6 mm column can translate to flow rates around the microliter-per-minute range when using a 0.1 mm capillary column.

The purpose is to maintain an appropriate linear velocity through the stationary phase while dramatically reducing the absolute volume of mobile phase passing through the system.

In simple terms, capillary LC combines smaller columns with much lower flow rates.

The Major Benefit: Dramatically Lower Solvent Consumption

One of the clearest advantages of capillary LC is solvent savings.

Because flow rates are orders of magnitude lower than in conventional HPLC, the total amount of mobile phase required for an analysis can be reduced dramatically.

Foster described reaction-monitoring experiments in which a reaction was followed continuously for approximately 72 hours while consuming less than a microliter of total sample and less than a milliliter of mobile phase.

That difference can become especially important when a laboratory uses expensive, hazardous, or difficult-to-dispose-of solvents.

The benefits extend beyond the purchase price of mobile phases. Lower solvent consumption can also reduce:

• Waste generation
• Disposal requirements
• Storage requirements
• Environmental burden
• Handling of hazardous materials

For laboratories operating many chromatographic systems continuously, even relatively small reductions per analysis can translate into substantial savings over time.

Why Lower Flow Can Increase LC–MS Sensitivity

Reducing flow does not necessarily mean sacrificing analytical sensitivity. When capillary LC is coupled to electrospray ionization mass spectrometry, the opposite can occur.

Foster explained that lower flow rates can improve ESI efficiency.

In conventional electrospray at analytical-scale flow rates, comparatively large droplets are generated. These droplets must undergo multiple evaporation and desolvation processes before gas-phase ions reach the mass spectrometer.

Heated gases and other source parameters are commonly used to accelerate this process.

At capillary-scale flow rates, much less solvent reaches the source. Smaller initial droplets can be generated, meaning less solvent must evaporate before ions are transferred into the gas phase.

The result can be improved ionization efficiency.

Although the precise improvement depends on the analyte and instrument configuration, Foster cited literature values suggesting approximately a four- to tenfold improvement in ESI-MS sensitivity when capillary LC is properly implemented.

This combination of reduced solvent consumption and potentially improved MS sensitivity is one of the major arguments for miniaturized LC–MS workflows.

Translating an Existing HPLC Method

Moving a method from analytical-scale HPLC to capillary LC is not necessarily as simple as reducing the flow rate.

Theoretical calculations can provide a strong starting point. Foster noted that Excend uses a method-translation calculator that allows users to enter parameters from an analytical-scale method and obtain corresponding capillary-scale conditions.

However, the calculated conditions may still require experimental optimization.

For example, a translated method may predict a flow rate of 1 µL/min, while practical testing could show that 1.5 µL/min provides the optimum separation.

Method translation can therefore bring the user close to the final conditions, but some fine-tuning is often necessary.

This is one of the practical barriers laboratories must consider when adopting capillary LC. Existing methods may not always transfer perfectly without further development.

Why Solvent Delivery Becomes More Difficult

Delivering mobile phase reproducibly at very low flow rates creates different engineering requirements from conventional HPLC.

Traditional analytical HPLC systems typically use reciprocating piston pumps. While one piston delivers solvent, another refills, allowing essentially continuous flow.

Such systems also commonly incorporate components including:

• Check valves
• Pulse dampeners
• Additional tubing and connections

At analytical-scale flow rates, the additional volume created by these components may have relatively little impact.

In capillary LC, however, every microliter becomes important.

Foster explained that the Excend system uses a syringe-based pumping architecture. Instead of continuously cycling reciprocating pistons, a syringe is filled with enough solvent for the chromatographic run and then dispenses that mobile phase in a controlled step.

This approach can eliminate components such as pulse dampeners and check valves, reducing both internal system volume and the number of components that can potentially contribute to problems.

Extra-Column Volume Can Destroy a Separation

Controlling extra-column volume is one of the most important requirements in capillary LC.

At conventional analytical-scale flow rates, one microliter of additional tubing volume is generally insignificant because the mobile phase passes through it almost immediately.

At a flow rate of approximately 1 µL/min, however, the same microliter represents roughly one minute of additional residence time outside the column.

That difference can severely broaden chromatographic peaks and reduce separation efficiency.

Foster therefore identified treating a capillary system like a conventional analytical HPLC system as one of the most common mistakes.

A piece of unnecessary tubing, excessive connection volume, or poorly designed fitting may have little impact in analytical-scale LC but can become a major source of dispersion in capillary chromatography.

Careful system configuration is therefore essential.

Radiopharmaceuticals as a Particularly Attractive Application

Among the potential applications discussed during the interview, Foster highlighted radiopharmaceutical analysis as one of the most promising.

The reason again comes down to solvent consumption.

Mobile phases used in radiochemical analysis may become contaminated with radioactive material and can require controlled storage until radioactivity has decayed sufficiently for disposal.

Reducing a waste volume from liters to milliliters can dramatically simplify storage, handling, and disposal.

Instead of managing large containers of radioactive mobile phase for extended periods, a laboratory could potentially reduce the waste volume by orders of magnitude.

Foster also sees broader potential across the pharmaceutical industry, particularly when standardized methods are operated on many instruments at multiple sites.

If comparable analytical performance can be obtained using substantially less solvent, the cumulative economic and environmental impact can become significant.

Lower Consumption of Challenging Mobile-Phase Additives

Miniaturization may also help laboratories reduce the amount of problematic mobile-phase additives used during LC analysis.

Foster specifically mentioned TFA and HFIP, compounds that can be required in certain chromatographic methods and that are increasingly receiving attention from an environmental perspective.

Rather than completely redesigning an established separation, capillary LC could potentially allow laboratories to retain an effective method while reducing the absolute amount of these chemicals consumed by several orders of magnitude.

This illustrates a broader advantage of miniaturization: greener chromatography does not always require replacing the chemistry of an existing method. In some cases, reducing the scale of the separation itself can substantially decrease chemical consumption.

Is Capillary LC Ready for Routine Laboratories?

Foster believes the technology is already technically ready for routine use.

Many of the problems historically associated with capillary chromatography have been reduced through improvements in instrumentation and system components.

The more difficult challenge may be regulatory acceptance.

Pharmaceutical laboratories in particular can be cautious about changing validated analytical methods. Even when method translation is scientifically straightforward, concerns over regulatory revalidation can discourage adoption.

Foster described work involving USP monograph methods, where analytical-scale procedures were translated to capillary conditions while remaining within the permitted framework.

The next important step, in his view, is wider implementation in regulated environments and greater confidence among laboratories that miniaturization does not necessarily require rebuilding a method from the beginning.

Why Some Chromatographers Remain Skeptical

Capillary LC is not a new concept. Early versions of the technology were already being investigated decades ago.

However, Foster believes that those historical experiences may actually slow current adoption.

Earlier systems could suffer from:

• Poor pump reproducibility
• Long equilibration times
• Frequent clogging
• Excessive dead volume
• Limited fitting technology
• Insufficient robustness

Researchers who used capillary LC during the 1980s, 1990s, or early 2000s may therefore remember it as technically difficult and unreliable.

Many of those limitations have since been addressed through better pumps, lower-volume connections, improved fittings, and more mature system design.

Foster’s message to users with disappointing past experiences is therefore simple: modern capillary LC deserves another look.

A Broader Trend Toward Smaller LC Columns

Capillary LC also fits within a much longer trend in liquid chromatography.

Historically, conventional HPLC frequently used 4.6 mm internal-diameter columns. Over time, laboratories moved toward smaller dimensions.

Columns around 3.0 mm were promoted as solvent-saving alternatives, followed by the widespread adoption of 2.1 mm narrow-bore columns. More recently, some manufacturers have continued pushing toward approximately 1.5 mm internal diameters.

From Foster’s perspective, capillary LC is a logical continuation of this progression.

Chromatography has consistently moved toward smaller columns, lower solvent volumes, and more efficient separations. His ideal future would see this evolution continue until capillary dimensions become a routine rather than specialized choice.

Portable HPLC and Higher Throughput

Excend itself originated from the laboratory of Milton Lee at Brigham Young University, where one of the original ideas was to develop an HPLC system compact enough to be transported to the point of analysis.

A portable chromatograph could potentially be taken directly to a contaminated environmental site, crime scene, or other location where immediate chemical analysis would be useful.

In practice, however, Foster said customers have shown particularly strong interest in two other advantages: solvent savings and compact instrument size.

If three or four capillary LC systems can occupy the same laboratory space as one conventional analytical-scale instrument, laboratories could potentially increase chromatographic throughput without expanding their physical footprint.

The result is a different value proposition from the one originally envisioned: rather than mobility alone, compact capillary LC can combine lower solvent costs with increased instrument density.

The Future of Capillary LC

Foster sees capillary LC becoming increasingly important as laboratories seek to reduce solvent use, improve sustainability, increase LC–MS sensitivity, and make better use of laboratory space.

Its advantages are particularly compelling when solvent or sample quantities are limited, when waste is difficult to manage, or when electrospray mass spectrometry is used for detection.

Challenges remain. Methods still require thoughtful translation, extra-column volume must be controlled carefully, and adoption in regulated laboratories will require confidence that performance and compliance can be maintained.

Yet the fundamental direction of LC technology already points toward miniaturization.

For laboratories interested in evaluating the approach, Foster recommends learning from groups already working with capillary systems, reviewing the available literature, and—most importantly—gaining direct hands-on experience with modern instrumentation.

After decades of technical development, capillary LC may be moving from a specialized technique toward a practical option for routine separation science.

This text has been automatically transcribed from a video presentation using AI technology. It may contain inaccuracies and is not guaranteed to be 100% correct.

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