Ultralow Flow Liquid Chromatography Used to Analyze Small Biological Samples

In a recent review article published in the Journal of Separation Science, researchers from Northeastern University and the University of Oslo provided an overview of ultralow flow liquid chromatography (ULF LC) and how it can be used to analyze small biological samples (1).

ULF LC uses ultra-narrow bore columns and mid-range pL/min to nL/min flow rates. These columns are typically 2-30 μm in inner diameter and provide high sensitivity and resolution. ULF LC be used in the analysis of limited-quantity biological samples like circulating tumor cells, organelles, extracellular vesicles and more. The technique is often coupled with mass spectrometry (MS).

Over the last decade, there have been multiple developments in ULF LC and its use in bioanalysis, particularly for amount limited samples, or samples that are not available in large quantities for analysis. In many cases, the LC technology must be miniaturized to effectively analyze these small samples.

The researchers focused their review on LC miniaturization, highlighting select column formats for LC chromatography including:

• Particle-packed columns: This the most common column variant in LC featuring capillaries packed with porous silica particles as a stationary phase, the researchers wrote.
• Monolithic columns: Introduced in the 1990s, these columns have a porous structure that does not require the use of frits, which results in decreased sample loss.
• Open tubular columns: These columns have a limited stationary phase, which has caused it only to be relevant in niche studies.

The researchers also outline specific uses for ULF LC in the analysis of biological samples. For example, silica-based open tubular columns can be used to analyze endogenous metabolites, peptides, and intact proteins. In another study, researchers found the technique to be useful for the isolation of rare cells from biological matrices, such as blood.

The review article also discussed the coupling of mass spectrometry and ULF LC as an effective method for analyzing biological samples. However, the researchers conclude, ULF LC is not necessarily dependent on MS.

“As microfluidic chip-based systems and other miniaturized analytical platforms are becoming more attractive research tools (take organ-on-a-chip platforms as an example), there literally might not be room for a mass spectrometer in an integrated device,” the researchers wrote. “However, it is a safe bet to assume that miniaturization will continue to be a critical direction, as one of the analytical research advancements, and the need for high-resolution separations and high sensitivity molecular detection, profiling, and characterization will be in substantial demand.”

Reference

Greguš, M.; Ivanov, A. R.; Wilson, S. R. Ultralow Flow Liquid Chromatography and Related Approaches: A Focus on Recent Bioanalytical Applications. Journal of Separation Science 2023. DOI:10.1002/jssc.202300440.