Open Tubular Liquid Chromatographic System for Using Columns with Inner Diameter of 2 µm. A Tutorial

Functionalization of High-Density Polyethylene Capillaries for Open Tubular Ion Chromatography

Ion chromatography is the anion analysis benchmark. A miniature form, Open Tubular Ion Chromatography (OTIC), has attractive attributes for efficient ion separations. Here, we fabricate and characterize high-density polyethylene (HDPE) open tubular anion exchange columns (OTCs). We attach positively charged latex particles onto negatively charged capillary surfaces. For efficient OTIC, column diameters need to be < ∼20 µm; functionalizing the bore is challenging. Methods to introduce acid groups to an HDPE capillary bore, e.g., sulfonation using chlorosulfonic or sulfuric acid solutions, with or without grafting of an aromatic ring through photo- or chemical grafting first, are explored. Following quaternary ammonium latex attachment, the ion exchange capacity and separating abilities of each OTC were measured as an index of OTC performance. Gradual loss of capacity was observed for many of these; high-resolution mass spectrometry confirmed the leaching of detached oxidized/sulfonated oligomeric fragments and consequent poisoning of the latex sites. Ways to ameliorate this and/or to rejuvenate the columns are also described.

Liquid phase detection in the miniature scale. Microfluidic and capillary scale measurement and separation systems. A tutorial review

Microfluidic and capillary devices are increasingly being used in analytical applications while their overall size keeps decreasing. Detection sensitivity for these microdevices gains more importance as device sizes and consequently, sample volumes, decrease. This paper reviews optical, electrochemical, electrical, and mass spectrometric detection methods that are applicable to capillary scale and microfluidic devices, with brief introduction to the principles in each case. Much of this is considered in the context of separations. We do consider theoretical aspects of separations by open tubular liquid chromatography, arguably the most potentially fertile area of separations that has been left fallow largely because of lack of scale-appropriate detection methods. We also examine the theoretical basis of zone electrophoretic separations. Optical detection methods discussed include UV/Vis absorbance, fluorescence, chemiluminescence and refractometry. Amperometry is essentially the only electrochemical detection method used in microsystems. Suppressed conductance and especially contactless conductivity (admittance) detection are in wide use for the detection of ionic analytes. Microfluidic devices, integrated to various mass spectrometers, including ESI-MS, APCI-MS, and MALDI-MS are discussed. We consider the advantages and disadvantages of each detection method and compare the best reported limits of detection in as uniform a format as the available information allows. While this review pays more attention to recent developments, our primary focus has been on the novelty and ingenuity of the approach, regardless of when it was first proposed, as long as it can be potentially relevant to miniature platforms.

Open tubular liquid chromatography: Recent advances and future trends

Nano-liquid chromatography (nanoLC) is gaining significant attention as a primary analytical technique across various scientific domains. Unlike conventional high-performance LC, nanoLC utilizes columns with inner diameters (i.ds.) usually ranging from 10 to 150 μm and operates at mobile phase flow rates between 10 and 1000 nl/min, offering improved chromatographic performance and detectability. Currently, most exploration of nanoLC has focused on particle-packed columns. Although open tubular LC (OTLC) can provide superior performance, optimized OTLC columns require very narrow i.ds. (< 10 μm) and demand challenging instrumentation. At the moment, these challenges have limited the success of OTLC. Nevertheless, remarkable progress has been made in developing and utilizing OTLC systems featuring narrow columns (< 2 μm). Additionally, significant efforts have been made to explore larger columns (10-75 μm i.d), demonstrating practical applicability in many situations. Due to their perceived advantages, interest in OTLC has resurged in the last two decades. This review provides an updated outlook on the latest developments in OTLC, focusing on instrumental challenges, achievements, and advancements in column technology. Moreover, it outlines selected applications that illustrate the potential of OTLC for performing targeted and untargeted studies.

Nano-liquid chromatography with monolithic stationary phase based on naphthyl monomer for proteomics analysis

Monolithic poly(2-vinylnaphthalene-co-divinylbenzene) columns were introduced, for the first time, and were evaluated as the separation media for nano-liquid chromatography (nano-LC). These columns were prepared by in-situ polymerization of 2-vinylnaphthalene (2-VNA) as the functional monomer and divinylbenzene (DVB) as the crosslinker in a fused silica capillary column of 50 µm i.d. Various porogenic solvents, including tetrahydrofuran (THF), dodecanol and toluene were used for morphology optimization. Final monolithic column (referred to as VNA column) was characterized by using scanning electron microscopy (SEM) and chromatographic analyses. Alkylbenzenes (ABs), and polyaromatic hydrocarbons (PAHs) were separated using the VNA column while the column offered excellent hydrophobic and π-π interactions under reversed-phase conditions. Theoretical plates number up to 41,200 plates/m in isocratic mode for ethylbenzene could be achieved. The potential of the final VNA column was demonstrated with a gradient elution in the  separation of six intact proteins, including ribonuclease A (RNase A), cytochrome C (Cyt C), lysozyme (Lys), β-lactoglobulin (β-lac), myoglobin (My) and α-chymotrypsinogen (α-chym) in nano LC system. The column was then applied to the peptide analysis of trypsin digested cytochrome C, allowing a high peak capacity up to 1440 and the further proteomics analysis of COS-7 cell line was attempted applying the final monolithic column in nano-LC UV system.