Modern instruments for physicochemical analysis typically employ miniature transfer tubing, such as metal or polyetheretherketone (PEEK) tubing. Widely used analytical methods include gas chromatography (GC) and liquid chromatography (LC). GC is used for analysing gases (volatile substances), while LC is applied to liquids (non-volatile substances), with tubing systems designed to transfer gases and liquids, respectively. The sample is introduced into the chromatographic column through a miniature transfer line. By interacting—through adsorption and partitioning—with the column packing materials of varying chemical properties, the analytes are then transported to the detection device, where eluate signals are recorded at different times. GC systems impose relatively lower demands on transfer tubing, as they commonly operate below 100 psi. In contrast, high-performance liquid chromatography (HPLC) uses high-pressure pumps to deliver samples, typically at pressures ranging from 300 to 6,000 psi. With technological advancements, newer ultra-high-performance liquid chromatography (UHPLC) instruments can reach pressure limits of up to 20,000 or even 30,000 psi.
A liquid chromatography system, commonly referred to as an HPLC or UHPLC system, comprises multiple components. These include a high-pressure plunger pump for solvent delivery, an injection valve or autosampler for introducing the analyte, an in-line filter to remove particulate from the analyte solution that could potentially clog the chromatographic column, a ghost peak eliminator designed to capture irreversibly adsorbed chemical substances, the liquid chromatography column itself, and a detector for analysing the elution. These various components are connected in series via miniature fluid conduits, such as metal or polymer tubing with inner diameters ranging from 0.003 to 0.040 inches.
Over the past fifteen years, the proportion of biologics among the global top 100 best-selling drugs has increased from less than 10% to 80%, and they remain a key focus in the research and development efforts of many pharmaceutical companies. In response, global manufacturers of liquid chromatography instrument systems have introduced bioinert chromatography systems, which primarily utilise fused silica capillary tubing. This represents a complete departure from the traditional stainless steel connections used in earlier liquid chromatography systems. In early high-performance liquid chromatography (HPLC) instrument systems, PEEK tubing was often preferred due to its bioinert properties. The radial inward pressure generated during the assembly of ferrule fittings caused deformation that, on the ductile PEEK material, was less likely to become permanent, allowing the tubing system to be reused for a period. However, its major limitation was its inability to withstand pressures exceeding 6,000 psi, making it unsuitable for ultra-high-performance liquid chromatography (UHPLC) systems. Today, PEEKsil capillary tubing has become the most widely used material. It offers excellent bioinertness, minimising dead adsorption of biological analytical samples withstand extremely high pressures.
The PUCKA fitting system, developed by Fresh Bioscience, applies to tubing of various inner and outer diameters, particularly for the use of brittle fused silica capillary tubing in ultra-high-performance liquid chromatography (UHPLC). The connection system formed with PUCKA fittings can be easily interfaced with all modular components featuring standard UNF 10-32 threaded ports, achieving a zero-dead-volume face-seal connection that withstands pressures up to 22,755 psi. Furthermore, the unique design allows it to be repeatedly disassembled and reinstalled at any fluidic path. Variations in the threaded port depths at the inlet of HPLC columns from different manufacturers, as well as machining tolerances even within the same manufacturer, often prevent traditional ferrule-based fittings from being reused after initial installation, as it becomes difficult to reliably achieve a zero-dead-volume connection again. By choosing the PUCKA ultra-high-pressure fitting system, bring in reliable true chromatography all the time.
