Cost-effective low-volume sample introduction system for open tubular capillary ion chromatography via a hybrid...

Open tubular capillary ion chromatography (OTIC) exhibits a minute sample/eluent volume separation with a low-pressure operation (<30 psi) and potentially develops for a portable analytical device. In this study, a novel and cost-effective low-volume sample-introduction system has been developed for the OTIC and applied for separating water-soluble small inorganic ions. This innovative design uses a hybrid negative pressure (HNP) system, considerably reducing sample consumption to ∼7 μL per injection while maintaining excellent repeatability (<4 % relative standard deviation) on a 50 μm bore capillary tube. Various sample-introduction parameters, such as moving time of the sample zone, injection pressure, and sample viscosity, were optimized for the separation of model anions (Cl^-, Br^-, NO₂^-, and NO₃^-) and cations (Na⁺, K⁺, Ca²⁺, and Mg²⁺) in a non-suppressed OTIC mode. The performance of this HNP-OTIC system was demonstrated through the analysis of water-soluble small inorganic ion determination in low-volume particulate matter extracted samples, yielding recovery percentages of 78-119 % for cation determination in PM₁₀ samples. In addition, the determination of K⁺ in PM_2.5 samples exhibited no significant difference from the results obtained using a commercial packed IC. The cost-effective and efficient OTIC system has the potential to become a promising alternative for atmospheric analysis, especially in tracking K⁺ as an ion tracer for PM_2.5 source identification.