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

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, NO, and NO) and cations (Na, K, Ca, and Mg) 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 PM samples. In addition, the determination of K in PM 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 source identification.