Open-channel chip-based solid-phase extraction combined with inductively coupled plasma-mass spectrometry for online determination of trace elements in volume-limited saline samples

In this study, we used an automated online chip-based solid-phase extraction (SPE)-inductively coupled plasma-mass spectrometry (ICP-MS) system for analyzing trace elements in small-volume saline samples (～15 μL). The proposed method involved the adsorption of trace metal ions in the interior of a functionalized poly(methyl methacrylate) (PMMA) channel in order to separate these ions from saline matrices. The adsorption of transition metal ions was presumably dominated by the surface complexation between the carboxylate moieties in the interior of the PMMA channel and the metal ions, which facilitated the formation of metal-carboxylate complexes. The components of the proposed online analytical system used for the simultaneous detection of multiple trace metals in saline samples involved microdialysis (MD) sampling, an established chip-based SPE procedure, and ICP-MS. The SPE-ICP-MS hyphenated system was optimized, and then, the analytical reliability of this system was further confirmed by using it to analyze the certified reference materials-SRM 2670 (human urine) and SRM 1643e (artificial saline water). The satisfactory analytical results indicated that the proposed on-chip SPE device could be readily used as an interface for coupling the MD probe with the ICP-MS system. The dramatically reduced consumption of chemicals and "hands-on" manipulations enabled the realization of a simplified and relatively clean procedure with extremely low detection limits in the range of 5.86-76.91 ng L(-1) for detecting Mn, Co, Ni, Cu, and Pb in 15-μL samples by ICP-MS. The effectiveness of an online MD-chip-based SPE-ICP-MS technique for continuous monitoring of trace elements in a simulated biological system was also demonstrated. To the best of our knowledge, this is the first paper to report the direct exploitation of a PMMA chip as an SPE adsorbent for online sample pretreatment and trace metal preconcentration prior to ICP-MS measurement.