Simultaneous in vivo monitoring of multiple brain metals using an online microdialysis-in-loop solid phase extraction-inductively coupled plasma mass spectrometry system

Abstract

Using a non-functionalized small-bore polytetrafluoroethylene (PTFE) sample loop as a preconcentrator, a novel hyphenated system—comprising microdialysis sampling, online automatic in-loop solid phase extraction (SPE), and inductively coupled plasma mass spectrometry (ICP-MS)—for monitoring the levels of trace metal ions in living rat brains was developed. Taking advantage of the selective polymer–ion interaction to online separate metal ions from highly saline operating in the in-loop PTFE SPE system, it could online remove the salt matrix selectively from the microdialysate of rat brain extracellular fluid after slightly adjusting the pH; the next analytical cycle could be performed without the need for a pre-conditioning procedure after the prior elution with HNO₃. Owing to the simplicity and convenience of the developed operation sequence, this method combines extremely low blank level and detection limits (0.003–0.5 μg L⁻¹) and acceptable spike recoveries (90–98%) with the ability to analyze multiple elements. To demonstrate analytical reliability and compatibility, the analysis of standard reference material NIST 1643e (trace elements in water) and 2670a (trace elements in human urine) as well as continuous long-term monitoring of the variations of multiple trace metal ions in rat brain were performed in this work. According to the analytical results, it showed that the developed hyphenation system had the ability to analyze the SRM samples accurately, and the basal values of Ni (0.36 ± 0.16 μg L⁻¹), Zn (3.09 ± 0.31 μg L⁻¹), and Mn (1.31 ± 0.06 μg L⁻¹) in rat brain extracellular fluid could also be measured.