Three-dimensional printed sample load/inject valves enabling online monitoring of extracellular calcium and zinc ions in living rat brains

[Display omitted] •A 3D printed sample load/inject valve interfaced between MD sampling and an ICP-MS.•The valve equipped a printed 5-μL sample loop can minimize the salt matrix effects.•The dynamic variations of brain extracellular Ca and Zn were investigated in vivo.•The physiological response to excitotoxic N-methyl-d-aspartate was also revealed. We have developed a simple and low-cost flow injection system coupled to a quadruple ICP-MS for the direct and continuous determination of multi-element in microdialysates. To interface microdialysis sampling to an inductively coupled plasma mass spectrometer (ICP-MS), we employed 3D printing to manufacture an as-designed sample load/inject valve featuring an in-valve sample loop for precise handling of microliter samples with a dissolved solids content of 0.9% NaCl (w/v). To demonstrate the practicality of our developed on-line system, we applied the 3D printed valve equipped a 5-μL sample loop to minimize the occurrence of salt matrix effects and facilitate an online dynamic monitoring of extracellular calcium and zinc ions in living rat brains. Under the practical condition (temporal resolution: 10h−1), dynamic profiling of these two metal ions in living rat brain extracellular fluid after probe implantation (the basal values for Ca and Zn were 12.11±0.10mgL−1 and 1.87±0.05μgL−1, respectively) and real-time monitoring of the physiological response to excitotoxic stress elicited upon perfusing a solution of 2.5mM N-methyl-d-aspartate were performed.