Online in-tube solid-phase extraction using a nonfunctionalized PVC tube coupled with ICPMS for in vivo monitoring of trace metals in rat brain microdialysates

We have developed a simple, automatic, online in-tube solid-phase extraction (SPE) method for the preconcentration of trace elements from saline samples. The method takes advantage of the adsorption of trace metal ions onto the interior of a nonfunctionalized PVC tube as a means of separation from the matrix salt. The adsorption of transition metal ions is presumably dominated by Lewis acid/base interactions, which facilitate the formation of metal-PVC complexes. For simultaneous determination of multiple trace metals in the extracellular fluid from the brains of anesthetized rats, we developed an online analytical system comprising microdialysis sampling, the established in-tube extraction procedure, and ICPMS. In the extraction step, the efficiency was optimal when the pH of the sample was adjusted to 8.0 using phosphate buffer. After extraction onto the interior of PVC tube, the adsorbed analytes were eluted with 0.5% HNO3 prior to online ICPMS measurement. For those elements present in the extracellular fluid at less than nanogram-permilliliter concentrations (i.e., Cu, Zn, and Mn), a temporal resolution of 12 min was required to collect enough microdialysate to meet the sensitivity requirements of the ICPMS instrument. Noteworthily, because washing and postconditioning the interior of PVC tube are not necessary, a relatively unsophisticated and clean procedure was attained and extremely low detection limits in the range of 5.0 to 510 ng L-1 were thus obtained for the analysis of Mn, Cu, Zn, Pb, Cd, Ni, and Co in microdialysate samples of 8 mu L by ICPMS. To the best of our knowledge, this study is the first to exploit PVC peristaltic tubing as an SPE adsorbent in the laboratory-on-valve mode for online sample treatment and trace metal preconcentration prior to ICPMS measurement. We confirmed the analytical reliability of this method through the analysis of the certified reference material SLEW-3 (estuarine water) and 2670a (human urine) and demonstrated its applicability through simultaneous in vivo monitoring of the basal concentrations and concentration profiles of multiple metal ions in the brain extracellular fluid of a living rat.