In Vivo Monitoring of Multiple Trace Metals in the Brain Extracellular Fluid of Anesthetized Rats by Microdialysis−Membrane Desalter−ICPMS

Abstract

We have developed an on-line analytical system involving microdialysis (MD) sampling, a carbohydrate membrane desalter (CMD), and an inductively coupled plasma mass spectrometer (ICPMS) system for the simultaneous determination of multiple trace metals in the extracellular fluid (ECF) in the brains of anesthetized rats. The microdialysate that perfused from the animal at a flow rate of 0.5 microL/min was on-line transferred to the CMD to remove the high-sodium matrix, followed by ICPMS measurement. The role of the CMD in this on-line system was investigated in detail. With prior addition of EDTA to the microdialysate to form anionic complexes of the metal analytes and the use of NH4Cl as a regenerant to exchange Na(+) with NH4(+) ions, both quantitative recovery of the trace metal analytes and quantitative removal of the sodium matrix could be achieved. Two experimental modes of the monitoring system were constructed. For those metals (e.g., Cu, Zn, and Mn) that existed at (sub)nanogram-per-milliliter concentrations in the microdialysate, the temporal resolution was 10 min when using a 10 microL loop for sample collection, followed by CMD and ICPMS; for those elements (e.g., Ca and Mg) that existed at microgram-per-milliliter levels (or greater), near-real-time analysis was possible because the microdialysate could be led, bypassing the sample loop, directly to the CMD for desalting without any time delay. Further improvement of the temporal resolution for the low-concentration elements was not possible without decreasing the detection limits of mass detection. Among the eight trace metals tested using this on-line system, the method detection limits for Cu, Zn, Mn, Co, Ni, and Pb reached subnanogram-per-milliliter levels; for electrolyte species such as Ca and Mg, the detection limits were in the range of 50-100 ng/mL. Analytical accuracy, expressed as spike recovery, was 100% +/- 15% for all of the elements tested. We demonstrate the applicability of the proposed system through the successful measurement of the basal values of Ca, Mg, Cu, Zn, and Mn in the ECF of a living rat brain and through in vivo monitoring of the concentration profiles of Mn and Pt in the ECF after the injection of drugs (MnCl2 and cisplatin) into the rats. This microdialysis system is the first to offer real-time, in vivo monitoring of trace elements such as Ca and Mg.

In vivomonitoring of the transfer kinetics of trace elements in animal brains with hyphenated inductively coupled plasma mass spectrometry techniques

“…To remove the salt matrix from the microdialysate, Chung et al (2007) developed an alternative on-line desalting system incorporating a membrane desalter. Their approach toward removing the Na matrix from the microdialysate in the membrane desalter was to convert the analyte cations into anionic complexes through their interactions with EDTA.…”

In vivo neurochemical measurements in cerebral tissues using a droplet-based monitoring system

“…We found for Cu 0.47 ± 0.05 μg L −1 and for Zn 0.58 ± 0.07 μg L −1 . We compared these values with recently reported basal concentration level of metal elements found in the rat hippocampus ECF measured using microdialysis 29 , 30 . The mean Zn and Cu and concentration found are in good agreement with the reported values (0.51–5.22 and 0.77–2.48 μg L −1 , respectively) although the mean copper concentration remained slightly under the range.…”

Mass spectrometric analysis of spatio-temporal dynamics of crustacean neuropeptides

“…Since its first introduction by Bito et al [107], studies employing the use of microdialysis have been expanded into a wide variety of tissues and organs in the body including liver, heart, skin, blood, placenta, stomach and ear, as summarized elsewhere [108, 109]. The types of analytes that microdialysis probe could sample have also been explored and proven to be rather diverse, from low molecular weight substances such as electrolytes [110], amines and amino acids [111], to higher molecular substances such as neuropeptides [13, 14]. …”