A microanalytical method using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was developed to measure element distribution in rat brain tissues for the detection of a small-size tumor. The stereotaxically guided tumor was implanted by injecting 5 μl of 103 F98 cells into the right Caudatus putamen of a male F344 Fisher rat brain hemisphere. The second non-treated rat brain hemisphere is used as control tissue. Tumor investigation of adjacent slices is carried out by LA-ICP-MS and, in addition, autoradiographically with a tritiated ligand (3H-PK11195) of the peripheral benzodiazepine-receptor, which is not expressed in the brain under normal, physiological conditions but during tumor development. Ion intensities of 63Cu+, 64Zn+, 31P+ and 32S+ in the rat brain section (thickness: 20 μm; analyzed area 12 mm by 6 mm) containing the local tumor and control area were measured by scanning with a focused laser beam at wavelength 213 nm, diameter of laser crater 50 μm and laser power density 3·109 W cm−2, in a cooled laser ablation chamber coupled to a double-focusing sector field ICP-MS. The quantitative determination of element distribution in a thin slice of the rat brain tissue was carried out using matrix-matched laboratory standards. The mass spectrometric analysis yielded an inhomogeneous distribution for Cu, Zn, S and P in the analyzed rat brain sections. For Cu and Zn a deficiency in and around the tumor region in comparison with the control brain tissue of the second hemisphere was found. The detection limits for distribution analysis of Zn and Cu measured by LA-ICP-MS are in the ng g−1 range. The capability and the limits of LA-ICP-MS will be studied for the imaging of element distribution in thin cross sections of brain tissues in order to create a new diagnostic method for the borders of small-size tumors.
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