A method based on ICP-MS for the analysis of Alzheimer's amyloid plaques

Inductively coupled plasma mass spectrometry (ICP-MS) was combined with flow injection (FI) and a selective extraction procedure (which isolates Alzheimer's amyloid plaques) for the multielemental analysis of plaque cores. FI-ICP-MS was also used to analyze the various reagents involved in the sample preparation to determine whether they were the source of the various elements detected in the plaque samples. An external calibration with matrix-matched standards (in terms of salt concentration) was carried out in all cases. The concentrations of Cr, Mn, Ni, Cu, and Pb were in the 0.2-0.8 mg L-1 range whereas that of Al, Fe, and Zn were 2-20 mg L-1 in the plaque sample. These values can be translated into a microgram per gram level in the plaque core by multiplying them by 29-500 (the exact factor depends on the weight of the plaques, which were not dried to prevent the loss of volatile elements). Although spectroscopic interferences arising from matrix elements of the sample cannot be ruled out in the case of Al, Cr, Ni, Cu, and Fe, the large levels detected (especially for Al and Fe), compared to the much lower or undetectable levels in the various reagents, strongly suggest the accumulation of these elements by the AD patient during life rather than contamination during sample processing.