Optimization of PIXE analysis for Cu and other trace elements in cerebrospinal fluid to improve the detection limits

An external beam PIXE system was optimized for the determination of the extremely low trace element content of normal cerebrospinal fluid. In order to improve the detection limits of the elements of interest, the ultrafiltrated cerebrospinal fluid samples were deposited onto ultrathin Formvar foils and measured in a helium atmosphere. Since the main emphasis was on copper, the absorber used in the measurements was optimized to give a favourable peak/background ratio for this element. The resulting detection limits for Fe, Cu, Zn and Br were (6.3 ± 2.9), (4.1 ± 1.4), (8.5 ± 2.6) and (18.1 ± 1.1) ppb, respectively. This allowed sufficiently precise determination of the low elemental concentrations in 50 μl of human cerebrospinal fluid.