The determination of trace quantities of copper in biological material by radioactivation analysis.

Aliquots of pure Cu standards were irradiated simultaneously under identical conditions with samples of unknown Cu content. After irradiation the Cu was separated selectively and quantitatively from the biological samples, and its radioactivity compared with the activity of the standards. Corrections were made for dilution and for radioactive decay. Interference due to fast neutrons was investigated since they might give rise to Cu formation by the reaction Zn/ sup 64/(n,p)Cu/sup 64/ from the Zn in biological specimens. The extent of this possible interference was determined under the actual irradiation conditions used for activation analyses. Zn specimens containimg 2 x 10/sup -3/% of Cu were separately irradiated in the central flux and in the thermal column of the BR-1 reactor. Irradiation in the thermal column exclusively gave rise to the Cu/sup 63/(n, gamma )Cu/sup 64/ reaction whereas centrally irradiated specimens had a higher specific Cu activity due to the simultaneous reactions: Cu/sup 63/(n, gamma )Cu/sup 64/ and An/sup 64/(n,P)Cu/sup 64/. For the Zn/Cu ratio of 5 x 10/ sup 4/ present in the samples, the interference was about 1%. However, the Zn/Cu ratio in biological material lies at least a factor of 100 lower, so these errors become negligible. Biological specimensmore » and Cu standards sealed in polyethylene containers were irradiated for 24 hr in a central flux of 5 x 10/sup 11/ to 8 x 10/sup 11/ n cm/sup -2/ sec/sup -1/. Cou nting was performed with a Tl-activated NaI-scintillation welltype crystal, combined with a Super-scaler SC 18. Calculations of the Cu concentration were based on comparison with the activity of standard samples irradiated under identical conditions. Compared with the spectrophotometric method, the results obtained by radioactivation analysis are om the average 3% too high, but reproducibility is good. The advantage or the radiometric method is in the considerible reduction of the sample size (from 10 ml for the spectrophotometric method down to 25 mu l). It should be possible to determine Cu down to the 0.1-0.05 mu g range. (BBB)« less