Assay for the elements chromium, manganese, iron, cobalt, copper and zinc simultaneously in human serum and sea water by X-ray spectrometry

Abstract

X-ray spectrometry can be applied for analysis of the elements important in biological systems with atomic numbers from 24–30. Human serum is ashed in platinum and the ash dissolved in dilute HCl. Sea water is evaporated to dryness and the residue is dissolved in a small quantity of dilute HCl. A mixture of acetic anhydride and glacial acetic acid is added. The amount of acetic anhydride used is calculated to react with all the water present. The sodium chloride precipitates, the chlorides of the elements assayed remaining in solution. An aliquot is evaporated to dryness in a test tube and the residue dissolved in acidified methanol. The methanol extract is evaporated on paper in a spot using a ring oven to confine the spot. The spot is then exposed to the x-ray field and scanned from 39–72 degrees 2θ. A titanium filter is used on the x-ray tube to remove chromium radiation from the tube. A flow counter is recommended to further cut down background from the white light hump. Background for each element is of the order of one cps, permitting assay of microgram quantities. In a typical experiment a pooled serum yielded values of Cr, not detectable; Mn, not detectable; Fe, 72 μg./100 ml.; Co, not detectable: Ni, 5.5 μ./100 ml.; Cu, 148 μ./100 ml.; Zn, 126 μ./100 ml. For water from Pelham Bay off Long Island Sound near shore we obtained Cr, not detectable; Mn, not detectable; Fe, 40 μ./100 ml.; Co, not detectable; Ni, 3.2 μ./100 ml.; Cu, 122 μ./100 ml.; Zn, 110 μ./100 ml. Using the ash from 5 ml. of serum or 5 ml. of sea water the limit of detectability with the present set up is 2 μ./100 ml. of the element. The Ti filter used was 0.005 in. in thickness. A thinner Ti filter (0.0013 in.) increased sensitivity by a factor of 3.4 for the elements Cr, Mn, Fe, Co and Ni. With the thinner filter the tungsten Lα lines came through and interfered with Zn and Cu analysis. An improved ring oven is described for transferring solutions to a spot on paper.