DETERMINATION OF MARKERS IN DIGESTA AND FECES BY DIRECT-CURRENT PLASMA EMISSION-SPECTROSCOPY

A method is described for the preparation of bovine ruminal contents, duodenal digesta, and feces for analysis of Co, Cr, La, Sm, Eu, and Yb by direct current plasma emission spectroscopy. Ground, dried sample was refluxed in concentrated nitric acid until 2 to 3 ml of acid remained. The ash was redissolved in 6N HCl. Lithium hydroxide was added to suppress ionization, and the samples were diluted with distilled water for analysis. Element recovery, expressed as the ratio of element recovered from digesta samples augmented prior to ashing compared with those augmented after sample digestion, ranged from 71.5 to 100.5% and was affected by digesta type. Addition of 1000 ppm of Li to the sample matrix improved recovery of Co and La from 93.4 and 83.3% to 97.8 and 98.3%, respectively. Lithium did not affect recovery of the other elements. Type of digesta matrix affected emission intensity. Addition of 1000 ppm of Li to the sample matrices enhanced signal output in the digesta matrices by 25 to 30% for each element. Lithium tended to minimize differences in signal output caused by the organic matrix but did not eliminate them. Increasing Li concentration from 1000 to 4000 ppm did not increase signal output or completely buffer out the higher emission intensity associated with the organic matrix. Sensitivity of analysis of Co, Cr, and rare earth elements was comparable with or better than sensitivities reported with neutron activation analysis. Results suggest that concentrations of Co, Cr, La, Sm, Eu, and Yb in digesta and feces as low as 2.44, 1.70, 4.20, 1.00, .24, and .92 ppm of DM can be analyzed by the described ashing procedure and analytical technique. It is recommended that sample standards be prepared in matched matrices for maximum accuracy.