An improved method for oxidation of chromium(III) oxide-containing fecal samples by using sodium peroxide fusion

A safer method of oxidation of Cr2O3-containing fecal samples from transit-time studies was developed using sodium peroxide to replace perchloric acid as the oxidizing agent. The percentage recovery of Cr2O3 with this method was compared with that of perchloric acid method for samples containing quantities of fecal ash and Cr2O3 typical of those from rodent transit-time studies. Both methods gave relatively constant percentage recoveries for Cr2O3 contents from 0.4 to 10 mg. Over this range, mean (+/- SD) percentage recoveries of Cr2O3 for sodium peroxide fusion and the perchloric acid method were 75.5 +/- 4.3 and 89.9 +/- 2.5, respectively. As long as percentage recovery is constant, the transit time as determined by calculation of the time of 80% excretion of the total recovered Cr2O3 is not affected. Sodium peroxide fusion provides a useful and safer alternative to perchloric acid oxidation in transit-time studies using Cr2O3 as a nonabsorbable marker.