Summary of accuracy and precision of compounds in diluted feces. The accuracy was determined by dividing the mean observed concentration by the nominal concentration. The root of mean square within groups was divided by the total mean to obtain the within-day precision. The between-day precision was calculated by dividing the difference between mean square between groups by mean square within groups by six, the root of this number was divided by the total mean. *: No statistically significant additional spread was found as a result of performing the analysis in different runs.