The assumptions that the regression residues followed normal
distribution and were homoscedastic and independent were confirmed:
the Ryan–Joiner coefficient of correlation indicated that
the normality deviations were not significant (p > 0.10); the error
variance over the concentrations estimated by the modified Levene
test was not significant (p > 0.05), suggesting homoscedasticity;
and Durbin–Watson statistics showed independence of the residues
(p > 0.10).