The result of LOF test
confirm linearity of calibration lines and
fitness of the regression
models (Plant-based foods: F = 1.78, P = 0.15; meat and processed
meats: F = 1.62, P = 0.24; dairy products: F = 1.84 and 1.96, P = 0.11
and 0.13, for nitrite and nitrate).