*3.1. Method Validation*

The linearity of each matrix was verified at five 4-n-NP different concentrations. All four matrices had correlation coefficients exceeding 0.998. The LOD and LOQ values for 4-n-NP were 0.37–1.79 and 1.11–5.41 μg/kg, respectively. The low-fat matrices had lower LOD and LOQ values than the high-fat matrices. The LOD and LOQ values were comparable to or lower than those in the corresponding matrices of previous investigations, with values of 0.83 and 2.5 μg/kg, respectively, for vegetable oils, 1.3 and 4.4 μg/kg for baby food, 1.3 and 3.9 μg/kg for beverages, and 0.3 and 1.0 μg/kg for vegetables and fruits [2]. Table 2 lists the results for linearity, LOD, and LOQ.


**Table 2.** Linearity, LOD, and LOQ for 4-n-NP in food matrices.

The accuracies of the high-fat matrices were 91.8–108.6% and 94.6–101.9% for intraday and interday assays of 4-n-NP, respectively; the corresponding values for the low-fat matrices were 86.8–107.3% and 92.6–101.3%. The accuracies of the high-fat matrices were 1.80–9.68% and 5.42–6.43% for intraday and interday assays of 4-n-NP, respectively; the

corresponding values for the low-fat matrices were 0.67–11.83% and 1.65–10.45%. Table 3 lists the results for accuracy and precision.


**Table 3.** Accuracy and precision for 4-n-NP in four food matrices (*n* = 3).
