*2.9. Investigation of Matrix Effects*

A homogenized blank tissue sample of 5 g ± 0.1 g, processed as delineated in Section 2.5, was utilized to generate a sample matrix solution. The mixed standard working solution from Section 2.3, amounting to 100 μL, was separately integrated into the sample matrix solution, thus forming matrix-matched samples at concentrations of 0.1 μg/kg, 0.5 μg/kg, 1 μg/kg, 5 μg/kg, 10 μg/kg, 20 μg/kg, and 50 μg/kg. These samples were analyzed by the method described in Section 2.4, and the matrix-matched sample curve was subsequently plotted. This experiment was conducted thrice.

The mixed standard working solution, described in Section 2.3, was diluted with methanol, resulting in concentrations of 0.1 μg/L, 0.5 μg/L, 1 μg/L, 5 μg/L, 10 μg/L, 20 μg/L, and 50 μg/L. The analysis was conducted as per the conditions specified in Section 2.4, enabling the derivation of the standard working solution curve.

The matrix effect, which refers to the extent of the sample matrix's influence on target compound determination, was evaluated by comparing the slope of the matrix-matched sample curve with the standard working solution of equivalent concentration. Matrix enhancement is indicated by ME > 0, while ME < 0 signifies matrix suppression. Low signal interference from the matrix, which can be overlooked, occurs when 0 ≤ |ME| ≤ 20%. Moderate matrix interference is signaled by 20% < |ME| < 50%, and strong matrix interference is inferred when |ME| ≥ 50%.

Matrix effect is calculated using the following formula:

$$\text{ME} = \left(\frac{S\_m}{S\_s} - 1\right) \times 100\% \tag{1}$$

ME: Matrix Effect;

*Sm*: Slope of the curve of matrix-matched samples; *Ss*: Slope of the curve of standard working solution.
