## 3 Results and Discussion  
### Optimization of Mass Conditions  
The identification and quantification were performed using multiple reaction monitoring (MRM). The data collection and optimization of mass spectrometry conditions in positive ion electrospray ionization (ESI+) mode were conducted to enhance the selectivity and sensitivity of the method ([PERSON] et al., 2009 [6]; [PERSON] et al., 2011 [7]; [PERSON] et al., 2017 [8]). Initially, electrospray ionization (ESI) was employed to perform a full mass spectrum scan of each drug at a high concentration level (typically 1 mg/mL) in positive ion mode, with the ion source temperature optimized to 320 \({}^{\circ}\)C. Previous studies have shown that this temperature ensures the effective desolvation and ionization of the analytes ([PERSON] et al., 2012 [9]), while scanning at a high concentration level guarantees sufficient signal intensity for accurate identification ([PERSON], 2005) [10]. However, molecular ion peaks for the fragmented molecules of MOX and MBL were difficult to detect. Subsequently, the ion source temperature was systematically optimized and adjusted to 100 \({}^{\circ}\)C ([PERSON], 2005) [11], a condition that significantly enhanced the detection of molecular ion peaks for MOX and MBL. This lower temperature not only improves the stability of molecular ions but also increases the response values of their respective product ions in both product ion scanning and MRM (multiple reaction monitoring). Additionally, the other four target analytes exhibited improved ionization efficiency and signal response under these optimized conditions. These findings suggest that a lower ion source temperature reduces thermal degradation and enhances the overall ionization efficiency of thermally unstable compounds. Consequently, based on these results, the ion source temperature for the final method was set to 100 \({}^{\circ}\)C to ensure optimal sensitivity and reproducibility for the simultaneous quantification of all target analytes. The product ions of the six target drugs were further analyzed through daughter ion scanning. Through the systematic optimization of the cone voltage and collision energy, the experimental conditions were fine-tuned to enhance the selectivity of the method. This optimization aimed to reduce interference from precursor ions by achieving a balance between minimizing the intensity of precursor ion peaks and maximizing the signal intensity of the target analytes ([PERSON] & [PERSON], 2008) [12]. Precursor ions refer to the parent ions that undergo fragmentation in mass spectrometry analysis, generated by the electrospray ionization source (ESI). Their mass-to-charge ratio (\(m/z\)) is the molecular ion or product ion of the compound to be analyzed. They serve as the starting point for fragmentation and are used to determine the molecular weight and structural features of the target compound. Meanwhile, product ions are the fragment ions produced by the precursor ions through collision-induced dissociation or other fragmentation techniques. Their mass-to-charge ratios and intensities are used to infer the structural information of the precursor ions. These precursor and product ions were subsequently used for multiple reaction monitoring (MRM) analysis. The daughter scans of the determined precursor ions are shown in Figure 2: for acetyl avermectin, \(m/2936.69\) produced \(m/z352.13\), \(m/z490.27\), \(m/z751.51\), and \(m/z368\); for abametcin B1a, \(m/z895.67\) produced \(m/z182.86\) and \(m/z327.12\); for Moxidectin, \(m/z198.53\) and \(m/z528.50\) was produced by \(m/z640.30\); for dorametcin, \(m/z921.61\) produced \(m/z353.15\) and \(m/z777.47\); for ivermectin H2B1a, \(m/z897.52\) produced \(m/z609.35\) and \(m/z753.30\). Milbemycin continued to be optimized to produce \(m/z129.11\) and \(m/z169.33\). And the numbers after the decimal point of the \(m/z\) value were adjusted based on the instrument detection statutes in the actual sample determination.