Determination of linear range and lower limit of 4 cephalosporin residues in milk and milk powder

5.
2.
7.
8 Linearity range and lower limit of determination

Prepare sample matrix mixed standard solutions (0.
5 LOD milk powder～20 LOD milk) containing cefpirin , cephalexin , cefalonine , and cefquinoxime at a concentration of 2.
5 to 200 ng/mL, and measure under selected conditions.
The sample volume is 20uL, and the peak area is plotted against the concentration of each component in the standard solution.
The absolute amounts of cefpirin, cephalexin, ceflonine, and cefquinome are linear in the range of 0.
04～2ng, respectively.
, Meet the quantitative requirements, the linear equation and correction factor are shown in Table 5-40
.

5.
2.
7.
9 Method recovery and precision

The addition recovery and precision experiments were carried out with samples containing no four cephalosporins, 4.
0-40μg/kg (LOD-10 LOD) was added to milk samples, and 20-200μg/kg (LOD-10 LOD) was added to milk powder samples.
, After four different levels of four cephalosporin standards, shake up to make the standard and sample fully absorbed, and then extract and purify according to this method, and use high performance liquid chromatography-tandem mass spectrometer to determine the recovery rate and precision The degree is shown in Table 5-50
.

Table 5-50 Addition recovery rate of four cephalosporins in milk and milk powder (%) (n=10)

5.

Repeatability and reproducibility

Under repeatability test conditions, the absolute difference between the two independent test results obtained does not exceed the repeatability limit (r).
If the difference exceeds the repeatability limit (r), the test results should be discarded and the two individual tests should be completed again.
Determination
.

Table 5-51 The content range of four cephalosporins and the reproducibility limit and reproducibility limit equation