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6.
2.
5.
7 Selection of analysis conditions
(1) Extract
Milk and milk powder matrix are high-protein and high-fat samples.
Methanol, acetonitrile and complex co-precipitating agents can effectively precipitate protein
.
According to the characteristics of the samples and references, the experiments were carried out with methanol-0.
(2) Purification
In the experiment of the method, has used a C BUNDELUT 18 is solid phase extraction column (3cm .
3 and 6cm .
3 ), OasisHLB SPE column (3cm .
3 and 6cm .
3 )
.
It was found that the recovery rate of the C 18 column with two specifications and the 3cm 3 HLB column was lower than that of the 6cm3 HLB column, and the concentrated solution was time-consuming to pass through the column and the flow rate was difficult to control
Figure 6-6 Cumulative elution curve
(3) Determination of monitoring ions
A peristaltic pump was used to inject 1μg/mL mixed standard solution at 10uL/min to establish the best mass spectrometry conditions for determining each compound, including selecting characteristic ion pairs, optimizing mass spectrometry analysis conditions such as electrospray voltage, sheath gas, auxiliary gas, and collision energy
.
The mixed standard solution of the analyte enters the ESI ionization source, and the analyte is analyzed by one-stage full-scan mass spectrometry in the positive and negative ion scanning modes, respectively, to obtain molecular ion peaks
6.
2.
5.
8 Linearity range and lower limit of determination
Prepare a series of standard working solutions of 0～100ng/mL (equivalent to 0～200μg/kg of milk samples) with a given solution, and prepare a series of matrix standard working solutions with a blank solution of milk and milk powder samples.
Under the selected chromatographic conditions and The measurement is performed under mass spectrometry conditions, the sample volume is 15uL, and the peak area of the analyte is plotted against the concentration of the measured component in the matrix standard working solution.
The linear range, linear equation and linear correlation coefficient are shown in Table 6-40
.
The linear equations of different matrices show that the matrix has a certain influence on the determination of the analyte, so the method uses matrix addition standards to calibrate the content of the sample to eliminate the interference of the matrix
Table 6-40 Linear equation and range, correlation coefficient
According to the sample volume represented by the final sample solution, the constant volume, the injection volume and the interference during the determination, the milk contains elixiromycin, erythromycin, tilmicosin, tylosin, and helix 1μg/kg of pyrithromycin and pyrithromycin, 8μg/kg of oleamicin, erythromycin, tilmicosin, tylosin, spiramycin, and pyrithromycin in milk powder
Related Links: Determination of Residues of 6 Macrolides in Milk and Milk Powder
