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11.
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3.
7 Selection of analysis conditions
(1) Optimization of sample pretreatment method
Milk and milk powder contain a lot of fat and protein, and traditional extraction methods are prone to emulsification
.
Try to use 10% trichloroacetic acid : acetonitrile (9:1) as the extractant, use HLB, 60mg/3cm 3 (WatersOasis) to purify, and the recovery rate of 7 quinolones is between 43% and 64%
Solid phase extraction technology is a relatively effective purification method.
This method compares the purification effects of HLB, 60mg/3cm 3 (WatersOasis), MCX60mg/3cm 3 (WatersOasis), BONDELUT-SCX, 500mg/3mL three solid phase extraction columns.
Experiments show that the purification effects of the three solid phase extraction columns are good, but the recovery rate of the HLB column is slightly higher, so the HLB column is selected as the purification column in this method
.
Since the HLB column is used for purification, the loading solution cannot contain too much acetonitrile, so the acetonitrile in the extract needs to be evaporated to dryness
When eluting, make an elution curve, and use 3mL 5% ammonia methanol to completely elute the 7 quinolones, so 4mL 5% ammonia methanol is used as the eluent
.
Among the seven drugs, danofloxacin is poor in thermal stability.
(2) Establishment of chromatographic conditions
The experiment used 0.
1% acetic acid-methanol as the mobile phase and gradient elution.
The analytes were effectively separated on a C 18 column with a size of 150 mm×2.
1 mm (id) and a particle size of 5 μum , and the peak shape was symmetrical and sharp
.
(3) Optimization of mass spectrometry conditions
A peristaltic pump was used to inject 1μg/mL of 7 quinolone mixed standard solutions at 10uL/min to determine the best mass spectrometry conditions for each compound, including selection of characteristic ion pairs, optimization of electrospray voltage, sheath gas, auxiliary gas, collision energy and other mass spectrometry analysis Condition
.
To determine the best mass spectrometry conditions for each compound, including selecting the mixed standard solution of the analyte to enter the ESI ionization source, performing the first-level full-scan mass spectrometry analysis on the analyte in the positive and negative ion scanning mode to obtain the molecular ion peak
(4) Selection of quantitative methods
The experiment compared the two quantitative methods of external standard method and internal standard method.
Related Links: Procedures for the determination of 7 quinolone drug residues in milk and milk powder