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11.
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7 Selection of analysis conditions
(1) Comparison of extraction efficiency of three solid phase extraction columns
With a conventional C 18 is solid phase extraction column three SPE solid phase extraction column OasisHLB acid type cation-exchange column and the like, of 14 types of quinolone extraction efficiency of the drugs studied were compared, the experimental results shown in Table 11 -12
.
From the data in Table 11-12, it can be seen that the Oasis solid phase extraction column has the highest extraction efficiency, the average recovery rate of 6 experiments is above 80%; the C 18 solid phase extraction column is the second, the average recovery rate is about 70% ; The average recovery rate of benzenesulfonic acid cation exchange column is mostly between 50% and 70%, while for oxolinic acid and flumequine, the recovery rate is only 4% to 7%
Table 11-12 Comparison of extraction efficiency of three solid phase extraction columns (%)
(2) Selection of buffer solution pH
Using solid phase extraction to purify the sample, its pH has a great influence on the extraction efficiency and recovery rate.
When different target substances are passed through the column, the pH of the sample solution is also different.
In order to find the best pH when the quinolones pass through the OasisHLB column, Adjust the phosphate buffer solution to 6 different pHs with phosphoric acid , and then add the same amount of standard to carry out the recovery experiment.
The experimental data is shown in Table 11-13.
From the data in Table 11-13, it can be seen that, in general, 14 quinolones at pH 2-4, more than 90% recovery rate, and the highest recovery of most varieties pH = 3; at pH 5 to 8, such as individual species sarafloxacin , norfloxacin , by The recovery rate of nofloxacin is below 85%
.
Therefore, this method determines that pH=3 is the optimal pH when the sample liquid passes through the OasisHLB solid phase extraction column
Table 11-13 The effect of buffer solutions of different pH on the recovery rate (%) when passing OasisHLB column
(3) Selection of eluent
In order to find the best eluent for eluting quinolones from the OasisHLB solid phase extraction column, 10 methanol water and methanol + ammonia water (19+1, v/v) solutions were prepared in different proportions
.
Take 5 mL of each eluate and perform the elution recovery experiment.
Table 11-14 The influence of different ratios of eluent on the recovery rate (%)
(4) Optimization of mass spectrometry conditions
A syringe pump is used for direct sample injection, and each 5uL/mL quinolone standard solution is injected into the ion source at 5uL/min.
Figure 11-3 The secondary mass spectra of fourteen quinolones
Select the qualitative ion pair and quantitative ion pair of each quinolone from Figure 11-3, connect the liquid chromatograph and tandem quadrupole mass spectrometer online, and then optimize the ion source temperature and auxiliary gas flow rate to make each sample liquid The ionization efficiency of quinolone is the best
Related Links: Procedures for the determination of 14 quinolone drug residues in honey
