Selection of analysis conditions for determination of 15 quinolones residues in eel and its products

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7 Selection of analysis conditions

(1) Extraction solution selection

Quinolone class of drugs for the amphoteric substance can be classified into a method for extracting three main types, - species that these drugs may be extracted under basic conditions in a neutral condition and extracted with an organic solution, such as with aqueous ammonia in acetonitrile Extraction can also be extracted under acidic conditions, such as using acetic acid and acetonitrile solution
.

The moisture in the matrix has an effect on the extraction of quinolone drugs.

(2) Selection of purification conditions

Acid-lye liquid-liquid extraction is the basic method to purify quinolones.
For example, it can be extracted with organic solvents such as chloroform after adjusting the pH to achieve the purpose of purification
.

In recent years, solid phase extraction has become the main purification method for the analysis of drug residues in animal-derived foods, and there are a variety of commercial solid phase extraction cartridges to choose from

In the experiment, it was found that if the acetonitrile extraction solution is used directly on the column, oxolinic acid, nalidixic acid and flumequine cannot be completely adsorbed by the solid phase extraction cartridge.
Therefore, the organic phase needs to be replaced with ammonium acetate solution after acetonitrile extraction.
Purify through the column to increase the recovery rate
.

The experiment found that oxolinic acid, nalidixic acid and flumequine can be eluted more completely with methanol, while ammonia methanol is needed to elute the other 12 quinolone residues

Table 11-6 The relationship between eluent volume and recovery rate (%)

(3) Optimization of mass spectrometry conditions

A syringe pump was used for direct injection, and standard solutions of 15 quinolone drugs were injected into the ion source of the tandem mass spectrometer at 8 μL/min
.

The positive ion scanning method was used for one-stage mass spectrometry, the quasi-molecular ion peak (M+1) was determined, and the de-clustering voltage was optimized

After colliding with the quasi-molecular ions of the analyte, the secondary mass spectrometry is performed to obtain the product ion mass spectrum, which optimizes the collision energy.
In addition, the ion source temperature, atomization gas, curtain gas, auxiliary gas and other parameters are optimized
.

(4) Chromatographic condition selection

When the liquid chromatography-tandem mass spectrometer in the multi-reaction monitoring mode is used for analysis, the components are not required to be completely separated on the liquid chromatography.
And the most abundant product ion is also the same, so the complete separation of these two substances is particularly important
.

In this method, the YMC Pack Pro C ₁₈ column (150mm×2.

(5) Stability of quinolones

Quinolone drugs are relatively stable.
Data shows that drugs such as enrofloxacin, flumequine, oxolinic acid, sarafloxacin and other drugs have higher concentrations in fish skin.
The fish meat is mixed and homogenized
.

Since eel skin is difficult to mash, microwave heating is used

The high-concentration stock solution of quinolones can be stored in methanol for more than 3 months, but the low-concentration working solution in the water phase is very easy to degrade and should be prepared immediately before use
.

Because some quinolone drugs such as norfloxacin are unstable to light, they should be stored in the dark, and brown glassware should be used as much as possible during the operation

In addition, it was also found in the experiment that the temperature during nitrogen blowing has an effect on the recovery rate of some quinolone drugs, and the recovery rate is reduced when the temperature is too high.