The durability of the test method is not good
1. Solvent effect
When the ratio of solvent to mobile phase initial organic phase is different, it will show different detection effects on different instruments.
The picture shows the detection effect of the same item on two different instruments. The solvent of the project is 50% acetonitrile, and the starting proportion of mobile phase is 25% acetonitrile. Figure 1 is the effect drawing on the instrument with large inner diameter of the pipeline in front of the column, and Figure 2 is the effect drawing on the instrument with small inner diameter management. The larger inner diameter of the pipeline makes the sample fully mixed before entering the column, eliminates the solvent effect and presents a better peak shape. This solvent effect can be solved by using a thicker pipeline instrument or reducing the injection volume. Of course, the safer way is to replace the sample solvent with a solvent with a polarity closer to the initial mobile phase.
2. Out of column effect
Excessive injection volume, large volume between injection valve chromatographic column detector, detection cell and joint will cause out of column effect and abnormal peak shape. Therefore, for such samples, the requirements for instruments in the method need to be more detailed.
3. Change of mobile phase composition
Incorrect selection of buffer solution, such as too low buffer salt concentration and exceeding the effective buffer pH range, may lead to poor reproducibility. For some samples that are particularly sensitive to pH value, subtle changes in the pH value of the mobile phase will make it impossible to reproduce. For such samples, special attention should be paid to the buffer range and concentration in the selection of buffer solution, so as to ensure that the mobile phase system can provide a stable pH value for sample detection.
Some samples are particularly sensitive to the change in the organic phase. For such samples, it is recommended to choose on-line mixing of the mobile phase.
4. The condition does not control the column temperature
Many samples will have different selectivity due to the change in column temperature. Therefore, if the column temperature is not controlled, the reproducibility of the sample will be caused by the change in column temperature. It is suggested to verify the durability of the column temperature at ± 10 ℃ during the development of the method. If it is sensitive to the change in column temperature, the detected column temperature should be included in the method.
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