How to handle incomplete dissolution of microbial limit testing samples

How to handle incomplete dissolution of microbial limit testing samples? In microbial limit testing, when encountering incomplete dissolution of the sample, the following measures can be taken to solve the problem:
1、 Sample pretreatment
Dilution: Dilute the sample with a suitable solvent (such as sterile water, physiological saline, buffer solution, etc.) to reduce its viscosity or increase its solubility. Dilution can reduce the impact of insoluble substances in the sample on the filtration membrane and improve filtration efficiency.
Heating: For thermally stable samples, slight heating can be applied to promote dissolution. But it is important to control the heating temperature and not exceed the sample's tolerance temperature to avoid damaging the microorganisms in the sample.
Stirring or oscillation: Use a magnetic stirrer or oscillator to help dissolve the sample. By stirring or oscillating, the contact area between the sample and the solvent can be increased, thereby promoting dissolution.

2、 Choose appropriate solvents and filtration membranes
Try different solvents: If the sample has poor solubility in commonly used solvents, you can try using other solvents such as alcohols, ketones, or other organic solvents. When choosing a solvent, its impact on microorganisms should be considered to ensure that the solvent does not inhibit or kill microorganisms.
Choose the appropriate filter membrane: Different filter membranes have different materials and pore sizes. The appropriate filter membrane should be selected based on the characteristics of the sample and experimental requirements. If the material or pore size of the filtration membrane is not suitable for the sample, it may lead to sample dissolution or a decrease in filtration efficiency.
3、 Optimize the filtering process
Control filtration speed: During the filtration process of the microbial limit filter, the filtration speed should be controlled. If the filtration speed is too fast, it may cause the filter membrane to rupture or the sample to dissolve. Therefore, the filtering process should be carried out slowly to avoid these problems.
Cleaning the filter membrane: If the filter membrane is clogged or contaminated during the filtration process, it should be cleaned in a timely manner. When cleaning, appropriate cleaning agents and methods should be used to ensure good cleaning effect and no impact on the sample.

4、 Other measures
Grinding or crushing the sample: If the sample is solid, it can be attempted to grind or crush the sample to increase its contact area with the solvent, thereby promoting dissolution.
Using ultrasonic treatment: Using an ultrasonic cleaner to sonicate the sample can help it dissolve better. But attention should be paid to controlling the ultrasound time and intensity to avoid damaging microorganisms.
Pre filtration: If the sample contains insoluble particles, pre filtration can be used to remove these particles before performing membrane filtration.
5、 Verification and adjustment
After taking the above measures, it is necessary to verify the filtering method to ensure that the improved measures do not affect the detection rate and counting accuracy of microorganisms. If the solubility issue of the sample still cannot be resolved, other detection methods such as pouring plate method or maximum possible number (MPN) method may need to be considered.
In summary, when encountering incomplete dissolution of samples in microbial limit testing, the problem should be solved through sample pretreatment, selection of appropriate solvents and filtration membranes, optimization of the filtration process, and other measures. Meanwhile, it is necessary to continuously validate and adjust the methods to ensure the accuracy and reliability of the experimental results.