The filtered solvent and sample will protect the chromatographic column and liquid phase injection system. Effect on the column: because the packing particles are very fine, the inner voids in the column are very small, and the solvent and the small particles in the sample will clog the column and the sieve plate.
Effects on liquid phase injection system: solvents and small particles in the sample will increase the plug and wear of the injection valve, as well as the wear of the sapphire piston rod and piston in the pump head.
Eliminate the impact of pollution on analysis results. For the commonly used ULTRAVIOLET detector and diode array detector, if the sample concentration is relatively low, the particles will cause large noise, unstable baseline, and infect the normal signal, which will affect the detection results.
Criteria for membrane filter adsorption test
Membrane filter adsorption should be less than 2%. The Recovery or adsorption rate is calculated according to the following formula: Recovery% = A(filtration)/A(before filtration or centrifugation) ×100%. Adsorption rate = 100%-Recovery%. Where: A is UV absorbance or HPLC peak area value. If the recovery rate is between 98% and 102%, i.e. the adsorption rate is no more than 2%, the adsorption effect of the membrane filter can be ignored.
The treatment method is as follows: boil the hydrophilic membrane filter in water for more than 1h and then try again. Change the filter material or brand. Or imported membrane filter. The adsorption effect of the different membrane filters and different formulation processes is different, so the correct conclusion should be drawn through experiments.
If the membrane filter disc does not adsorb the API, but the sample dissolution rate is low, the excipient adsorption API can be considered and then filtered.
For varieties with obvious adsorption, the material, brand, and specification of the membrane filter used should be indicated in the internal control standard, as well as the volume of the primary filtrate to be discarded, so as to ensure the accuracy and reproducible of the test results.
What kind of sample is prone to membrane filter adsorption
The adsorbed varieties are usually the main drugs that are insoluble in water and have undergone micronization and other treatments when making preparations. At this time, the particle size of API becomes smaller, the specific surface energy becomes larger, and the electrostatic adsorption capacity is enhanced, so the adsorption effect with the membrane filter will be more obvious.
In the solution of some small-size preparations, the concentration of the main drug is low, the volume of the primary filtrate required to reach saturation increases significantly, and the interference will also increase.
Determination of content and related substances
The content and the solvent used by the relevant substances can generally make the main drug completely dissolve out of the sample, so the sample solution can be used to investigate the adsorbability. For the detection of relevant substances, if the proportion of the organic phase in the solvent is higher, more attention should be paid to whether the membrane filter will produce new impurities after filtration.