Precautions for solid phase extraction technology(part 1)
Be as slow as possible.
One of the problems we face when using solid phase extraction is at what rate the liquid should flow out of the column. My experience is as slow as possible.
If we look at the filler of the solid phase extraction column in a magnified view, we can see that they have a lot of voids. There are many channels for liquid circulation. If the flow is fast, a considerable proportion of the components to be tested flow through without react with the fillers. Hence, be slow and give them a chance to make a full effect.
How to slow it? A trick is do not use the so-called solid phase extractor which used with the air extractor, but to use the ordinary gravity method. The action of gravity causes the liquid to flow downward. In terms of experimental speed, the gravity method is far less than the suction method, but in terms of experimental results, the gravity method is far superior to the suction method. The suction method can only obtain the band adsorption, but the gravity method can get the column head adsorption. To balance the speed and effect, we still tend to give priority to ensuring good results.
For example, a 3ml 500mg C18 cartridge, if activated with methanol, will flow all of the methanol to the sieve plate in about 20 minutes. While in the case of the sample liquid, it takes up to 2 hours for 25ml sample liquid, and If the gravity method is properly carried out, the working rate may not much worse than the suction method. There must be someone waiting by the suction method, while the gravity method can make full use of the lunch break and the evening time to pass the column because the electricity is not needed. When the liquid volume is large, a stacking joint and an extension pipe can be connected. In addition, the gravity method does not require an aspirator and a solid phase extractor.