When we use solid-phase extraction, one of the problems we face is: at what rate should the liquid flow through the column, to get good results, we need to be slow, as slow as possible. For solid-phase extraction column packing, if we look at the local magnification, we can see that they are actually a lot of gaps, the liquid flow channels, if the flow is fast, a significant proportion of the components to be measured is not enough to fully interact with the packing from the channel loss; so slow, give them a full opportunity to act.
How to slow down? One trick is not to use the so-called automated solid phase extraction system used with the extractor, but to use the more common gravity method. Use gravity to cause the liquid to flow downward. In the experimental speed, gravity method is far inferior to the suction method, but in the experimental effect, gravity method is far superior to the suction method, with suction method can only get the spectrum band adsorption, with gravity method can get the column head adsorption, in the balance of speed and effect of both, we still tend to give priority to ensure good results.
In the automated solid-phase extraction system conditions selection, some people in order to improve extraction efficiency, try to add more liquid, or choose a large amount of packing small column, it is not necessary to do so. Especially when using the gravimetric method, due to the high efficiency, in many cases is the column head adsorption, not all the packing is working, packing more not only liquid outflow will be slower, and the diffusion in the elution will be very obvious. Therefore, it is recommended that enough is enough, when the efficiency can be guaranteed, filler as little as possible, and should not add more liquid.
Solid phase extraction cartridge from the principle of chromatographic separation, but in operation it is best to use it only as an adsorbent extractant, due to the nature of the filler, the elasticity often varies, so in the actual experiments do not have to pursue the effect of optimizing the design of very complex elution procedures. In the establishment of conditions, we should try to use more readily available information, as soon as possible to establish the system, while maintaining vigilance over the operation of too complex steps, in the experimental effect, the experimental rate and ease of operation to achieve a balance between the three.
All suppliers will recommend SPE solid phase extraction column at the same time, the marketing of solid-phase extractor, the simplest solid-phase extractor is also several thousand, if labeled with an imported trademark price to add several times, such prices do not include the extractor. But such a configuration is coupled with a speed switch, it is also difficult to get good results, the main problem is the small column of non-parallelism amplified. As for the fully automatic solid phase extractor, it should be said that there is no more ideal and suitable machine for food testing on the market, the main problem is that it cannot solve the problem of inconsistent liquid level drop in a batch of small columns, plus the price is very expensive, and the cost performance is naturally not high. The one with liquid level measurement also cannot detect multiple batches of small columns at the same time, and there is a risk of cross-contamination.