Precautions for Solid Phase Extraction Technology

To perform SPE as slowly 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 reacting with the fillers. Hence, be slow and give them a chance to make a full effect.

How do slow it down?

A trick is not to use the so-called solid phase extractor which is 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 band adsorption, but the gravity method can get 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 SPE 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 be 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.

Choose the SPE cartridge as small as possible

In the selection of solid phase extraction conditions, some people add liquid more to improve the extraction efficiency or choose a column with a large amount of filler, but I don’t think it is necessary. Especially when using the gravity method, due to the high efficiency, it’s the column head that adsorbs in many cases, not all the fillers are working. Moreover, too many fillers slow down the liquid flow rate, and the diffusion during elution will be obvious.

Therefore, it is recommended that it is sufficient. When efficiency can be ensured, the filler should be as little as possible, and the addition of liquid should not be much.

The experimental conditions should not be excessively refined

Solid phase extraction is a sort of chromatographic separation in principle, but it is best to use it only as an adsorbent extractant in the operation. Due to the discrepancy between the nature of the filler and the tightness of the packing, it is not necessary to design a very complicated elution procedure for the effect of the actual experiment.

In the establishment of conditions, we should make full use of ready-made materials. Establish the system as soon as possible. and at the same time be vigilant to the steps that are too complicated to operate, and achieve a balance among the results, rate, and ease of operation of the experiment.

Use the SPE cartridge only once

The solid phase extraction column is preferably used only once. Because in a strict sense, the adsorption of many substances is irreversible, and can not be eluted, which affects the next adsorption. Although some people have done repeated experiments in order to save money, in general, it is very uneconomical behavior as it greatly increased the unreliability and uncertainty of the results.

Therefore it is recommended to use it only once. If you want to save money, you can start with stacking joints and extension tubes by reducing the amount of filler and using small-volume tubes.

Use a solid phase extractor with caution

All suppliers promote the solid phase extractor with the solid phase extraction column. The price for the simplest solid phase extractor is several hundred dollars and might be several times for the leading brands. The air extractor will make it more. However, it is difficult to obtain good results even with a speed switch. The main problem is that enlarges the non-parallelism of the small column.

Recommendation: use a solid phase extractor only when It is not suitable for the gravity method.

As for the automatic solid phase extractor, there is no ideal machine for food testing on the market. The main problem is that it cannot solve the problem of inconsistent liquid level drop in a small column, and the price is very expensive. It is impossible to simultaneously detect multiple batches of small columns with liquid level measurement, and there is a risk of cross-contamination.

The current automatic solid phase extractor is basically a gravity-traffic route, but it avoids the problem of sealing.

Do not ignore traditional liquid extraction

Some people think that it can replace liquid extraction when they first come into contact with solid-phase extraction. In fact, capillary electrophoresis cannot replace liquid chromatography. Solid phase extraction is more suitable than liquid extraction in some cases, but in many cases, traditional liquid extraction is more reliable and suitable. This can be confirmed by the actual development of current experimental techniques.

Regarding liquid-solid extraction, we should not just regard it as an extraction process. From another point of view, it is still a purification process, which is a process of eliminating solid interferences. Understanding this helps us optimize the choice of experimental methods.

In summary: Practicality is the ultimate criterion for the success of the experimental design

When designing an experiment, it should be considered whether it is technically advanced at the beginning. In practice, it is practicality that decided finally whether this method is feasible or not.

An experimental method not only solves the problem, but also achieves balance in terms of manpower, material resources, and financial resources, and meets the requirements of a sustainable and repeatable operation.

Therefore, advanced technology must also be subject to practicality.