FAQ of SPE Cartridge

There is no doubt that there are various problems shown in the use of the Hawach SPE cartridge, such as Reversed Phase C18 SPE Cartridges, SCX SPE Cartridges, SAX SPE Cartridges, Normal Phase PR Grade Florisil SPE Cartridges and other SPE Cartridges using. In particular, several typical problems would be analyzed below, which could be greatly useful for operators and future customers.

Several conditions that often occur during the operation of a solid phase extraction device (SPE) are as follows:

1. The sieve plate is blocked

Most solid-phase extraction columns are usually composed of three parts: column tube, sieve plate and packing. The sieve plate is a material with a porous structure, which plays the role of fixing the packing and filtering the solution.

If the sample liquid contains a lot of particles and impurities, these particles will continue to accumulate on the sieve plate to form a layer of particles. As the pressure increases and the time prolongs, the particle layer will become stronger, and eventually the sieve plate will be completely blocked. , the solution cannot pass through the solid phase extraction column.

In this case, you can centrifuge or filter at high speed before loading the sample, and then take the supernatant or filtrate to pass through the solid phase extraction column to reduce the influence of particulate impurities.

For example, in the determination of synthetic coloring agents in food, when the samples are liquids such as beverages and prepared wines, it is easy to pass through polyamide solid-phase extraction columns or g3 vertical melting funnels, but when the samples are pastry solid-phase extraction devices, cereal products, etc. And when it comes to jelly, high-speed centrifugation or filtration is required before loading the sample, otherwise the sieve plate is prone to clogging.

2. Slow flow

The flow rate during solid phase extraction should not be too fast. Too fast flow rate is not conducive to the retention of the target compound on the filler and the interaction between the solvent and the target compound or filler, thus affecting the retention or elution process. Of course, the flow rate should not be too slow, otherwise the pre-treatment time will be greatly extended.
Reasons for slow flow rates during solid phase extraction are:

(1) The viscosity of the sample is high. For example, when concentrated juice or candy is encountered in food, the sample needs to be fully diluted to reduce the concentration of the sample solution;
(2) There are too many packings or too tight. At this time, it is necessary to increase the negative pressure or reduce the amount of packing used;
(3) The polarity of the solvent does not match. For example, when washing the solid phase extraction column in sn/t1924-2011, first wash with water, methanol, and then with n-hexane. The polarity of n-hexane and the first two is different, resulting in a flow rate Very slow, in this case, you can increase the negative pressure or choose a suitable solvent for the transition.

3. The purification effect is not ideal

Generally, there are two purification modes for solid-phase extraction columns, one is to use the mode of retaining the target compound, and the other is to use the mode of retaining impurities. No matter which mode is used, it is necessary to choose a suitable packing material so that the target compound or impurities can be adsorbed. In the packing, the components that do not need to be retained at the same time flow out of the solid phase extraction column with the solvent as much as possible.

When purifying a sample in the retained compound mode, it usually goes through three steps: sample loading, washing and elution. Improper selection of eluting and eluting solvents will also lead to poor purification effect results.

For example, the elution strength of the eluent is too weak, and the impurities cannot be washed away during leaching, or the strength of the eluent is too strong, and the impurities are eluted together during elution, both of which will lead to poor purification effect. ideal.

It can be seen that the selection of filler, eluent and eluent is particularly important when using solid phase extraction column to purify samples. When encountering some complex samples and one packing cannot meet the purification effect, you can choose to connect solid phase extraction columns in series or use mixed packing to operate.

A permanent way to improve the purification effect is definitely to choose the most suitable SPE cartridge. Besides, operators could also change the pretreatment method used or eluent strength. Conducting the proper SPE operation is also necessary.

4. Poor reproducibility

The following situations could trigger the occurrence of poor reproducibility, including the poor matrix removal effect, sample blockage phenomenon, the fast flow rate, and human operation error. Changing the pre-processing method is a clever move to better reproducibility.

Poor reproducibility in SPE is usually related to product quality, flow rate, and handling. The quality, uniformity and tightness of the filler in the solid phase extraction column may affect the reproducibility of the method, so it is very important to choose a manufacturer with reliable quality. When encountering an experiment with poor reproducibility, you can choose to use a standard solution to check the solid phase. Extraction column reproducibility.

The speed of the flow rate in the solid phase extraction process is also one of the important factors affecting the reproducibility. The flow rate is appropriately reduced during the sample loading, rinsing, and elution processes. Generally speaking, the results are more stable when the flow rate is lower than 5ml/min. Some experiments Slower flow rates may be required. Of course, the level of the operator will also affect the reproducibility of the results.

For example, it is usually necessary to activate the solid-phase extraction column before loading the sample, the filler must not be dried up during the sample loading process, there must be no loss during the concentration process, and it must be fully dissolved during reconstitution, etc. These are closely related to operating skills.

5. The recovery rate is not ideal

In the experiment, the operator may pay more attention to the recovery rate of the standard addition. The quality of the solid phase extraction column, whether the solid phase extraction method is suitable, and the level of the operator’s operation skills can all be determined through the standard addition recovery experiment. verify. In principle, the recovery rate of standard addition should be between 80% and 120%. Of course, this index can be appropriately relaxed for simultaneous detection of multi-component targets.

Usually, two main reasons will cause the result of a low recovery rate.

• The first one is that the sample remains insufficient on the filler – the actual detection concentration of the sample solution and the eluent exceeds 5%. no matter the excessive elution strength of the solution, the dry cartridge or high volume of the sample solution would all cause an insufficient sample.
• The second reason is that the sample is not completely eluted. Either improving the eluting strength or the eluent volume would solve this problem.

The problem of recovery rate is usually reflected in the following three aspects:

(1) The target object is not recovered;
(2) The recovery rate of the target substance is low;
(3) The recovery rate of the target substance is too high.

When encountering the above situation, it is necessary to check the solid phase extraction process, find the right medicine after finding the problem, and correct the experimental method. How to find the problem is actually not difficult.

In a complete solid phase extraction process, the target compound may only exist in the effluent, eluent, eluent and filler of the sample. We only need to measure these three liquids one by one to find the problem.