Some SPE Cartridge Operation Skills Help You Solve It Easily

Frequently occurred problems

Why is there a slow or inconsistent flow rate, low recovery rate, and poor parallelism during SPE cartridge operation? Is the inappropriate choice of the small column? is there a problem with the method? Or is the filler particle size distribution uneven and the packing tightness unstable? In fact, the flow rate of each batch of SPE cartridges has a strict quality control range. The cartridges within the quality control range can ensure the stability of the flow rate, and the cartridges outside the quality control range will be treated as abnormal products. Is it possible to completely avoid these problems by using a stable method and using cartridges that have passed the factory flow rate test?

There is another detail that is easy to be ignored by everyone, which can also cause the flow rate to be too slow: the sieve plate and the packing of the SPE cartridge may be slightly loose during the transportation process, causing air to enter the packing (generally not easy to be detected by the naked eye). The air filler causes the solvent to flow slowly under the action of air pressure. At this point, everyone can understand why the flow rate of the same batch of small columns is uneven. So how do we solve this problem in the SPE experiment operation?

1. Bubble-remove
1.1 How to remove bubbles
Positive pressure to remove bubbles
For fewer samples and fillers, it is more convenient to manually apply positive pressure, which can use the syringe to connect the adapter for positive pressure to eliminate air bubbles.

Negative pressure to remove bubbles
For more samples and filler, it is inconvenient to apply positive pressure manually, a vacuum pump can be used to connect the solid phase extraction device to remove bubbles under negative pressure.

1.2 When are bubbles to be removed?
SPE operation generally includes four steps: activation balance, sample loading, rinsing, and elution. Is it necessary to remove bubbles at every step? Of course not. Generally, when there are gaps between the fillers, the operation of debubbling is required. For example, after adding the activation equilibrium solution, the operation of debubbling is required so that the solution can better contact the filler.

There is also an easily overlooked step that needs to be drained. Generally, it needs to be drained after rinsing. After draining, air will also enter the packing room. After adding the eluent, it also needs to be drained. Otherwise, a large number of bubbles will seriously affect the flow rate of the eluent and the elution effect.

1.3 Precautions for debubbling
When exhausting bubbles, generally eliminate 1/3 of the column volume of the solvent to eliminate the bubbles in the packing, remember not to drain the solution. To prevent draining, the speed of manually discharging bubbles is not easy to be too fast or too slow.
What if the activation balance solution is accidentally drained? Just re-add the activation solvent to remove the bubbles. The correct removal of air bubbles can avoid slow or inconsistent flow rates to a certain extent.

2. Draining
2.1 When to drain?

The activation balance solution and sample loading solution do not need to be drained.
There are two main purposes of the activation equilibrium process. One is to clean the filler and to remove the background in the filler, and the other is to facilitate the development of the bonded phase molecules, which are mainly some long-chain functional groups, for example, C18 is not fully expanded when the filler is dry. Activation can make the filler functional groups wet, stretch and maintain the maximum adsorption activity for the target compound. Therefore, the process of activation equilibrium does not need to be drained.

2.2 The eluent needs to be drained
There are two main reasons why the eluent needs to be drained:

①Generally, the polarity of the eluent will be quite different (for example, the eluent is water, and the elution solvent is n-hexane or dichloromethane). The two solvents are immiscible or have poor solubility, which will cause the eluent to not flow down or the flow slowly, then hinder the contact between the elution solvent and the target, resulting in poor elution effect and low recovery rate.

②If the eluent is water, part of the eluent will be collected in the eluent without being drained. If the eluent is blown with nitrogen, the water-containing eluent is also difficult to blow-dry. The time nitrogen blowing to dry a small amount of aqueous solution will lead to a low recovery rate, so it is necessary to perform a draining operation after leaching.

After elution, some of the elution solvents will remain on the packing. When the amount of packing is large, even 1~2mL of eluent will remain, and the eluent cannot be fully recovered, resulting in low recovery rate and poor parallelism. In order to ensure that the elution solvent and the target are completely recovered, it is also necessary to drain.