Solid phase extraction cartridges are a widely used and increasingly popular sample preparation technique. Most are used to process liquid samples, which extract, concentrate, and purify the semi-volatile and non-volatile compounds; it can also be used for solid samples, but the solid samples must be processed into a liquid first. The application of solid phase extraction column has been developed rapidly, and it has been widely used in food, environment, pharmaceutical, and other industries, becoming one of the effective means of sample pretreatment and purification.
In addition to the required specifications, the key to selecting a solid phase extraction column is its packing material that determines the separation performance. To get a suitable extraction column, we need to consider the packing based on the samples to be tested and their characteristics. SPE fillers are usually chromatographic adsorbents, which can be roughly divided into three categories, which are based on silica gel, polymers, and inorganic materials.
However, various problems can also be encountered in the process of using solid phase extraction cartridges. It is necessary to master certain knowledge about the problems and solutions of the SPE cartridges and HAWACH has summarized several matters and hoping it would provide help for users. The following is about the common faults of the solid phase extraction column. Welcome to contact HAWACH team for more information.
1. Low recovery rate In a complete SPE operation, the target compound may be present in the sample solution effluent, eluent, or adsorbent. When the phenomenon of “the target is not recovered or the recovery rate is low” occurs, the target compound may be added to the sample solution. Add the standard solution, and then perform a complete SPE operation and collect and analyze the sample effluent, and eluent separately. First, determine where the target compound exists, and then determine where the problem comes from 1) the target compound is insufficiently retained on the adsorbent; 2) the target compound is not completely eluted; 3 )Other links.
1.1 The target compound is insufficiently retained on the adsorbent When more than 5% of the target compound appears in the sample effluent or eluent, it can be concluded that “the retention of the target compound on the adsorbent is insufficient”. 1. 2 The target compound is not completely eluted When the target compound does not appear in the sample solution effluent and eluent but only a small amount or does not appear in the eluent, it can be judged that “the target is not completely eluted”.
2. Poor extraction reproducibility When using a solid phase extraction cartridge for sample pretreatment, if the reproducibility of the extraction effect is poor, the possible reasons and improvement methods are as follows:
Before loading the sample, the column bed dries up
Reactivate and balance
The adsorbent is not packed tightly
Ask for an exchange, or squeeze the column bed with a small stick
The sample fluid flow rate is too fast
Reduce the flow rate, usually when the flow rate is less than 5ml/min, the result is stable.
Exceeding the sample loading capacity of the column
Reduce the sample load, or use a larger SPE cartridge
Insufficient amount of eluent
Increase the amount of eluent or use a smaller SPE cartridge
3. Undesriable purification effect 3.1 Improvement of purification mode Generally speaking, the mode of retaining the target compound is better than the mode of retaining the impurities. If the item being analyzed is a certain type of compound analysis, it is best to use the mode of retaining the target compound; For example, it is also the analysis of carbendazim and thiabendazole (a kind of alkaline pesticide) in vegetables. The use of cation exchange columns can specifically retain these pesticides so that they are basically completely separated from the interferences, while the use of normal phase adsorbents or graphitized carbon black to retain the interferences can only remove the main interferences, and there are still many interferences remain.
In addition, if more than one SPE cartridge can be used to purify the target compound, an adsorbent with good selectivity should be selected; in terms of selectivity, the choice would be ion exchange>normal phase>reversed phase.
3.2 Optimization of leachate and eluant For reversed-phase mode and normal-phase mode, the elution intensity of leachate should be increased and the elution intensity of the eluent should be reduced without affecting the recovery rate.
For reversed-phase mode, the target compound can be loaded in an aqueous solution and then eluted with 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100% methanol aqueous solution, collect the eluate and analyze separately, establish the elution curve, find out the solvent system when the target compound is eluted. The methanol content in the eluent should be slightly lower than the solvent system when the target compound is eluted, and when the target compound is eluted completely, the methanol content in the eluent should be slightly higher than the solvent system; The methanol-methyl tert-butyl ether mixed solution’s elution curve should be tested, when pure methanol cannot elute the target compound; for some ionic compounds that are neither soluble in water nor methanol, acid can be added to the solvent system or alkali.
For normal phase systems, the target compound can be loaded with n-hexane solution and then eluted with 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100% n-hexane methyl tert-butyl ether solution, and collect separately, analyze the eluent, establish an elution curve, and find out the solvent system when the target compound is eluted. The content of methyl tert-butyl ether in the eluent should be slightly lower than the solvent system when the target compound is just eluted, and the content of methyl tert-butyl ether in the eluent should be slightly higher than the solvent system when the target compound is just completely eluted.
3.3 Properly treat the SPE cartridges The adsorbent in the SPE cartridges may contain a small amount of interfering substances. The activation solution should select the solvent system with the strongest elution strength in the entire operation; in reversed phase mode, In reversed phase mode, from the sample solution to the eluent mainly involves 0%-100% methanol aqueous solution, the activation solution should be pure methanol, when the target compound needs to be eluted with a methanol-methyl tert-butyl ether mixture. The activation solution should be methyl tert-butyl ether; In the normal phase mode, from the sample solution to the eluent mainly involves 0%-100% n-hexane-methyl tert-butyl ether solution, the activation solution should be pure methyl tert-butyl ether.
4. Too slow SPE column flow rate In the process of using the solid phase extraction cartridge, if the flow rate of the SPE cartridge is too low, the possible reasons and improvement methods are as follows:
The sample solution contains more particulate impurities, which block the sieve
Centrifuge or filter the sample solution before loading
The sample solution viscosity is too high
Dilute the sample with the sample solution
The SPE column bed is too high, and the resistance to the liquid is too large
Use auxiliary tools; use a solid phase extraction instrument and depressurize at the outlet of the liquid path; pressurize at the liquid inlet