SPE Phase & Solvent Selection

Table 1 shows the basic mechanism of separation for each of these phases, while Figure 1 shows that phase selection starts with determining if your sample is soluble in water or organic solvent, your analyte’s characteristics, and which SPE stationary phase to use for each. Figure 1 also shows typical SPE stationary phases used for different applications. Figure 1 is an SPE Phase Selection Flow Chart that shows which Thermo Scientific SPE phase to use depending on your analytes’ solubility and charge.

Figure 1. shows the phase (sorbent) depending on if your sample is soluble in a polar, moderately polar, or non-polar organic solvent polar or if your sample is soluble in water soluble if it is ionic or non-ionic.

The stationary phase, differing in particle size and distribution, can be packed in a cartridge, 96-well plates, and even pipette tips.

SPE 96-well plates

• SPE 96-well plates are ideal when simultaneously processing a large number of small-volume samples in high throughput environments. Is there a strategy for using these that the cartridges don’t have?

SPE cartridges

• Plastic SPE cartridges are the most common format used for SPE. They vary in size (e.g., 1mL, 3mL, 6mL, 12mL) and amount of stationary phase (e.g., what?). 3mL cartridges are a popular size and a good starting point for many applications.
• Smaller cartridges contain smaller amounts of sorbent and require less solvent for elution. This can make a more efficient separation which is useful if evaporation is required.
• Larger cartridges can be used when larger volumes of solvent are required. A larger sorbent amount can be helpful when analytes are difficult to retain on a column.
• As a general rule, the cartridge size should
• Closely match the volume of wash solvent use.
• Be appropriate for your sample load: Typically, one can load a sample that is approximately 5-10% of the sorbent weight.
• Take extraction speed and sample capacity into consideration. For example, a faster extraction speed or a higher sample capacity requirement will need a larger cartridge.

Table 3. Typical sorbent mass, sample size, and elution volumes used for different SPE cartridge sizes

The choice of solvent is dependent upon the sample matrix and the retention mechanism used. The table below shows the differing polarities of solvents commonly used in SPE.

Recommended SPE elution solvents

The choice of solvent to extract the analyte is dependent on the analyte properties.

• Nonpolar solvents such as ethyl acetate are strong solvents in reversed phase applications.
• Polar solvents such as methanol and water are strong solvents in normal phase interactions.