SPE vs ILE
Solid Phase Extraction (SPE)
Immobilized Liquid Extraction (ILE)
SPE uses up to 220 times more solvent than ILE
Ex: An SPE extraction of PCBs from 1 liter of water uses 85 mL of solvent (as per EPA method 3535a), whereas an ILE cap would use <300 µL of solvent to perform a similar extraction.
Even the most simplified SPE procedure has at least 6 more steps than ILE
SPE is a labor-intensive, multi-step sample preparation method in which each step introduces additional possibility of error, or loss of analytes.
A simplified SPE procedure for a reversed-phase extraction still requires 8 steps:
- Wash solid phase sorbent with organic solvent or mixture of solvents to remove potential interferants from SPE system.
- Condition, or activate, the solid sorbent with organic solvents or a mixture of organic solvents and reagent water.
- Prepare sample, typically by addition of methanol, then extract sample by forcing it through solid sorbent.
- Dry solid sorbent by flowing air or nitrogen through disk or cartridge.
- Clean sample extract to remove possible contaminants in sample that may be trapped in the sorbent.
- Elute organic analytes from solid sorbent with organic solvent or a mixture of solvents.
- Dry sample eluate with sodium thiosulfate to remove any residual water.
- Concentrate sample extract and perform solvent exchange if necessary.
The complimentary ILE procedure is composed of only 2 steps:
- Place extraction cap on sample vial and shake for 1 hour.
- Place extraction cap on new vial with 200 µL methylene chloride and shake for 15 minutes.
ILE increases throughput by approximately 140%
A well-trained lab technician can perform approximately 55 SPE extractions during a typical 8-hour shift, whereas approximately 133 ILE extractions can be performed in the same period of time.
Dirty samples may plug SPE disks or cartridges.
ILE caps are immune to clogging by dirty samples, particulates, and viscous samples.
Choice of sorbent is critical to SPE method development
Poor sorbent selection can result in the loss of a sample
Analyte breakthrough is a significant problem with SPE, and may result in partial or complete loss of a sample
Because ILE is an equilibrium extraction, it avoids the problem of analyte breakthrough.
LLE vs ILE
Liquid-Liquid Extraction (LLE)
Immobilized Liquid Extraction (ILE)
LLE is a labor-intensive, multi-step procedure
The LLE procedure is a multi-step operation, in which each step, especially concentration, can introduce errors and losses (especially when analyzing volatile compounds).
The ILE procedure is composed of only two non-laborious steps, extraction and back-extraction.
ILE drastically decreases solvent usage (and associated disposal)
Ex: an LLE extraction from 1 Liter of water uses 300-500 mL of solvent (as per EPA method 3510), whereas ILE would use less than 300 µL of solvent in the same extraction.
Solvent usage would thus be decreased by a factor greater than 1000, which entails savings of up to $7 per sample at bulk solvent rates.
Further, the need for frequent disposal of large quantities of solvent is eliminated.
ILE provides emulsion-free sample preparation
The LLE procedure is often complicated by emulsions forming, which may require centrifugation or another technique to remedy.
ILE increases throughput by more than 333%
A well-trained lab technician can perform approximately 30 LLE extractions during a typical 8-hour shift, whereas approximately 133 ILE extractions can be performed in the same period of time.
LLE requires an extensive inventory of glassware and other supporting materials
The required materials for ILE are cheap and few (2 vials, one of which is conical).
LLE requires excessively large sample sizes
Most LLE procedures require a 1 L sample.
ILE is capable of analyzing samples as small as 10 µL, and as large as 1 L.