Dnyanasadhana College, Thane. Department of Chemistry M. Sc Dnyanasadhana College, Thane. Department of Chemistry M.Sc. Analytical Chemistry Sem-I UNIT- 3.3 SOLID PHASE EXTRACTION Dr.G.R.Bhgaure

3.3 Solid phase extraction: principle, process and applications. [2L]

Principle: Solid-Phase Extractions In a solid-phase extraction the sample is passed through a Cartridge containing solid particulates that serve as the adsorbent material. For liquid samples the solid adsorbent is isolated in either a disk cartridge or a column. The choice of adsorbent is determined by the properties of the species being retained and the matrix in which it is found. Representative solid adsorbents. Solid-phase extraction (SPE) is a separation process  by which compounds that are dissolved or suspended in a liquid mixture are separated from other compounds in the mixture according to their physical and chemical properties.

Column cartridge Disk Cartridge Direction of Solvent flow Pours retainer Solid adsorbent Disk Cartridge Pours retainer Column cartridge

A typical solid phase extraction involves four basic steps. Step-1: First, the cartridge is equilibrated with a non-polar or slightly polar solvent, which wets the surface and penetrates the bonded phase. Step-2: Then water, or buffer of the same composition as the sample, is typically washed through the column to wet the silica surface. Step-3: The sample is then added to the cartridge. As the sample passes through the stationary phase, the polar analyte's in the sample will interact and retain on the polar sorbent while the solvent, and other non-polar impurities pass through the cartridge. After the sample is loaded, the cartridge is washed with a non-polar solvent to remove further impurities. Step-4: Then, the analyte is eluted with a polar solvent or a buffer of the appropriate pH.

A STATIONARY PHASE A stationary phase of polar functionally bonded silicas with short carbons chains frequently makes up the solid phase. This stationary phase will adsorb polar molecules which can be collected with a more polar solvent. The stationary phase comes in the form of a packed syringe-shaped cartridge, a 96 well plate, a 47- or 90-mm flat disk. Solid phase extraction cartridges and disks are available with a variety of stationary phases, each of which can separate analyte's according to different chemical properties. Most stationary phases are based on silica that has been bonded to a specific functional group. Some of these functional groups include hydrocarbon chains of variable length (for reversed phase SPE), quaternary ammonium or amino groups (for anion exchange), and sulfonic acid or carboxyl groups (for cation exchange).

For example, sedatives, such as secobarbital and phenobarbital, can be isolated from serum by a solid-phase extraction using a C-18 solid adsorbent. Typically a 500-mL sample of serum is passed through the cartridge, with the sedatives being retained by a liquid–solid extraction. The cartridge is then washed with distilled water to remove any residual traces of the serum’s matrix. Finally, the retained sedatives are eluted from the cartridge by a solid–liquid extraction using 500 mL of acetone. For many analyses, solid–phase extractions are replacing liquid–liquid extractions due to their ease of use, faster extraction times, decreased volumes of solvent, and their superior ability to concentrate the analyte's. The last advantage is discussed in more detail in the final section of this chapter.

Application Sedatives, such as secobarbital and phenobarbital,can be isolated from serum by a solid-phase extraction using a C-18 solid adsorbent. Some of the examples included are caffeine from coffee, polyaromatic hydrocarbons from water, parabens from cosmetics, chlorinated pesticides from water, and steroids from hydrocortisone creams. Extracted analyte's may be determined quantitatively by gas (GC) or liquid chromatography (LC).

Applications: