SOLIDPHASE EXTRACTION APPARATUS Equipment required for SPE is

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SOLID-PHASE EXTRACTION APPARATUS û Equipment required for SPE is generally very simple. û Two

SOLID-PHASE EXTRACTION APPARATUS û Equipment required for SPE is generally very simple. û Two basic formats, a. cartridges and b. discs û For small sample volumes SPE microscale system is used. a. CARTRIDGES û Standard SPE cartridge (column) is fabricated in syringe barrel. û The sorbent bed occupies about one-third of syringe barrel volume. û Underneath is a porous discs, usually of polyethylene, stainless-steel or teflon. û The remainder of cartridge volume is used as sample or solvent reservoir. û Size of cartridge depends on sorbent amount, controlled by analyte mass or contaminants in sample to be extracted.

û Cartridges are available with sorbent bed masses of 10 mg-10 g. û Analyte

û Cartridges are available with sorbent bed masses of 10 mg-10 g. û Analyte should be no more than about 5% of sorbent weight û Practical approaches to optimizing bed mass are considered in 1. volume of solution that is necessary to detect a particular concentration of analyte. 2. sensitivity of the analytical method 3. amount of eluting solvent necessary to remove solute from sorbent. 4. in some cases, amount of solution containing analyte may be limited, such as physiological fluids. 5. for wastewater or drinking water there is no problem for sample size

û sample is passed through column using a vacuum to force liquid over sorbent

û sample is passed through column using a vacuum to force liquid over sorbent bed. û for small columns (mg-scale), to pass a liter of liquid with a vacuum of 20 mm. Hg requires 1 hr. û for larger columns (g-scale), same volume may require 20 minutes or less, û but a larger column will also require more eluting solvent. û final sample solution may be evaporated to increase concentration detectable by analytical method. û So while a larger column can save time in extraction step due to higher flow rates, this time could be lost in evaporation following elution. û Therefore, analyst has to judge sample and cartridge size limitation in developing an SPE method

b. DISCS û Three types of construction have been developed into commercial products: 1)

b. DISCS û Three types of construction have been developed into commercial products: 1) sorbent contained between inert porous discs to solvent of extraction process (essentially a very thin, wide SPE cartridge); 2) sorbent is enmeshed into a web of teflon or some other inert polymer; 3) sorbent is trapped in a glass fiber or paper filter, or silica, modified silica, other oxides and modified oxides, and polymers. û However, commercial production of wide variety of potential disc phases has lagged behind that of cartridges by a long way.

û disc devices can be placed into a syringe barrel or other housing û

û disc devices can be placed into a syringe barrel or other housing û thin layer of small sorbent particles between two glass fiber pads, creating a disc-like packed bed with high flow and large particle size sorbent. û the original benefit identified for extraction discs was faster flow rate in extraction step per unit mass of sorbent. û wider diameter of apparatus results in a faster flow but still preserves good contact between the sample solution and the sorbent bed. At a vacuum of 20 mm. Hg one liter of solution can pass through system in less than 10 min. û time saving particularly for laboratories performing hundreds or even thousands of analyses per week. û however, recent developments of "high-flow" cartridges have reduced advantage this format. û development of disc cartridge is practical due development of 96 -well plate technology for small sample size.

c. MICROSYSTEMS û miniaturization of SPE apparatus reduce solvent use û since analytical techniques

c. MICROSYSTEMS û miniaturization of SPE apparatus reduce solvent use û since analytical techniques used for samples prepared by SPE require very small volumes (HPLC, GCIMS, capillary electrophoresis, etc. ), then reduction in sample size is reccomended. û solid-phase microextraction (SPME) utilizes a fine fused silica fiber that can either be uncoated or modified with a thin layer of a selected coating û In all cases the fiber surface acts as the extraction sorbent.

CONCLUSIONS û Solid-phase extraction is still a developing field. û Many advances in sorbent

CONCLUSIONS û Solid-phase extraction is still a developing field. û Many advances in sorbent technology parallel are similar to stationary phases in HPLC. û So where appropriate, technology developed for HPLC is transferred to SPE for specific applications. û Because the mode of operation for SPE is single use, sorbent ruggedness is often not as crucial a factor as in HPLC. û It is also probable that more on-line applications and miniaturization are likely in the development of new SPE methods and sorbents. û The base materials for sorbents is bonded silicas. û Despite comprehensive surface modification, "secondary" interactions from the base material is experienced

SPE Technology - Principles and Practical Consequences û solid-phase extraction is governed by same

SPE Technology - Principles and Practical Consequences û solid-phase extraction is governed by same physico-chemical principles that influence a wide variety of sorptive processes. û These are present in such diverse technologies as purification of biologically useful materials,

Ø Ø Ø Catalysis Toxic substance monitors Organic synthesis, biopolymer blotting Ionic exchange and,

Ø Ø Ø Catalysis Toxic substance monitors Organic synthesis, biopolymer blotting Ionic exchange and, Water and wastewater clean-up. Most of these areas of applied chemistry have several elements in common: Ø transport of molecules or ions through a fluid of given properties to surface. Ø adsorption onto or partition into a solid phase. Ø selective desorption or partition from this phase into fluid of same or different properties.