| Introduction: Oasis® and Sep-Pak® Brand SPE Sorbent chemistries The wide variety of sorbent chemistries available from Waters lets you tailor a sample preparation step to the specific needs of your application. There are hydrophilic phases that range from high to intermediate to low polarity; nonpolar phases which vary from high to low degrees of hydrophobicity; strong and weak ion-exchangers; and specialty sorbents. For the adsorption of the analytes of interest, you can take advantage of a variety of adsorptive forces from the weaker van der Waals, hydrogen-bonding, and dipole-dipole interactions, to the progressively stronger hydrophobic-interaction and ion-exchange processes, to the extreme of chemical modification of the analyte by on-cartridge derivatization reactions. Many sorbents can be used in more than one mode. - For example, silica can be used for adsorption by hydrogen bonding or dipole-dipole interaction, for support of a stationary-phase liquid in liquid-liquid partition, and even for ion-exchange.
- Some sorbents, like Florisil or DNPH, have been designated, and are certified, for specific separations, but can be used in other applications as well.
- Aluminas are available with acidic [A], neutral [N], and basic [B] surfaces.
- Cation and anion exchangers are available in both strongly- and weakly-ionized forms, which can be advantageously altered in function by changing pH.
- Non-polar sorbents can be used in reversed-phase mode to extract analytes from aqueous solvents and, then, in non-aqueous normal-phase mode for preferential elution of adsorbed analytes. Typical non-polar sorbents are C18, C8 or C2 bonded-silica phases. HPLC users are familiar with these packings and their versatility.
A unique, next-generation family of Oasis® brand copolymer sorbents continues to be developed by Waters. The first three members are designed specifically for optimum reversed-phase and mixed-mode SPE. - Oasis® HLB sorbent is universal in its application. A single, simple SPE method takes advantage of the water-wettable, yet hydrophobic, surface to isolate both polar and non-polar compounds from the same sample matrix.
- Two-dimensional methods can be developed using not only solvent strength, but pH, as a variable to produce cleaner sample extracts.
- Even more specificity can be obtained by using Oasis® ion exchange sorbents such as Oasis® MCX and MAX.
- Many references in this bibliography give details of these extraordinary, patented products [use the search term "Oasis"].
The table below lists, by separation mode, the SPE sorbents currently available from Waters. General properties, physicochemical characteristics, and some typical applications of these SPE sorbents are described.
 Sorbent Properties and Typical Applications: by Separation Mode
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| | Reversed-Phase |
| | Sorbent | Properties & Applications |
| | Oasis® HLB | An exceptionally clean, highly reproducible, patented copolymer synthesized with a unique composition that is hydrophilic-lipophilic-balanced for both strong reversed-phase retention and water-wettability. Compatible with sample or eluents from pH 1 to 14. Used to adsorb both polar and non-polar compounds simultaneously from aqueous media; typical applications include drugs and their metabolites from biological fluids, environmental pollutants from water. HLB can be substituted for, has a wider spectrum of retention, and is more reproducible than C18 and all other silica- or polymer-based reversed-phase media. Oasis® HLB is the ideal starting point for new reversed-phase SPE method development. Pore Size (nominal): 80 Å Particle Size: 30 µm [or 60 µm for LP grade] Surface Functionality: m-Divinylbenzene & N-vinylpyrrolidone copolymer |
| | C18 | Strongly hydrophobic silica-based bonded phase. Used to adsorb analytes of even weak hydrophobicity from aqueous solutions; typical applications include drugs and their metabolites in serum, plasma or urine, desalting of peptides, trace organics in environmental water samples, organic acids in beverages; similar to reversed-phase HPLC columns in elution behavior. Pore Size (nominal): 125 Å Particle Size: 55-105 µm Bonding Chemistry: Monofunctional silane Surface Functionality: -Si(CH3)2C18H37 Carbon Content: 12% End-Capped?: Yes |
| | tC18 | Strongly hydrophobic silica-based bonded phase; trifunctional bonding chemistry gives it increased hydrolytic stability over C18. Applications similar to those of C18. Pore Size (nominal): 125 Å Particle Size: 37-55 µm Bonding Chemistry: Trifunctional silane Surface Functionality: -SiC18H37 Carbon Content: 17% End-Capped?: Yes | |
| | C8 | Moderately hydrophobic silica-based bonded phase; use for methods requiring less retention than C18. Typical applications include drugs and their metabolites in serum, plasma or urine, peptides in serum, plasma. Pore Size (nominal): 125 Å Particle Size: 37-55 µm Bonding Chemistry: Monofunctional silane Surface Functionality: -Si(CH3)2C8H17 Carbon Content: 9% End-Capped?: Yes | |
| | tC2 | Silica-based bonded phase with low hydrophobicity; use for methods requiring less retention than C8. Applications are similar to C18 and C8. Pore Size (nominal): 125 Å Particle Size: 37-55 µm Bonding Chemistry: Trifunctional silane Surface Functionality: -SiC2H5 Carbon Content: 2.7% End-Capped?: Yes | |
| | Porapak RDX | Specially cleaned, hydrophobic copolymer resin [poly(divinyl-benzene-vinylpyrrolidone)]. Can be used as an alternative to octadecyl-bonded silica for preparation of analytes that weakly adsorb to silica-based reversed phase sorbents. Compatible with sample or eluents at high and low pH. Specifically designed for the concentration of high explosives in aqueous samples. Pore Size (nominal): 200 Å Particle Size: 125-150 µm Surface Functionality: m-Divinylbenzene & N-vinylpyrrolidone copolymer |
| | Normal- or Reversed-Phase |
| | Aminopropyl [NH2] | Silica-based, moderately polar, bonded phase with weakly basic surface; can be used as a polar sorbent, like silica, with different selectivity for acidic/basic analytes or as weak anion exchanger in aqueous medium below pH 8. Applications include phenols and phenolic pigments, petroleum fractionation, saccharides, drugs and drug metabolites. Pore Size (nominal): 125 Å Particle Size: 55-105 µm Bonding Chemistry: Trifunctional silane Surface Functionality: -Si(CH2)3NH2 Carbon Content: 3.5% End-Capped?: No | |
| | Cyanopropyl [CN] | Silica-based bonded phase of low hydrophobicity; can be used as less polar alternative to silica in normal-phase applications or as less hydrophobic alternative to C18 or C8 in reversed-phase applications. Typical applications include drugs, drug metabolites, and pesticides. Pore Size (nominal): 125 Å Particle Size: 55-105 µm Bonding Chemistry: Monofunctional silane Surface Functionality: -Si(CH2)(CH2)3CN Carbon Content: 6.5% End-Capped?: Yes | |
| | Diol | Silica-based, moderately polar, bonded phase with neutral surface; can be used as an alternative to silica in normal phase applications, where the acidic character of silica is undesirable or as very weakly interacting hydrophobic phase in aqueous media. Applications include antibiotics from cosmetics; isolation of proteins or peptides by hydrophobic interaction chromatography. Pore Size (nominal): 300 Å Particle Size: 37-55 µm Bonding Chemistry: Trifunctional silane Surface Functionality: -Si(CH2)3OCH2CH(OH)CH2OH Carbon Content: 2% End-Capped?: No |
| | Normal-Phase |
| | Silica | Polar sorbent, used primarily to adsorb analytes from non-polar solvents like hydrocarbons, chloro- or fluoro-substituted hydrocarbons or less polar esters and ethers; elution with more polar solvents like polar esters, ethers, alcohols, acetonitrile or water; the binding mechanism can be hydrogen bonding or dipole-dipole interaction. Silica can also be used in aqueous medium as a cation exchanger of intermediate strength, or as a support for liquid-liquid partition separations with a polar stationary phase. Pore Size (nominal): 125 Å Particle Size: 55-105 µm Activity Grade: High pH of a 10% aqueous slurry: 7 Moisture content:  3.2% Surface Functionality: -SiOSi-; -SiOH; -Si(OH)2 | |
| | Alumina A, N, B | Similar in use to silica; available in acidic [A], neutral [N], and basic [B] grades; highly active, polar surface. Alumina also exhibits specific interactions with the pi-electrons of aromatic hydrocarbons, making it useful for applications like crude oil fractionation; acidic and basic grades can also be used as low-capacity ion-exchangers, which, unlike polymer-based exchangers, are unaffected by high energy, radioactive materials. Pore Size (nominal): 120 Å Particle Size: 50-300 µm Activity Grade: 1 on Brockmann activity scale pH of a 10% aqueous slurry: A: 4-5; N: 7-8; B: 9-10 Moisture content: 1.5% Surface Functionality: -AlOAl-; -Al(OH)1 or 2 [NOTE: acidic and neutral grades are typically made by washing basic alumina with HCl until the desired pH of an aqueous slurry is reached; thus some residual -AlCl functionality may be present.] | |
| | Florisil™ | Highly active, polar sorbent with a slightly basic surface for adsorption of low to moderate polarity species from nonaqueous solutions. Specifically designed for the adsorption of pesticides using official AOAC and EPA methods. Other applications include polychlorinated biphenyls in transformer oil. Pore Size (nominal): 60 Å Particle Size: 50-200 µm Activity Grade: High pH of a 10% aqueous slurry: 8.5 Moisture content: 2.5% Surface Functionality: -SiOSi-; -SiOH; -Si(OH)2; -MgOH [Note: Florisil is a co-precipitate of silica and magnesia.] |
| | Mixed-Mode and Ion Exchange |
| | Oasis® MCX | Obtained by precisely controlled sulfonation of an exceptionally clean, highly reproducible, patented copolymer synthesized with a unique composition that is hydrophilic-lipophilic-balanced for both strong reversed-phase retention and water-wettability. Compatible with sample or eluents from pH 1 to 14. Used to adsorb both polar and non-polar, neutral and cationic compounds simultaneously from aqueous media via Mixed-mode strong Cation eXchange and reversed-phase mechanisms. Typical applications include basic drugs and their metabolites from biological fluids, environmental pollutants from water, drugs of abuse and their metabolites from urine. MCX can be substituted for, has a wider spectrum of retention, and is more reproducible and stable than all silica-based mixed-mode media. Pore Size (nominal): 80 Å Particle Size: 30 µm [or 60 µm for LP grade] Surface Functionality: m-Divinylbenzene & N-vinylpyrrolidone copolymer, with sulfonic acid substituents [-SO3H, 1.0 meq/gm]  | |
| | Oasis® MAX | Obtained by precisely controlled functionalization of an exceptionally clean, highly reproducible, patented copolymer synthesized with a unique composition that is hydrophilic-lipophilic-balanced for both strong reversed-phase retention and water-wettability. Compatible with sample or eluents from pH 1 to 14. Used to adsorb both polar and non-polar, neutral and anionic compounds simultaneously from aqueous media via Mixed-mode strong Anion eXchange and reversed-phase mechanisms. Typical applications include acidic drugs and their metabolites from biological fluids, environmental pollutants from water, drugs of abuse and their metabolites from urine. MAX can be substituted for, has a wider spectrum of retention, and is more reproducible and stable than all silica-based mixed-mode anion exchange media. Pore Size (nominal): 80 Å Particle Size: 30 µm [or 60 µm for LP grade] Surface Functionality: m-Divinylbenzene & N-vinylpyrrolidone copolymer, with quaternary amine substituents as shown below. [0.3 meq/gm]  | |
| | Accell™ Plus QMA | Silica-based, hydrophilic, strong anion-exchanger with large pore-size. Extraction of anionic analytes in aqueous and non-aqueous solutions. Due to the large pore-size, it is excellent for the isolation of anionic proteins, e.g., immunoglobulins, enzymes. Other applications include the removal of acidic pigments from wines, fruit juices and food extracts, isolation of phenolic compounds, peptide pool fractionations. Pore Size (nominal): 300 Å Particle Size: 37-55 µm Bonding Chemistry: Polymeric: - An acrylamide copolymer on Diol silica
- Ligand density: 220 µmoles/g
- Approximate protein binding capacity = 200 mg BSA/g of packing or 72 mg/Accell Plus QMA Classic or Plus cartridge.
Surface Functionality: -C(O)NH(CH2)3N(CH3)3+ Cl- pH of a 10% aqueous slurry: 9 Carbon Content: 6% | |
| | Accell™ Plus CM | Silica-based, hydrophilic, weak cation-exchanger with large pore-size. Extraction of cationic analytes in aqueous and non-aqueous solutions. Due to the large pore-size, it is excellent for the isolation of cationic proteins. Other applications include pesticides, herbicides, steroids. Pore Size (nominal): 300 Å Particle Size: 37-55 µm Bonding Chemistry: Polymeric: - An acrylic acid/acrylamide copolymer on Diol silica
- Ligand density: 350 µmoles/g
- Approximate protein binding capacity = 175 mg Cytochrome c/gm of packing or 63 mg/Accell Plus CM Classic or Plus cartridge.
Surface Functionality: -CO2- Na+ pH of a 10% aqueous slurry: 4 Carbon Content: 5.5% |
| | Specialty Sorbents |
| | DNPH-Silica | Contains acidified dinitrophenylhydrazine reagent coated on a silica sorbent. Special handling and packaging procedures minimize carbonyl contamination and assure a consistent, low hydrazone background level, cartridge-to-cartridge, lot-to-lot. Used for quantitation of aldehydes and ketones in air samples by in situ reaction to form hydrazone derivatives, which are then eluted and analyzed by HPLC. DNPH-silica is specified in several procedures for the analysis of carbonyl compounds in automobile engine exhaust. It has also been used to isolate carbonyl compounds in human breath which may be disease state indicators. Sep-Pak® DNPH-Silica Cartridges meet the requirements of EPA Method TO-11 and ASTM-D-5791-1. Pore Size (nominal): 125 Å Particle Size: 55-105 µm Bonding Chemistry: Coated: - Bare silica coated with 14 µmoles DNPH/g of packing or 5 µmoles/cartridge.
Surface Functionality: 2,4-Dinitrophenylhydrazine  | |
| | XPoSure™ | Contains acidified dinitrophenylhydrazine reagent coated on a larger particle silica sorbent. Special handling and packaging procedures minimize carbonyl contamination and assure a consistent, low hydrazone background level, cartridge-to-cartridge, lot-to-lot. Used for quantitation of aldehydes and ketones in large air samples by in situ reaction to form hydrazone derivatives, which are then eluted and analyzed by HPLC. XPoSure™ is specified in several procedures for the analysis of carbonyl compounds in ambient air. Larger particle size and higher porosity frits make XPoSure™ Aldehyde Sampler Cartridges compatible with low-pressure, personal air sampling pumps. Pore Size (nominal): 125 Å Particle Size: 500-1000 µm Bonding Chemistry: Coated: - Bare silica coated with 14 µmoles DNPH/g of packing or 5 µmoles/cartridge.
Surface Functionality: 2,4-Dinitrophenylhydrazine [DNPH] | |
| * Adapted in part from: pp 21-26 of Solid Phase Extraction Applications Guide and Bibliography: a Resource for Sample Preparation Methods Development , Sixth Edition, Patrick D. McDonald, Ph.D., and Edouard S.P. Bouvier, Ph.D., editors, 645 pp, Waters, Milford, 1995 [P/N 52853].
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