Solid Phase Extraction Flashcards
What is solid phase extraction?
Sorption of analytes from solution on solid phase based on affinity of analytes for the solid phase
Types of solid phase extraction?
Normal phase
Reversed phase
Ion exchange
Mixed mode
What is the application of normal phase SPE?
Extraction of polar analytes from non polar samples
What sorbent is used in normal phase SPE?
(Polar particles), Activated alumina, silica gels
What interactions are used in normal phase SPE?
Polar interactions (hydrogen bonding, dipole dipole)
What eluents are used in normal phase SPE?
Polar solvents (need to break polar bonds)
Example of normal phase SPE sorbents?
Silica (SiO2)
Alumina (Al2O3)
Bonded silica sorbents
Problems with OH groups on diol modified silica?
Not all OH groups or silanol groups will react due to steric reasons so will have remaining OH groups which is annoying because they give secondary interactions analytes behave in different ways to what is expected, end capping can be used to stop this
What is the application of reversed phase SPE?
Extraction of non polar analytes from polar samples
What sorbent is used in reversed phase SPE?
Bonded phase silica, copolymers
What interactions are used in reversed phase SPE?
Nonpolar interactions (Van der Waals forces)
What eluents are used in reversed phase SPE?
Non polar solvents, hexane, ethyl acetate, acetone but also methanol, acetonitrile
Example of reversed phase SPE sorbents?
Bonded phase silica
C8 bonded phase (octyl)
C18 bonded passed (octadecyl)
Modified silica to extract non polar analytes from polar matrix need non polar environment so silica won’t work need to be modified with long aliphatic hydrocarbon chains, longer chain higher hydrophobicity
What is chemically modified silica?
Silanol groups on the surface of silica are chemically modified to give statuary phases with specific properties
How to get chemical modified silica?
Reaction with mono or dichlorosilane - subsequent treatment with trimenthylchlorosilane may reduce the number of silanol groups that remain unreacted for steric reasons end capping (a simple reaction to modify the silica surface and block functional groups, make sure polar reactant groups on surface of silica are neutralised by reactions of agents)
What is the most widely used of the chemically modified products?
Octadecylsilane
How is end capped octadecyl used as a reversed phase SPE sorbent?
Extraction from aqueous matrices using non polar interactions (for acidic, neutral and basic compounds) silica has long aliphatic hydrocarbon chain no OH groups present so no secondary interactions that interfere with analytes, large number of carbons so hydrophobic, greater efficiency in the extraction of non polar compounds from a polar matrix
Matrix, analytes and retention mechanism used for end capped octadecyl?
Aqueous matriz, wide polarity range of analytes and primary non polar retention mechanism, endcapped sorbent to minimise secondary silanol interactions
How is non end capped octadecyl used as a reversed phase SPE sorbent?
Extraction of acidic, basic and neutral compounds from aqueous matrices using primary non polar and secondary silanol interactions, secondary silanol or ionic interactions can be used to enhance extract purity and method robustness for basic compounds
Matrix, analytes and retention mechanism used for non end capped octadecyl?
Aqueous matrix, wide polarity range of analytes, primary non polar, secondary polar and weak cation enhance retention mechanisms
What are the three most common solvents for reversed phase SPE?
Hexane, chloroform, ethyl acetate, needs to break non polar interaction with non polar solvents, sometimes use methanol depending on how strong interactions are
What are the most common solvents for normal phase SPE?
Methanol and water, use polar solvent to break polar interactions
What is the application of ion exchange SPE?
Extraction of ionic analytes from polar samples, (can be charged at different pH)
What is needed in ion exchange?
Need charge on analytes and ion exchange, opposite charges, if basic has a positive charge so sorbent will have negative charge (although negative charge will still be called cationic exchanger) cation exchange will have negatively charged surface, anion exchanger will have positively charge surface
What sorbent is used in ion exchange SPE?
(Ion exchange particles) silica gel or polymers containing cation or anion functional groups
What interactions are used in ion exchange SPE?
Cation and anion exchange
What eluents are used in ion exchange SPE?
(High ionic strength, required pH) buffers, salt solution to break anion exchange acid base interactions
Why does the extraction step needs charged compounds?
To break bonds and change pH of mobile phase so make sure no charge and hence the products get eluted
What are ion exchange SPE sorbents?
Apolar polymeric resins or silica sorbents containing ionised or ionisable functional groups
Example of ion exchange SPE sorbents?
Primary amine (weak anionic) Quarternary amine (strong anionic) Carboxylic acid (weak cationic) Aromatic sulphonic acid (strong cationic)
Anion exchange SPE sorbents, how is a non end capped primary amine used for extraction?
The amine is a weak base, extraction of strong acidic analytes from aqueous matrices using anion exchange interactions, at pH lower than 9.8 the functional groups will be charged (protonated), at 7.8 will be full charge on anionic exchanger, use at pH below 7.8
Anion exchange SPE sorbents, how can elution be performed with non end capped primary amine?
Elution can be performed by neutralising charge of the sorbent
Anion exchange SPE sorbents, matrix, analytes and retention mechanism used for non end capped primary amine?
Aqueous matrix, anionic analytes, weak anion exchange retention mechanism
Anion exchange SPE sorbents, how is a non end capped quaternary amine used for extraction?
Functional groups charged throughout whole range of pH, extraction of acidic analytes from aqueous matrix using anion exchange interactions
Anion exchange SPE sorbents, matrix, analytes and retention mechanism used for non end capped quaternary amine?
Aqueous matrix, anionic analyte, strong anionic exchange retention mechanism
Cation exchange SPE sorbents, how is non end capped carboxylic acid used for extraction?
Weak acid functional group need to maintain right pH to maintain charge on the functional group of stationary material and analyte, extraction of strong bases from aqueous matrix using cation exchange interactions, will be fully deprotonated at 6.8, will be protonated at pH 2.8
Cation exchange SPE sorbents, how can elution be performed with non end capped carboxylic acids?
Elution can be performed by neutralising charge of the sorbent
Cation exchange SPE sorbents, matrix, analytes and retention mechanism used for non end capped carboxylic acids?
Aqueous matrix, cationic analytes, weak cation exchange retention mechanism
Cation exchange SPE sorbents, how is non end capped sulphonic acid used for extraction?
Strong acid functional group so will carry charge throughout whole charge and pH range, extraction of basic analytes from aqueous matrix using cation exchange interactions
Cation exchange SPE sorbents, matrix, analytes and retention mechanism used for non end capped sulphonic acids?
Aqueous matrix, cationic analytes, strong cation exchange retention mechanisms
How can a complex matrix complicate extraction?
With reverse phase, anion exchange and cation exchange, difficult to extract only cations of interest, will extract all cations in sample
For weakly and basic analytes what stationary material is important to use?
Use strongly acidic and basic stationary materials for weakly acidic and basic analytes
Mixed mode sorbents?
Have multiple retentive sites on an individual particle that exploit different retention mechanisms - most widely used gives better capability, (pulls together reversed phase and ion exchange)
Types of interaction in mixed mode sorbents?
Interaction with different functional groups on a single analyte
Interaction of different functional groups on multiple analytes
Why would mixed mode be more selective?
If two types of interaction possible this process will be more selective, uses functionality of long aliphatic hydrocarbon change with ion exchange ability
Mixed mode anion exchange SPE sorbents, how is octadecyl and quaternary amine used for extraction?
Quaternary amine is a strong base, extraction of acidic analytes from aqueous matrix using dual non polar and strong anion exchange interaction
Mixed mode anion exchange SPE sorbents, matrix, analytes and retention mechanism used for octadecyl and quaternary amine?
Aqueous matrix, non polar (due to long carbon chains) and anionic analytes, non polar and strong anion exchange retention mechanisms
Mixed mode anion exchange SPE sorbents, how is octadecyl and primary amine used for extraction?
Weak base functional group, can be used for both strong and weak acids, extraction of strong acidic analytes from aqueous matrix using dual non polar and weak anion exchange interactions
Mixed mode anion exchange SPE sorbents, matrix, analytes and retention mechanism used for octadecyl and primary amine?
Aqueous matrix, non polar and anionic analytes, non polar and weak anion exchange retention mechanisms
Mixed mode cation exchange SPE sorbents, how is octadecyl and sulphonic acid used for extraction?
Strong acid functional group charged over whole range of pH will extract weak bases, extraction of basic analytes from aqueous matrix using dual non polar and strong cation exchange interactions
Mixed mode cation exchange SPE sorbents, matrix, analytes and retention mechanism used for octadecyl and sulphonic acid?
Aqueous matrix, non polar and cationic analytes, non polar with strong cation exchange retention mechanisms
Mixed mode cation exchange SPE sorbents, how is octadecyl and carboxylic acid used for extraction?
Weak acid functional group dissociated at pH 68 or higher used fro both strong and weak bases, need to make sure they carry a positive charge, pH at which this will take place is very narrow range, extraction of strong basic analytes from aqueous matrix using dual non polar and weak cation exchange interactions
Mixed mode cation exchange SPE sorbents, matrix, analytes and retention mechanism used for octadecyl and carboxylic acid?
Aqueous matrix, non polar and cationic analytes, non polar and weak cation exchange retention mechanisms
Anion exchanger primary amine pKa 9.8 best retention of acidic analytes?
Best retention of acidic analyte at 2 pH units above its own pKa and 2 pH units below the pKa of the anion exchanger
Anion exchanger quarternary amine best retention of acidic analytes?
Best retention of acidic analyte 2 pH units above its own aka
Cation exchanger carboxylic acid pKa 4.8 best retention of basic analytes?
Best retention of basic analyte at 2 pH units below its own pKa and 2 pH units above pKa of the cation exchanger
Cation exchanger sulphonic acid best retention of basic analytes?
Best retention of basic analyte at 2 pH units below its own pKa
Mixed mode anion exchanger primary amine pKa 9.8 best retention of acidic analyte?
Best retention of acidic analyte at 2pH units above its own pKa and 2 pH units below pKa of anion exchanger
Mixed mode anion exchanger quaternary amine best retention of acidic analyte?
Best retention of acidic analyte at 2 pH units above its own pKa
Mixed mode cation exchanger carboxylic acid pKa 4.8 best retention of basic analyte?
Best retention of basic analyte at 2 pH units below its own pKa and 2 pH units above pKa of the cation exchanger
Mixed mode cation exchanger sulphonic acid best retention of basic analyte?
Best retention of basic analyte at 2 pH units below its own pKa
