Efficient SPE (Part 2 of 2)
Already in the end of 80s polymer phases for SPE have been manufactured. One of the first polymeric sorbents, which was already used in column chromatography, is polyamide (PA). Polymer phases, based on polystyrene-divinylbenzene copolymers (PS/DVB) became important in environmental analysis, because new multimethods required a broad selectivity spectrum. Thus, methods have been developed, which can enrich up to 50 pesticides and metabolites from drinking water in a single run. Today polystyrene-divinylbenzene copolymers, modified with ion exchangers (mixed-mode phases) are also used for environmental analytical, food chemical and pharmaceutical applications.
|Phase||Material|| Key feature
|HR-X *)||spherical, hydrophobic PS/DVB||“modern” PS/DVB phase|
|HR-P||highly porous, hydrophobic PS/DVB||“classical” PS/DVB phase|
|Easy||polar, bifunctional PS/DVB||for applications without conditioning|
|PA||medium polar polyamide||relatively high polarity (RP/NP-mode)|
|HR-XC *)||strong mixed-mode cation exchanger||for basic compounds|
|HR-XCW *)||weak mixed-mode cation exchanger||for strong bases|
|HR-XA *)||strong mixed-mode anion exchanger||for acidic compounds|
|HR-XAW *)||weak mixed-mode anion exchanger||for strong acids|
|PS-H+||strong PS/DVB cation exchanger||Removal of cations from water|
|PS-OH–||strong PS/DVB anion exchanger||Removal of anions from water|
Less polar polymers (e.g. Oasis® HLB (Waters), StrataTM X (Phenomenex), CHROMABOND® HR-P and HR-X (MACHEREY-NAGEL)) gained high popularity due to their broad applicability in RP-mode.
SPE columns with non-polar, hydrophobic PS/DVB phase HR-P were already introduced as “special columns for the extraction of phenols and pesticides from water” for around 20 years. Rapidly, their great application spectrum (broad selectivity, high capacity, pH 1-14) and their easy handling (fast drying) had been recognized, so that they were able to replace the classical C18 silica in many fields.
The successfully improved, spherical HR-X polymer additionally allows ideal flow behaviour also of biological matrices, low solvent consumption due to an optimized pore structure and an operation with extremely low blind values due to highest pureness of the adsorber material. Many application notes for pharmaceutical, food and environmental sector can be found in SORBTECH application database (e.g. penicillin sor sulfonamides from serum).
Polar, bifunctionally modified PS/DVB phases (e.g. Easy) are distinguished by a high affinity to aqueous matrix, so that a conditioning step is dispensable. That saves time and money, especially for a high sample throughput (e.g. pesticides from water).
The medium polar polyamide phase PA is primarily used for analytes from food (e.g. flavonoids in fruits and vegetables). As polymer it is characterized by a relatively high polarity, which also allows NP besides RP applications.
For an extraction of polar or ionic analytes from complex matrices (e.g. urine, plasma, serum, drugs, food) ion exchanger polymers based on PS/DVB are suitable. As mixed-mode phases, they feature distinct ion exchange and RP properties.
With strong and weak cation exchangers (e.g. HR-XC or HR-XCW) very good enrichment of basic analytes (e.g. amines) is achieved. Strong cation exchangers have been proven of value for the extraction of melamine from diary products for example.
Strong and weak anion exchangers (e.g. HR-XA or HR-XAW) are accordingly used for an enrichment of weak or strong acids (z.B. acidic drugs or perfluorinated acids).
Besides the mixed-mode phases, there exist “defined” polymeric ion exchangers without RP part (e.g. PS-H+, PS-OH–), which are applied for the sample preparation of ion chromatography.
Selection of a suitable SPE phase
For a selection of an SPE phase a decision between silica, polymer or further sorbents is necessary. The question “Which is better?” is not important, but rather “Which is better suitable for a specific separation task?” To find this SPE phase SORBTECH offers a considerable support:
The SORBTECH application database in Internet and the application guides provide numerous application notes. With the assistance of selected application notes and product information about CHROMABOND®silica and polymer phases, an appropriate phase can often be found for an effective and efficient sample preparation.
Every application is unique to some degree. As a result , a directly comparable application note cannot be found in every case due to the diversity of chromatographic tasks. Standard protocols (see SORBTECH application database, keyword: „ standard SPE procedure“) for the most important CHROMABOND® phases can therefore form the base for successful method development. Selection schemata support a limitation of possible SPE phases and elution solvents in relation to the sample and analyt properties. Specially adjusted SPE method development kits facilitate a cost-efficient development.
For the successful selection of modern polymer phases CHROMABOND® HR-Xpert – the professional concept of innovative SPE phases – is designed. HR-Xpert features the suitable sorbent and the optimal method for sample preparation, cleaning and enrichment depending to the character of the analyte.
The CHROMABOND® HR-Xpert – concept
for neutral, acidic and basc analytes
The SORBTECH customer service team is pleased to provide samples free of charge and advises on every question concerning SPE and chromatography.
Whether the base adsorbent of an SPE phase is silica or polymer, the selection of a SPE base phase that offers the best properties for an effective and efficient sample preparation concerning the individual separation task is decisive. It can be quite a decision for a silica-based phase to use the advantages of specific selectivity for example; but it can also be a decision for a polymer phase to carry out economically a multi-step method, or to achieve high purity of samples with complex matrices.
The comprehensive service of SORBTECH for all CHROMABOND® SPE phases facilitates to find the “best-suitable phase” for the user.
Very fast separation of 16 EPA-PAHs with new
NUCLEODUR® C18 PAH, 1.8 µm
With increasing cost pressure in environmental analysis, ever faster methods will be necessary, which allows a high sample throughput.
Based on a sub-2 µm phase, NUCLEODUR® C18 PAH, 1.8 µm was developed. 16 EPA-PAHs can be reliably separated with it in less than 2.4 min.
More information on PAH analysis can be found in our former SORBTECH blog posts.