Compound retention and compound loading are two important attributes that help decide which column will be most useful for your separation. The properties and attributes listed here help us recommend a column or column family for you based on the method attributes that you consider being important. Choosing a column based on retention is analyte specific; the column choice is tailored to the majority of the compounds of interest. However, some methods require columns that are tolerant to high mass loading conditions.
Chromatographic sorbents are chosen for their ability to retain a certain class or mixture of compounds. In most cases, using a column that increases retention will allow you to increase the separation between closely eluting chromatographic peaks. The columns in this section can be chosen by how well they can retain compound classes as well as those that are suited for polar compound retention.
Polar compounds often elute in the void when organic modifiers are used in the mobile phase making accurate quantification difficult or impossible. It is common to use 100% aqueous mobile phases to retain polar compounds, such as metabolites or small organic acids. The columns listed here are designed to maximize retention under these aqueous mobile phase conditions.
HILIC (Hydrophilic Interaction Chromatography) is a technique that is commonly used when reversed-phase columns, such as the Atlantis T3, do not provide enough compound retention, even with 100% aqueous mobile phases.
Columns are recommended based on their ability to provide the widest retention capability for polar and non-polar compound mixtures using standard reversed-phase mobile phases.
My recommendation is to use a general purpose column that is capable of using a wide mobile phase pH range, which gives the user the greatest ability to influence compound retention by modifying additive choice. For example, the general rule for a basic analyte:
- Low pH mobile phases decrease the retention of bases
- High pH mobile phases increase the retention of bases
Retaining non-polar acidic compounds is most achievable using specialized phases other than C18; however, reproducibility and column lifetimes have been the two biggest concerns for users. Generally, these columns are used with low pH mobile phases.
Compound loading ability is an indicator of how well a chromatographic sorbent can tolerate extreme mass loading of an analyte before resolution or peak shape is compromised. High load capabilities are important in areas such as impurity profiling and natural product isolation and are valued by preparative and dissolution scientists.
For acidic analytes, the best chromatographic performance under high loading conditions is achieved using low pH mobile phases and columns that are designed for chemical stability under these conditions.
For basic analytes, there are two ways to maintain separation and peak shape under high loading conditions. For the highest analyte loading for basic compounds, many users prefer to use high pH mobile phases. The high pH mobile ensures that the analyte is in a neutral charge state, thus maximizing reversed-phase retention and reducing any unwanted ionic interactions with the sorbent substrate. When the compound is chemically unstable at high pH, it is common to use ion-pairing agents and low mobile phase pH conditions.
In some circumstances you will need a column to perform based on its chemical properties to improve analyte-stationary phase interactions. The column properties listed here are the most commonly referred to characteristics that aid chromatographic separations.
Selectivity refers to the extent to which a column can separate compounds in mixtures without interferences from other components. In general, most methods are developed using a classical C18 phase. More recent phases, such as those containing embedded polar groups, provide alternative selectivity, while providing similar retention.
Columns that exhibit C18-like selectivity are classified using the USP designation L1, and are often referred to as “ODS” phases. These general purpose columns are widely used to solve the most common problems for reversed-phase separations.
These columns are classified with a USP L1 designation; however, they contain specialized ligand bonding or endcapping that gives preferential selectivity to a particular compound class. These columns include embedded polar (shield) columns and columns designed for polar retention.
Columns that contain alternative ligands have markedly different selectivity when compared to standard reversed-phase C18 columns. They are ideally suited for method development, where it is desirable to discriminate between critical pairs or to significantly increase the separation of chromatographic interferences.
A non-endcapped stationary phase can provide different analyte selectivity compared to one that is endcapped, although sometimes at the expense of chromatographic peak shape and pH stability. A non-endcapped stationary phase exposes un-bonded silanol groups for potential interaction with the analyte. Such chemistries are valuable method development tools.
The stability of a chromatographic sorbent refers to its ability to resist chemical attack from the mobile phase under a variety of operating conditions. Chemical attack, including ligand loss through hydrolysis and particle dissolution, results in reduced column lifetime, peak deterioration, and changes in analyte selectivity.
Column lifetime performance using mobile phases with pH less than 3 can be controlled by optimizing ligand density and bonding. Under these acidic conditions a tri-functionally bonded ligand and chemically stable base particle will outperform a mono- or di- functionally bonded stationary phase.
Column lifetime performance is often compromised when using mobile phases that exceed pH 7 and most silica based columns begin to degrade rapidly beyond pH 8. Hybrid based particles with high ligand densities exhibit the longest lifetimes and provide the ability to routinely use mobile phases that exceed pH 10 for extended periods.
Some columns are designed to have characteristics that can be applied to common application needs, such as general purpose LC/MS columns or those specific to biomolecular analysis.
Most modern LC columns are compatible with MS instrumentation; however, column bleed can compromise MS performance. It is for this reason that following columns are selected for their mechanical and chemical stability under a wide range of operating conditions.
Column efficiency or plate count measures peak dispersion. A highly efficient column will generate chromatograms with tall, sharp peaks and enhance resolution, speed and sensitivity. The following high performance columns utitilize solid-core technology, which provides an efficiency advantage when compared to similar columns of a fully porous nature.
The best performing and most desirable columns maintain good peak shape for basic compounds under a wide set of operating conditions, including the use of reduced ionic-strength mobile phases (e.g: 0.1% formic acid). These columns will also maintain this symmetrical peak shape as the analyte mass load in increased.
These columns are design and QC tested for biomolecular separations, specifically protein and peptides using reversed-phase conditions. These columns have wider pore volumes making them more suitable for these larger molecule separations.
HILIC (Hydrophilic Interaction Chromatography) is a secondary technique that is commonly used when specialized reversed-phase polar retentions columns, such as the Atlantis T3, do not provide enough compound retention, even with 100% aqueous mobile phases.
Polar stationary phases, such as unbonded silica are typically used with polar solvents such as acetonitrile to achieve separation of polar analytes. Stronger retention is observed when the polarity of the stationary increases (hybrid particle versus silica particle) and the polarity of the mobile phase decreases (methanol versus acetonitrile).
The Column Advisor recommends the most appropriate columns depending on the application requirements you need to consider or the column characteristics you are looking for. Click on the appropriate tab and move your mouse on the left hand side table to reveal the corresponding application or column characteristics in the middle of the screen.
Waters is on the forefront of modern HPLC columns. Using industry-leading BEH, CSH, and HSS particle technology, our HPLC products eliminate time and cost per sample from your analytical process—while improving the quality of laboratory results. As one of the world’s primary column manufacturers, our ability to control column to column reproducibility, as well as produce some of the most innovative new chemistries, is second to none in the industry.
XSelect CSH HPLC columns provide you with alternate selectivity compared to other commercially available reversed-phase columns. The high efficiency of the XSelect CSH column family provides seamless transferability between particle size and column formats (UPLC-HPLC-Preparative scale) without compromising peak shape and loading capacity for basic compounds.
XSelect CSH C18 columns can be used as general purpose columns that provide alternative selectivity compared to other C18 sorbents. Charged Surface Hybrid (CSH) technology helps you overcome column related problems such as peak shape asymmetry and poor loading for basic compounds, column bleed, and slow mobile-phase re-equilibration.
Designed to maximize selectivity differences, the XSelect CSH Fluoro-Phenyl column provides you with maximum method development freedom, especially when using low pH mobile phases. The non-encapped sorbent provides you with enhanced retention of acidic compounds.
XSelect CSH Phenyl-Hexyl columns provide you with alternative analyte selectivity compared to traditional reversed-phase columns and are a valuable tool for method development. The trifunctionally bonded C6 phenyl-ligand is a robust, low bleed sorbent that selectively retains polyaromatic compounds through pi-pi interactions.
The HSS C18 packing is the most stable commercially available bonded phase and does not suffer from peak shape issues that plague older stationary phases that rely upon steric protection (and lack of endcapping) to produce stability at low pH. The HSS C18 HPLC columns are fully scalable and are completely transferable to UPLC separations.
HSS C18 SB columns are intended for low pH separations that contain complex mixtures of basic and non-basic compounds. HSS C18 SB columns give you alternative analyte selectivity compared to most modern, high coverage, fully endcapped C18 stationary phases. HSS C18 SB HPLC columns are fully scalable and transferable to UPLC separations.
The trifunctional alkyl C18 bonded phase used for the HSS T3 sorbents is compatible with 100% aqueous mobile phase and provides ultra-low MS bleed, while promoting superior polar compound retention. HSS T3 HPLC columns are fully scalable and transferable to UPLC separations.
The XSelect HSS CN chemistry is an ultra-performance general purpose propyl cyano bonded phase that provides superior peak shape for bases, increased retention, and extremely long column lifetimes at low pH. XSelect HSS CN HPLC columns are fully scalable and transferable to ACQUITY UPLC separations.
The XSelect HSS PFP is a non-endcapped silica-based HPLC column designed for low pH separations that require alternative selectivity compared to a fully endcapped, high coverage C18 phase. XSelect HSS PFP HPLC columns are fully scalable and transferable to ACQUITY UPLC separations.
Waters is on the forefront of modern HPLC columns. Using industry-leading BEH, CSH, and HSS particle technology, our HPLC products eliminate time and cost per sample from your analytical process—while improving the quality of laboratory results. As one of the world’s primary column manufacturers, our ability to control column to column reproducibility, as well as produce some of the most innovative new chemistries, is second to none in the industry.
XBridge HPLC columns are designed for maximum flexibility in HPLC method development. You can achieve robust separations in less time and with greater confidence, while using the full range of mobile phase pH. Industry leading manufacturing and product quality give you the most trusted columns for your most demanding chromatographic separations.
As a workhorse for HPLC method development, XBridge BEH C18 sorbent can be used over an entire range of mobile phase pH (1-12). The trifunctionally bonded C18 ligand provides you with a universal column for most HPLC separations and gives you the widest usable pH range, superior low pH stability, and ultra-low column bleed.
The XBridge BEH300 C18 Peptide Separation Technology (PST) columns are optimized and QC tested for peptide separations. The wide-pore (300Å) trifunctionally bonded BEH particle offers you the widest usable pH range, superior low pH stability, and ultra-low column bleed to assay samples for proteomics, protein characterization, and peptide synthesis.
The XBridge BEH130 C18 Peptide Separation Technology (PST) columns are optimized and QC tested for peptide separations. The small-pore (130Å) trifunctionally bonded BEH particle offers you the widest usable pH range, superior low pH stability, and ultra-low column bleed to assay samples for proteomics, protein characterization, and peptide synthesis.
Waters Protein Separation Technology (PrST) columns are QC tested and optimized to separate proteins based on size, hydrophobicity and isoelectric point. If you compare traditional to C18 phases, the C4 ligand is less retentive and will minimize protein carryover, increase protein recovery and improve peak capacity.
Waters Oligonucleotide Separation Technology (OST) columns are used to separate detritylated synthetic oligonucleotides based on ion-pair, reversed-phase chromatography. Each column is QC tested using Waters MassPrep OST standards to ensure repeatable performance for your most demanding oligonucleotide assays
XBridge BEH Shield RP18 columns complement the XBridge BEH C18 and C8 phases and provide a necessary and powerful tool for HPLC method development. The embedded carbamate group in the bonded phase ligand provides alternate selectivity, especially for phenolic compounds compared to straight chain alkyl columns.
XBridge BEH Phenyl columns provide complementary selectivity to C18 stationary phases, especially for polyaromatic compounds. This most chemically stable commercially available Phenyl sorbent on the market and provides you with ultra-low column bleed, long column lifetimes and excellent peak shape.
XBridge BEH HILIC columns contain unbonded BEH substrate and are designed to retain and separate very polar compounds. These unique columns are optimized and tested to produce efficient, reproducible separations under HPLC HILIC conditions. More rugged than silica based HILIC phases, the BEH particle’s chemical stability results in long column lifetimes.
XBridge BEH Amide columns retain extremely polar compounds, including carbohydrates and sugars. XBridge Amide columns offer you a chemically stable, trifunctionally bonded amide phase that is stable from pH 2 to 12 to enable the separation of polar analytes spanning a wide range of polarity, structural moiety and pKa.
TBA
Achieve faster separations and improve sample throughput without sacrificing HPLC/UHPLC separation performance. CORTECS HPLC Columns offer the unique advantage of operating at lower back pressure and higher flow rates without sacrificing efficiency or resolution. Compared to a fully porous particle, the CORTECS particle provides unique characteristics and innovative charged surface modifications that are suitable for wide variety of applications.
The C18 ligand is the most popular choice in method development because of its stability and ability to retain a variety of analytes. CORTECS C18 is a traditional C18 solid-core bonded phase which exhibits high efficiency with a balanced retention of acids, bases and neutrals at low- and mid-range pH. It provides superb resolution and retention for complex mixtures.
CORTECS C18+ is a general purpose, high efficiency, solid-core, reversed-phase column which features a positively charged surface modification. Charged-surface technology utilizes a controlled, low-level surface charge for enhanced selectivity and exceptional peak shape for basic compounds when using acidic, low-ionic strength mobile phases such as formic acid.
CORTECS HILIC Columns are designed specifically for the retention of very polar compounds using HILIC methods of separation. CORTECS HILIC Columns features an unbonded CORTECS solid-core silica particle that offers high efficiency under low pH conditions.
.
The Atlantis family of HPLC columns provides leading performance for polar compound retention, while maintaining versatility, reproducibility and accuracy in quantitative bioanalytical assays. Atlantis reversed-phase and HILIC columns are chosen to improve chromatographic retention of moderately polar to very polar analytes and metabolites.
Atlantis T3 columns are universal, silica-based, reversed-phase C18 columns that provide balanced retention of polar and hydrophobic molecules and should be your first choice when developing separations of polar and non-polar compounds.
Atlantis HILIC Silica columns are used in combination with high organic mobile phases (>80% acetonitrile) to provide retention of analytes that are simply too polar to be retained by reverse-phase chromatography. HILIC separation mechanisms provide orthogonal analyte selectivity compared to traditional chromatographic reversed-phase approaches.
SunFire C18 HPLC columns set the standard for state-of-the-art silica bonding are often selected for their resolving power and reliability to meet both analytical and preparative method needs. For general purpose use, SunFire Columns exhibit high efficiency, excellent peak shape, and unmatched batch-to-batch reproducibility.
SunFire C18 columns are used for general purpose method development at low pH. The C18 ligand is highly retentive, especially for basic compounds and it is ideally suited for purification and impurity profile assays.
Waters is on the forefront of modern HPLC columns. Using industry-leading BEH, CSH, and HSS particle technology, our HPLC products eliminate time and cost per sample from your analytical process—while improving the quality of laboratory results. As one of the world’s primary column manufacturers, our ability to control column to column reproducibility, as well as produce some of the most innovative new chemistries, is second to none in the industry.
XSelect CSH HPLC columns provide you with alternate selectivity compared to other commercially available reversed-phase columns. The high efficiency of the XSelect CSH column family provides seamless transferability between particle size and column formats (UPLC-HPLC-Preparative scale) without compromising peak shape and loading capacity for basic compounds.
XSelect CSH C18 columns can be used as general purpose columns that provide alternative selectivity compared to other C18 sorbents. Charged Surface Hybrid (CSH) technology helps you overcome column related problems such as peak shape asymmetry and poor loading for basic compounds, column bleed, and slow mobile-phase re-equilibration.
Designed to maximize selectivity differences, the XSelect CSH Fluoro-Phenyl column provides you with maximum method development freedom, especially when using low pH mobile phases. The non-encapped sorbent provides you with enhanced retention of acidic compounds.
XSelect CSH Phenyl-Hexyl columns provide you with alternative analyte selectivity compared to traditional reversed-phase columns and are a valuable tool for method development. The trifunctionally bonded C6 phenyl-ligand is a robust, low bleed sorbent that selectively retains polyaromatic compounds through pi-pi interactions.
The HSS C18 packing is the most stable commercially available bonded phase and does not suffer from peak shape issues that plague older stationary phases that rely upon steric protection (and lack of endcapping) to produce stability at low pH. The HSS C18 HPLC columns are fully scalable and are completely transferable to UPLC separations.
HSS C18 SB columns are intended for low pH separations that contain complex mixtures of basic and non-basic compounds. HSS C18 SB columns give you alternative analyte selectivity compared to most modern, high coverage, fully endcapped C18 stationary phases. HSS C18 SB HPLC columns are fully scalable and transferable to UPLC separations.
The trifunctional alkyl C18 bonded phase used for the HSS T3 sorbents is compatible with 100% aqueous mobile phase and provides ultra-low MS bleed, while promoting superior polar compound retention. HSS T3 HPLC columns are fully scalable and transferable to UPLC separations.
The XSelect HSS CN chemistry is an ultra-performance general purpose propyl cyano bonded phase that provides superior peak shape for bases, increased retention, and extremely long column lifetimes at low pH. XSelect HSS CN HPLC columns are fully scalable and transferable to ACQUITY UPLC separations.
The XSelect HSS PFP is a non-endcapped silica-based HPLC column designed for low pH separations that require alternative selectivity compared to a fully endcapped, high coverage C18 phase. XSelect HSS PFP HPLC columns are fully scalable and transferable to ACQUITY UPLC separations.
Waters is on the forefront of modern HPLC columns. Using industry-leading BEH, CSH, and HSS particle technology, our HPLC products eliminate time and cost per sample from your analytical process—while improving the quality of laboratory results. As one of the world’s primary column manufacturers, our ability to control column to column reproducibility, as well as produce some of the most innovative new chemistries, is second to none in the industry.
XBridge HPLC columns are designed for maximum flexibility in HPLC method development. You can achieve robust separations in less time and with greater confidence, while using the full range of mobile phase pH. Industry leading manufacturing and product quality give you the most trusted columns for your most demanding chromatographic separations.
As a workhorse for HPLC method development, XBridge BEH C18 sorbent can be used over an entire range of mobile phase pH (1-12). The trifunctionally bonded C18 ligand provides you with a universal column for most HPLC separations and gives you the widest usable pH range, superior low pH stability, and ultra-low column bleed.
The XBridge BEH300 C18 Peptide Separation Technology (PST) columns are optimized and QC tested for peptide separations. The wide-pore (300Å) trifunctionally bonded BEH particle offers you the widest usable pH range, superior low pH stability, and ultra-low column bleed to assay samples for proteomics, protein characterization, and peptide synthesis.
The XBridge BEH130 C18 Peptide Separation Technology (PST) columns are optimized and QC tested for peptide separations. The small-pore (130Å) trifunctionally bonded BEH particle offers you the widest usable pH range, superior low pH stability, and ultra-low column bleed to assay samples for proteomics, protein characterization, and peptide synthesis.
Waters Protein Separation Technology (PrST) columns are QC tested and optimized to separate proteins based on size, hydrophobicity and isoelectric point. If you compare traditional to C18 phases, the C4 ligand is less retentive and will minimize protein carryover, increase protein recovery and improve peak capacity.
Waters Oligonucleotide Separation Technology (OST) columns are used to separate detritylated synthetic oligonucleotides based on ion-pair, reversed-phase chromatography. Each column is QC tested using Waters MassPrep OST standards to ensure repeatable performance for your most demanding oligonucleotide assays
XBridge BEH Shield RP18 columns complement the XBridge BEH C18 and C8 phases and provide a necessary and powerful tool for HPLC method development. The embedded carbamate group in the bonded phase ligand provides alternate selectivity, especially for phenolic compounds compared to straight chain alkyl columns.
XBridge BEH Phenyl columns provide complementary selectivity to C18 stationary phases, especially for polyaromatic compounds. This most chemically stable commercially available Phenyl sorbent on the market and provides you with ultra-low column bleed, long column lifetimes and excellent peak shape.
XBridge BEH HILIC columns contain unbonded BEH substrate and are designed to retain and separate very polar compounds. These unique columns are optimized and tested to produce efficient, reproducible separations under HPLC HILIC conditions. More rugged than silica based HILIC phases, the BEH particle’s chemical stability results in long column lifetimes.
XBridge BEH Amide columns retain extremely polar compounds, including carbohydrates and sugars. XBridge Amide columns offer you a chemically stable, trifunctionally bonded amide phase that is stable from pH 2 to 12 to enable the separation of polar analytes spanning a wide range of polarity, structural moiety and pKa.
TBA
Achieve faster separations and improve sample throughput without sacrificing HPLC/UHPLC separation performance. CORTECS HPLC Columns offer the unique advantage of operating at lower back pressure and higher flow rates without sacrificing efficiency or resolution. Compared to a fully porous particle, the CORTECS particle provides unique characteristics and innovative charged surface modifications that are suitable for wide variety of applications.
The C18 ligand is the most popular choice in method development because of its stability and ability to retain a variety of analytes. CORTECS C18 is a traditional C18 solid-core bonded phase which exhibits high efficiency with a balanced retention of acids, bases and neutrals at low- and mid-range pH. It provides superb resolution and retention for complex mixtures.
CORTECS C18+ is a general purpose, high efficiency, solid-core, reversed-phase column which features a positively charged surface modification. Charged-surface technology utilizes a controlled, low-level surface charge for enhanced selectivity and exceptional peak shape for basic compounds when using acidic, low-ionic strength mobile phases such as formic acid.
CORTECS HILIC Columns are designed specifically for the retention of very polar compounds using HILIC methods of separation. CORTECS HILIC Columns features an unbonded CORTECS solid-core silica particle that offers high efficiency under low pH conditions.
.
The Atlantis family of HPLC columns provides leading performance for polar compound retention, while maintaining versatility, reproducibility and accuracy in quantitative bioanalytical assays. Atlantis reversed-phase and HILIC columns are chosen to improve chromatographic retention of moderately polar to very polar analytes and metabolites.
Atlantis T3 columns are universal, silica-based, reversed-phase C18 columns that provide balanced retention of polar and hydrophobic molecules and should be your first choice when developing separations of polar and non-polar compounds.
Atlantis HILIC Silica columns are used in combination with high organic mobile phases (>80% acetonitrile) to provide retention of analytes that are simply too polar to be retained by reverse-phase chromatography. HILIC separation mechanisms provide orthogonal analyte selectivity compared to traditional chromatographic reversed-phase approaches.
SunFire C18 HPLC columns set the standard for state-of-the-art silica bonding are often selected for their resolving power and reliability to meet both analytical and preparative method needs. For general purpose use, SunFire Columns exhibit high efficiency, excellent peak shape, and unmatched batch-to-batch reproducibility.
SunFire C18 columns are used for general purpose method development at low pH. The C18 ligand is highly retentive, especially for basic compounds and it is ideally suited for purification and impurity profile assays.
The Column Advisor recommends the most appropriate columns depending on the application requirements you need to consider or the column characteristics you are looking for. Click on the appropriate tab and move your mouse on the left hand side table to reveal the corresponding application or column characteristics in the middle of the screen.
Compound retention and compound loading are two important attributes that help decide which column will be most useful for your separation. The properties and attributes listed here help us recommend a column or column family for you based on the method attributes that you consider being important. Choosing a column based on retention is analyte specific; the column choice is tailored to the majority of the compounds of interest. However, some methods require columns that are tolerant to high mass loading conditions.
Chromatographic sorbents are chosen for their ability to retain a certain class or mixture of compounds. In most cases, using a column that increases retention will allow you to increase the separation between closely eluting chromatographic peaks. The columns in this section can be chosen by how well they can retain compound classes as well as those that are suited for polar compound retention.
Polar compounds often elute in the void when organic modifiers are used in the mobile phase making accurate quantification difficult or impossible. It is common to use 100% aqueous mobile phases to retain polar compounds, such as metabolites or small organic acids. The columns listed here are designed to maximize retention under these aqueous mobile phase conditions.
HILIC (Hydrophilic Interaction Chromatography) is a technique that is commonly used when reversed-phase columns, such as the Atlantis T3, do not provide enough compound retention, even with 100% aqueous mobile phases.
Columns are recommended based on their ability to provide the widest retention capability for polar and non-polar compound mixtures using standard reversed-phase mobile phases.
My recommendation is to use a general purpose column that is capable of using a wide mobile phase pH range, which gives the user the greatest ability to influence compound retention by modifying additive choice. For example, the general rule for a basic analyte:
- Low pH mobile phases decrease the retention of bases
- High pH mobile phases increase the retention of bases
Retaining non-polar acidic compounds is most achievable using specialized phases other than C18; however, reproducibility and column lifetimes have been the two biggest concerns for users. Generally, these columns are used with low pH mobile phases.
Compound loading ability is an indicator of how well a chromatographic sorbent can tolerate extreme mass loading of an analyte before resolution or peak shape is compromised. High load capabilities are important in areas such as impurity profiling and natural product isolation and are valued by preparative and dissolution scientists.
For acidic analytes, the best chromatographic performance under high loading conditions is achieved using low pH mobile phases and columns that are designed for chemical stability under these conditions.
For basic analytes, there are two ways to maintain separation and peak shape under high loading conditions. For the highest analyte loading for basic compounds, many users prefer to use high pH mobile phases. The high pH mobile ensures that the analyte is in a neutral charge state, thus maximizing reversed-phase retention and reducing any unwanted ionic interactions with the sorbent substrate. When the compound is chemically unstable at high pH, it is common to use ion-pairing agents and low mobile phase pH conditions.
In some circumstances you will need a column to perform based on its chemical properties to improve analyte-stationary phase interactions. The column properties listed here are the most commonly referred to characteristics that aid chromatographic separations.
Selectivity refers to the extent to which a column can separate compounds in mixtures without interferences from other components. In general, most methods are developed using a classical C18 phase. More recent phases, such as those containing embedded polar groups, provide alternative selectivity, while providing similar retention.
Columns that exhibit C18-like selectivity are classified using the USP designation L1, and are often referred to as “ODS” phases. These general purpose columns are widely used to solve the most common problems for reversed-phase separations.
These columns are classified with a USP L1 designation; however, they contain specialized ligand bonding or endcapping that gives preferential selectivity to a particular compound class. These columns include embedded polar (shield) columns and columns designed for polar retention.
Columns that contain alternative ligands have markedly different selectivity when compared to standard reversed-phase C18 columns. They are ideally suited for method development, where it is desirable to discriminate between critical pairs or to significantly increase the separation of chromatographic interferences.
A non-endcapped stationary phase can provide different analyte selectivity compared to one that is endcapped, although sometimes at the expense of chromatographic peak shape and pH stability. A non-endcapped stationary phase exposes un-bonded silanol groups for potential interaction with the analyte. Such chemistries are valuable method development tools.
The stability of a chromatographic sorbent refers to its ability to resist chemical attack from the mobile phase under a variety of operating conditions. Chemical attack, including ligand loss through hydrolysis and particle dissolution, results in reduced column lifetime, peak deterioration, and changes in analyte selectivity.
Column lifetime performance using mobile phases with pH less than 3 can be controlled by optimizing ligand density and bonding. Under these acidic conditions a tri-functionally bonded ligand and chemically stable base particle will outperform a mono- or di- functionally bonded stationary phase.
Column lifetime performance is often compromised when using mobile phases that exceed pH 7 and most silica based columns begin to degrade rapidly beyond pH 8. Hybrid based particles with high ligand densities exhibit the longest lifetimes and provide the ability to routinely use mobile phases that exceed pH 10 for extended periods.
Some columns are designed to have characteristics that can be applied to common application needs, such as general purpose LC/MS columns or those specific to biomolecular analysis.
Most modern LC columns are compatible with MS instrumentation; however, column bleed can compromise MS performance. It is for this reason that following columns are selected for their mechanical and chemical stability under a wide range of operating conditions.
Column efficiency or plate count measures peak dispersion. A highly efficient column will generate chromatograms with tall, sharp peaks and enhance resolution, speed and sensitivity. The following high performance columns utitilize solid-core technology, which provides an efficiency advantage when compared to similar columns of a fully porous nature.
The best performing and most desirable columns maintain good peak shape for basic compounds under a wide set of operating conditions, including the use of reduced ionic-strength mobile phases (e.g: 0.1% formic acid). These columns will also maintain this symmetrical peak shape as the analyte mass load in increased.
These columns are design and QC tested for biomolecular separations, specifically protein and peptides using reversed-phase conditions. These columns have wider pore volumes making them more suitable for these larger molecule separations.
HILIC (Hydrophilic Interaction Chromatography) is a secondary technique that is commonly used when specialized reversed-phase polar retentions columns, such as the Atlantis T3, do not provide enough compound retention, even with 100% aqueous mobile phases.
Polar stationary phases, such as unbonded silica are typically used with polar solvents such as acetonitrile to achieve separation of polar analytes. Stronger retention is observed when the polarity of the stationary increases (hybrid particle versus silica particle) and the polarity of the mobile phase decreases (methanol versus acetonitrile).