All categories
Featured selections
Trade Assurance
Buyer Central
Help Center
Get the app
Become a supplier
(212 products available)
High-Performance Liquid Chromatography (HPLC) is a vital technique in various analytical laboratories. It is known for precisely separating, quantifying, and purifying chemical compounds. Essential to this process is the choice of column, especially the C18 columns, which offer universal applicability due to their robustness and efficiency.
C18 columns navigate both polar and nonpolar compounds effectively. This versatile functionality makes them ideal in pharmaceutical, environmental, and food safety testing sectors. Below are the highlighted HPLC C18 column types based on packing material, particle size distribution, and column geometry.
The column packing refers to how the stationary phase, which is an HPLC C18 layer, is distributed in the column. There are two types of packing: bonded and partitioned. Each type interacts differently with analytes, hence influencing separation mechanisms. Therefore, understanding the packing types advantages ensures optimal column selection for specific analytical tasks.
Biphenyl Columns
Biphenyl HPLC C18 columns pack a unique stationary phase containing a biphenyl ligand. The ligand is then incorporated into the packing material. This packing interacts with polar compounds using, for instance, stacking or dipole-multipole interactions rather than the standard π-π method alone. Such interactions result in improved separation and retention of compounds that traditional C18 columns would let pass too quickly or poorly separate.
The columns are, therefore, ideal for separating complex mixtures containing both polar and nonpolar compounds. Application areas include separating pharmaceutical compounds, agrochemicals, and vitamin complexes. Other notable users are food additives and pigments used in the food industry.
Core-Shell Columns
Core-shell columns consist of beads with an inner core of silica and an outer shell of another material. The author posits that the shell may be a porous layer or even another type of silica, depending on the manufacturers. An example of the inner-core material is that it often consists of nonporous particles that provide the column with a solid base. On the other hand, the outer shell is generally porous to allow the diffusion of solute molecules easily.
The primary advantage of core-shell columns is their low back pressure. This property stems from the nonporous core that limits the solute's access to the pores of the shell. Lower back pressures enable these columns to be used in HPLC at higher flow rates.
Endcap Columns
Endcap HPLC C18 columns are built with stationary phases, which have endcapped silanol groups. This detail is crucial because free silanol groups are often found on the silica packing of regular columns. These groups may cause undesired interactions with analytes that bind to them.
End-capping silanol removes free silanol groups by bonding them with an endcapping group. The groups are usually -OH or -Si-OH. The elimination of the free silanol groups ensures that there's no interaction with analytes likely to carry out a free silanol group.
The choice of particle size is important because it significantly affects resolution, efficiency, and feasible operating pressure. Here is the effect of using different particle sizes on these parameters.
Sub-2μm Columns
These columns feature packing particles with a diameter size of less than 2 microns. Such fine packing considerably boosts the column surface area. The larger area translates to higher interactions between the stationary and mobile phases during chromatography. Increased interactions will directly lead to better separation or, in other words, resolution.
Therefore, sub-2μm columns are developed to maximize resolution for complex mixtures whose constituents are difficult to separate. An example of such mixtures is those that contain -hydroxylated and epimerized pharmaceutical compounds. Such compounds may be challenging to separate using standard columns.
3-5μm Columns
Standard HPLC setups predominantly use 3-5μm columns. They are ideal for quantifying samples and analyzing compounds in method development. The protection of these columns from high-pressure damage makes them suitable for routine tests. Routine tests conduct under moderate conditions that prevent the columns from suffering the effects of high pressure do well. These columns are commonly found in stability assays, impurity profiling, and residual chemical examination.
10μm Columns
10μm columns offer an affordable alternative to sub-2μm in laboratories with low sample complexity. Their coarser packing demands less system pressure for effective separation. In turn, lower pressure reduces operational costs.
These columns handle samples containing high concentrations of analytes, like in bulk material or raw reagent. They also help in preliminary screen-up of complex samples before further analysis using more efficient columns.
Column geometry significantly impacts the column's efficiency, flow rate, and separation capabilities. Below is the effect of using different HPLC C18 column geometries.
Mini-Columns
Scientists consider mini columns favored due to their small sizes. The small size allows them to fit in the often-limited spaces of modern analytical labs. These columns enhance the separation by increasing the flow rate. Increased flow rate reduces the time on the instrument. Mini-columns have internal diameters of 2.1 mm or sometimes less. This characteristic makes them ideal for performing analyses on samples with minimal concentrations.
Wide-Bore Columns
Quick note: Wide columns handle larger sample sizes without excessive back pressure. Such an ability makes them a go-to choice in bulk sample analysis like food and environmental matrices. Quick note also adds that they are useful in method development, where variable factors affecting separation are studied. These columns have internal diameters ranging from 4.6 mm to 15 mm. Their wider geometry, combined with greater sample capacity, offers these highly specialized columns.
Short Columns
Efficiency-wise, chromatography is slower with longer columns since the molecules travel a longer distance to achieve separation. This chronicality presents a huge problem when compounds being analyzed are highly purified. The compounds can take a long time to separate fully, delaying the analysis.
To solve this issue, short columns are used since their shorter lengths do not affect the efficiency. Therefore, short columns offer an effective means of speeding up the process without sacrificing separation quality for purified compounds. They are ideal in high-throughput environments that require quick analysis of stable pharmaceutical compounds.
It's crucial that the HPLC C18 column's durability stands the rigorous demands of analytical chemistry. It has to, considering it faces constant pressure, varying temperatures, and a wide range of solvents. Also, how often the column has to be run with the same solvents can cause wear and tear. This wear and tear can come from either physical erosion or chemical breakdown of the material comprising the column.
The key to maintaining a robust HPLC column lies in choosing the right construction materials and shapes. This choice is critical in determining the functional lifespan of the column as well as how consistently it performs. Below is a rundown of the factors that affect a column's durability.
Inertness Of Bonding
The strength and inertness of the phase's bonding are directly related to the column's durability. Strong bonds make the stationary phase more resistant to wear while inert bonds reduce the chances of unwanted interactions between the stationary phase and the solutes.
Column Material
Manufacturers use stainless steel, polymer, or silica as the material for making HPLC columns. Each of these materials has its own advantages. While stainless steel columns can withstand high temperatures and pressures, polymers are more chemical-resistant. Silica, on the contrary, balances between the two properties but is more susceptible to wear and tear.
For that reason, silica columns are frequently endcapped to improve inertness. Moreover, polymer columns can also be reinforced to increase durability.
Column Shape
Columns with tightly packed beds of stationary phase particles usually possess greater durability. Columns with larger internal diameters, on the other hand, are more likely to experience flow dispersion. Dispersion, in turn, can result in uneven packing and, therefore, poor separation. It also causes increased wear on the particles and the column wall.
Protective Coatings
Manufacturers add various protective coatings to the columns to increase durability. For instance, applying a thin layer of an inert metal like gold can shield the stationary phase from aggressive solvents.
Similarly, a diamond-like carbon coating will protect the stationary phase by absorbing much of the mechanical stress encountered during operation. The less stress the column experiences, the longer it lasts.
Maintenance Features
Lastly, some columns possess built-in features that facilitate maintenance and thus enhance durability. For instance, columns with cleaning functions that, for example, reverse the flow of solvents through the column can help remove deposits and extend column life. Similarly, columns with removable frits allow for easy physical cleaning without the need to replace the column altogether.
Mobile Phase Selection
Selecting the right mobile phase for column durability is critical. Harsh solvents frequently degrade the stationary phase. The phase degradation can be so bad that even a few runs can reduce the column's efficiency. Choosing less aggressive solvents preserves the stationary phase and extends the column's functional life.
Proper Cleaning
Cleaning the column properly removes deposits that accumulate over time. For this reason, develop methods that incorporate appropriate cleaning techniques. Techniques that reverse the solvent flow or use specially designed cleaning solutions remove deposits more effectively.
Temperature Control
Operating temperatures beyond recommended thresholds will cause premature wear. One of the factors that affect the column's durability the most is extreme temperatures. These extremes are either too high or low. High temperatures speed up the stationary phase's degradation. Low temperatures, on the other hand, cause contractions that lead to numerous micro-fractures in both the stationary phase and the column itself. It's best to avoid operating the column beyond its recommended range to preserve its integrity.
When choosing the HPLC C18 column, there are several factors to consider. Some of them are different types, lab sizes, current inventory, and customer needs. Understanding these factors helps make more informed decisions. Below are these factors elaborated on more deeply.
Type
Different types of HPLC C18 columns produce different results, which makes them ideal for specific applications. For instance, if an HPLC C18 column is needed for method development, a core-shell column would be ideal for this as it offers low back pressure.
Conversely, if the client specifically requests a wide variety of compounds to be analyzed, go for a biphenyl column. One property that makes C18 ideal for generic analyses is its ability to navigate both polar and nonpolar compounds effectively.
Lab Size
Labs that are just starting and have a small clientele typically focus on columns commonly used in general analyses. One of the most popular columns when it comes to general analysis is the HPLC C18 column. Moreover, small labs mostly carry mini columns.
Conversely, larger labs may specialize and therefore require HPLC columns for specific tasks. For instance, they may need columns for separating just enantiomers or columns made from special materials.
Current Inventory
This factor is crucial because it complements what the lab already has in stock. For instance, if the lab already possesses an HPLC C18 column, forgo purchasing another one of the same type. Instead, opt for a different one. Perhaps choose one with a unique stationary phase.
The variety will provide greater flexibility in experiments. The increased flexibility will, in turn, lead to more breakthroughs. More breakthroughs or effective separations results in lab efficiency and happy customers.
Customer Needs
Understanding the customers' analytical needs is critical for selecting the most appropriate column for them. Knowing the type of analyses customers usually carry out helps in choosing columns that optimize their workflows.
For example, customers mainly focused on separating small molecules would appreciate having 3-5μm columns. These columns provide optimal resolution for such samples. On the other hand, customers analyzing complex mixtures would prefer columns with specialized stationary phases.
HPLC C18 columns are particularly ideal in high-throughput clinical testing environments. The high-throughput clinical testing environments value the columns' ability to efficiently separate a wide range of compounds. It is this efficiency that makes them indispensable for quick and accurate pharmaceutical analyses.
Routine maintenance practices like the use of appropriate solvents have to be incorporated so as to extend the lifespan of HPLC C18 columns. It includes avoiding harsh solvents that degrade the stationary phase. Constantly using such solvents wears down the stationary phase until it becomes ineffective.
Properly maintaining the columns increases them' effectiveness and, as a result, increases their resale value. A worn-out column is less effective at separations. It also gets a lower resale value despite being properly maintained because it's a less effective column.
Cation-exchange columns can work in the same environment and, therefore, have the added advantage of being good separations for ionic compounds while being retained by the C18 column.
One of the most effective practices is cleaning the column after every use so that deposits can't accumulate on the column.
