Welch Materials HPLC Columns
Welsh Materials HPLC Columns
The Chinese manufacturer Welch Materials specializes in products for chromatography. Welch Materials develops numerous innovative product series, including the silica-based Ultisil® HPLC column series. Ultisil® columns offer a purity of > 99.999 % as well as tested and proven low contamination with trace metals. Excellent reproducibility, efficiency, symmetry and lifetime are big assets of Ultisil® HPLC columns.
Column description
Here you will find the brand name of the respective manufacturer for the column, e.g. "XBridge" columns from Waters. It is not necessarily recognizable which type of column the respective name refers to. If you have any questions, please do not hesitate to contact us.
Package specification
The packing specification describes the material of the stationary phase. The name indicates whether a functional group is bound to the carrier material (silica gel, polymer) and, if so, which functional group. Depending on the bound functional group (e.g. C18 chain), this results in the separation mode of the column (reversed phase).
Length
Depending on the type of application or system, different lengths of HPLC columns are used. The length of the column together with the internal diameter defines the column volume. For preparative separations, for example, columns from 250 mm in length with a larger internal diameter are often used; this allows more material to be separated in one run. If you have any questions about suitable HPLC column dimensions for your analysis, please do not hesitate to contact us.
Inner diameter
In addition to the length of the column, the inner diameter (ID) determines the column volume. The larger the internal diameter, the larger the volume and the higher the consumption of solvent. The inner diameter also influences the concentration of the analyte in the detector. For analyses where only a small amount of sample is available, it is advisable to use the smallest possible inner diameter. If an existing method is optimized from a larger to a smaller inner diameter, it must be ensured that the flow is adjusted for a comparable separation so that a constant linear velocity u is obtained
Particle Size
The choice of particle size for the column depends initially on the HPLC system used. Particle sizes <2µm can be used with a UHPLC. In an HPLC system, which can operate at pressures of up to 400 bar, particles of 5 µm are commonly used. The smaller the particle in the column, the higher the resulting back pressure in the HPLC system.
pH Range
HPLC columns have a certain pH stability. The manufacturer usually specifies a recommended pH value range for a particular column at which the column can be operated in the long term. A pH value >7 is considered critical for silica gels, as they gradually dissolve. This dissolution is slowed down by a special polymer coating or the introduction of hybrid material. If a pH value >8 is used during the routine, it is advisable to use a polymer-based material, for example.
Endcapping
In C18 columns, there are still free silanol groups on the carrier material between the bound C18 chains or other functional groups. These silanol groups interact strongly with alkaline molecules in particular, which can lead to an undesirable broadening of the peaks. In so-called endcapping, these silanol groups are usually "protected" with a trimethylsilyl group (TMS). The unwanted interaction and the resulting peak broadening can thus be suppressed.
Carbon load
The higher the percentage carbon level with the same packing density (g/ml), the higher the occupancy with e.g. C18 chains. The stationary phase is therefore more hydrophobic (non-polar). A non-polar sample molecule is therefore retained longer on a phase with a higher carbon content, which means that the retention time is slightly longer.
USP number
Monograph methods are frequently used, especially in the pharmaceutical industry. Users must then adhere to the requirements of the European Pharmacopeia (EP) or the US Pharmacopeia (USP), for example. The USP classification is based on the type of packaging material used. Classification "L1", for example, refers to an octadecylsilyl phase, better known as a C18 phase.
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