A Comprehensive Guide to Welch C18 Columns Family: Features and Applications
Chromatography columns are the core components of chromatographic analysis, and the bonded phases of chromatographic packing materials vary to meet different separation needs. As a result, these materials have developed into a large "family."
Welch offers dozens of chromatographic columns, and even though many of them are C18 columns, their selectivity can differ significantly depending on the bonding methods. Using different columns for the same project can yield different separation effects, peak order, and retention times.
Therefore, selecting the right column is crucial in chromatographic analysis. In this article, we will introduce the various C18 columns from the Welch brands.
01 Welch C18 Column Parameters
| HPLC Column | Particle Size | pH Range | Carbon Load | Surface Area (m²/g) |
|---|---|---|---|---|
| Ultisil® XB-C18 | 1.8, 3, 5, 10 μm | 1.5-10.0 | 17% (120Å), 8% (300Å) | 320 (120Å), 90 (300Å) |
| Ultisil® AQ-C18 | 1.8, 3, 5, 10 μm | 1.5-10.0 | 12% (120Å) | 320 (120Å) |
| Ultisil® LP-C18 | 1.8, 3, 5 μm | 0.5-8.0 | 14% (120Å), 5% (300Å) | 320 (120Å), 90 (300Å) |
| Ultisil® LP-AQ | 5 μm | 1.0-8.0 | 5% (120Å) | 320 (120Å) |
| Ultisil® Polar RP | 1.8, 3, 5, 10 μm | 1.5-10.0 | 18% (120Å) | 320 (120Å) |
| Ultisil® AA (Amino Acid) | 5 μm | 1.5-10.0 | 17% (120Å) | 320 (120Å) |
| Ultisil® PAH | 3, 5 μm | 1.5-10.0 | 20% (120Å) | 320 (120Å) |
| Ultisil® ALK C18 | 5 μm | 1.5-10.0 | 12% (120Å) | 320 (120Å) |
| Ultisil® Plus C18 | 3.5, 5 μm | 2.0-8.0 | 10% (130Å) | 160 (130Å) |
| Ultisil® ODS-3 | 3, 5 μm | 2.0-8.0 | 15% (100Å) | 380 (100Å) |
| Ultisil® XS-C18 | 3, 5 μm | 2.0-10.0 | 23% (120Å) | 320 (120Å) |
| Ultisil® Plus-LP | 5 μm | 0.5-8.0 | 9% (160Å) | 130 (160Å) |
| Xtimate® C18 | 1.8, 3, 5, 10 μm | 1.0-12.5 | 14% (120Å) | 320 (120Å) |
| Xtimate® Polar RP | 5 μm | 1.0-12.5 | 16% (120Å) | 320 (120Å) |
| Welchrom® C18 | 5 μm | 1.5-10.0 | 19% (120Å) | 320 (120Å) |
| Topsil® C18 | 3, 5 μm | 2.0-9.5 | 12% (150Å) | 260 (150Å) |
| Boltimate® C18 (Core-shell) | 2.7 μm | 2.0-8.5 | 9% (90Å) | 120 (90Å) |
| Boltimate® EXT-C18 (Core-shell) | 2.7 μm | 1.5-12.0 | 8% (90Å) | 120 (90Å) |
| Boltimate® LP-C18 (Core-shell) | 2.7 μm | 1.0-8.5 | 7% (90Å) | 120 (90Å) |
| Blossmate® C18 | 5 μm | 2.0-8.0 | 14% (100Å) | 300 (100Å) |
| Blossmate® Aqs C18 | 5 μm | 2.0-8.0 | 10% (100Å) | 300 (100Å) |
| Blossmate® ST-C18 | 5 μm | 1.0-11.0 | 12% (100Å) | 300 (100Å) |
| Welchrom® Vantage C18 | 5 μm | 2.0-8.0 | 13% (130Å) | 280 (130Å) |
02 Characteristics and Specialties of Welch C18 Columns
· Ultisil® LP-C18: The Preferred Choice for Low pH Conditions
Packing Material Features: Utilizes steric hindrance protection from side chains; non-endcapped.
Chromatographic Separation Characteristics:
- Side chain steric hindrance protection allows the column to tolerate lower pH values.
- Steric hindrance protection groups impart unique selectivity, particularly effective in separating isomers.
- Non-endcapped, leaving more residual silanol groups on the surface, which affects selectivity.
- Under strong acidic conditions, ELSD detectors can achieve ideal baseline noise, indicating minimal loss of bonded phase.
- Tolerates 100%-0% aqueous conditions.
Example: Mobile phase: 10mM phosphate buffer (2g/L sodium hexanesulfonate, pH adjusted to 1.8 with phosphoric acid) / acetonitrile gradient.
In the example, the mobile phase pH of 2.5 resulted in peak splitting due to incomplete ionization of the sample, which did not meet detection requirements. By lowering the pH to 1.8, the sample fully ionized, yielding improved peak shapes that met detection needs.
Most C18 columns struggle to handle such low pH conditions, which can shorten column lifespan. However, the Ultisil® LP-C18 can handle this condition without issue.
· Ultisil® XS-C18
Packing Material Features: Unique multi-layer bonding process with high bonding density.
Chromatographic Separation Characteristics:
- The multi-layer bonding process and high bonding density create excellent steric selectivity.
- High column efficiency, high capacity, and high carbon loading.
- Outstanding selectivity for small molecule isomers, such as positional and structural isomers.
Example: Mobile phase: Acetonitrile/water gradient.
In this example, using the Ultisil® XB-C18 resulted in peak merging of two components. When switched to the Ultisil® XS-C18 and Ultisil® LP-C18, both achieved full separation of the two peaks. The Ultisil® XS-C18 demonstrated superior separation compared to the Ultisil® LP-C18.
· Xtimate® C18: The First Choice for High pH Conditions
Packing Material Features: Xtimate® C18 uses Welch's patented organic-inorganic hybrid surface technology to modify the silica matrix.
Chromatographic Separation Characteristics:
- The organic-inorganic hybrid surface technology allows usage across a wide pH range, with stable performance and longer lifespan under harsh alkaline conditions.
- Excellent peak shapes for basic compounds that tend to tail.
- The hybrid surface technology imparts unique selectivity compared to other types of columns.
Example: Mobile phase: 5g/L ammonium acetate solution (pH adjusted to 7.0 with ammonia) / acetonitrile gradient.
In this case, metoclopramide and its impurities were separated using the Xtimate® C18 column. Compared to the Ultisil® XB-C18, the peaks were more symmetrical and narrower, improving the resolution from 2.5 to 4.65. Theoretical plate count also increased from 15,000 to 25,000.
· Ultisil® Polar RP Column
Packing Material Features: Embedded polar groups.
Chromatographic Separation Characteristics:
- Embedded polar groups increase hydrophilicity, allowing tolerance of pure aqueous mobile phases.
- The embedded polar groups provide unique selectivity.
- Better retention and selectivity for polar compounds.
- Excellent peak shapes for basic compounds.
Example: Mobile phase: Acetonitrile / 0.05 mol/L ammonium dihydrogen phosphate solution = 2/98.
In the detection of impurities in calcium dobesilate, two impurities with a retention time of 1.4 minutes were fully merged with the solvent peak when using the Ultisil® XB-C18.
After switching to the Ultisil® Polar RP, the two impurities were separated from the solvent peak, achieving a resolution of 1.5. The embedded polar groups in the Ultisil® Polar RP enhanced the retention of these weakly retained compounds. Additionally, the amide groups in the Polar RP, with their weak positive charge, interacted electrostatically with the sulfonic acid group in calcium dobesilate, causing greater tailing of the main peak compared to the Ultisil® XB-C18.
· Ultisil® ALK C18
Packing Material Features: Mixed-mode stationary phase; polar functional group end-capping.
Chromatographic Separation Characteristics:
- Exhibits hydrophobic and electrostatic interactions.
- Polar functional group end-capping replaces many silanol groups, effectively preventing interactions between alkaloids and silanols, improving peak shapes for basic compounds.
- Polar functional group end-capping imparts hydrophilic properties, allowing for rapid separation of similar samples by adjusting the mobile phase.
- Mixed-mode stationary phase provides selectivity distinct from other column types.
Example: Mobile phase: Potassium hydrogen phosphate buffer (containing 1.7g/L tetrabutylammonium hydrogen sulfate, pH adjusted to 4.6 with phosphoric acid) / acetonitrile = 98/2.
In this example, aztreonam exhibited double peaks with poor peak shapes on the Xtimate® C18 and other columns, failing to meet detection requirements. However, using the Ultisil® ALK C18 produced a single, well-formed peak that met the detection needs. The aztreonam molecule contains terminal amine and carboxyl groups that form a zwitterion, with weak basicity in other nitrogen atoms but strong sulfonic acid.
At pH 4.6, aztreonam was not fully dissociated, resulting in double peaks on the Xtimate® C18. The Ultisil® ALK C18, with its higher negative charge under these conditions, repelled the molecule, yielding better peak shapes.
· Ultisil® AQ-C18
Packing Material Features: Polar group end-capping; dual end-capping process.
Chromatographic Separation Characteristics:
- Polar group end-capping enhances hydrophilicity, enabling tolerance of 100%-0% aqueous conditions.
- Polar group end-capping provides unique selectivity.
· Ultisil® Plus C18
Packing Material Features: Dual end-capping process; low surface area; low carbon loading.
Chromatographic Separation Characteristics:
Highly resistant to contamination, making it the first choice for the analysis of traditional Chinese medicine and herbal formulations. Compared to other C18 columns, it exhibits weaker retention but is not suitable for pure water conditions, requiring at least 10% organic content in the mobile phase.
Relevant Products
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