Analytical Columns: Pro Family: YMC-Pack Pro C18 RS |
| |
- highly hydrophobic due to carbon content of 22%
- exhibits extraordinary steric selectivity
- extended pH and temperature stability
- for the separation of hydrophobic, acidic and basic molecules
|
Click here to view the full list of Pro C18 RS parts
|
|
Specification |
Particle size / µm |
|
Pore size / nm |
8 |
Surface area / m2g-1 |
510 |
Carbon content / % |
22 |
Recommended pH range |
|
|
| *it is recommended to use at least 10% organic solvent composition near the pH limits and over 50% at pH values above pH 9.0 to perserve column lifetimes |
| |
| |
General
YMC-Pack Pro C18 RS is the latest ProFamily member designed to provide a selectivity resulting from a high carbon load of 22% and a broader pH stability range. For the separation of large non-polar molecules highly hydrophobic stationary phases are required. In many cases it is only with this kind of columns that the chromatographer is able to separate positional isomers that are often by-products in pharmaceutical and other industrial manufacturing processes.
YMC-Pack Pro C18 RS fulfils these demands and additionally gives further opportunities in method development due to its extended pH stability.
Properties
The relatively high carbon load of YMC-Pack Pro C18 RS (22%) amplifies the selectivity’s ability to discriminate between closely related compounds such as positional or steric isomers.
A good system to test this steric selectivity is a mixture of o-, m- and p-terphenyl separated under methanol/water conditions. These three compounds differ only in their three-dimensional structure and not in their hydrophobicity or polarity. YMC-Pack Pro C18 RS recognizes even small differences as shown in the chromatogram on the right, whilst a standard C18 selectivity, such as Inertsil ODS-3V, does not.
|
| Steric selectivity* |
 |
Column: 150 x 4.6 mm i.d.
Eluent: methanol / water (85/15)
Flow rate: 1.0 ml/min
Temperature: 37° C
Detection: UV at 254 nm |
|
|
| |
For the analysis of ionisable compounds with reversed phase HPLC it is recommended to adjust the pH of the mobile phase to a value which is two units higher or lower than the pK value of the individual analytes to insure a complete protonation or deprotonation of acids or bases. This guarantees that a poor peak symmetry is not based on interactions between e.g. protonated and unprotonated forms of a base.
Conventional RP selectivities are normally restricted in their pH stability and typically they can be used between pH 2 and pH 8, where a lower pH “cleaves” the alkyl chains from the silica support and an alkaline pH dissolves the silica support itself. As a result it is very difficult to separate a base with a pK of more than 6 in its electronically neutral state, which is sometimes important for a good separation of complicated molecules.
YMC-Pack Pro C18 RS exhibits an extended pH-stability from pH 1 to 10. Its long-term stability at pH 1 and at pH 10 respectively has been tested under very harsh conditions as shown below.
The first figure shows the stability at pH1 where the column was flushed with acetonitrile/water/TFA (10/90/1) at 70 °C for 80 hours! The comparison of the initial chromatogram (left side) and the final chromatogram (right side) shows that there is almost 100% constant retention time for all compounds tested even hydrophobic substances. This is a good indication that there was virtually no cleavage of C18 chains! |
| |
|
| |
| Stability under acidic conditions |
 |
Eluent: acetonitrile / water (60/40)
Flow rate: 1.0 ml/min
Temperature: 37° C
Detection: UV at 260 nm |
|
| |
YMC-Pack Pro C18 RS: Ideal for the separation of steric demanding
compounds and/or for the usage under broader pH conditions! |
| |
Note: When assessing pH stability data, please take care to certify that complete chromatographic conditions are presented.
For example, (even very) basic sample substances have relatively limited effect on the stationary phase, since they are only applied in small concentrations. In contrast, overall basic conditions due to applying basic eluents may significantly affect silicas and traditional bonding chemistries. Therefore, stability data should be considered only after verifying that the buffer system used maintains the selected pH during preparation and use. Furthermore, it must be verified that the eluent is not recycled, since the “active” basic sites may equilibrate to a saturation level with time, resulting in no further interactions taking place. Consequently, only continous flow of “fresh” and thoroughly buffered eluent will provide accurate and meaningful performance data. |
| |
| Stability under basic conditions |
 |
| For pH 10, a borate buffer system (20 mM H3BO3-NaOH (pH 9.8) /methanol 50/50 at 30°C) was selected to be continuously pumped through the column, while checking the number of theoretical plates for methyl benzoate every 50 hours. |
|
| |
