Parameters 

Crown Ether Chiral Stationary Phases - CROWNPAK® CR(+) / CR(−) columns

These columns contain a chiral crown ether as a chiral selector which is a coated onto a 5μm silica support. Acidic mobile phases such as Perchloric acid pH 1 to 2, are used to operate these columns under standard conditions. Note that to shorten the retention time of hydrophobic samples, the addition of Methanol ( 15% maximum v/v) has been shown to be effective. These columns are the reference columns for achieving amino acid separations, with the advantage that the elution order of the enantiomers can be reversed when necessary ( CR(-) column gives the reversed elution order compared to CR(+) column).

Crown Ether Columns

CROWNPAK^® CR(+) & CR(-) contain a chiral crown ether as a chiral selector, which is coated onto a 5-µm silica support. CROWNPAK selectors are mainly used to separate chiral amino acids and other small molecules with primary amine groups. The elution order of the enantiomers can be reversed when necessary.

Acidic mobile phases such as perchloric acid (pH 1 to 2), are used to operate these columns under standard conditions. To shorten the retention time of hydrophobic samples, the addition of methanol (15% maximum v/v) has been shown to be effective for CROWNPAK CR(+) & CR(-).

CROWNPAK CR-I(+) & CR-I(-) columns and stationary phases are the newest addition to this family of chiral selectors. The crown ether selectors are immobilized on 5-µm silica support. Immobilization extends the range of solvents used for mobile phases such as acetonitrile and ethanol, thereby enhancing enantioselective resolution of chiral compounds. Use of the immobilized CROWNPAK CR-I(+) & CR-I(-)  selectors also provides longer column life time.

Operating Procedure

• Typical pH range of the mobile phase: from pH 1 to pH 2 (column stable up to pH 9).
• Lower pH will result in a good resolution but in a shorter column life. Choose the highest pH giving a satisfactory separation to prolong column life time.
• Decreasing the temperature is also effective to increase the selectivity.
• Other acids such as nitric acid and TFA can also be used. However, we recommend to use perchloric acid preferably which gives, in most cases, better resolutions and also for its low UV-absorption.
• To shorten the retention time of hydrophobic compounds, the addition of methanol (15% max.) has been shown to be efficient. Exceeding 15% of Methanol or using a different organic modifier is likely to damage the stationary phase contained in the column

Operating Restrictions

1.  The maximum flow rate depends on the mobile phase viscosity (mobile phase composition and temperature). Flow rate should be adjusted in accordance with pressure limitations. The back pressure value that should be taken into account is the one generated by the column itself. This value is measured by calculating the difference between the pressure of [LC system + column] and the pressure of the LC system free of the column.
2.  Ideal value for maximum column life, but stable up to 200 Bar.
3. Generally, the lower the temperature is, the better the resolution becomes, especially for hydrophilic samples. Note that some hydrophobic samples may be strongly retained on the stationary phase at low temperatures.