36
September 2009
ADVERTISING FEATURE
Chiral separation – Efficient, fast and productive
By.Mattias Bengtsson* and Kristina Hallman – AkzoNobel/Kromasil Email:
mattias.bengtsson@
akzonobel.com, Telephone: + 46 709 57 73 37,Website:
www.kromasil.com
Chromatographic analysis and purification of optically active compounds are still areas with large potential for improvement. In the analytical field, chiral stationary phases (CSP) with better performance giving enhanced resolution and shorter analysis time are desirable.Within recent years the Kromasil group has launched two new polysaccharide CSP’s; Kromasil® amylose selector and, Kromasil®
AmyCoat™ which is based on a tris-(3,5-dimethylphenyl)carbamoyl CelluCoat™ which is based on a tris-(3,5-dimethylphenyl)carbamoyl cellulose selector. The stationary phase
Figure 1. FE-SEM pictures. a and b: pictures of uncoated Kromasil wide pore silica used for AmyCoat and CelluCoat; c: picture of CelluCoat
The in-house developed wide pore silica is specially designed to minimize the amount of achiral interactions with the silica surface while maintaining the mechanical strength of Kromasil silica. This mechanical strength allows operating the columns without pressure restriction within standard HPLC pressure range (≤400 bar).
The amylose and cellulose selectors are well known for their ability to resolve a broad range of racemates. This unique coating technology ensures homogenous distribution of the selector and an optimal thickness —both important to generate a high-performing, yet stable, product.
High efficient 3 µm particles Kromasil AmyCoat and CelluCoat are available in 3, 5, 10 and, 25 µm particle sizes. The small particle size, 3 µm, gives high efficiency and consequently a high resolution. Table 1 illustrates the similarity in chiral recognition capability between Kromasil AmyCoat 3 µm and 5 µm. The higher resolution obtained using Kromasil AmyCoat 3 µm is a result of the higher plate count achieved with a smaller particle size.
For difficult separations reducing the particle size could make the crucial difference between achieving baseline separation or not, as illustrated in figure 2.
Figur 3a. Separation of Tröger’s base in heptane/2-propanol/DEA (90/10/0.1), detection UV @ 220 nm, temp. 22°C, column: Kromasil AmyCoat, 3µm, 4.6 x 150 mm.
Figure 3b. van Deemter plots for Kromasil AmyCoat 3 and 5µm.
Figure 2. Separation of 2-phenyl-1-cyclohexanol in heptane/2-propanol (95/5), detection UV @ 220 nm, temp. 25°C, flow rate 1 ml/min, column size: 4.6 x 150 mm
High speed chromatography The mechanical strength of Kromasil AmyCoat and CelluCoat allow the columns to be operated at high flow rates. High flow rate combined with short column length provides very short analysis time. Figure 3a shows high speed chromatography with baseline separation in less than 1 minute. Since the van Deemter plot, figure 3b, is more flat for the smaller particle size, Kromasil AmyCoat 3 µm should be the first choice when running at elevated flow rates.
Table 1. Selectivity and resolution comparison of Kromasil AmyCoat 3 µm and 5 µm. Column size: 4.6 x 150 mm
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