Chiral Separations 4: Separation with Rt-βDEXm, Rt-βDEXsm and Rt-βDEXse

In my previous chiral column blogs, I’ve discussed how they compare, how to optimize the separations and column capacity. This blog focuses on individual columns and specific separations. We’ll start with Rt-βDEXm, Rt-βDEXsm and Rt-βDEXse (Table 1).

Table 1: Resolution of selected chiral compounds by Rt-βDEXm, Rt-βDEXsm and Rt-βDEXse

	Rt-βDEXm	Rt-βDEXsm	Rt-βDEXse
α-pinene	3.89	3.14	0.82
limonene	1.53	5.60	3.10
linalool	1.01	3.10	5.96
α-terpineol	1.84	4.72	5.20
isoborneol	2.20	3.76	3.35
menthol	1.73	1.24	1.24
2,3-butanediol	2.94	6.44	7.10
1-phenylethanol	6.93	7.52	6.52
α-ionone	3.45	5.67	3.31
menthone	4.11	0.59	5.76
ethyl-2-methylbutyrate	1.00	3.94	4.66
linalyl acetate	ns	ns	2.36
styrene oxide	3.34	4.53	10.77
trans-linalool oxide	9.74	9.71	2.96
cis-linalool oxide	5.65	6.06	4.28

All chromatograms were collected using the following method: Oven temp.: 40°C (hold 1 min.) to 230°C @ 2°C/min. (hold 3 min.); Carrier gas: hydrogen; 80cm/sec. set @ 40°C; Detector: FID set @ 220°C.

Rt-βDEXm

Let’s start with the most basic chiral column, the Rt-βDEXm, which is permethylated β-cyclodextrin added into midpolarity cyano/phenyl polymer (the same as 1701 phase). Based on our table (Table 1), Rt-βDEXm resolves well α-pinene, menthol, 1-phenylethanol, methone and linalool oxides. In addition, this column resolved menthol better than any other chiral column in our study. Figure 1 shows the separation of menthol (A) and menthone (B) on Rt-βDEXm, because these two compounds are commonly found together in mint oils.

Figure 1: Methol (A) and Menthone (B) resolution on Rt-βDEXm (30m, 0.32mm ID, 0.25µm; cat. # 13101)

Rt-βDEXsm

Rt-βDEXsm separates 20 of the 21 tested compounds, with 16 being baseline resolved. This column provides very good enantiomeric separation (Table 1) of α-pinene, α-ionone (Fig 2A), α-terpineol (Fig 2B), isoborneol (Fig 2C), 1-phenylethanol, 2,3-butanediol and linalool oxides (Fig 3).

Figure 2: α-ionone (A), α-terpineol (B) and isoborneol (C) resolution on Rt-βDEXsm (30m, 0.32mm ID, 0.25µm; cat. # 13104)

Figure 3: Trans-linalool oxide (1) and cis-linalool oxide (2) resolution on Rt-βDEXsm (30m, 0.32mm ID, 0.25µm; cat. # 13104)

Rt-βDEXse

The Rt-βDEXse is similar in performance to the Rt-βDEXsm, but it provides better resolution for limonene, α-terpineol, linalool, linalyl acetate (Fig 4), ethyl-2-methylbutyrate (Fig 5A), 2,3-butanediol, menthone (Fig 5B) and styrene oxides.

Figure 4: Linalool and linalyl acetate resolution on Rt-βDEXse (30m, 0.32mm ID, 0.25µm; cat. # 13106)

Figure 5: Ethyl2-methylbutyrate (A) and menthone (B) resolution on Rt-βDEXse (30m, 0.32mm ID, 0.25µm; cat. # 13106)

Sometimes extensive separation results in overlap of enantiomeric pairs (Fig 6B).

Figure 6: Limonene (A), camphor and styrene oxide (B) resolution on Rt-βDEXse (30m, 0.32mm ID, 0.25µm; cat. # 13