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

7 October 2021
By
  • Jana Hepner
Tags
  • #Product Selection
  • #Method Development
  • #Method Optimization
  • #Columns
  • #GC Columns
  • #Fused Silica Capillary Columns
  • #Blogs
  • #Botanicals
  • #Food & Agriculture
  • #GC
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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.

blog-chiral-separation-4-separation-with-RT-BDEXM-RT-BDEXSM-and-RT-BDEXSE-01.png

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).

blog-chiral-separation-4-separation-with-RT-BDEXM-RT-BDEXSM-and-RT-BDEXSE-02.png

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

blog-chiral-separation-4-separation-with-RT-BDEXM-RT-BDEXSM-and-RT-BDEXSE-03.png

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.

blog-chiral-separation-4-separation-with-RT-BDEXM-RT-BDEXSM-and-RT-BDEXSE-04.png

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

blog-chiral-separation-4-separation-with-RT-BDEXM-RT-BDEXSM-and-RT-BDEXSE-05.png

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).

blog-chiral-separation-4-separation-with-RT-BDEXM-RT-BDEXSM-and-RT-BDEXSE-06.png

Figure 6: Limonene (A), camphor and styrene oxide (B) resolution on Rt-βDEXse (30m, 0.32mm ID, 0.25µm; cat. # 13106)

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