Achiral and chiral separations using MEKC, polyelectrolyte multilayer coatings, and mixed mode separation techniques with molecular micelles

Abstract

Mixed mode (MM) separation using a combination of MEKC and polyelectrolyte multilayer (PEM) coatings is herein reported for the separation of achiral and chiral analytes. Many analytes are difficult to separate by MEKC and PEM coatings alone. Therefore, the implementation of a MM separation provides several advantages for overcoming the limitations of these well-established methods. In this study, it was observed that achiral separations using MEKC and PEM coatings individually resulted in partial resolution of eight very similar aryl ketones when the molecular micelle (sodium poly(N-undecanoyl-L-glycinate)) concentration was varied from 0.25 to 1.00% w/v and the bilayer number varied from 2 to 4. However, when MM separation was introduced, baseline resolution was achieved for all eight analytes. In the case of chiral separations, temazepam, aminoglutethimide, benzoin, benzoin methyl ether, and coumachlor were separated using the three separation techniques. For chiral separations, the chiral molecular micelle, sodium poly(N-undecanoyl-L-leucylvalinate), was employed at concentrations of 0.25-1.50% w/v for both MEKC and PEM coatings. Overall, the results revealed partial separation with MEKC and PEM coatings individually. However, MM separation enabled baseline separation of each chiral mixture. The separation of achiral and chiral compounds from different compound classes demonstrates the versatility of this MM approach.

Figure 1

Structures of analytes; A. Chiral analytes; B: Achiral aryl ketones

Figure 2

A. Structural representation of (I) Poly-SUG and (II) Poly-l-SULV B. Structural representation of PDADMAC.

Figure 3

Influence of poly-SUG concentration on the separation of 8 aryl ketones using MEKC Conditions: A: 0.25% (w/v) p-SUG; B: 0.5% (w/v) p-SUG; C: 0.75% (w/v) p-SUG; D: 1.00% (w/v) p-SUG Buffer: 100mM Tris, pH 10; Analyte concentration: 0.1mg/ml, Capillary Length: 57cm total (50 cm effective length); Capillary I.D.: 50 µm; Temperature: 15 °C; Voltage: 15kV, Injection: 5psi for 5s; Detection: 220nm; Analytes: 1. Acetophenone, 2. Propiophenone, 3. Butyrophenone, 4. Valerophenone, 5. Hexanophenone, 6. Heptanophenone, 7. Octanophenone, 8. Decanophenone

Figure 4

Influence of bilayer number on the separation of 8 aryl ketones using PEM coatings Conditions: A: 2 bilayers; B: 3 bilayers; C: 4 bilayers; Coating: 0.5% (w/v) PDADMAC and 0.5% (w/v) p-SUG; Buffer: 100 mM Tris, pH 10; Analyte concentration: 0.1 mg/ml, Capillary Length: 57 cm total (50 cm effective length); Capillary I.D.: 50 µm; Temperature: 15 °C; Voltage: 15 kV, Injection: 5 psi for 5 s; Detection: 220 nm; Analytes: 1. Acetophenone, 2. Propiophenone, 3. Butyrophenone, 4. Valerophenone, 5. Hexanophenone, 6. Heptanophenone, 7. Octanophenone, 8. Decanophenone

Figure 5

Influence of poly-SUG concentration on the separation of 8 aryl ketones using mixed mode separation technique Conditions: All PEM coatings were constructed using 2 bilayers of 0.5% PDADMAC and 0.5% p-SUG (A-D); A: MEKC: 0.25% (w/v) p-SUG; B: MEKC: 0.5% (w/v) p-SUG; C: MEKC: 0.75% (w/v) p-SUG; D: MEKC: 1.00% (w/v) p-SUG; Buffer: 100 mM Tris, pH 10; Analyte concentration: 0.1 mg/ml, Capillary Length: 57 cm total (50 cm effective length); Capillary I.D.: 50 µm; Temperature: 15 °C; Voltage: 15 kV, Injection: 5 psi for 5 s; Detection: 220 nm; Analytes: 1. Acetophenone, 2. Propiophenone, 3. Butyrophenone, 4. Valerophenone, 5. Hexanophenone, 6. Heptanophenone, 7. Octanophenone, 8. Decanophenone

Figure 6

Influence of separation mode on the resolution of temazepam Conditions: A. PEM coatings: 2 bilayers of 0.5% (w/v) PDADMAC and 0.75% (w/v) p-SULV; B. MEKC: 1.00% (w/v) p-SULV; C: Mixed mode: PEM Coating: 2 bilayers of 0.5% (w/v) PDADMAC and 0.75% (w/v) p-SULV and MEKC: I. 0.25% (w/v); II. 0.5% (w/v); III. 0.75% (w/v); IV. 1.00% (w/v) poly-l-SULV; Buffer: 50 mM phosphate, pH 9.2; Analyte concentration: 0.2 mg/ml, Capillary Length: 57 cm total (50 cm effective length); Capillary I.D.: 50 µm; Temperature: 15 °C; Voltage: 30 kV, Injection: 5 psi for 5 s; Detection: 254 nm

Figure 7

Influence of poly-l-SULV concentration in the mobile phase on the resolution of aminoglutethimide using mixed mode separation technique Conditions: All PEM coatings were constructed using 2 bilayers of 0.5% (w/v) PDADMAC and 0.75% (w/v) p-SULV (A-D). A. Mixed Mode: MEKC: 0.25% (w/v) p-SULV; B. Mixed Mode: MEKC: 0.5% (w/v) p-SULV; C. Mixed Mode:, MEKC: 1.00 %(w/v) p-SULV; D. Mixed Mode: MEKC: 1.50% (w/v) p-SULV Buffer: 50 mM phosphate, pH 7.5; Analyte concentration: 0.2 mg/ml, Capillary Length: 57 cm total (50 cm effective length); Capillary I.D.: 50 µm; Temperature: 15 °C; Voltage: 30 kV, Injection: 5 psi for 5 s; Detection: 254 nm