Synthesis, characterization, and application of polysodium N-alkylenyl α-d-glucopyranoside surfactants for micellar electrokinetic chromatography-tandem mass spectrometry

Abstract

Sugar-based ionic surfactants forming micelles are known to suppress ESI of various compounds due to decrease in surface tension upon micelle formation . For the first time, poly (sodium N-undecylenyl-α-d-glucopyranoside 4,6-hydrogen phosphate, (poly-α-d-SUGP) based surfactants with different chain lengths and head groups have been successfully synthesized, characterized, and applied as compatible chiral selector for MEKC-ESI-MS/MS. First, the effect of polymerization concentration of the monomer, α-d-SUGP, was evaluated by enantioseparation of one anionic compound (1,1'-binaphthyl-2,2'diyl-hydrogen phosphate) and one zwitterionic compound (dansylated phenylalanine) in MEKC-UV to find the optimum molar surfactant concentration for polymerization. Next, MEKC-UV and MEKC-MS were compared for the enantioseparation of 1,1'-binaphthyl-2,2'diyl-hydrogen phosphate. The influence of polymeric glucopyranoside based surfactant head groups and carbon chain lengths on chiral Rs was evaluated for two classes of cationic drugs (ephedrine alkaloids and β-blockers). Finally, enantioselective MEKC-MS of ephedrine alkaloids and β-blockers were profiled at their optimum pH 5.0 and 7.0, respectively, using 20 mM NH4 OAc, 25 mM poly-α-d-SUGP at 30 kV and 25°C under optimum spray chamber conditions. The LOD for most of the enantiomers ranges from 10 to 100 ng/mL with S/N of at least ≥3.0.

Keywords: Beta-blockers; Enantioseparations; Ephedrine alkaloids; MEKC-ESI-MS/MS; Poly(sodium N-alkenyl-α-d-glucopyranoside) surfactants.

Figure 1

Effect of polymerization concentrations (mM) of sodium N-undecylenyl α-D-glucopyranoside 4,6-hydrogen phosphate (α-D-SUGP) surfactant monomers on chiral Rs of zwitterionic compound (DNS-PA, left) and anionic compound (BNP, right) in MEKC. Conditions: Panel (A): 56 cm effective length (375 μm O.D., 50 μm I.D.) fused silica capillary; sample concentration: 1.0 mg/mL in MeOH/-H₂O (50/50). Buffer: 12.5 mM NaH₂PO₄ +12.5 mM Na₂HPO₄, pH 7.0, 45 mM poly-α-D-SUGP. Applied voltage: +20 kV, injection: 5 mbar, 10 s. Panel (B) sample concentration: 1.0 mg/mL in MeOH/H₂O (50/50). Buffer: 20 mM NH₄OAc, pH 10.8, 15 mM poly-α-D-SUGP. Conditions for applied voltage, injection and capillary dimensions are the same as panel A. Peak identification: 1= R- DNS-PA, 1′ = S-DNA-PA, 2 = R-BNP, 2′ = S′-BNP.

Figure 2

Comparison of ESI-MS signal of DNS-PA obtained by direct infusion positive ion ESI-MS in the presence of (A) no surfactant, (B) 50 mM unpolymerized α-D-SUGP, and (C) 50 mM poly-α-D-SUGP.

Figure 3

Comparison of MEKC-UV (A), and MEKC-MS/MS (B) for chiral separation of BNP. Conditions: (A) 56 cm effective length (375 μm O.D., 50 μm I.D.) fused silica capillary. BNP concentration: 1.0 mg/mL in MeOH/H₂O (50/50). Buffer: 20 mM NH₄OAc, pH 10.8, 15 mM poly-α-D-SUGP. Applied voltage: +20 kV, injection: 5 mbar, 10 s. The capillary dimension in (B) are the same as (A) except for 60 cm effective length. BNP concentration: 0.1 mg/mL in MeOH/H₂O (50/50, v/v). Spray chamber parameters: nebulizer pressure: 3 psi; drying gas temp: 250 °C, drying gas flow rate: 6 L/min; capillary voltage: −3000 V; fragmentor voltage: 200 V, collision energy: 41 eV, MRM transition: 347.1 −> 79.1. Sheath liquid: MeOH/H₂O (80/20, v/v), 5 mM NH₄OAc, pH 6.8 with a flow rate of 5 μL/min. Peak identification: 1 = R-BNP, 1′ = S′-BNP.

Figure 4

Bar plots illustrating the effect of chain length and head groups of sugar surfactants on chiral Rs of ephedrine alkaloids (top, A) at pH 5.0 and β-blockers (bottom, B) at pH 7.0 in MEKC-MS/MS. The * indicates Rs = 0. Conditions: 75 cm long (375 μm O.D., 50 μm I.D.) fused silica capillary. Buffer: 25 mM NH₄OAc, pH 5.0, 30 mM poly-α-D-SUGP, poly-α-D-SUGS, poly-α-D-SOGP and poly-α-D-SOGS. Applied voltage, +20 kV, injection, 5 mbar, 10 s. Spray chamber and sheath liquid conditions are the same as Fig. 3. Sample concentration: 10 μg/mL in MeOH/H₂O (10/90, v/v). MEKC-MS conditions are the same as Fig. 3 except the optimum fragmentor voltage, collision energy and MRM of ephedrines and β-blockers are listed in Table 2.

Figure 5

(A) Bar plots illustrating the effect of pH on chiral Rs of ephedrine alkaloids (top, A) and β-blockers (bottom, B) in MEKC-MS/MS. Buffer conditions and spray chamber parameters are the same as in Fig. 4 and 3, respectively except 30 mM poly-α-D-SUGP was used at pH 5.0–6.0 in (A), and 6.0–9.5 in (B). The * indicates Rs = 0.

Figure 6

Electropherograms for enantioseparation of ephedrine alkaloids using sugar surfactant with optimum head group and chain length at optimum pH 5.0 in MEKC-MS/MS. The MEKC conditions and spray chamber parameters are the same as Fig. 5. Peak identifications: 1 = (1R,2S)-(−) norephedrine, 1′ =(1S,2R)-(+)norephedrine, 2 = (1R, 2R ) (−) pseudoephedrine, 2′ = (1S,2S)(+) pseudoephedrine; 3 = (1R,2S)-(−)ephedrine, 3′ = (1S,2R)-(+)ephedrine; 4 = (1R,2S)-(−)N-methylephedrine, 4′ = (1S,2R)-(+)N-methylephedrine.

Figure 7

Electropherograms for enantioseparation of β-blockers using sugar surfactant with optimum head group and chain length at optimum pH 7.0 in MEKC-MS/MS. The MEKC conditions and spray chamber parameters are the same as Fig. 5. Peak identifications: 1,1′ = atenolol, 2,2′ = carteolol, 3,3′ = metoprolol, 4,4′ = talinolol. For each β-blocker the R-enantiomer always eluted earlier than S-enantiomer.

Scheme 1

Synthesis of poly(sodium N-alkylenyl α-D-glucopyranoside 4,6-hydrogen phosphate) (poly-α-D-SAGP) and poly(sodium N-alkylenyl α-D-glucopyranoside 6-hydrogen sulfate) (poly-α-D-SAGS).