Submicellar and micellar reversed-phase liquid chromatographic modes applied to the separation of beta-blockers.
The behaviour of a reversed-phase liquid chromatographic (RPLC) system (i.e. elution order, resolution and analysis time), used in the analysis of beta-blockers with acetonitrile-water mobile phases, changes drastically upon addition of an anionic surfactant (sodium dodecyl sulphate, SDS). Surfactant monomers cover the alkyl-bonded phase in different extent depending on the concentration of both modifiers, in the ranges 1 x 10(-3)-0.15M SDS and 5-50% acetonitrile. Meanwhile, the surfactant is dissolved in the mobile phase as free monomers, associated in small clusters or forming micelles. Four characteristic RPLC modes are yielded, with transition regions between them: hydro-organic, micellar, and low and high submicellar. The mobile phases in the two latter modes contain a concentration of SDS below or well above the critical micellar concentration (CMC) in water (i.e. 8 x 10(-3)M), and more than 30% acetonitrile. High submicellar RPLC appeared as the most promising mode, as it allowed full resolution of the beta-blockers in practical times, while these were unresolved or highly retained in the other RPLC modes. The strong attraction of the cationic solutes to the anionic SDS makes a direct transfer mechanism between surfactant molecules in the stationary and mobile phases likely.
Ruiz-Angel
M J
MJ
Departament de Química Analítica, Universitat de València, Burjassot, Spain. Maria.J.Ruiz@uv.es
Torres-Lapasió
J R
JR
García-Alvarez-Coque
M C
MC
Carda-Broch
S
S
D000097:Acetonitriles / Q000737:chemistry; D000319:Adrenergic beta-Antagonists / Q000302:isolation & purification*; D000465:Algorithms; D002853:Chromatography, Liquid / Q000379:methods*; D008823:Micelles; D008956:Models, Chemical; D012680:Sensitivity and Specificity; D012967:Sodium Dodecyl Sulfate / Q000737:chemistry; D012997:Solvents / Q000737:chemistry
D000097:Acetonitriles; D000319:Adrenergic beta-Antagonists; D008823:Micelles; D012997:Solvents; D012967:Sodium Dodecyl Sulfate; C032159:acetonitrile