General adjustment of system retention is often inadequate to resohestrueturally similar compounds in micellar electrokinetic capiOary chromatography (MECC). The use of cyciodextrins (CDs) as mobile-phase additives is described for separations of structural isomers. CDs are shown to provide dramatic and selective effects on the retention of benzopyrene isomers. Efficient separations of six methyl-substituted and three 1-position-substituted benzopyrene isomers are presented.Derhtatized 7-CD discriminates between substitutional isomers less than native 7-CD. A comparison of sodium dodecyl sulfate (SDS) and sodium cholate (NaC) surfactant systems indicates that SDS-CD mobile phases are more favorable for separation of benzopyrene isomers. Possible separation mechanisms are discussed and evaluated based on results of these studies. The computational procedures of a commercial molecular modeling system are modified and used to determine interaction energies for various host-guest (ke., 7-CD-benzopyrene) combinations. By use of the average of the five best energy values from interaction energy matrices, correct elution order is predicted for the 1 -position-substituted and most of the methyl-substituted benzopyrene isomers. Consideration of different possible CDbenzopyrene orientations must be made to correctly predict elution order. Inspection of the interaction energy matrices revealed no obvious energy barriers that would inhibit inclusion complex formation.A very useful characteristic of capillary electrophoresis (CE) and micellar electrokinetic capillary chromatography (MECC) is the ability to change quickly and easily the mobilephase composition of these techniques to allow for increased separation selectivity. As representative examples, CE-MECC running buffers have incorporated soluble polymers for size discrimination in oligonucleotide separations,1-1 2 complexing agents or crown ethers to separate metal cations,3-4 and organic solvents and/or bile salt micelles to separate hydrophobic compounds.5-6 Since the micellar (secondary) phase in MECC is a fluid component of the system, it can also be easily changed to alter selectivity.2-7 (

A capillary electrokinetic chromatography technique is described that employs neutral cyclodextrins (CDs) as a primary phase, transported with electroosmotic flow, and charged CDs as an electrophoretically mediated secondary phase. Neutral, hydrophobic solutes are separated on the basis of their differential distribution between these CD phases. The technique resembles micellar electrokinetic capillary chromatography (MECC) with regard to instrumentation and the fundamental relationships for resolution and capacity factor, which are influenced by the existence of a finite elution window. Conversely, the CD technique offers unique and beneficial characteristics when compared to MECC. Efficiency, selectivity, and system retention are evaluated on the basis of separations of polyaromatic hydrocarbons (PAHs). mciency is comparable to that of MECC (> lo5 platedm). The specificity associated with solute-CD inclusion complexation provides elution orders for PAHs that do not follow the hydrophobicity trends of MECC. Moreover, since the CD phases are largely noninteractive, complex CD systems can be used to enhance selectivity. Capacity factors can be altered in a convenient and predictable fashion simply by changing the CD phase ratio. The technique is rather robust with regard to the use of running buffers containing organic solvents; the effects or organic modifier and pH on system retention are demonstrated.

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The fluorescence derivatizing agent, o-phthalaldehyde (OPA), has been applied to the separation and detection of cyanide and several structurally similar thiols by capillary electrophoresis (CE)-laser induced fluorescence (LIF). Of particular interest to this investigation was the separation of 2-dimethylaminoethanethiol, 2-diethylaminoethanethiol, and cyanide, each of which are hydrolysis products or hydrolysis product simulants of the chemical warfare (CW) agents O-ethyl S-2-diisopropylaminoethyl methylphosphonothiolate (VX), O-isobutyl S-2-diethylaminoethyl methylphosphonothiolate (R-VX), and tabun (GA). Other structurally similar thiols simultaneously resolved by this method include 1-pentanethiol and 2-mercaptoethanol. Instrumental parameters were probed and optimum values for capillary length (50 cm) and inner diameter (75 microm), injection time (30 s) and field strength (15 kV) were determined. Sample stacking methods enabled detection limits of 9.3 microg/L for cyanide, 1.8 microg/L for 2-diethylaminoethanethiol, 35 microg/L for 2-dimethylaminoethanethiol, 15 microg/L for 2-mercaptoethanol, and 89 microg/L for 1-pentanethiol. The linearity of the method was verified over an order of magnitude and the reproducibility was found to be 3.0%.

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