P-EOF

Fig. 8 Multicompartment micelle formation from p-EOF star terpolymers and binary blends of p-EOF/EO. (a) Hamburger micelle from p-EOF with a very long PEO block, (b) Segmented wormlike micelle from p-EOF with a short PEO block, (c) Hamburger micelle from blends of p-EOF/EO. Reprinted with permission from Hillmyer et al. [79]. Copyright 2006 American...

This value is within 0.15 of the increase in temperature that was calculated above using (jleof-The overall process is far more straightforward than the method based on p-eof and is less sensitive to slight changes in wall chemistry that can occur over a period of time. 

From the above equations, it could be easily understood that the key properties of the analytes are the hydration radius, the p A, the diffusion coefficient, and the mass fraction. They will play a role in the separation. Another important factor is the /tjff of the ion and the fidi of the EOF in accordance with Equation (8). For /tapp.AT Oj they need to have the same sign or the /teff of the ion must be smaller than the effective mobility of the EOF. 

We have seen that a BGE for analysis of anions and organic acids needs to have (a) a pH above the p A 2 of the analyte, (b) a sufficient buffering effect, and (c) a co-ion as a probe for indirect UV detection, with mobility close to that of the analytes of interest. Furthermore, care should be taken to reverse the EOF of the capillary and to work in the anodic or reverse mode. 

When using PFT with a neutral selector, it is quite difficult to avoid any entrance of the chiral selector into the ionization source, particularly at a high pH, where EOF is important. The use of BGE at low pH and/or coated capillary to minimize EOF is therefore mandatory. However, the coaxial sheath gas, which generally assists the ionization process, leads to an aspirating phenomenon of the chiral selector in the MS direction. Javerfalk et al. were the first to apply PFT with a neutral methyl-/i-CD for the separation of racemic bupivacaine and ropivacaine with a polyacrylamide-coated capillary and an acidic pH buffer (pH 3). Cherkaoui et al. employed another neutral CD (HP-/1-CD) with a PVA-coated capillary for the analysis of amphetamines and their derivatives. To prevent a detrimental aspiration effect, analyses were carried out without nebulization pressure. Numerous other studies presented excellent results such as the enantioselective separation of adrenoreceptor antagonist drugs using tandem mass spectrometry (MS/MS) the separation of clenbuterol enantiomers after solid-phase extraction (SPE) of plasma samples or the use of CD dual system for the simultaneous chiral determination of amphetamine, methamphetamine, dimethamphetamine, and p-hydroxymethamphetamine in urine. 

In the absence of EOF and separation mechanism other than electrophoresis, each analyte migrates with its own velocity which, according to Equation 6.8, is proportional to the strength of the electric field applied across the capillary tube. The constant of proportionality of the observed velocity of the charged analyte is defined as the observed mobility (p bs) and can be directly calculated by the migration time and the other experimental parameters, according to the following equation ... 

The effective mobility, expressed by Equation 6.16, can be directly calculated from the observed mobility by measuring the electroosmotic mobility using a neutral marker, not interacting with the capillary wall, which moves at the velocity of the EOF. Accordingly, the effective mobility p of cations in the presence of cathodic EOF is calculated from p ts by subtracting p gf ... 

Fig. 3. Trace determination of some inorganic and organic anions in pure water, after an electrophoretic enrichment at 5 kV for 45 s with an addition of 75 p,M octanesulfonate to the sample [42]. The electrolyte 10 mM sodium chromate and 0.5 mM OFM-BT (a surfactant used as the EOF modifier), adjusted to pH 8 with sulfuric acid 15 kV 60 cmX75 fjim I.D. capillary, distance to detector, 52 cm UV photometric detection at 254 nm. Anions (concentrations in mg/1) 1, chloride (3.5) 2, sulfate (4.8) 3, nitrate (6.2) 4, oxalate (5) 5, fluoride (1.9) 6, formate (5) 7, phosphate (3.2) 8, acetate (5) 9, propionate (5).

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