Capillary electrophoresis of methyl-substituted phenols in acetonitrile

Porras, Simo P.; Kuldvee, Ruth; Palonen, Sami; Riekkola, Marja‐Liisa

doi:10.1016/s0021-9673(02)01965-9

Cited by 29 publications

(35 citation statements)

References 29 publications

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“…Note that the discussion about selectivity does not include the effect of additional separation mechanisms, like heteroconjugation [24] and ion pair formation, on the selectivity coefficient. Heteroconjugation, e.g., can pronouncedly affect selectivity in organic solvents like ACN [49,[55][56][57][58], DMF [10], NM [13], and propylene carbonate [58].…”

Section: Resultsmentioning

confidence: 99%

Are the asserted advantages of organic solvents in capillary electrophoresis real? A critical discussion

Porras

Kenndler

2005

Electrophoresis

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Are the asserted advantages of organic solvents in capillary electrophoresis real? A critical discussionBackground electrolytes (BGEs) prepared in pure organic solvents are common alternatives to aqueous BGEs in capillary electrophoresis. Several general advantages of organic solvents over water have been asserted in the literature, namely (i) organic solvents increase the separation selectivity; (ii) organic solvents increase the separation efficiency; (iii) high separation voltages and/or high BGE ionic strengths can be used in organic solvents due to lower electric current compared to water. Related assumptions are that (iv) due to higher field strengths applicable in organic solvents the analysis time is shorter than in aqueous BGEs, and (v) the solubility and/or stability of components (either analytes or BGE chemicals) is higher/better in organic solvents. In the present work, these asserted advantages were critically evaluated based on the physical principles of ion transport and zone dispersion in solution. The result was that many of the above-mentioned general advantages are overestimated or even inexistent; often they have no fundamental basis.

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Section: Resultsmentioning

confidence: 99%

Are the asserted advantages of organic solvents in capillary electrophoresis real? A critical discussion

Porras

Kenndler

2005

Electrophoresis

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“…[23] for water uptake of ACN). Like in our previous works with ACN [20,[29][30][31], the water uptake could not be fully avoided, and, thus, we have measured the water content of the solvent and some selected BGEs before and after the electrophoretic measurements by coulometric Karl Fischer titration (756 KF Coulometer, Metrohm, Herisau, Switzerland). The water content of ACN solvent was 0.003-0.008% w/w, for freshly prepared BGEs it was 0.006-0.014% w/w (except when water was intentionally added), and for the BGE in the running vials after one electrophoretic run it was 0.008-0.020% w/w.…”

Section: Methodsmentioning

confidence: 99%

“…In addition, other interactions, like nonsolvent related hydrogen bonding and ion association, are more pronounced in ACN compared to water. Pyrene was previously used as a marker for EOF under similar experimental conditions [20]. Another common EOF marker used in ACN is NM [29][30][31].…”

Section: Selection Of Experimental Conditionsmentioning

confidence: 99%

“…Later Okada [17] enlarged the investigations also to cover other anions (bromide, chloride, methanesulfonate, nitrate and tetrafluoroborate) and uncharged alcohols. Subsequent work in ACN has included heteroconjugation reactions of phenols with carboxylates [18], phenols and benzoic acids with acetates, bis(triflyl)amide and hexafluorophosphate [19], methyl-substituted phenols with various anions (including acetate, chloride and bromide) [20], and phenols with acetate and trifluoroacetate [21]. In addition, heteroconjugation of phenolic compounds with acetate, chloride, heptafluorobutanoate and trifluoroacetate has been investigated in propylene carbonate [21], benzoic acids with chloride in NM [22] and phenols with salicylate in DMF [23].…”

Section: Introductionmentioning

confidence: 99%

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Electromigration of a heteroconjugated imidazole–acetate complex in ACN

Porras

Jussila

2007

Electrophoresis

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ACN is an extremely poor hydrogen bond donor and therefore the anions dissolved in it are solvated mainly by other hydrogen bond donors (e.g. uncharged acids) possibly present in the solution. Under properly selected experimental conditions stabilization via hydrogen bonding can be used for separation in CE as has been demonstrated for uncharged acids by several authors. Electromigration based on heteroconjugation can be of importance, e.g. when aqueous separation medium cannot be used due to stability reasons. It also allows CE to be used as a tool for solution chemistry measurements, if the required physicochemical properties of the studied system are known or they can be predicted with sufficient accuracy by existing theories. In the present work we showed that also an uncharged base can stabilize an anion via hydrogen bonding in ACN. In the setup imidazole was chosen as a model base and acetate ion as complexing anion in equimolar acetic acid-acetate buffer. The resulted hydrogen-bonded imidazole-acetate complex (i.e. heteroconjugate) possesses a charge and can thus migrate in CE. It was shown that the studied complexation in ACN is sensitive to competition by other hydrogen bond donors such as water and methanol. On the other hand, acetone, which is a poor hydrogen bond donor, did not have much effect on the complexation. To take the effect of ionic strength on mobility into account, mobilities of the imidazole-acetate complex measured at various ionic strengths were corrected to zero ionic strength by the aid of conductivity equation. A fit of the 1:1 binding isotherm to the ionic strength corrected mobility versus acetate concentration data led to rather good correlation. However, x-reciprocal linear transformation of the binding isotherm showed nonlinearity, which could be partly explained by homoconjugation of acetic acid and acetate ion. Since the homoconjugation constant for acetic acid under present experimental conditions was not available, theoretical simulations were used to demonstrate the effects of homoconjugation. The possibility of multiple complexation of imidazole was discussed as well.

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“…Moreover, the lower conductivity of electrolyte solutions in some organic solvents than in water enables the use of higher electric fields for the separation resulting in higher separation efficiencies. Our better understanding today of molecular interactions in nonaqueous media and of solvation behavior in organic solvents has made it possible to utilize separation mechanisms that cannot take place or are too weak in aqueous media [29][30][31][32].…”

Section: Introductionmentioning

confidence: 99%

Separation of fluorescein isothiocyanate‐labeled amines by microchip electrophoresis in uncoated and polyvinyl alcohol‐coated glass chips using water and dimethyl sulfoxide as solvents of background electrolyte

et al. 2004

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On-chip capillary electrophoresis with uncoated and polyvinyl alcohol-coated glass channels in aqueous and nonaqueous dimethyl sulfoxide (DMSO) background electrolyte (BGE) solutions was applied in the separation of five amines derivatized with fluorescein-5-isothiocyanate. In aqueous BGE at pH 9.2, baseline separation of the analytes was not achieved on uncoated glass chips, but the separation was clearly improved when the chip channels were coated with polyvinyl alcohol (PVA). Separation was successful in nonaqueous DMSO electrolyte solution containing ammonium acetate and sodium methoxide, on both uncoated and PVA-coated glass microchips. The differences in the pK(a) values of analytes were probably amplified in DMSO, and all five analytes were at least partly dissociated and were separated. Because the viscosity of DMSO is higher than that of water, the migration times were longer in DMSO.

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Capillary electrophoresis of methyl-substituted phenols in acetonitrile

Cited by 29 publications

References 29 publications

Are the asserted advantages of organic solvents in capillary electrophoresis real? A critical discussion

Are the asserted advantages of organic solvents in capillary electrophoresis real? A critical discussion

Electromigration of a heteroconjugated imidazole–acetate complex in ACN

Separation of fluorescein isothiocyanate‐labeled amines by microchip electrophoresis in uncoated and polyvinyl alcohol‐coated glass chips using water and dimethyl sulfoxide as solvents of background electrolyte

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