Migration Time Data Research Articles

Characterization of Athabasca lean oil sands and mixed surficial materials: Comparison of capillary electrophoresis/low-resolution mass spectrometry and high-resolution mass spectrometry.

Oil sands mining in Alberta, Canada, requires removal and stockpiling of considerable volumes of near-surface overburden material. This overburden includes lean oil sands (LOS) which cannot be processed economically but contain sparingly soluble petroleum hydrocarbons and naphthenic acids, which can leach into environmental waters. In order to measure and track the leaching of dissolved constituents and distinguish industrially derived organics from naturally occurring organics in local waters, practical methods were developed for characterizing multiple sources of contaminated water leakage. Capillary electrophoresis/positive-ion electrospray ionization low-resolution time-of-flight mass spectrometry (CE/LRMS), high-resolution negative-ion electrospray ionization Orbitrap mass spectrometry (HRMS) and conventional gas chromatography/flame ionization detection (GC/FID) were used to characterize porewater samples collected from within Athabasca LOS and mixed surficial materials. GC/FID was used to measure total petroleum hydrocarbon and HRMS was used to measure total naphthenic acid fraction components (NAFCs). HRMS and CE/LRMS were used to characterize samples according to source. The amounts of total petroleum hydrocarbon in each sample as measured by GC/FID ranged from 0.1 to 15.1mg/L while the amounts of NAFCs as measured by HRMS ranged from 5.3 to 82.3mg/L. Factors analysis (FA) on HRMS data visually demonstrated clustering according to sample source and was correlated to molecular formula. LRMS coupled to capillary electrophoresis separation (CE/LRMS) provides important information on NAFC isomers by adding analyte migration time data to m/z and peak intensity. Differences in measured amounts of total petroleum hydrocarbons by GC/FID and NAFCs by HRMS indicate that the two methods provide complementary information about the nature of dissolved organic species in a soil or water leachate samples. NAFC molecule class Ox Sy is a possible tracer for LOS seepage. CE/LRMS provides complementary information and is a feasible and practical option for source evaluation of NAFCs in water.

High-resolution method for regulatory control of Echinacea species in Nutraceuticals by CD-MEKC

One problem in the international regulatory control of Echinacea, a therapeutic Nutraceutical, is recognition of caffeoyl solutes and alkamides in different products. Cyclodextrin-modified micellar electrokinetic chromatography (CD-MEKC) has been applied to Echinacea spp. in combination with pattern recognition of some caffeoyl solutes. A novel metric based on relative migration time (RMT) data has been developed in CE to address the problem of variable reported migration time. The CD-MEKC method of Gotti's group using hydroxypropyl-β-cyclodexrin (HP-β-CD; 100 mM) with sodium dodecyl sulphate (SDS; 110 mM), in a triacid background electrolyte (10 mM, pH 8) under 19 kV was adapted to identify two key hydrophilic solutes: chlorogenic acid and cichoric acid present in all commercial products. Two internal markers were taken as reference points to calculate the RMT of any target peak: RMT = t m (target)/ t m (marker). The RMT method was robust to temperature change from 20 to 40 °C, but sensitive to pH. The lateral shift and reproducibility of the target peak t m (target) were significantly reduced by this novel transformation. In the worst cases migration time variability ranged up to 12% ( n = 6); the RMT algorithm reduced this to less than 1%. In general, the RMT transformation reduced the variability of migration time data by a factor of 2–5. For systematic comparison of electrophoretic profiles for test sample and standard, a new pattern recognition algorithm permits sequential peak-by-peak comparison using specified segments of the electropherograms for comparison of test and Echinacea purpurea (root product) as a standard. This algorithm was capable of rapidly characterising the similarity of target peaks in a test sample relative to those in the reference standard. Combination of the RMT algorithm and pattern recognition in CE is expected to offer a robust approach to international regulatory characterisation and control of Nutraceuticals.

Determination of protein-ligand affinity constants from direct migration time in capillary electrophoresis.

A simple method to calculate dissociation constants for protein-ligand interactions by partial-filling capillary electrophoresis is demonstrated. The method uses raw migration time data for the ligand and needs only additional information about capillary inner radius and the absolute amount of protein loaded. A theoretical study supported by experimental data also demonstrates that the retention of analyte in affinity capillary electrophoresis (ACE) using the partial-filling technique depends linearly on the absolute amount of selector added but is independent of both selector zone length and selector mobility. Factors such as field strength and electroosmotic flow are also cancelled out if they are kept constant. The theory is confirmed and the usefulness of the method is demonstrated by enantioseparations using alpha-acid glycoprotein (AGP) and cellulase (Cel 7A) as chiral selectors.

Electrophoretic behaviour of oligonucleotides and mono-, di- and triphosphate nucleotides by capillary zone electrophoresis.

A systematic investigation has been made into the mechanisms of the capillary zone electrophoresis (CZE) separation of 12 common nucleotides (mono-, di- and triphosphorylated) and polydeoxythymidylic acid oligonucleotides (pd(T)5-18) using electrophoretic mobility values calculated from migration time data. Relationships between electrophoretic mobility and the physicochemical characteristics of the analytes (charge, dissociation constants, charge-to-mass ratio) and the background electrolyte conditions (buffer strength, percentage organic modifier and buffer pH) were characterised. Nucleotide migration was dominated by the negatively charged phosphate groups. Additionally, there were important contributions to migration behaviour from the ionised amide groups of the nucleobases guanine and uracil at higher buffer pH values or with the presence of methanol in the electrolyte. Calculated electrophoretic mobility values for the nucleotides showed a substantially improved (5-fold) inter-run repeatability compared with migration time data. These studies show the value of representing nucleotide migration data as electrophoretic mobility in CZE for obtaining a more thorough analysis of separation mechanisms and to compensate for variation in migration time data caused by small changes in electrosmotic flow. Oligonucleotides pd(T)5-11 could be adequately resolved from their nearest neighbour, but the limit of single-base separation was pd(T)10 from pd(T)11 under the conditions used. It was calculated that a difference in charge-to-mass ratio of 2.64 x 10(-5) was required for resolution under the CZE conditions used.

Optimization of the cyclodextrin-assisted capillary electrophoresis separation of the enantiomers of phenoxyacid herbicides

An ethylcarbonate derivative of β-cyclodextrin (β-CD) with three substituents per molecule, hydroxypropyl-β-CD and native α-CD have been tested as resolving agents in the capillary zone electrophoresis (CZE) separation of the four enantiomers of the herbicides mecoprop and dichlorprop. The performances of the three compounds have been quantified by means of two-levels full factorial design and the inclusion constants were calculated from CZE migration time data. Possible structure of inclusion complexes have been proposed, on the basis of molecular mechanics simulations.

New derivatives of cyclodextrins as chiral selectors for the capillary electrophoretic separation of dichlorprop enantiomers

α-, β- and γ-cyclodextrins (CDs), as well as some of their chemical derivatives, have been tested as chiral resolving agents for the capillary zone electrophoretic resolution of the racemic herbicide dichlorprop, (±)-2-(2,4-dichlorophenoxy)propionic acid, of which only the (+)-isomer is herbicidally active. The complexation constants of the herbicide enantiomers with the cyclodextrin host molecules have been calculated from the electrophoretic migration time data at variable cyclodextrin concentration. The experimental results showed that several of the investigated CDs allowed dichlorprop enantiomer resolution. In particular, a newly synthesised ethylcarbonate derivative of β-CD showed the best enantiomer resolution properties among the tested compounds, while the remaining ones showed inferior or no performances at all. The calculated inclusion constants allowed identification of the best conditions for enantioresolution, and an explanation of the different complexation properties of the investigated compounds has been proposed on the basis of molecular modeling.

Determination of chromate ion in chromium plating baths using capillary zone electrophoresis with micellar solution

Chromate anion (CrO 2− 4) has been determined by capillary zone electrophoresis with on-column UV detection at 273 nm by using a negative power supply. A fused-silica capillary (53 cm × 0.05 mm I.D.) was employed and a high voltage of 20 kV was applied. The addition of a cationic surfactant, tetradecyltrimethylammonium bromide (TTAB) in the buffer solution reverses the direction of the electroosmotic flow (EOF) in the capillary, so that EOF augments the mobility of the anion. This results in an exceedingly short analysis time of under 2 min. From migration time data, the electroosmotic mobility, the electrophoretic mobility of the micelle and apparent electrophoretic mobility of the chromate ion in the micellar solution were determined as a function of the concentration of TTAB. Linear calibration for chromate ion was established over the concentration range 25–300 pg with a detection limit of 1.2 pg/nl by using a 0.01 M carbonate buffer and 5 m M TTAB solution (pH 10). The method was applied to the determination of the chromate anion in a rinse water from chromium plating baths.

Controlled changes of selectivity in the separation of ions by capillary electrophoresis

The selectivity of low-molecular-weight inorganic and organic anions is evaluated on a capillary electrophoresis system utilizing a negative power supply and indirect UV detection at 254 nm. The background electrolyte chromate was found to be most useful for highly mobile inorganic anions and short chain carboxylates. Incorporated in this lectrolyte is an additive that reverses the direction of electroosmotic flow (EOF) in the capillary, so that the EOF augments the mobility of the analytes. This results in exceedingly short analysis times, under 5 min, with efficiencies aproaching 600 000 theoretical plates. From migration time data, a correlation between ionic equivalent conductance andanalyte mobility in the electrolyte is established. This empirical correlation equation aids in the prediction of migration order (selectivity) of a separation. Other parameters evaluated on the chromate electrolyte are ionic strength, pH and EOF modifier concentration. It was found that pH and the EOF modifier provided significant selectivity control over the analytes while the other electrolyte parameters pemitted only subtle changes in selectivity.