pH-independent large-volume sample stacking of positive or negative analytes in capillary electrophoresis

In capillary electrophoresis, the short optical path length associated with on-column UV detection imposes an inherent detection problem. Detection limits can be improved using sample stacking. Recently, large-volume sample stacking (LVSS) without polarity switching was demonstrated to improve detection limits of charged analytes by more than 100-fold. However, this technique requires suppression of the electroosmotic flow (EOF) during the run. This necessitates working at a low pH, which limits using pH to optimize selectivity. We demonstrate that LVSS can be performed at any buffer pH (4.0-10.0) if the zwitterionic surfactant Rewoteric AM CAS U is used to suppress the EOF. Sensitivity enhancements of up to 85-fold are achieved with migration time, corrected area, and peak height reproducibility of 0.8-1.6%, 1.3-3.7%, and 0.8-4.9%, respectively. Further, it is possible to stack either positively or negatively charged analytes using zwitterionic surfactants to suppress the EOF.

Altering the selectivity of inorganic anion separations using electrostatic capillary electrophoresis

A new method for altering the selectivity of inorganic anion separations in capillary electrophoresis is described. Addition of the zwitterionic surfactant 3-(N,N-dimethyldodecylammonio)propane sulfonate (DDAPS) to the background electrolyte modifies the migration order via electrostatic ion chromatography type interactions. Variation of the DDAPS surfactant concentration from 4 to 120 mM monotonically alters the selectivity from electrophoretic mobility based to that of electrostatic ion chromatography, without increasing Joule heating. This technique was applied to the determination of nitrate, nitrite, bromide and iodide in artificial seawater. Detection limits for the anions in 1:5 diluted seawater were 11, 5, 7 and 11 microM, respectively.

Ultra-rapid analysis of nitrate and nitrite by capillary electrophoresis

Rapid analysis of nitrate and nitrite by capillary electrophoresis (CE) has been limited by the ions' very similar electrophoretic mobilities. With a pKa of 3.15, the mobility of nitrite can be selectively reduced using a low pH buffer in CE. A much shorter capillary can be used and separation voltages can be increased. With this method, nitrate and nitrite are separated in just over 10 s. This is roughly 20 times faster than current separation methods. Direct UV detection at 214 nm was employed and offered sub microM detection limits. Total analysis time (pre-rinse, injection, and separation) was less than 1 min, making this method ideal for high-throughput analysis.

Simultaneous separation of cationic and anionic proteins using zwitterionic surfactants in capillary electrophoresis

The zwitterionic surfactant Rewoteric AM CAS U forms a dynamic wall coating that prevents the adsorption of cationic proteins as well as suppresses the electroosmotic flow (EOF). Addition of polarizable anions to buffers containing this zwitterionic surfactant increases the once suppressed EOF to values nearing +3 x 10(-4) cm2/(V s). The retention of the EOF allows for the separation of analytes of widely different mobilities and is demonstrated by the simultaneous separation of cationic and anionic proteins. Using a buffer containing optimal amounts of the polarizable anion perchlorate and surfactant CAS U, the proteins lysozyme, ribonuclease A, alpha-chymotrypsinogen A, and myoglobin are separated in less than 15 min. Efficiencies as high as 1.5 million plates/m and recoveries greater than 91% are observed for proteins injected in distilled water. Migration time reproducibility is approximately 1% RSD within 1 day and approximately 3% RSD from day to day. The anionic and cationic proteins can be separated over a pH range of 5.5-9, all yielding good efficiencies.

How to succeed in analytical chemistry: a bibliography of resources from the literature

Technical excellence is necessary to succeed in a career in analytical chemistry. However there are many other skills necessary for success for which analysts receive no formal training. Talanta has had a tradition of publishing articles on practical aspects of our profession, such as how to write a paper in spectrophotometry or on ion selective electrodes. This article culls the literature for advice on how to purchase equipment, how (and when) to write a manuscript, how to review an article, how to give oral, poster and computer presentations, and how to get a job in analytical chemistry.

Ultrahigh-resolution capillary electrophoretic separation with indirect ultraviolet detection: isotopic separation of [14N]- and [15N]ammonium

Separation of isotopically labeled [14N]/[15N] ammonium was performed with capillary electrophoresis. This ultrahigh-resolution separation was based on mobility counterbalance with precise control of the anodic electroosmotic flow. Mixtures of zwitterionic surfactant (Rewoteric AM CAS U) and cationic surfactant (cetyltrimethylammonium bromide) were used as buffer additives to modify the electroosmotic mobility. Indirect ultraviolet detection was used with benzyltributylammonium as the buffer coion. Baseline-resolved peaks of [14N]- and [15N]ammonium were obtained within 11 min. The detection limit was 0.01 mM for both [14N]-and [15N]ammonium. Linear calibration in concentration was observed up to 1.0 mM for [15N]ammonium and 2.0 mM for [14N]ammonium. Calibration of the isotopic ratio, [15N]ammonium concentration to total ([14N] and [15N])ammonium, was valid from 5 to 95%.

Factors affecting selectivity of inorganic anions in capillary electrophoresis

Capillary zone electrophoretic separations of inorganic anions are largely governed by the intrinsic (infinite dilution) mobility of the anion. This in turn is a function of the hydrodynamic friction caused by the size of the ion and the dielectric friction caused by the charge density of the anion re-orienting the surrounding solvent. The influence of these factors on the mobility of anions is examined in both water and nonaqueous solvents. The influence of other experimental parameters, such as ionic strength, ion association, electroosmotic flow modifier concentration, and the addition of complexing agents such as polymeric cations, cyclodextrins, crown ethers and cryptands are also reviewed. From this discussion, some rules of thumb as to when different approaches will be most effective are drawn.

1998 W.A.E. McBryde Medal Lecture: Searching for the Holy Grail in analytical separations

This paper describes the chemistry presented during the W.A.E. McBryde Medal address given at the 81st Chemistry in Canada Conference held in Whistler. The narrative chronicles our Quest to perform isotopic separations in the solution phase using as our Excalibur, capillary zone electrophoresis. The narrative takes you through the highs of our early success in separating 35Cl- and 37Cl-. This separation was achieved by adjusting the electroosmotic flow to be equal in magnitude but opposite in direction to the chloride mobility. The narrative then takes you through the dark days, when we could not extend the isotopic separations to cationic species or even explain why there was an isotopic effect on mobility. Since those dark days, we have made numerous discoveries that have aided our Quest. Firstly, the development of mixed surfactant wall coating procedures yielded control of the reversed electroosmotic flow. This control enabled us to perform isotopic separations of systems such as 15N-/14N-aniline and 15NH4+/14NH4+. In terms of understanding electrophoretic mobility, we demonstrate the importance of dielectric friction to mobility. Further, the effect of ionic strength in capillary zone electrophoresis is explained using the Pitts treatment, which is analogous to the extended Debye-Hückel equation for ionic activity. So, have we completed our Quest? Read on.Key words: capillary zone electrophoresis, isotopic, electroosmotic flow, mobility modeling, ionic strength.

High-resolution determination of 147Pm in urine using dynamic ion-exchange chromatography

A procedure has been developed for measuring 147Pm in bioassay samples, based on the separation and preconcentration of 147Pm from the urine matrix by adsorption onto a conventional cation-exchange column with final separation and purification by HPLC using dynamic ion-exchange chromatography. The concentration of 147Pm is determined by collecting the appropriate HPLC fraction and measuring the 147Pm by liquid scintillation counting. The limit of detection is 0.1 Bq (3 fg) 147Pm based on a 500-mL sample of urine and a counting time of 30 min with a background of 100 cpm. Ten samples can be processed in 1.5-2 days.