Biomedical subjects

M C Breadmore

Publications and source records attributed to M C Breadmore.

8 recordsLinked to original sources

PubMed2001

Ion chromatography on-chip.

On-chip separation of inorganic anions by ion-exchange chromatography was realized. Micro separation channels were fabricated on a silicon wafer and sealed with a Pyrex cover plate using standard photolithography, wet and dry chemical etching, and anodic bonding techniques. Quaternary ammonium latex particles were employed for the first time to coat the separation channels on-chip. Owing to the narrow depths of the channels on the chip, 0.5-10 microm, there were more interactions of the analytes with the stationary phase on the chip than in a 50-microm I.D. capillary. With off-chip injection (20 nl) and UV detection, NO2-, NO3-, I-, and thiourea were separated using 1 mM KCl as the eluent. The linear ranges for NO2- and NO3- are from 5 to 1000 microM with the detection limits of 0.5 microM.

Chromatography, Ion Exchange↗

PubMed2001

Optimisation of the separation of anions by ion chromatography-capillary electrophoresis using indirect UV detection.

The separation of a complex mixture of inorganic and organic anions by ion chromatography-capillary electrophoresis using a cationic polymer added to the background electrolyte and indirect UV detection has been studied. The addition of unmodified polymer to an electrolyte suitable for indirect detection resulted in the appearance of a system peak due to the counter-anion on the polymer and while the position of the analytes relative to this system peak could be changed, this was found to be an unacceptable approach for mixtures of large numbers of analytes. Although conversion of the polymer to replace the counter-ion with the indirect UV detection probe ion simplified the system, this approach restricted the flexibility of the system because the probe and polymer concentration were necessarily linked. This limitation could be overcome by selecting the appropriate type of probe ion, with probes having a low ion-exchange selectivity coefficient providing greater retention of analytes than probes with a high ion-exchange selectivity coefficient. Three electrolyte systems with different probes (benzoate, chromate and phthalate) were modelled using a previously derived migration equation and this was used to optimise the electrolyte composition to enable the separation of a mixture of 24 inorganic and organic anions within 7 min. The electrolyte composition was then optimised for the analysis of anions in Bayer liquor with the final separation selectivity being substantially improved for selected key analytes.

Anions↗

PubMed2001

On-capillary ion-exchange preconcentration of inorganic anions in open-tubular capillary electrochromatogrpahy with elution using transient-isotachophoretic gradient. 2. Characterization of the isotachophoretic gradient.

Diffuse transient-isotachophoretic boundaries can be used as an elution gradient of increasing eluotropic strength to elute inorganic anions that have been preconcentrated on an open-tubular ion-exchange stationary phase prior to electrophoretic separation. The generation and characteristics of these gradients for elution after preconcentration have been investigated. The gradients are generated by placing a low-mobility, weak ion-exchange competing anion in the capillary (weak electrolyte, WE), and a high-mobility, strong ion-exchange competing anion in the electrolyte vials (strong electrolyte, SE). Application of voltage establishes a diffuse boundary with the composition changing from the weak anion to the strong anion. Comparison of elution gradients generated with different electrolyte systems was accomplished by comparing the eluotropic strength (a function of eluent concentration, ion-exchange selectivity coefficient, and charge) and the shape of the profile as it changes from WE to SE. The ion-exchange selectivity coefficient of the SE competing anion is important in establishing a sharp change in elution strength. A large difference in mobility between the WE and SE competing anions gives an SE with a higher final eluotropic strength, but the slope of the gradient is shallower. This results in a reduction in the efficiency of analyte focusing. To ensure maximum focusing efficiency, the WE and SE electrolytes should be selected such that the SE has the highest possible eluotropic strength for a given concentration of WE. The SE competing anion should also have a sufficiently low electrophoretic mobility to ensure focusing for the maximum number of analytes, and the mobility difference between the WE and SE competing anions should be as small as possible.

Journal Article↗

PubMed2001

Modelling of migration behaviour of inorganic anions in ion-exchange capillary electrochromatography.

A theoretical model to explain the observed mobility of inorganic anions in capillary electrochromatography (CEC) using ion-exchange (IE) stationary phases has been derived. The model divides contributions to the observed mobility of an analyte ion into capillary electrophoretic (CE) and IE components. The CE component includes the influence of varying the ionic strength of the background electrolyte on the electrophoretic mobility of the analyte, while the IE component accounts for the variation in retention of the analyte ion caused by changing the composition of the background electrolyte. The model was verified using a mixture of UV-absorbing inorganic ions in electrolytes of differing eluotropic strength in both packed and open-tubular CEC systems, with excellent agreement (r2 > 0.98) for both systems. Values of constants in the model equation determined by nonlinear regression were used to estimate the relative strengths of the interactions of different analytes with the stationary phase and these were found to agree well with elution orders observed in conventional IE chromatography.

Anions↗

PubMed2001

Approaches to enhancing the sensitivity of capillary electrophoresis methods for the determination of inorganic and small organic anions.

One of the major problems facing the development of capillary electrophoresis (CE) is the relatively high limits of detection when compared to traditional high-performance liquid chromatographic (HPLC) methods. While the use of an alternative detector can offer better sensitivity, a more universal approach is sample preconcentration. Numerous on-line methods have been developed to improve the sensitivity of CE, and are based on electrophoretic principles, chromatographic principles, or a combination of both. This review will discuss all forms of on-line preconcentration methods for CE, with emphasis given to those that have shown particular merit when applied to inorganic and small organic anions.

Anions↗

PubMed2000

Peak shapes in open tubular ion-exchange capillary electrochromatography of inorganic anions.

An experimental study of parameters influencing peak shapes in ion-exchange open tubular (OT) capillary electrochromatography (CEC) was conducted using adsorbed quaternary aminated latex particles as the stationary phase. The combination of separation mechanisms from both capillary electrophoresis and ion-exchange chromatography results in peak broadening in OT-CEC arising from both these techniques. The sources of peak broadening that were considered included the relative electrophoretic mobilities of the eluent co-ion and analyte, and resistance to mass transfer in both the mobile and stationary phases. The parameters investigated were the mobility of the eluent co-ion, column diameter, separation temperature and secondary interactions between the analyte and the stationary phase. The electromigration dispersion was found to influence peak shapes to a minor extent, indicating that chromatographic retention was the dominant source of dispersion. Improving the resistance to mass transfer in the mobile phase by decreasing the capillary diameter improved peak shapes, with symmetrical peaks being obtained in a 25 microm I.D. column. However, an increase in temperature from 25 degrees C to 55 degrees C failed to show any significant improvement. The addition of p-cyanophenol to the mobile phase to suppress secondary interactions with the stationary phase did not result in the expected improvement in efficiency.

Anions↗

PubMed2000

Modelling and optimization of the separation of anions in ion chromatography--capillary electrophoresis.

The influence of varying experimental conditions on the mobilities of inorganic and organic anions in ion chromatography-capillary electrophoresis (IC-CE) was studied. A theoretical model derived from both IC and CE was used to explain the influence on analyte mobility caused by varying the concentration of polymer and increasing the salt concentration in the background electrolyte. The influence of the type of competing ion was also accounted for by including the analyte selectivity coefficient in the model equation. The validity of the model was shown using electrolyte systems containing four different competing anions, with correlation between experimental and mobilities predicted being excellent (r2 > 0.98) for all systems. Selectivity coefficients determined via nonlinear regression enabled quantitative comparisons of different competing ion strength, with the eluting strength increasing in the order of fluoride, acetate, chloride, and sulfate. Optimization of the polymer and eluent concentration was performed for all electrolyte systems using the normalized resolution product optimization criterion, requiring only seven experiments to obtain the optimum conditions for complete separation. The minimum resolution criterion was used to optimize the fluoride system which gave a different separation selectivity from both CE and IC.

Anions↗

PubMed1999

Manipulation of separation selectivity for alkali metals and ammonium in ion-exchange capillary electrochromatography using a suspension of cation exchange particles in the electrolyte as a pseudostationary phase.

The viability of using ion-exchange particles as a pseudostationary phase in capillary electrochromatography for the separation of monovalent inorganic cations has been investigated. Using sulfonated polymeric particles (average diameter 225 nm) as the pseudostationary phase, the separation selectivity for alkali metals and ammonium was examined under a range of background electrolyte compositions and employing indirect absorbance detection. Addition of ion-exchange particles to the background electrolyte resulted in a reduction in the observed electrophoretic mobility of the analytes due to the establishment of ion-exchange interaction with the pseudostationary phase, with the decrease in mobilities following the ion-exchange interaction order for these analytes with a sulfonated stationary phase. Increasing the concentration of the particles resulted in a uniform reduction in the electrophoretic mobility of the analytes, similar to that observed in micellar electrokinetic chromatography. Conversely, increasing the concentration of the cationic indirect detection probe (which also acted as an ion-exchange competing cation) resulted in a decrease in the ion-exchange interaction with the particles and a reduction of the relative ion-exchange contribution to the overall separation mechanism. Plots of log[retention factor] versus log[electrolyte concentration] were linear, as is the case for ion-exchange chromatography, but the observed slopes were greater than predicted from ion-exchange theory. Indirect absorbance detection was found to give poor sensitivity due to light scattering effects caused by the particles of pseudostationary phase.

Cations↗