Molecularly imprinted capillary electrochromatography for selective determination of thiabendazole in citrus samples.

In this work, the suitability of the combination of molecular imprinting and capillary electrochromatography (MIP-CEC) to be used as powerful tool in environmental or food analysis has been for the first time studied and successfully demonstrated. A molecularly imprinted monolith (MIM) has been synthesised and evaluated as stationary phase for the selective determination of the fungicide thiabendazole (TBZ) in citrus samples by non-aqueous capillary electrochromatography. The influence of the mobile phase composition, the voltage of the power supply and the separation temperature on the recognition of TBZ by the imprinted polymer has been evaluated, and the imprint effect in the MIM was clearly demonstrated. Once optimum recognition conditions were established, other variables affecting mechanical properties and chromatographic performance of MIM were adjusted using computational approach. The high selectivity achieved by the MIP-CEC developed procedure allowed unambiguous detection and quantification of TBZ in citrus samples by direct injection of the crude sample extracts, without any previous clean-up, in less than 6 min. The developed method was properly validated and the calculated detection limits were below the established maximum residue limits (MRLs), clearly demonstrating the suitability of the method to be used for the control of the selected fungicide.

On-line process control of gradient elution liquid chromatography.

The typical measure of the stability of analytical HPLC methods in the pharmaceutical laboratory is standards injected repeatedly throughout the sample sequence. To obtain improved control of the analysis and reduction of the number of standards and replicates, a novel approach to treat the analytical run as a process, where the chromatographic data is the product, is proposed. Thus, an alternative and continuous system suitability test procedure is described. This is obtained by continuous monitoring of several parameters of the chromatographic system such as pressure, temperature, and conductivity. The data are analyzed in real time with chemometrics to produce easily interpreted control charts. Gradient elution LC is extensively employed in pharmaceutical analysis. A gradient elution system is inherently dynamic due to the mobile-phase composition being changed during the chromatographic run. To handle the dynamics, suitable chemometric tools are needed. In this report, we extend the use of liquid chromatography process control (LCPC) to gradient elution LC by creating partial least-squares regression batch models of the data collected. The gradient elution LCPC system was evaluated by inducing disturbances, and it was shown to easily detect any real or simulated deviation.

Molecularly imprinted polymers in capillary electrochromatography: recent developments and future trends.

The developments in molecularly imprinted polymer (MIP)-based capillary electrochromatography (CEC) achieved during the past years are reviewed in this article. The MIP is prepared using a templated polymerization reaction and results in a material with a high selectivity towards a predetermined target. The selectivity of the MIP is comparable to that of the biological antibodies, however, the MIP is much more stable and is thus able to withstand extremely harsh conditions in terms of pH, temperature, and organic solvents. The high selectivity and stability of the MIP made it an interesting candidate for application as stationary phase sorbent in chromatography. However, due to slow kinetics the efficiency of the early MIP columns, which were predominantly applied in high-performance liquid chromatography (HPLC), were limited. The use of CEC was thought to improve the efficiency of the MIP-based separation system. The small dimensions of the capillary format employed in CEC have put demands on the polymer systems which have resulted in the development of many different polymer formats. Thus, this need for novel MIP formats for applications in CEC has contributed a lot to the general development of MIP formats as well as to the knowledge in MIP synthesis and characteristics.

Selectivity toward multiple predetermined targets in nanoparticle capillary electrochromatography.

Two unique methods to achieve selectivity toward multiple predetermined targets employing molecular imprinting technology have been developed. Partial filling capillary electrochromatography (CEC) was utilized to evaluate and compare the two techniques. The first approach, the mixed singly templated molecularly imprinted polymer (MIP) nanoparticle approach, is based on the mixing of two types of MIP nanoparticles with inherently different selectivity. The second approach, the multiply templated MIP nanoparticle approach, is based on the incorporation of two different templates during the preparation of the MIP nanoparticles. The use of MIPs in analytical chemistry applications has been extensively investigated during the past years. However, MIP nanoparticles with tailored multiple selectivity toward predetermined enantiomers has not yet been explored. The relative amounts of the two templates studied, i.e., (S)-ropivacaine and (S)-propranolol, were found to strongly affect the affinity of the multiply templated MIP nanoparticles for the predetermined targets. The amount of (S)-propranolol template had to be decreased to concentrations rarely applied in MIP synthesis in order to achieve 2-fold selectivity. Even though strongly decreased to 10% of the usual concentration employed, the MIP could efficiently separate the enantiomers of propranolol when applied in partial filling CEC. This opens up for new possibilities to decrease the need for an initial high amount of template in order to be able to produce an efficient MIP. The multiple enantiomer separation ability of the multiply templated MIP nanoparticles was compared with that of singly templated MIP nanoparticles that were mixed prior to analysis. It was concluded that the multiply templated MIP potentially can offer many new and interesting applications in chromatography as well as in sensor technology and solid-phase extraction.

Molecularly imprinted polymer coatings for open-tubular capillary electrochromatography prepared by surface initiation.

Molecularly imprinted polymer coatings were synthesized in fused-silica capillary columns by the use of a surface-coupled radical initiator. The coatings were prepared using either toluene, dichloromethane, or acetonitrile in the prepolymerization mixtures and were 0.15-2 microm thick as determined by scanning electron microscopy. Solvent-dependent differences in appearance were observed. All the molecularly imprinted polymer-based open-tubular capillary columns were able to separate the enantiomers of propranolol by means of electrochromatography. Electrochromatographic performance was found to be dependent on the type of solvent used during the synthesis.

Molecularly imprinted CEC sorbents: investigations into polymer preparation and electrolyte composition.

The influence of the sorbent preparation protocol and separation parameters on the selectivity and chromatographic efficiency of super-porous molecularly imprinted polymer (MIP) monoliths in capillary electrochromatography (CEC) was studied. Chiral templates were employed and enantiomer separation and resolution were used as measures of imprint selectivity and column efficiency, respectively; the latter was in addition studied by chromatography of non-related aromatic structures. The polymer preparation was varied with respect to monomer composition in the pre-polymerisation mixture and also the use of single versus multiple template(s). The separation parameters investigated were type and content of organic solvent and surfactant modifier in the electrolyte. It was found that acetone and acetonitrile in buffer mixtures provided enantiomer separation of enantiomers of the template and also structural analogues; however, the degree of separation was greatly influenced by the content in the electrolyte. Three surfactants, sodium dodecylsulfate (SDS), cetyltrimethylammonium bromide (CTAB) and polyoxyethylene sorbitanmonolaurate (Tween 20), were examined as electrolyte modifiers. It was found that addition of SDS decreased and CTAB and Tween 20 increased the enantiomer separation. SDS and CTAB could be used up to 1 mM concentration whereas Tween could be used up to 90 mM concentration without causing baseline disturbances. The effects found and demonstrated strongly suggest that these parameters are to be considered during optimisation of an MIP-CEC system.