Ruth Kuldvee

Therapeutic drug monitoring of antiepileptics by capillary electrophoresis. Characterization of assays via analysis of quality control sera containing 14 analytes.

Quality assurance is an important aspect in therapeutic drug monitoring (TDM). Capillary electrophoresis (CE) assays for determination of (i) ethosuximide via direct injection of serum or plasma, (ii) lamotrigine after protein precipitation by acetonitrile and analysis of an aliquot of the acidified supernatant, and (iii) carbamazepine and carbamazepine-10,11-epoxide after solute extraction followed by analysis of the reconstituted extract are characterized via analysis of a large number of commercial quality control sera containing up to 14 analytes (9 of them are anticonvulsants) in sub-therapeutic, therapeutic and toxicologic concentration levels. CE data obtained in single determinations are shown to compare well with the spike values and the mean of data determined in other laboratories using immunoassays and/or high-performance liquid chromatography, values that are reported by the external quality control scheme. Carbamazepine and ethosuximide drug levels are also shown to agree well with those determined in our departmental drug assay laboratory using automated immunoassays. The presented data reveal the effectiveness of assay assessment via analysis of quality control sera and confirm the robustness of the assays for TDM in a routine setting.

Capillary electrophoresis of methyl-substituted phenols in acetonitrile

The separation of mono- and dimethylphenols by capillary electrophoresis in pure acetonitrile was investigated. In acetonitrile, uncharged phenols interact with background electrolyte anions forming negatively charged complexes, which can be separated from each other by capillary electrophoresis. The background electrolyte anions tested were acetate, bromide and chloride. The calculated formation constants for phenol-anion complexes were highest with acetate and smallest with bromide. Complex formation was found to be sensitive to traces of water in the background electrolyte. The separation of methylphenols was also carried out in acetonitrile at high pH using background electrolytes prepared from diprotic acids and tetrabutylammonium hydroxide. At high pH the phenols were partly dissociated, providing an additional mechanism for the separation. All methylphenols were separated with the use of malonate background electrolyte. However, this approach was prone to interference from methanol resulting from the tetrabutylammonium hydroxide solution.

Nonconventional Samplers in Capillary Electrophoresis

Developments in nonconventional sample introduction in capillary electrophore- sis have focused on the possibility of forcing the sample stream to pass the separation capillary inlet. The advantages of such input devices are the absence of a voltage rise/drop time during sampling, ease of operation because no vial manipulations are involved, and ease of automation and computerization. However, besides these the main advantage of such input devices seems to be the fact that they facilitate easy, multiple input from a single sample vial. This opens the possibility of monitoring the concentration changes taking part in inside the vessel — an important task for — analytical biotechnology. This article describes some possible designs of CE nonconventional samplers and discusses applications of such samplers in sample preparation, in coupling CE with flow injection analysis (FIA) and HPLC, in multiple input experiments (with or without stacking) for reduction of detection limits and for monitoring of reaction kinetics.

Head column field‐amplified stacking from the flow: Stabilization of the sample plug position by using backpressure

Head column‐field amplified sample stacking (HC‐FASS) is one of the most powerful concentration techniques in capillary electrophoresis. In the present work we demonstrate that a laboratory‐designed pneumatic sampler not only enables us to easily perform HC‐FASS from stagnant sample solutions but also permits us to carry out HC‐FASS from sample stream, which creates an opportunity to lower the detection limit of analytes further. The influence of stacking time in case of the flowing sample on peak efficiencies and resolution is discussed. It is demonstrated that the sample plug length can be kept constant by monitoring the current in the capillary, which controls a feedback system based on backpressure at the capillary outlet.

Stacking from the Sample Stream in CZE Using a Pneumatically Driven Computerized Sampler.

It is demonstrated that a pneumatically driven computerized sampling device for capillary electrophoresis facilitates sample stacking by the head-column field amplification (HCFA) technique. This device utilizes a rapid exchange between buffer and sample in a narrow channel at the separation capillary inlet and makes possible the combination of two classical injection modes [Formula: see text] the electrokinetic and hydrodynamic modes. Detection limits obtained were about 9 nM for alkylbenzylamine cations with common UV detection.

Correlation and digital signal processing techniques for the reduction of detection limits of bromate and bromide in model water samples by ion chromatography with direct ultraviolet detection

Bromate is a well known by-product produced by the ozonation (disinfection) of drinking water, of which the concentration is considered to be regulated to a low μg/l level. Successful ion chromatographic methods of determination involve the implementation of concentration columns. As an alternative to concentration, it is demonstrated that the low μg/l level can easily be attained using a simple and foolproof experimental arrangement of direct pseudo random injections of large quantities of the sample and ultraviolet (UV) detection at 204 nm with subsequent decorrelation of the detector signal. The approach, known as correlation chromatography, makes high demands to the reproducibility and other properties of the injection system. Although correlation chromatography is less sensible to spikes and baseline drift compared with normal chromatography, optimum results will be achieved by applying digital detector processing prior to decorrelation, combined with a proper modification of the eluent. This is demonstrated here.