M.A.J. van Opstal

Chromatographic determination of phenylurea herbicides and their corresponding aniline degradation products in environmental samples. I.

Abstract Several chromatographic procedures for the determination of fifteen phenylurea herbicides and their corresponding degradation products are reported. Methods of analysis for each separate class of compounds and multiresidue methods which allow selective determination of herbicides and anilines in each others presence are discussed. The various procedures involve steps such as extraction, clean-up, catalytic hydrolysis of herbicides to anilines, liquid or gas chromatographic fractionation and/or separation, chemical derivatization and detection.

The use of various chromatographic techniques for the determination of phenylurea herbicides and their corresponding anilines in environmental samples. II: Applications

In earlier work, various strategies have been developed for the trace-level determination of phenylurea herbicides and the anilines which are their main degradation products. They include catalytic hydrolysis of the phenylureas on silica, liquid chromatographic fractionation of complex mixtures of herbicides and anilines, derivatization of anilines and herbicides with electron-capture-sensitive reagents, and final analysis by means of capillary gas chromatography. In the present paper, the application of these principles to trace-level analysis of surface water, soil and crop samples is demonstrated.

FLOW-INJECTION SYSTEM WITH PHOTODIODE ARRAY DETECTION AND MULTIVARIATE DATA EVALUATION FOR QUANTIFYING TENIPOSIDE IN BLOOD PLASMA

Abstract Teniposide in blood plasma is quantified by using a flow-injection system with photodiode array detection. For calibration, a partial least-squares model is used. Three different ways of using the recorded data for building this model are compared.

Optimization criteria for a single bead-string reactor in flow injection analysis based on consecutive kinetic reactions

Abstract In flow-injection methods based on chemical reactions, simple one-step reactions are desirable, but more complex kinetics cannot always be avoided. The consecutive reaction considered here is A + reagent (s)→B→C. The response signal depends on the dispersion of the sample zone in the system and on the kinetics of the chemical reaction. The dispersion in a single-bead-string vector is described by the tanks-in-series model. The reaction of paracetamol with hexacyanoferrate (III) and phenol is used for experimental verification. Rules for optimum reactor design are given, the reactor length being used as the optimization parameter. Comparison of the experimental and calculated peak heights at different reactor lengths confirms the optimization rules.

On-line electrochemical derivatization combined with diode-array detection in flow-injection analysis : Rapid Determination of Etoposide and Teniposide in Blood Plasma

Abstract On-line electrochemical derivatization combined with diode-array u.v./visible detection in flow-injection systems greatly enhances the selectivity. The system is applied for the determination of the antineoplastic agents etoposide (VP 16-213) and teniposide (VM 26) in blood plasma. The optimum oxidation potential, detection wavelength, solvent composition, pH and flow rate are established. Calibration graphs for spiked plasma are linear in the range 1–50 μg ml−1 for both etoposide and teniposide. The detection limit in absolute amount is 6 ng for each compound at a signal-to-noise ratio of 3. The injection frequency can be as high as 40 h−1. The method is validated by quantifying teniposide in plasma of a patient treated with teniposide.

Comparative study on the determination of the anti-neoplastic drug teniposide in plasma using micellar liquid chromatography and surfactant-mediated plasma clean-up

The potential of micellar liquid chromatography and of an on-line surfactant-mediated sample cleanup, which involves column-switching prior to conventional reversed-phase high-performance liquid chromatography, has been evaluated for the determination of the anti-neoplastic drug teniposide in plasma by using electrochemical detection. A major advantage of surfactant-mediated techniques is that they allow fully automated processing of plasma samples, because protein precipitation is prevented by the addition of the surfactant sodium dodecylsulphate. With the automated column-switching technique, a degree of sample enrichment and of selectivity can be attained, which is similar to that for the conventional procedure which, however, involves a labour-intensive off-line isolation of teniposide, using liquid-liquid extraction prior to chromatography. An inherent drawback of automated micellar liquid chromatography is that no sample clean-up or preconcentration can be carried out, which results in only a moderate detection limit and selectivity. The linearity, reproducibility and recovery of the surfactant-mediated techniques are similar to those of the conventional procedure. Based on the presented results, it was concluded that the surfactant-mediated column-switching technique is a highly attractive sample enrichment technique with respect to simplicity, speed and cost.