Jan Piet Franke

Solid-phase extraction procedures in systematic toxicological analysis.

In systematic toxicological analysis (STA) the substance(s) present is (are) not known at the start of the analysis. In such an undirected search the extraction procedure cannot be directed to a given substance but must be a general procedure where a compromise must be reached in that the substances of interest are isolated at a yield as high as possible and the interfering substances from the biological material are removed. When using solid-phase extraction (SPE) it is desirable to have procedures using just one column. An overview of screening procedures using diatomaceous earth, polystyrene-divinylbenzene copolymer and mixed-mode bonded silica as column material in SPE is given. The latter type of sorbent is most popular at the moment and the critical steps in the procedure are outlined in more detail. Recent developments of SPE disks look very promising for STA.

Screening for the presence of drugs in serum and urine using different separation modes of capillary electrophoresis

Capillary electrophoresis (CE) is a modern separation technique that has some distinct advantages for toxicological analysis, such as a high efficiency, fast analysis, flexibility, and complementary separation mechanisms to chromatographic methods. CE can be applied in various modes, which each have a different separation mechanism or selectivity. The most common mode is capillary zone electrophoresis (CZE), in which charged analytes migrate in a buffer under the influence of an electric field. In micellar electrokinetic chromatography (MEKC), micelles are added to the buffer which interact with the analytes. MEKC can also be used for the separation of neutral compounds. In non-aqueous CE (NACE), the aqueous buffer is replaced by a background of electrolytes in organic solvents. A sample that needs to be screened can easily be analyzed subsequently by these CE modes using the same instrumentation. The aim of the study was to develop procedures for the analysis of basic and acidic drugs in serum and urine using CZE, MEKC, and NACE. A test mixture that consisted of six basic and six acidic compounds was used to study the separation behavior of five CE methods. The results showed that three methods (based on CZE, MEKC, and NACE) were suitable for the analysis of basic compounds and three methods (based on CZE and MEKC) for the analysis of acidic compounds. For the extraction of analytes from serum and urine, a solid-phase extraction (SPE) and a liquid-liquid extraction (LLE) method were compared. Both SPE and LLE methods provided clean extracts after extraction of the basic compounds from serum and urine. The extracts of acidic compounds contained more matrix interferences, especially for urine. The SPE method had some advantages compared to LLE, as it lead to cleaner extracts and higher peaks, and as it elutes basic and acidic compounds in one fraction. The potentials and pitfalls of the various methods for screening purposes in analytical toxicology are discussed.

Potential and pitfalls of chromatographic techniques and detection modes in substance identification for systematic toxicological analysis

The potential and the constraints of thin-layer chromatography (TLC), gas chromatography (GC) and high-performance liquid chromatography (HPLC) towards substance identification, together with their detection modes, are considered. The latter include colour reactions on the plate, molecular masses through chemical ionization mass spectrometry (MS) and diode-array UV spectrophotometry. Evaluations are carried out by the mean list length approach. Not surprisingly, GC-MS and HPLC-diode array detection qualify as the two most powerful combinations. However, one does not necessarily need to have access to these sophisticated detection modes: the identification power of TLC and colour reactions plus GC or HPLC retention indices is high and even a suitable combination of TLC and colour reactions remains a valuable tool. After analysis, the findings for the unknown substance(s) must be matched against databases containing the behaviour of reference substances. The search process for the computerized retrieval of potential candidates must allow the handling of all possible combinations of identification techniques applied.

An overview on the standardization of chromatographic methods for screening analysis in toxicology by means of retention indices and secondary standards

SummaryIn systematic toxicological analysis, in which a logical analytical search for a potentially harmful substance has to be carried out, chromatographic methods are of utmost importance since the retention parameter can be used for primary identification. In gas chromatography the Kováts retention index (RI) system is generally accepted for standardization of the retention. In order to increase the reproducibility of the interlaboratory RI, secondary standards for RI calculation have proven to be very useful. The best secondary standards are those that are structurally resembling the substances under investigation. For example, for general toxicological screening analysis, mixtures of drugs are recommended. Stationary phases consisting of Carbowax are most extensively used for solvents and volatile compounds; for less volatile compounds SE-30/OV-1/dimethylsilicone stationary phases have proven to be useful. For these types of stationary phases extensive data compilations comprising over 6000 substances are available for use in toxicology.

FUNDAMENTAL COMMENTS ON CELL POLAROGRAPHY ACCORDING TO VELAZQUEZ AND ROSADO

Some fundamental comments are made on cell polarography according to Velázquez and Rosado (Fertil Steril 23:562, 1972). The results which they have obtained cannot be reliable because fundamental mistakes are made against the principles of the electroanalytic techniques used. We comment upon the conductometry, the amperometric titrations, and the alternating-current polarography as carried out by Velázquez and Rosado.

Chapter 16 ‘General unknown’ analysis

Publisher Summary The three major tasks in the forensic toxicological analysis of a given specimen are: (1) to detect if the specimen contains any harmful substance(s); (2) to identify the substance(s) involved; and (3) to quantitate the substance(s) involved and to interpret the outcomes in regard to the reason for carrying out the analysis. This chapter explains that the three steps of detection, identification, and quantitation are mandatory. The first two relate to qualitative analysis and often go hand in hand, yet are by far the most difficult. Depending on the circumstances or the purpose, two approaches can be distinguished. In this chapter, the principles of systematic toxicological analysis (STA) and the present state of the art is discussed. Since organic substances with molecular weights in the order of 100–400, are most often encountered, the primary focus is on the qualitative analysis of these substances. Thus, the ultimate aim of STA is: (1) to detect all toxicologically relevant agents present and to identify them beyond reasonable doubt; and (2) to exclude the presence of all other relevant agents.