Wolfgang Kleiböhmer

Determination of explosives residues in soils by micellar electrokinetic capillary chromatography and high-performance liquid chromatography: A comparative study

Micellar electrokinetic capillary chromatography (MECC) is investigated for application as a complementary technique to reversed-phase high-performance liquid chromatography (HPLC) in the analysis of explosives residues. Separation efficiency, specificity, sensitivity, reproducibility, analysis time and calibration linearity are examined by comparing the suitability of HPLC and MECC in parallel analyses. Authentic soil samples from a former trinitrotoluene plant are examined, and the results show MECC to be a useful new technique in explosive analysis, yielding good sensitivity, high resolution and short analysis times.

Supercritical fluid extraction of polycyclic aromatic hydrocarbons from a marine sediment and analyte collection via liquid-solid trapping

Abstract A standard reference marine sediment (SRM HS-3) certified for polycyclic aromatic hydrocarbons (PAHs) was extracted with pure and toluene- modified supercritical carbon dioxide at various temperatures while the pressure was maintained at 400 atm (1 atm = 101 325 Pa). The best results were achieved with toluene-modified carbon dioxide at 140°C. Similar results were obtained when carbon dioxide was replaced with nitrous oxide. Analyte collection after off-line supercritical fluid extraction (SFE) was carried out with liquid—solid traps whereby analyte losses due to aerosol formation during the depressurization of the supercritical fluid were reduced. As the liquid—solid traps were developed from conventional clean-up systems, further clean-up steps became unnecessary in this study. Such traps yielded better PAH recoveries than SFE with analyte trapping in pure organic solvents. The results of the optimized procedure were compared with the certified PAH values, with the results obtained by Soxhlet extraction with toluene and n-hexane—acetone and with published SFE results. With SFE instead of conventional Soxhlet extraction, the complete time required for the extraction, evaporation and clean-up steps can be reduced from ca. 27 h to ca. 3 h per sample.

Supercritical CO2 assisted liquid extraction of nitroaromatic and polycyclic aromatic compounds in soil

Abstract In this work we present a supercritical fluid extraction method based on the technique of direct modifier addition. This supercritical CO 2 assisted liquid extraction method proves to be superior to conventional liquid extraction methods such as sonication or Soxhlet extraction. Furthermore we investigated the influences of polar additives in the modifier on extraction behaviour. Analytes of interest were polycyclic aromatic hydrocarbons and for the first time the extraction of nitroaromatic compounds and other explosive residues was attempted in real-world soil samples. Due to the use of an especially developed solid-liquid trapping system we were able to integrate a clean-up step (ICUS). Additionally, this trapping system allows quantitative recovery of even volatile nitroaromatics.

Determination of pentachlorophenol in leather using supercritical fluid extraction with in situ derivatization

An in situ supercritical fluid extraction (SFE) and derivatization procedure for the determination of pentachlorophenol (PCP) in leather is described. PCP was extracted from leather with supercritical carbon dioxide and in situ derivatized with acetic anhydride in the presence of a base (e.g., triethylamine). The influence of several extraction and derivatization parameters (e.g., pressure, temperature, extraction time in the static and dynamic extraction mode, amount of the base and of acetic anhydride) on the extraction efficiency has been investigated. Since the leather sample had no certified PCP content, the SFE results were compared with those obtained by Soxhlet extraction with methanol. With SFE instead of conventional Soxhlet extraction, the overall time required for sample preparation, extraction, derivatization, evaporation, clean-up and analysis steps can be reduced from about 2 days to approximately 3 h.

Monitoring polycyclic aromatic hydrocarbons in waste gases

A fast off-line monitoring system based on supercritical fluid extraction (SFE) and supercritical fluid chromatography (SFC) is introduced that allows the quantification of polycyclic aromatic hydrocarbons (PAHs) in the crude gas of fuel-oil-stoked industrial boiler plants. In this paper we present a comparison of our recently developed monitoring system with a standard method of a reference laboratory. Samples were taken according to VDI-3873 (dilution method) on polyurethane foam (PUF) plugs. The PUF plugs were extracted with toluene-modified carbon dioxide within 60 min. The extracts were analysed using packed column SFC with fluorescence detection.

Matrix independent supercritical fluid extraction of polycyclic aromatic hydrocarbons by employing binary modifiers

A universal extraction method has been developed for polycyclic aromatic hydrocarbons using supercritical fluids. The method is nearly matrix-independent and therefore applicable to different kinds of matrices with only minor changes. New binary modifiers, containing small amounts (1%) of active additives in organic solvents have been used. In contrast to extractions with neat CO2 or CO2 modified with neat co-solvents, the use of binary modifiers has resulted in significantly higher extraction efficiencies for different kinds of matrices. The applicability of the new modifier-solutions has been shown for three different matrices, a fly ash, a sediment and a sewage sludge.

Supercritical CO2-assisted liquid extraction of polycyclic aromatic hydrocarbons and polychlorinated dibenzo-p-dioxins and -furans from solid matrices

Abstract In this work we present a supercritical fluid extraction method based on the technique of direct modifier addition. This supercritical CO2-assisted liquid extraction method is shown to be superior to conventional liquid extraction methods such as e.g. Soxhlet extraction. Analytes of interest were polycyclic aromatic hydrocarbons and polychlorinated dibenzo-p-dioxins and -furans in real-world soil samples.

Separation of hydroxylated polycyclic aromatic hydrocarbons by micellar electrokinetic capillary chromatography

Abstract A capillary electrophoretic method for effective separation of hydroxylated polycyclic aromatic hydrocarbons (OH-PAHs) is presented. The effect of urea as secondary modifier on the retention behaviour of 10 hydroxylated PAHs using cyclodextrin modified micellar electrokinetic capillary chromatography (CD-MECC) is investigated. The changes of analyte migration times have been attributed to a ternary analyte–cyclodextrin–urea complex. The separation of 10 common hydroxylated PAHs using the developed CD-MECC method is compared to the results gained by high-performance liquid chromatography (HPLC) separation using common reversed-phase conditions.

Fast chromatographic separation techniques as competitors to chemical and biochemical sensor systems

Fast chromatographic methods, e.g. chromatography with supercritical fluids, ion chromatography and especially capillary electrophoresis, are important competitors of chemical sensors in environmental monitoring and process control. These methods show high selectivity and low interferences and it is possible to determine several parameters within a single chromatographic run. In order to show the potential and limitation of sensor systems and chromatographic separation methods in environmental analysis this review is limited to applications in this field.With regard to practical problems a comparison of ion chromatography (IC), capillary electrophoresis (CE) and electrochemical sensors is given for a special example, the ion analysis in waste water. Authentic water samples with a high surfactant content from a car-wash are examined, proving the suitability of IC, CE and electrochemical sensors in terms of specifity, sensitivity, reproducibility, analysis time and calibration linearity. The results show that the chromatographic methods are useful techniques in water analysis, yielding good sensitivity, high resolution and short analysis times. In comparison the chemical sensor also shows short analysis times, good sensitivity and a simple instrumental set-up. The disadvantage is the lack of selectivity and the instability of the sensor signal, when the sensor is exposed to the extremely complex matrix. Good results could only be achieved by pretreatment of the sample solution.

Supercritical fluid chromatography of polychlorinated biphenyls on packed columns

Abstract The supercritical fluid chromatographic behaviour of polychlorinated biphenyls using carbon dioxide and nitrous oxide as mobile phases was studied on packed columns. Factors affecting the retention and separation of these compounds were investigated and an application to sediment samples is described.