U.A.Th. Brinkman

Recent developments in the application of comprehensive two-dimensional gas chromatography

The literature on comprehensive two-dimensional gas chromatography (GC x GC) is reviewed, with emphasis on application-oriented studies published in the period 2004-2006. The various strategies that can be used in such studies, the state-of-the-art analytical performance and the high potential of GC x GC combined with time-of-flight mass spectrometric detection are highlighted.

Current use of pressurised liquid extraction and subcritical water extraction in environmental analysis.

This review updates our knowledge about pressurised liquid extraction (PLE) and subcritical water extraction (SWE), two sample preparation techniques which are increasingly used for the extraction of moderately and non-volatile organic pollutants from a variety of solid and semi-solid environmental matrices. Parameters influencing the extraction yield and selectivity are discussed. The results deriving from the analysis of several different classes of compounds in a variety of matrices are compared with a reference method, e.g., Soxhlet extraction. PLE and SWE are both promising techniques due to the short extraction times and low solvent consumption. In addition, SWE offers a wide range of polarities by changing the temperature and can easily provide class-selective extraction by temperature programming and/or the addition of modifier(s). This indicates that, even though many applications have already been reported, more can be expected.

High-resolution separation of polychlorinated biphenyls by comprehensive two-dimensional gas chromatography

Comprehensive two-dimensional gas chromatography (GC x GC) with micro electron-capture detection (microECD) has been optimised for the separation of polychlorinated biphenyl congeners with emphasis on the separation of 12 toxic non- and mono-ortho chlorinated biphenyls (CBs), viz. CBs 77, 81, 105, 114, 118, 123, 126, 156, 157, 167, 169 and 189. The selection of the first- and second-dimension columns and the temperature programme optimisation were carried out with a mixture of 90 CBs and the results are compared with those of one-dimensional GC. A complete separation of all 12 priority CBs was obtained with two column combinations, HP-1-HT-8 and HP-1-SupelcoWax-10. With the HP-1-HT-8 column set, ordered structures show up in the two-dimensional plane, with the number of chlorine substituents and their position (ortho vs. non-ortho) being the main parameters of interest. This can help with congener identification. Estimated detection limits are excellent, i.e. about 10 fg. To illustrate the potential and the versatility of GC x GC-microECD, a cod liver extract and a standard mixture of the 17 most toxic polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans together with 90 CBs were analysed as an application.

Coupling of biological sample handling and capillary electrophoresis

The analysis of biological samples (e.g., blood, urine, saliva, tissue homogenates) by capillary electrophoresis (CE) requires efficient sample preparation (i.e., concentration and clean-up) procedures to remove interfering solutes (endogenous/exogenous and/or low-/high-molecular-mass), (in)organic salts and particulate matter. The sample preparation modules can be coupled with CE either off-line (manual), at-line (robotic interface), on-line (coupling via a transfer line) or in-line (complete integration between sample preparation and separation system). Sample preparation systems reported in the literature are based on chromatographic, electrophoretic or membrane-based procedures. The combination of automated sample preparation and CE is especially useful if complex samples have to be analyzed and helps to improve both selectivity and sensitivity. In this review, the different modes of solid-phase (micro-) extraction will be discussed and an overview of the potential of chromatographic, electrophoretic (e.g., isotachophoresis, sample stacking) and membrane-based procedures will be given.

On-line trace enrichment in high-performance liquid chromatography using a pre-column

Abstract The potential of on-line trace enrichment on a pre-column in high-performance liquid chromatography is demonstrated using phthalate esters as model compounds. The esters are concentrated onto a very shortr, i.e.,ca. 2 mm long, plug of an apolar chemical bonded stationary phase (5-μm LiChrosorb RP-18). Analysis is performed on LiChrosorb RP-18 with a methanol step gradient as mobile phase; detection is done by UV absorption measurement at 233 nm. Phthalate ester recoveries are 95-100% even after enrichment from sample volumes of 500–1000 ml, with pumping speeds varying between 5 and 25 ml min-1. The single-column and the column-to-column reproductivity of the technique are usually 4–6% (relative standard deviation); band broadening due to the insertion of the pre-column is negligible. As an application, the determination of two esters in tap, distilled, mineral and river water, and in soft drinks, is reported. The trace enrichment of mixtures of polychlorinated biphenyls, and of chloroanilines, is also described.

Gas chromatographic methods for oil analysis

In the past 50 years. gas chromatography (GC) has played a most important role in the analysis of oil. In this review, the early history is briefly reviewed; next developments in this highly relevant application area since about 1985 are highlighted. The main topic of interest are the introduction and decisive role of capillary GC, the use of selective detection techniques, the versatility of coupled-column techniques and, specifically, the additional power of comprehensive two-dimensional GC.

Membrane-based sample preparation for chromatography

Abstract The use of membrane-based systems for sample preparation prior to chromatographic analysis is reviewed. A categorization of membrane separation techniques (dialysis with porous and with non-porous membranes, electrodialysis and ultrafiltration) for sample preparation purposes is presented and the theoretical background of membrane separation is shortly discussed. The applicability of these techniques is demonstrated by presenting examples of the use of membrane-based devices, on-line coupled to gas or liquid chromatography, for sample preparation in the biomedical, environmental and biotechnological field. Finally, the relative merits of the various membrane separation techniques are compared, with special emphasis on speed, recovery, selectivity and robustness.

Rapid Screening of a Large Group of Polar Pesticides in River Water by On-Line Trace Enrichment and Column Liquid Chromatography

Abstract Column liquid chromatography on a reversed-phase (C-18) analytical column using a linear acetonitrile-water gradient and diode-array detection is used in an on-line early-warning system of over 50 pesticides in surface water. It allows the separation of most compounds with detection limits of about 1–5 μg/1 after preconcentration of 30 ml of sample. Problems encountered for co-eluting pesticides with similar spectra and pesticides with weak ultraviolet absorption over 230 nm, are discussed. If the system is combined with on-line trace enrichment on a styrene-divinylbenzene copolymer (PLRP-S) precolumn, the overall resolution is only slightly affected, and the qualitative information obtained remains about the same. Chromatograms of spiked (2–10 μg/1) surface (river Rhine) water containing 54 test compounds are shown. Preliminary studies show the stability of several pesticides in water to be rather low. Some degradation products have been detected in 1-month-old methanolic and aqueous solutions.

Determination of polycyclic aromatic hydrocarbons in surface water by column liquid chromatography with fluorescence detection, using on-line micelle-mediated sample preparation

Abstract Column liquid chromatography with fluorescence and diode-array UV detection has been used for the trace-level determination of sixteen EPA-priority polycyclic aromatic hydrocarbons. The procedure involves on-line micellemediated preconcentration on selective sorbents. Using Brij-35 as the surfactant, unwanted adsorption of the analytes on inner walls or surfaces is prevented. The system has been used for the analysis of surface water samples, and detection limits typically are at the low- to sub-ng/l level. The system is robust and repeatability is excellent.

Analytical strategies for the screening of veterinary drugs and their residues in edible products

The development of analytical strategies for the regulatory control of drug residues in food-producing animals is discussed. Analytical methods for the determination of veterinary drugs in edible products are based on microbiological, immunochemical and physicochemical principles. Because of complexity of biological matrices such as egg, milk and meat, well designed, and often sophisticated, off-line or on-line sample treatment procedures are essential, especially when utilising physicochemical multi-residue screening procedures. Since large series of samples have often to be analysed, automation is increasingly becoming important. Confirmation of the identity of drug residues and validation of the analytical results implies the use of adequate analytical methods. In its turn, this requires well established criteria for those methods and/or equivalent reference methods.