Nicole De Brucker

Determination of hexavalent chromium by species specific isotope dilution mass spectrometry and ion chromatography–1,5-diphenylcarbazide spectrophotometry

The accuracy of the determination of hexavalent chromium (Cr6+) in solid matrices remains a challenging field of effort and improvement. An alkaline digestion (0.5 M NaOH–0.28 M Na2CO3) followed by ion chromatography and spectrophotometric determination by post-column derivatisation with 1,5-diphenylcarbazide (DPC) provides accurate and reproducible results. To gain a better insight into the species interconversion during the digestion, the concept of species specific isotope dilution mass spectrometry by adding enriched chromium isotopes that have been chemically converted into trivalent (Cr3+) and hexavalent chromium was used. For the analysis of the digestion solutions ion chromatography coupled to inductively coupled plasma-mass spectrometry (IC-ICP-MS) was peformed. The limit of detection in the digestion solution by the latest technique amounted 0.8 ng ml−1 Cr6+. The accuracy of an alkaline digestion on solid waste materials was compared with a water extraction (leaching test industrial waste), indicating that the alkaline digestion is accurate from the point of view of minimal species interconversion on one hand and the maximum amount of Cr6+ extracted on the other, while significant oxidation and reduction reactions were observed during leaching tests with water. In the framework of European Directive 94/62/EC on Packaging and Packaging Waste, the developed analytical method has been used to compare the concentrations of Cr6+ on 40 packaging materials against the regulatory limit value of 100 mg kg−1 by weight (sum of concentration levels of lead, cadmium, mercury and hexavalent chromium).

Combining HPLC-GCXGC, GCXGC/ Tof-MS, and Selected Ecotoxicity Assays for Detailed Monitoring of Petroleum Hydrocarbon Degradation in Soil and Leaching Water

HPLC-GCXGC/FID (high-performance liquid chromatography followed by comprehensive two-dimensional gas chromatography with flame-ionization detection) and GCXGC/ToF-MS (comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry) were used to study the biodegradation of petroleum hydrocarbons in soil microcosms during 20 weeks. Two soils were studied: one spiked with fresh diesel and one field sample containing weathered diesel-like oil. Nutrient amended and unamended samples were included. Total petroleum hydrocarbon (TPH) levels in spiked soil decreased from 15,000 to 7,500 mg/kg d.m. and from 12,0O0 to 4,000 mg/kg d.m. in the field soil. Linear alkanes and aromatic hydrocarbons were better biodegradable (>60% degraded) than iso-alkanes; cycloalkanes were least degradable (<40%). Aromatic hydrocarbons up to three rings showed better degradability than n-alkanes. GCXGC/ToF-MS analysis of leaching water showed that initially various oxygenated hydrocarbons were produced. Compound peaks seemed to move up and rightward in the GCXGC chromatograms, indicating that more polar and heavier compounds were formed as biodegradation proceeded. Nutrient amendment can increase TPH removal rates, but had adverse effects on ecotoxicity and leaching potential in our experiment This was explained by observed shifts in the soil microbial community. Ecotoxicity assays showed that residual TPH still inhibited cress (Lepidium sativum) seed germination, but the leaching water was no longer toxic toward luminescent bacteria (Vibrio fischeri).

Detailed analysis of petroleum hydrocarbon attenuation in biopiles by high-performance liquid chromatography followed by comprehensive two-dimensional gas chromatography.

Enhanced bioremediation of petroleum hydrocarbons in two biopiles was quantified by high-performance liquid chromatography (HPLC) followed by comprehensive two-dimensional gas chromatography (GCXGC). The attenuation of 34 defined hydrocarbon classes was calculated by HPLC-GCXGC analysis of representative biopile samples at start-up and after 18 weeks of biopile operation. In general, a-cyclic alkanes were most efficiently removed from the biopiles, followed by monoaromatic hydrocarbons. Cycloalkanes and polycyclic aromatic hydrocarbons (PAHs) were more resistant to degradation. A-cyclic biomarkers farnesane, trimethyl-C13, norpristane, pristane and phytane dropped to only about 10% of their initial concentrations. On the other hand, C29-C31 hopane concentrations remained almost unaltered after 18 weeks of biopile operation, confirming their resistance to biodegradation. They are thus reliable indicators to estimate attenuation potential of petroleum hydrocarbons in biopile processed soils.

Aqueous solubility calculation for petroleum mixtures in soil using comprehensive two-dimensional gas chromatography analysis data

An assessment of aqueous solubility (leaching potential) of soil contaminations with petroleum hydrocarbons (TPH) is important in the context of the evaluation of (migration) risks and soil/groundwater remediation. Field measurements using monitoring wells often overestimate real TPH concentrations in case of presence of pure oil in the screened interval of the well. This paper presents a method to calculate TPH equilibrium concentrations in groundwater using soil analysis by high-performance liquid chromatography followed by comprehensive two-dimensional gas chromatography (HPLC-GCXGC). The oil in the soil sample is divided into 79 defined hydrocarbon fractions on two GCXGC color plots. To each of these fractions a representative water solubility is assigned. Overall equilibrium water solubility of the non-aqueous phase liquid (NAPL) present in the sample and the water phases chemical composition (in terms of the 79 fractions defined) are then calculated using Raoults law. The calculation method was validated using soil spiked with 13 different TPH mixtures and 1 field-contaminated soil. Measured water solubilities using a column recirculation equilibration experiment agreed well to calculated equilibrium concentrations and water phase TPH composition.

Total uncertainty budget as method evaluation criterion for the determination of tracer (111Cd) cadmium and indigenous cadmium in soil column effluents with ICP-MS

For the evaluation of different analytical methods the best achievable final uncertainty can be used as the criterion. Evaluation of an analytical method on this basis includes the magnitude and also the robustness of the uncertainty budget. This evaluation was applied to laboratory-scale migration experiments on soil columns. These experiments were performed in order to estimate soil transport parameters of heavy metal pollutants (cadmium). In these studies a tracer (stable 111Cd isotope), having nearly the same physico-chemical properties as the pollutant of concern, was added on top of a contaminated soil and the column effluents were fractionally collected at the bottom. This paper presents three different calculation models, derived from the isotope dilution equation, for the simultaneous determination of the concentration tracer cadmium, [Cdt], and indigenous cadmium, [Cdn], in soil column effluents with ICP-MS. The methods differ in the method of calculation but are, in principal, based on the same measurements. The uncertainty budgets of the different methods were used in the evaluation. In addition to the magnitude of the total uncertainty, the boundary conditions of some parameters were investigated in detail. The influence of the following parameters on the uncertainty budget was studied: the concentration level of cadmium, the isobaric interference of tin and the molar fraction of indigenous cadmium.

Full uncertainty calculation on quantitative determination of tracer (111Cd) cadmium and natural cadmium in soil column effluents with ICP-MS

In laboratory-scale migration experiments a tracer (stable 111 Cd isotope) is added on top of a contaminated soil and the column effluents are fractionally collected. This paper describes an analytical method for the simultaneous low level quantitative determination with inductively coupled plasma mass spectrometry (ICP-MS) of contaminant (natural) and tracer ( 111 Cd) cadmium in soil column effluents by adaptation of the isotope dilution equation. For the calculation of the full uncertainty on the quantitative determination of tracer and natural cadmium, a method has been proposed emphasising the practical, realistic approach of estimating uncertainties based on statistical assumptions. The GUM Workbench© program, the computations of which follow the rules of the ‘ISO guide to the expression of uncertainty in measurement’, was used. At low concentrations of cadmium (<0.2 ng ml –1 Cd) the uncertainty due to counting statistics is the major source of uncertainty. At higher concentrations the signal instability of the ICP-MS instrument, partially due to clogging of the sampling cone by calcium salts present in the leachant (1 mM CaCl 2 ), forms the largest contribution to the total uncertainty. For concentrations of 0.5 ng ml –1 Cd and higher, the expanded uncertainty U amounts to ±4% (coverage factor 2; 95% probability).

Do ICP-MS based methods fulfill the EU monitoring requirements for the determination of elements in our environment?

Undoubtedly, the most important advance in the environmental regulatory monitoring of elements of the last decade is the widespread introduction of ICP-mass spectrometry (ICP-MS) due to standards developed by the European Committee for Standardization. The versatility of ICP-MS units as a tool for the determination of major, minor and trace elements (Al, As, Ba, Ca, Cd, Co, Cr, Cu, Fe, Hg, K, Mg, Mn, Mo, Na, Ni, P, Pb, Sb, Se, Sn, Ti, V and Zn) in surface water, groundwater, river sediment, topsoil, subsoil, fine particulates and atmospheric deposition is illustrated in this paper. Ranges of background concentrations for major, minor and trace elements obtained from a regional case study (Flanders, Belgium) are summarized for all of these environmental compartments and discussed in the context of a harmonized implementation of European regulatory monitoring requirements. The results were derived from monitoring programs in support of EU environmental quality directives and were based on a selection of (non-polluted) background locations. Because of the availability of ICP-MS instruments nowadays, it can be argued that the main hindrance for meeting the European environmental monitoring requirements is no longer the technical feasibility of analysis at these concentration levels, but rather (i) potential contamination during sampling and analysis, (ii) too limited implementation of quality control programs, validating the routinely applied methods (including sampling and low level verification) and (iii) lack of harmonization in reporting of the chemical environmental status between the individual member states.