Valentina Lyubomirova

Multielement Analytical Spectroscopy in Plant Ionomics Research

Abstract: The study of the ionome (ionomics) is defined as quantitative and simultaneous measurement of the element composition of living organisms and changes in this composition in response to physiological stimuli, development stage, and genetic modifications (Salt et al., Ann. Rev. Plant Biol., Vol. 59, 2008). The necessity of understanding the regulation processes of elements in the organisms demands determination of many elements in the organism, tissue, and cell (Baxter, Plant Biol., Vol. 12, 2009). A prospect for ionomics is environmental pollution where great variety of conditions and pollutants exist resulting in concentration and interelemental changes in the plant ionome. The capabilities of and problems with several multielement analytical techniques, including instrumental neutron activation analysis (INAA), X-ray fluorescence, inductively coupled plasma–atomic emission spectrometry (ICP-AES), inductively coupled plasma–mass spectrometry (ICP-MS), and atomic absorption spectrometry (AAS), which are adequate and most promising in ionomic and environmental studies of plants, are reviewed. References are confined mainly to the last 10–15 years. Information about concentrations, roles, binding forms, and pollution sources of the elements and comparison between methods with respect to limits of detection, determined elements, interferences, and economic considerations are tabulated. Some combinations of instrumental techniques supplementing each other are highly valued, namely, ICP-MS and ICP-AES and INAA and AAS or ICP-AES.

Optimization of sample preparation and ICP-MS analysis for determination of 60 elements for characterization of the plant ionome

An ICP-MS method for determination of 60 elements in plant samples is proposed based on optimization of digestion, recommending use of HF besides HNO3 and H2O2 and calibration procedures, using CRMs for construction of calibration curves. Adequate choice of analytical isotopes and various measurement conditions (cold plasma for the determination of Al, Ba, Ca, Fe, K, Mg, Mn, Na, Si and Sr and DRC mode for determination of Ag, As, Ni, Pd, Pt, Se and V) as well as introduction of appropriate corrections lead to determination of as large number of elements with quadropole ICP-MS as with the more expensive SF-ICP-MS. Two measurements are performed: cold plasma and standard/DRC mode. The analytical characteristics of the method are demonstrated by analysis of five CRMs and the agreement of the experimental results with the certified/information/literature values is very good. Detection limits are low enough to permit the determination of all elements but platinum metals at background level. The applicability of the method is demonstrated by analysis of Taraxacum officinale (dandelion) samples collected from regions with different anthropogenic influence. The results indicate high degree of pollution round the Pb-Zn smelter with As, Cd, Cu, Ni, Pb and Zn and increased concentrations of B, Be, Bi, Hg, In, Mn, Sb, Se, Sn, Ti, Tl, V and Zr. The dandelion sample, collected along a highway has increased concentrations of traffic released elements: Pt, Pd, Rh, Ce, La, Pb as well as Cu, Zn, Ba and Rb.

Mass spectrometric techniques for characterisation of platinum–humic substance complexes in soil and street dust samples

Abstract Increased platinum concentrations have been detected in environmental samples since the introduction of catalytic converters in Europe. It was previously believed that PGE are relatively inert and that the soluble fraction of automobile catalyst emitted PGE is only a few percent. However, new studies suggested that metallic Pt is oxidised in the soil and that the majority of the Pt species could be humic substance complexes. The aim of the present paper is the characterisation of platinum-humic acid complexes in spiked soil and street dust samples. A number of different soft ionisation mass spectrometric techniques, such as ESI-Q-MS, ESI-ION TRAP-MS and MALDI-TOF-MS have been tested. The ESI mass spectra of the soil humic acids were characterised by high complexity and irreproducibility. MALDI-TOF-MS was used for humic acid complexes characterisation in positive and negative modes. Positive ionisation was less effective and produced more simple and less informative spectra than negative ionisation. Two different MALDI matrices (CHCA, DHBA) were tested for use with humic substances. DHBA yielded better results, exhibiting superior ionisation efficiency, low spectral background and the matrix peaks were almost completely suppressed causing no interferences with identified analyte peaks. The application of MALDI-TOF-MS shows its suitability for humic substance characterisation. The comparison of the MALDI-spectra of humic acids, extracted from spiked and native soil proved that Pt undergoes transformation in the environment to humic acid complexes.

Identification of Pt and Pd bound to humic acid species in spiked soils and street dusts by size exclusion chromatography and ICP-MS

Abstract The formation of PGE-humic acid (HA) complexes in soil and street dust samples was investigated. In order to assess the distribution of Pt and Pd among molecular weight fractions of humic substances, the HA extracts (extracted by 0.1 mol L−1 sodium pyrophosphate) were analysed by size exclusion chromato-graphy coupled on-line with UV-Vis detection. Similar chromatograms were obtained for soils and street dust samples (254 nm, 280 nm) and two size fractions were operationally defined as high (1600–5000 Da) and low molecular (< 1600 Da) HA fractions. The concentration of Pt and Pd in the separated extracts was determined by ICP-MS. The results indicate that up to 43% of Pt is in the high molecular and up to 52% in the low molecular HA fraction. In both type of soil samples, Pd is preferentially bound to the low molecular HA fraction. Dependence of Pd–HA and Pt–HA formation on the sample type both in the soils and in the street dust sample as well as on Pt oxidation state was established. Metallic Pt shows a tendency for complexation with the fractions of HA higher than 5000 Da. In the street dust samples, the distribution of Pt and Pd is similar and is strongly dependent on the sample type, being bound mainly to the fractions: higher than 5000 Da, 1600–5000 Da and the fraction lower than 1600 Da.

Accumulation and Distribution of Pt and Pd in Roadside Dust, Soil and Vegetation in Bulgaria

The concentration of Pt and Pd in Bulgaria resulting from traffic pollution has never been investigated. Samples of roadside dust, soils and Taraxacum officinale, collected along highways, some major and secondary roads and a smelter region during the summer of 2012 are analyzed by ICP-MS. The comparison to literature values shows that the average concentrations in road dusts along Bulgarian roads are lower than the average for Pt and around the average for Pd. Hotspots with concentrations of Pd up to 800 ng/g and Pt up to 220 ng/g were established. The transfer factors (plant/soil) determined in the present study and the results form the analysis of washed and unwashed plant samples give a serious indication that a substantial part of Pt and Pd, released into the environment enters the plants.

Effects of soil properties and anthropogenic activity on the transfer of 52 elements in the system soil/Taraxacum officinale

PurposeIt is commonly assumed that the concentration of an element in a plant relates linearly to its concentration in the soil. However, the wide range of reported transfer factors shows that soil concentration of the element is not the only factor influencing its uptake. Recently, the transfer of elements from polluted soils to plants is recognized as a serious problem with a potential impact on human and animal health. The aim of the present research was to combine different factors: soil characteristics, anthropogenic influence, and fractionation of elements for evaluation of their influence on the soil-plant transfer of the elements.Materials and methodsUsing inductively coupled plasma mass spectrometry (ICP-MS), the concentrations of 52 elements were determined in 27 types of soils after microwave aqua regia digestion. The soil samples were collected from 12 background regions and 15 sites in Bulgaria with different anthropogenic influence. The bioavailability of the elements was established applying BRC sequential extraction scheme. Cluster and factor analyses were performed using STATISTICA 7.0 software package. The estimation of accuracy was done by the analysis of five standard reference materials: reference stream sediments STD-1, STD-3 and STD-4 (Canada Center for Mineral and Energy Technology, Geological Survey of Canada), IAEA Soil-5, and IAEA-Soil-7.Results and discussionThe bioavailable part of the majority of essential elements: B, Ca, Mg, Mn, Na as well as Sr was mainly found in the carbonate and easily available fraction of Ba, Cd, Co, Ni, Rb, V, Zn—in the oxide fraction, but Cd, Co, Ni, and Zn were also found in a similar percentage in the organic/sulfide fraction. The rest of the elements were in the organic/sulfide fraction. Cluster and factor analyses revealed the interelement correlations and relations in the investigated soils, as well as the dependence of transfer factors (TFs) on the pseudo total soil concentration, concentration of the element in the soil fractions, pH, cation exchange capacity (CEC), and the organic carbon content.ConclusionsThe investigation of the bioavailability of 52 elements in 27 soils and the transfer in the system soil/Taraxacum officinale established that for the majority of the elements, the TF is stable irrespective of the type of soil and pollution. This confirms the linearity assumption and indicates that the plant species is a very important parameter. The fractionation analysis proved that in polluted regions, the major polluting elements are more bioavailable than in clean regions.