Katarzyna Pytlakowska

Determination of rare earth elements by spectroscopic techniques: a review

An overview of publications focussed on the period since 2000 and outlining modern methods of sample preparation as well as advanced techniques for determination of rare earth elements (REE) in various matrices is presented in this paper. The review discusses the problems of REE determination in diverse samples i.e. from biological through environmental and geological to advanced materials. The preferable procedure of sample digestion and the most frequently applied methods of sample preparation for determination of trace elements are discussed in this paper. The case of direct analysis of samples for REE determination is also discussed. The review outlines determination of REE employing many techniques such as, inter alia, flame or graphite furnace atomic absorption spectrometry, atomic absorption with chemical vapor generation, X-ray fluorescence spectrometry, inductively coupled plasma optical emission spectrometry, inductively coupled plasma mass spectrometry and neutron activation analysis. This article summarizes and classifies materials in which rare earth elements are present, main places of their occurrence and the methods of their analysis.

Multi-element analysis of mineral and trace elements in medicinal herbs and their infusions

Twelve mineral and trace elements (Al, B, Ba, Fe, Zn, Mn, Mg, K, Na, P, Cu, Sr, and Ca) were determined in the herbs and their infusions consumed for medical purposes in Poland such as chamomile (Matricaria chamomilla L.), peppermint (Mentha xpiperita), melissa (Melissa officinalis), sage (Salvia officinalis), nettle (Urtica dioica), linden (Tilia vulgaris) and St. Johns wort (Hypericum calycinum). Dry digestion procedure for total concentration and wet digestion procedure for infusions were applied under optimized conditions for dissolution of medicinal herbs. Element concentrations in herbs and their infusions were determined by ICP-OES. The accuracy and precision were verified against NCS DC 73349 - bush branches and leaves certified reference material. The result of total concentrations of elements in herb leaves shows that all herbs contain most of the elements, except K and P, in the μg/g range, and that elemental concentrations varied widely. Moreover, on the basis of experimental results for the extraction efficiencies, the elements in herb infusions were classified into three specific groups: highly-extractable (>55%) including K; moderately-extractable (20-55%) including Mg, Na, P, B, Zn and Cu and poorly-extractable (<20%) including Al, Fe, Mn, Ba, Ca and Sr. The results of analysis were evaluated statistically using ANOVA one-way and three-way analysis of variance, variance correlation test and Spearmans test.

Liquid-phase microextraction as an attractive tool for multielement trace analysis in combination with X-ray fluorescence spectrometry: an example of simultaneous determination of Fe, Co, Zn, Ga, Se and Pb in water samples

In recent years, liquid-phase microextraction (LPME) has become one of the most valuable techniques for the preconcentration and separation of trace and ultratrace elements. LPME can be combined with an atomic technique which requires only a few microlitres of liquid to perform a measurement, e.g. electrothermal atomic absorption spectrometry. In this study, combining LPME with X-ray fluorescence spectrometry (XRF), a dried-spot technique is proposed. Since the X-ray beam can be focused on a small spot size and simultaneously LPME produces a very small drop of a volume ranging from 2 to 30 μL, the combination of these two techniques is a very promising tool for multielement trace and ultratrace analyses. The present research was performed using dispersive liquid–liquid microextraction (DLLME) with APDC as a chelating agent. Nevertheless, any LPME technique, e.g. single-drop microextraction (SDME), can be applied in combination with XRF. Because XRF measurement follows the microextraction, deposition and drying of the small drop, the influence of the diameter of the dried residue on the intensity of fluorescent radiation is discussed in detail. Pipetting and spray-on techniques are proposed for the deposition of the small drop onto the substrate (membrane filter or Mylar foil). Under the optimized conditions, the detection limits were 2.8, 1.6, 2.5, 1.7, 2.1 and 4.1 ng mL−1 for Fe, Co, Zn, Ga, Se and Pb, respectively, with a preconcentration factor of 250 for 5 mL of the water sample.

Speciation of inorganic chromium in water samples by energy dispersive X-ray fluorescence spectrometry

A simple and effective speciation procedure for the determination of inorganic chromium species in water samples was developed. The method is based on the combination of dispersive micro solid-phase extraction (DMSPE) and energy dispersive X-ray fluorescence spectrometry (EDXRF). In this system graphene oxide nanoparticles were used as solid sorbents for preconcentration of Cr(III) species. After the reduction of Cr(VI) ions with concentrated H2SO4 and ethanol, the procedure was applied for the determination of the total chromium concentration. The Cr(VI) content was calculated from the difference between the total chromium and Cr(III) concentration. In order to obtain the best recovery of Cr(III) ions some parameters affecting the sorption process, including pH, amount of graphene oxide, sample volume and sorption time, were investigated. Under optimal preconcentration conditions a detection limit of 0.06 ng mL−1 with a relative standard deviation lower than 1.7% for Cr(III) determination was obtained. A linear response between the chromium concentration and fluorescent radiation intensity was achieved in the 1–150 ng mL−1 range with a recovery of 98 ± 3%. The proposed method was successfully applied to the speciation of trace chromium in water samples. The accuracy of the developed system was tested with the use of samples spiked with a known concentration of the studied element and by the determination of the total chromium concentration in the certified material NIST 1640a (trace elements in natural water).

Glycine modified graphene oxide as a novel sorbent for preconcentration of chromium, copper, and zinc ions from water samples prior to energy dispersive X-ray fluorescence spectrometric determination

A novel and selective sorbent for micro-solid phase extraction was synthesized by chemical functionalization of graphene oxide with glycine. The structure of this nanomaterial, referred to as GO-Gly, was confirmed by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy. GO-Gly was used for preconcentration of chromium, zinc, and copper ions from water samples prior to their determination by energy dispersive X-ray fluorescence spectrometry (EDXRF). The proposed procedure is based on dispersion of micro amounts of GO-Gly in aqueous samples. After adsorption of metal ions on its surface, samples were filtered under vacuum and then membrane filters were directly submitted to energy dispersive X-ray fluorescence spectrometric measurements. In order to obtain optimal preconcentration conditions, some parameters affecting sorption process, such as pH, amount of GO-Gly, sorption times, and sample volume, were examined. Under optimal conditions the calibration curves were linear in a 1–150 ng mL−1 range with recoveries higher than 97%. The obtained detection limits for Cr(III), Zn(II), and Cu(II) determinations are 0.15, 0.07, and 0.08 ng mL−1, respectively. A relative standard deviation of the proposed procedure (at a 10 ng mL−1 level for n = 10) is lower than 2.3%. The proposed method was successfully applied for determination of Cr(III), Zn(II), and Cu(II) ions in water samples.

Energy-dispersive X-ray spectrometry combined with directly suspended droplet microextraction for determination of dissolved silicate in surface water via silicomolybdenum blue complex

Energy-dispersive X-ray fluorescence spectrometry (EDXRF) is a well-established analytical technique successfully applied with good precision and accuracy to determination of many elements. However, in the case of elements of low atomic number, such as silicon, direct determination is hampered due to low fluorescence yield and relatively low energy easily absorbed by sample matrix. An indirect method for determining surface water silicate is thus proposed. The method is based on silicate determination via molybdenum present in silicomolybdenum blue complex. Determination follows directly suspended droplet microextraction. Optimum conditions for both microextraction and EDXRF measurement were studied. A good ratio of silicon to molybdenum (1-41) and a sensitive Kα line of molybdenum make it possible to determine low concentrations of silicate. Under optimized conditions, good linearity, up to 3 μg mL(-1) (r=0.9990), and good detection limit (6 ng mL(-1)) were achieved. The total RSD for the EDXRF determination of silicate following DSDME was 6.7%. Taking into account all steps preceding the determination and the uncertainty of XRF measurements, the proposed method can be recognized as precise. The enrichment factor was 140. The developed method was used to determine dissolved silicate content in surface water samples. The accuracy and repeatability of the proposed procedure were checked by standard addition method and compared to the results obtained using ICP-OES technique. The recovery (92.2-96%) was satisfactory and indicates usefulness of the developed procedure.

Antioxidant Activity of Selected Thyme (Thymus L.) Species and Study of the Equivalence of Different Measuring Methodologies.

This study presents the results of comparative evaluation of the antioxidant activity of the phenolic fraction exhaustively extracted with aqueous methanol from 18 different thyme (Thymus L.) specimens and species. This evaluation is made with use of the same free radical source (DPPH• radical), three different free radical scavenging models (gallic acid, ascorbic acid, and Trolox), and three different measuring techniques (the dot blot test, UV-Vis spectrophotometry, and electron paramagnetic resonance spectroscopy, EPR). A comparison of the equivalence of these three different measuring techniques (performed with use of hierarchical clustering with Euclidean distance as a similarity measure and Wards linkage) is particularly important in view of the fact that different laboratories use different antioxidant activity measuring techniques, which makes any interlaboratory comparison hardly possible. The results obtained confirm a semiquantitative equivalence among the three compared methodologies, and a proposal is made of a simple and cost-effective dot blot test that uses the DPPH• radical and provides differentiation of antioxidant activity of herbal matter comparable with the results of the UV-Vis spectrophotometry and EPR.

A study on adsorption of metals by activated carbon in a large-scale (municipal) process of surface water purification

AbstractElements that enter the aquatic environment may pose a health risk to wildlife and humans. The aims of this study were: to determine how the introduction of activated carbon for a water purification system will improve the quality of the water produced; and to investigate the sorption of metals on activated carbons, including determination of the accumulation, as well as changes in concentrations of elements in carbons. The tests were carried out on three types of activated carbons with different granular structure. All samples were collected from Water Treatment Plant Goczalkowice, Poland. Concentrations of elements were measured using an optical emission spectrometer with inductively coupled plasma. The experiment showed that metals accumulating in the activated carbons during the operation included: Ca, Mn, Zn, and Cu. In each of the three types of carbons, it can distinguish such elements as Ba, Al, Cr, Ni, Ti, which are characterized by irregular accumulation during the operation of the filter. The introduction of carbon sorbent for water treatment largely contributed to improvement in the quality of raw material supplied to customers, mainly with regard to taste and smell, as well as to reduction of basic parameters: color, absorbance in the UV range and oxidability.

Energy-dispersive X-ray fluorescence spectrometry combined with dispersive liquid–liquid microextraction for simultaneous determination of zinc and copper in water samples

A dispersive liquid–liquid microextraction technique was successfully used as a sample preparation method for determination of trace amounts of zinc and copper ions in surface water by energy-dispersive X-ray fluorescence spectrometry (EDXRF). The extraction method is based on the formation of sparingly soluble in water complexes of Zn and Cu with 2-(5-bromo-2-pyridylazo)-5-diethylamino-phenol (5-Br-PADAP). Some effective parameters of extraction and complex formation, such as extraction and disperser solvent type and their volume, pH, concentration of the chelating agent, and salt effect, have been optimized. Under the optimum conditions, the enrichment factor 250 was obtained from only 5 mL of a water sample. The calibration graph was linear from 0.02 to 0.4 μg mL−1 with detection limits of 1.8 ng mL−1 and 1.7 ng mL−1 for copper and zinc, respectively. The total RSD values for the EDXRF determination of Cu and Zn ions were 6.7% and 6.9%. Taking into account all steps preceding the determination and the uncertainty of EDXRF, the proposed method can be recognized as precise. The accuracy and repeatability of the proposed procedure were checked by the standard addition method and compared to the results obtained using the ICP-OES technique. The recovery in the range 91–95% was satisfactory and indicated the usefulness of the developed procedure.

Directly suspended droplet microextraction combined with energy-dispersive X-ray fluorescence spectrometry to determine nano levels of phosphate in surface water

Directly suspended droplet microextraction (DSDME) for determination of phosphate by energy-dispersive X-ray fluorescence spectrometry (EDXRF) is proposed. The method is based on the determination of phosphate, through molybdenum in the phosphomolybdenum blue complex. Because phosphorus is determined indirectly via molybdenum fluorescent radiation the difficulties of low fluorescent yield and low energy of phosphorus radiation are successfully overcome. A good ratio of phosphorus to molybdenum (1 to 37) and a sensitive Kα line of molybdenum give the possibility to determine a low concentration of phosphorus. Under the optimized conditions, good linearity, up to 20 μg of phosphorus (r = 0.9995), and the detection limit (2.8 ng mL−1) for the sample of 1.5 mL were achieved. The total RSD for the EDXRF determination of phosphorus followed by DSDME was 2.6% and taking into account all steps preceding the determination and the uncertainty of EDXRF measurements, the proposed method can be recognized as highly precise. The enrichment factor was equal to 56.8. The developed method was used to determine the total phosphorus content in surface waters. The accuracy and repeatability of the proposed procedure were checked by the standard addition method. The recovery in the range 93.5–97% was satisfactory and indicated the usefulness of the developed procedure.