X-ray fluorescence spectrometry for environmental analysis: Basic principles, instrumentation, applications and recent trends.

In recent years, the conceptual advancement on green analytical chemistry (GAC) has moved in parallel with efforts to incorporate new screening or quantitative low-cost analytical tools to solve analytical problems. In this sense, the role of solid state techniques that allow the non-invasive analysis (or with a minimum sample treatment) of solid samples cannot be neglected. This review describes the basic principles, instrumentation and advances in the application of X-ray fluorescence instrumentation to the environmental sciences research topics, published between 2006 and 2020. Obviously, and because of the enormous number of works that can be found in the literature, it is not possible to exhaustively cover all published articles and the diversity of topics related to the environment in which a solid state technique like XRF has been applied successfully. It is a question of making a compilation of the instrumentation in use, the significant advances in XRF spectrometry and sample treatment strategies to highlight the potential of its implementation for environmental assessment.

Application of benchtop total-reflection X-ray fluorescence spectrometry and chemometrics in classification of origin and type of Croatian wines.

The contents of selected metals (K, Ca, Fe, Cu, Zn, Mn, Sr, Rb, Ba, Pb, Ni, Cr and V) in 70 wine samples from Continental and Adriatic part of Croatia and different types of wine (red and white) were determined by TXRF. The aim of this study was to compare the elemental composition of wines from two different regions and to determine the discriminant ability of each variable and to indicate which variables discriminate between the four categories considered. Principal component analysis and cluster analysis showed that K, Mn, Ba and Ni can be considered as the most important characteristics to distinguish between Continental red and white wines, Rb, Ni and Ba for Continental red and Adriatic red wines while Sr is the only metal that completely distinguishes the samples of each category. Finally, linear discriminant analysis showed good recognition (100%) and prediction abilities (96.43%) using these selected elements.

Analytical potential of total reflection X-ray fluorescence (TXRF) instrumentation for simple determination of major and trace elements in milk powder samples.

In this contribution, the analytical potential of total reflection X-ray fluorescence (TXRF) instrumentation has been evaluated for the determination of major and trace elements in milk powder. TXRF allows the possibility of direct analysis of solid suspensions without the need for a digestion process and therefore it can be a potential analytical candidate for simple and cost-effective analysis. A detailed study to select sample preparation and measurements conditions was carried out. Different quantification approaches (including internal standardization and empirical calibration) were also tested. Finally, the developed TXRF methods (W anode) were validated by a strict comparison with the data from the reference methods on a set of twenty-three samples using robust statistics. Results showed that acceptable results can be obtained for K, Ca, Fe and Zn determination if using adequate calibration approaches. Otherwise, only screening results can be obtained for light elements (P and Cl) in milk powder samples.

Analytical potential of total reflection X-ray fluorescence spectrometry for simultaneous determination of iron, copper and zinc in human blood serum and plasma.

Due to many roles of trace elements such as Fe, Cu and Zn in various physiological and pathophysiological processes, their determination in serum and plasma is of high clinical relevance. In the present study, for the first time, the effect of serum and plasma preparation parameters (dilution factor and sample deposition volume) on the quality of results obtained by TXRF analysis was evaluated by means of experimental design tools (response surface analysis). It was found that the best strategy was the direct analysis of both human fluids without a previous dilution step. The accuracy and precision of the proposed methods were evaluated by analysis of reference materials (ClinChek® Plasma Control Level II and Seronorm™ Trace Elements Serum L-1). TXRF results agreed with the reference values and no significant differences at 95% confidence level were found. Limits of detection for the elements of interest were also adequate, taking into account their typical concentration ranges in real serum and plasma samples. Finally, the developed TXRF methods were applied to a set of serum and plasma samples from patients with different genders, ages and diagnoses, previously analysed by ICP-OES and ICP-MS techniques. The results showed good agreement between both analytical approaches. These results suggest that the proposed TXRF method provides reliable results thus being suitable for plasma and serum analysis, but in a simpler and more sustainable way.

Possibilities and drawbacks of total reflection X-ray fluorescence spectrometry as a fast, simple and cost-effective technique for multielement analyses of cosmetics.

This paper shows a simple, rapid and cost-effective method for multielement analyses of cosmetics. Total reflection X-ray fluorescence spectrometry (TXRF) is used to determine the composition, particularly the presence of potentially toxic elements, of cosmetics. Three sample preparation methods based on suspension preparation were developed for different types of cosmetic samples, e.g. lipsticks, eye shadows and body creams. Limits of detection within the low mg kg-1 range were obtained and enabled cosmetic screening for compliance with the legal thresholds for some major toxic elements. A good accuracy of the results on a wide range of concentration levels (>10000 mg kg-1) was found without the need of sample dilution. Results obtained for most elements in the lipstick and cream samples agreed with those obtained by the reference method recommended by the Food and Drug Administration, based on using inductively coupled plasma techniques after microwave digestion. However, for eyeshadow analysis, a more sophisticate approach is needed to improve the analytical results.

Presence, mobility and bioavailability of toxic metal(oids) in soil, vegetation and water around a Pb-Sb recycling factory (Barcelona, Spain).

The work was conducted to establish contamination from improper disposal of hazardous wastes containing lead (Pb) and antimony (Sb) into nearby soils. Besides other elements in the affected area, the biological role of Sb, its behaviour in the pedosphere and uptake by plants and the food chain was considered. Wastes contained 139532 ±â€¯9601 mg kg-1 (≈14%) Pb and 3645 ±â€¯194 mg kg-1 (≈0.4%) Sb respectively and variability was extremely high at a decimetre scale. Dramatically high concentrations were also found for As, Cd, Cu, Mn, Ni, Sn and Zn. In adjacent natural soils metal(oid)s amounts decreased considerably (Pb 5034 ±â€¯678 mg kg-1, Sb 112 mg kg-1) though largely exceeded the directives for a given soil use. Metal(oid)s potential mobility was assessed by using H2O→KNO3→EDTA sequential extractions, and EDTA extracts showed the highest concentration suggesting stable humus-metal complexes formation. Nevertheless, selected plants showed high absorption potential of the investigated elements. Pb and Sb values for Dittrichia viscosa grown in wastes was 899 ±â€¯627 mg kg-1 and 37 ±â€¯33 mg kg-1 respectively. The same plant showed 154 ±â€¯99 mg kg-1 Pb and 8 ±â€¯4 mg kg-1 Sb in natural soils. Helichrysum stoechas had 323 ±â€¯305 mg kg-1 Pb, and 8 ±â€¯3 mg kg-1 Sb. Vitis vinifera from alongside vineyards contained 129 ±â€¯88 mg kg-1 Pb and 18 ±â€¯9 mg kg-1 Sb, indicating ability for metal uptake and warning on metal diffusion through the food chain. The biological absorption coefficient (BAC) and the translocation factor (TF) assigned phytoextraction potential to Dittrichia viscosa and Foeniculum vulgare and phytostabilization potential to Helichrysum stoechas. Dissolved metal (oid)s in the analysed water strongly exceeded the current directive being a direct threat for livings. Data warned against the high contamination of the affected area in all its compartments. Even though native plants growing in metal-contaminated sites may have phytoremediation potential, high risk of metal diffusion may threat the whole ecosystem.

Long-term use of biosolids as organic fertilizers in agricultural soils: potentially toxic elements occurrence and mobility.

The presence of potentially toxic elements (PTEs) may hinder a more widespread application of biosolids in agriculture. At present, the European Directive 86/278/CEE limit the total concentrations of seven metals (Cu, Cr, Ni, Pb, Zn, Cd and Hg) in agricultural soils and in sewage sludges used as fertilizers but it has not taken into consideration the potential impacts of other emerging micropollutants that may be present in the biosolids as well as their mobility. The aim of this study was to evaluate the accumulation and mobility of 13 elements (including regulated metals and other inorganic species) in agricultural soils repeatedly amended with biosolids for 15 years. Firstly, three digestions programs using different acid mixtures were tested to evaluate the most accurate and efficient method for analysis of soil and sludge. Results demonstrated that sewage sludge application increased concentrations of Pb and Hg in soil, but values did not exceed the quality standard established by legislation. In addition, other elements (As, Co, Sb, Ag, Se and Mn) that at present are not regulated by the Spanish and European directives were identified in the sewage sludge, and significant differences were found between Ag content in soils amended with biosolids in comparison with control soils. This fact can be related to the increasing use of silver nanoparticles in consumer products due to their antibacterial properties. Results from the leaching tests show up that, in general, the mobility degree for both regulated and non-regulated elements in soils amended with biosolids was quite low (<10 %).

Analytical possibilities of total reflection X-ray spectrometry (TXRF) for trace selenium determination in soils.

Selenium content of soils is an important issue due to the narrow range between the nutritious requirement and toxic effects upon Se exposure. However, its determination is challenging due to low concentrations within complex matrices that hamper the analysis in most spectroscopic techniques. In this study, we explored the possibilities of several analytical approaches combined with total reflection X-ray (TXRF) spectrometry for soil Se determinations. The direct analysis of a solid suspension using 20 mg of fine ground material (<50 µm) has a relatively high Se limit of detection (LOD) of 1 mg/kg (worldwide Se average in soils = 0.4 mg/kg) and is therefore only suitable for seleniferous soils. Several fast and simple analytical strategies were developed to decrease matrix effects and improve the LOD for Se determination in soil digests. On one hand, the application of a liquid-liquid extraction procedure using ethyl ether and the introduction of a Cr absorbent in the instrument configuration were carried out to avoid the associated problems on TXRF analysis of soil extracts due to the high Fe concentrations (∼700 mg/L). On the other hand, a dispersive liquid-liquid microextraction procedure (DLLME) before the TXRF analysis of the soil digest was also developed. The effects of various experimental parameters such as sample volume, effect of major elements present in the soil matrix (Fe), and Se concentration in the sample were investigated. The LOD using this analytical methodology (0.05 mg/kg of Se) was comparable to or lower than those obtained in previous works using other popular spectrometric techniques such as GFAAS, ICPMS, and AFS. The calculated Se concentration for JSAC-0411 ([Se] = 1.32 ± 0.27 mg/kg) using the combination of DLLME and TXRF ([Se] = 1.40 ± 0.23 mg/kg) was in agreement with the certified value.

Analytical approaches for Hg determination in wastewater samples by means of total reflection X-ray fluorescence spectrometry.

At present, there is a considerable interest in Hg monitoring in wastewater samples due to its widespread occurrence and the high toxicity of most of its compounds. Hg determination in water samples by means of total reflection X-ray fluorescence spectrometry (TXRF) entails some difficulties due to the high vapor pressure and low boiling point of this element that produce evaporation and loss of Hg from the surface of the reflector during the drying process, commonly used for sample preparation in TXRF analysis. The main goal of the present research was to develop a fast and simple chemical strategy to avoid Hg volatilization during the analysis of wastewater samples by TXRF spectrometry. Three different analytical procedures were tested for this purpose: (i) increasing the viscosity of the wastewater sample by adding a non-ionic surfactant (Triton X-114), (ii) Hg immobilization on the quartz reflectors using the extractant tri-isobutylphosphine (Cyanex 471X) and (iii) formation of a stable and non-volatile Hg complex into the wastewater sample. The best analytical strategy was found to be the formation of a Hg complex with thiourea (pH=10) before the deposition of 10 microL of sample on the reflector for following TXRF analysis. Analytical figures of merit such as linearity, limits of detection, accuracy and precision were carefully evaluated. Finally, the developed methodology was applied for the determination of Hg in different types of wastewater samples (industrial effluents, municipal effluents from conventional systems and municipal effluents from constructed wetlands).

Analysis of inlet and outlet industrial wastewater effluents by means of benchtop total reflection X-ray fluorescence spectrometry.

The monitoring of heavy metals in industrial waste water effluents is an important activity in many laboratories. Of special interest is the screening of elemental composition of inlet effluents and quantitative analysis of outlet effluents to study the efficiency of chemical treatment process to eliminate metals and to comply with current established concentration limits, respectively. In this sense, fast analytical methodologies which entail simple sample preparation are desired. In the present work, the possibilities and drawbacks of a benchtop total reflection X-ray fluorescence spectrometer (TXRF) for the rapid and simple determination of some inorganic impurities (As, Ba, Cd, Cu, Cr, Sn, Fe, Mn, Ni, Pb, Se and Zn) in inlet and outlet industrial waste water effluents from metallurgical and tanning leather factories have been tested. An evaluation of different simple sample treatments is presented and it is followed by a discussion of spectral and chemical matrix effects when dealing with this type of samples. Analytical figures of merit such as accuracy, precision and limits of detection have also been carefully studied. Finally, the data obtained by direct TXRF analysis has been compared to that obtained by ICP-OES/ICP-MS after a microwave digestion.

Application of small-spot energy dispersive X-ray fluorescence instrumentation in phytoremediation activities around metal mines.

In view of the considerable number of analyses necessary in phytoremediation and plant biology studies, it is important that the analytical procedures used for elemental determination in plant tissues should be fast and cheap, with simple sample preparation, and of adequate accuracy and precision. The aim of the present work was focused on the possibilities and drawbacks of a low-cost benchtop energy dispersive X-ray fluorescence (EDXRF) instrument to be used as an analytical technique for studying the potential use of sunflowers (Helianthus annuus) for the phytoremediation of an abandoned Pb/Zn mining area. The simplicity and the ability to operate at room temperature and open air conditions provides a flexible setup for the rapid analysis of vegetation material without complicated previous sample pretreatments. With the help of different collimator caps, a modest lateral resolution (from 200 mum to 1 mm) was achieved and it was thought to be small enough to study the accumulation of Pb and Zn and its distribution between parts of the vegetation specimens (roots, stems, and leaves); the limits of detection achieved (0.6 ng for Zn and 3.0 ng for Pb) proved to be suitable for the intended purpose. Therefore, obtained data revealed that EDXRF spectrometry could be a useful tool to better understand the metal uptake, translocation, and tolerance mechanisms in vegetation species related to biomonitoring and phytoremediation studies.

Method for the determination of Pd-catalyst residues in active pharmaceutical ingredients by means of high-energy polarized-beam energy dispersive X-ray fluorescence.

In medicinal chemistry, Pd is perhaps the most-widely utilized precious metal, as catalyst in reactions which represent key transformations toward the synthesis of new active pharmaceutical ingredients (APIs). The disadvantage of this metal-catalyzed chemistry is that expensive and toxic metal residues are invariably left bound to the desired product. Thus, stringent regulatory guidelines exist for the amount of residual Pd that a drug candidate is allowed to contain. In this work, a rapid and simple method for the determination of Pd in API samples by high-energy polarized-beam energy dispersive X-ray fluorescence spectrometry has been developed and validated according to the specification limits of current legislation (10 mg kg(-1) Pd) and the International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH guidelines). Sample and calibration standards preparation includes a first step of homogenization and then, in a second step, the pressing of the powdered material into pellets without any chemical treatment. The use of several synthetic calibration standards made of cellulose to simulate the API matrix appears to be an effective means to obtain reliable calibration curves with a good spread of data points over the working range. With the use of the best measuring conditions, the limit of detection (0.11 mg kg(-1) Pd) as well as the limit of quantitation (0.37 mg kg(-1) Pd) achieved meet rigorous requirements. The repeatability of the XRF measurement appeared to be less than 2%, while the precision of the whole method was around 7%. Trueness was evaluated by analyzing spiked API samples at the level of the specification limit and calculating the recovery factor, which was better than 95%. To study the applicability of the developed methodology for the intended purpose, three batches of the studied API were analyzed for their Pd content, and the attained results were comparable to those obtained by the daily routine method (acid digestion plus atomic spectroscopy) used in most pharmaceutical laboratories.

Heavy metals' content of automotive shredder residues (ASR): evaluation of environmental risk.

Every year between 8 and 9 millions of vehicles in the European Union arrive to their end of life. Car wastes can have a very high metal content, falling into hazardous waste class. A preliminary evaluation of these wastes could be made by metals' leaching test runs which is the main objective of the present study. Evaluation of the total metal content was carried out by X-ray fluorescence and the mobility of these metals using two simple standardized extractions such as the TCLP (Toxicity Characterisation Leaching Procedure) of the US EPA and the German leaching test DIN 38414-S4. Additionally, an extraction test with acetone was performed in order to recognise metals bounded to organic matter. The results show that the total metal content of the ASR can overpass the established values for inert residues. Lead and zinc contents are fairly well correlated with grain-size, whilst other metals' contents do not exhibit clear grain-size dependence.

Assessment of metal availability to vegetation (Betula pendula) in Pb-Zn ore concentrate residues with different features.

In this work, characterisation of several ore concentrate remains from an abandoned Pb-Zn mining factory was performed determining chemical and physical properties such as pH, organic carbon content, particle size distribution, total heavy metal content (Pb, Zn, Cu, As and Cd) as well as mineralogical composition which showed, in most cases, the oxidization of the parent ore material (mostly galena: PbS and sphalerite: ZnS) to more mobile fractions as anglesite (PbSO(4)) and goslarite (ZnSO(4)). Moreover, two operational defined extraction procedures commonly used in soil and sediment studies (first and second steps of BCR procedure and DTPA extraction protocol) were applied in the different mining wastes in order to study Pb and Zn mobility and likely bioavailability to Betula pendula growing on the same mining spoils, which presents lead and zinc contents in leaves over ten times background values.

Precise and accurate determination of lead isotope ratios in mining wastes by ICP-QMS as a tool to identify their source.

A methodology for a precise and accurate determination of lead isotope ratios in mining wastes by inductively coupled plasma quadrupole-based mass spectrometry (ICP-QMS) has been developed. The study of instrumental bias factors led to the conclusion that internal correction to compensate mass discrimination is required as well as an interference equation correction when Hg is present. The proposed method has been applied to determine lead isotope ratios in several mining wastes, soils and sediments collected at three mining areas in Spain (Aran Valley, Cartagena and Osor). Statistical analysis highlights that (206)Pb/(207)Pb and (208)Pb/(207)Pb lead isotope ratios can be used as a fingerprint of mining waste origin which is related to the geological age of the lead ore. On the other hand, no statistically significant isotopic differences between original ore samples (galena) and processing wastes within a mining district were found, corroborating a unique lead source. Moreover, the lead isotopic composition of soil and sediment samples collected at the studied mining areas is close to that determined in the mining tailings from the same areas, suggesting that the unusual high content of lead in these samples is derived from mining activities rather than from other lead sources.

Lead isotope ratio measurements by ICP-QMS to identify metal accumulation in vegetation specimens growing in mining environments.

The use of variations in stable Pb isotope ratios has become a well-established diagnostic technique for characterising sources of lead contamination. In this work, lead isotope ratios in mining wastes (lead content 320-130,000 mg kg-1) and vegetation specimens (lead concentration 7-650 mg kg-1) have been determined by inductively coupled plasma quadrupole-based mass spectrometry (ICP-QMS) in order to investigate lead bioaccumulation in Buddleia davidii growing on wastes from two abandoned Pb/Zn mining areas in Spain. The accuracy of the isotope ratio measurements was evaluated by analysing a certified isotopic standard NIST SRM 981. Good agreements were obtained between the lead isotope ratios measured and the certified values (deviations within 0.01-0.2%). The results indicate that the lead isotopic ratios in vegetation samples collected in the mining areas differed from those of a specimen from an uncontaminated site (control sample). However, close lead isotope ratio values were found between vegetation specimens and mining tailings. Therefore, the results suggest that lead in the collected vegetation specimens is most likely related to the influence of mining activities rather than to other sources like past leaded-petrol emissions.