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The need for elemental analysis in quality control of food, pharmaceuticals and cosmetics, taking into account human safety, has become an essential requirement for any product destinated for commercialization and targets in particular potentially toxic elements. The main objective is to obtain reliable data on elemental content that enables end-users to make informed decisions and to address problems effectively. To align with the principles of green and sustainable analytical chemistry, recent efforts have focused on incorporating new, low-cost screening and quantitative analytical tools such as total reflection X-ray fluorescence spectrometry (TXRF). This paper provides an overview of recent TXRF applications in the elemental analysis of food, pharmaceuticals, and cosmetic samples. The state-of-the-art procedures for sample preparation with details on the sample type and amount, dilution steps, mixing agents, analysed elements, and addition of internal calibration standards are presented together with analytical parameters such as limits of detection and quantification. The current challenges for applying TXRF to each of these research fields are discussed. [ABSTRACT FROM AUTHOR]

In view of the large number of soil analyses in environmental studies dealing with metal contamination, the use of simple, fast, sustainable and cost-effective methodologies is desired. In this sense, the role of total reflection X-ray fluorescence spectrometry (TXRF) has to be highlighted due to the possibility of direct analysis of solid suspensions without the need for a digestion process. Internal standardization is successfully used as a quantification approach in multielement TXRF analysis of liquid samples, including soil digests. However, its application for the analysis of soil suspensions is not always possible. In the present manuscript we found that although acceptable results were obtained for TXRF quantification by internal standardization when considering soil certified reference materials (recoveries: 80–120%), a systematic underestimation of the concentration values was found when using the same approach for real soil sample analysis (recoveries <70%). In view of these problems, we explored the possibilities of different quantification approaches, including external calibration, which can be used in combination with soil suspension preparation and TXRF analysis to obtain reliable results for metal determination in soils. Data obtained showed that the best strategy was the use of internal standardization with correction of the TXRF results using a calibration curve obtained in the analysis of a set of soil samples with a matrix similar to the unknown ones by using a reference technique (digestion and ICP-OES analysis). With this analytical approach quantitative results were obtained for all the studied metals with recovery values around 95%. As a study case, the proposed TXRF method has been applied for the specific determination of Pb, Zn and Cd concentrations in soils from an abandoned metal mining area but the developed methodology could be extended to other environmental studies dealing with the determination of other metals and soil types. Taking into account the selectivity and sensitivity limitations when determining high Z elements such as Cd using TXRF systems equipped with Mo X-ray tubes, we compare the analytical performance of TXRF systems with different sources (Mo and W) as well. [ABSTRACT FROM AUTHOR]

The development of methods for the analysis of silver nanoparticles (AgNPs) is of special relevance to achieve detailed insights into the fate, transport and exposure of these emerging pollutants in the environment. In the present contribution, for the first time, the possibilities and drawbacks of cloud point extraction (CPE) in combination with total reflection X-ray fluorescence spectrometry (TXRF) have been evaluated for the determination of AgNPs content in soil and consumer product water extracts. The experimental conditions for the separation and preconcentration of AgNPs with different coatings (PVP, PEG and citrate) and sizes (40–100 nm) were evaluated, paying attention to possible modifications required by the characteristics of the TXRF technique. Single particle inductively coupled plasma mass spectrometry (SP-ICPMS) analysis of the same aqueous extracts was also carried out in order to confirm the presence and percentage of AgNPs. Good agreement with respect to AgNPs concentrations in the analysed soil extracts was obtained between CPE-TXRF and SP-ICPMS, confirming the absence of matrix effects for this type of sample by CPE. On the contrary, large discrepancies were found between both analytical approaches for the studied consumer product water extracts. SP-ICPMS analysis evidenced the presence of ionic silver with a heterogeneous mixture of different sizes including relatively large Ag particles (＞100 nm). This fact was also verified by SEM-EDS analysis. The results from this study highlight the necessity to study in more detail the effectiveness of existing methodologies (including CPE-based methods and SP-ICPMS) for the monitoring of AgNPs in complex aqueous matrices involving mixtures of different NPs sizes and coatings. [ABSTRACT FROM AUTHOR]

In this paper the combination of dispersive micro solid-phase extraction (DMSPE), using multiwalled carbon nanotubes (MWCNTs) as solid sorbents, with total-reflection X-ray fluorescence spectrometry (TXRF) is proposed for preconcentration and determination of lead and cadmium ions in water samples. The proposed sample preparation is quite simple and economic. After the sorption processes of the metals on the MWCNTs, the aqueous sample is separated by centrifugation and the metal loaded MWCNTs are suspended using a small volume of an internal standard solution and analyzed directly by TXRF. Parameters affecting the extraction process (complexing agent, pH of the aqueous sample, amount of MWCNTs) and TXRF analysis (volume of the deposited suspension on the reflector, drying mode, and instrumental parameters) have been carefully evaluated to test the real capability of the developed methodology for the determination of Cd and Pb at trace levels. For both elements the linear range is observed up to 50 ng mL−1. Under optimized conditions detection limits are 1.0 ng mL−1 and 2.1 ng mL−1 for Cd(ii) and Pb(ii) ions, respectively. Both of the examined elements can be determined with quantitative recoveries (ca. 100%) and with an adequate precision (RSD = 6.0% and 10.5% for Cd(ii) and Pb(ii), respectively). Our results give insight into the possibilities of the combination of DMSPE and TXRF for trace metal determination in different types of environmental waters (sea, river and waste water). [ABSTRACT FROM AUTHOR]

Until now, the determination of Cd at trace levels in aqueous samples by TXRF has been restricted. When Mo-target X-ray tubes are used, low sensitivity and interferences with Cd L-lines used for quantification prevent trace analysis. Alternatively, when W-target X-ray tubes are used Cd excitation is limited. For this reason, a sample pretreatment is usually necessary to extract, isolate and concentrate Cd prior to TXRF analysis. In the present contribution, the feasibility of a dispersive liquid-liquid microextraction approach (DLLME) combined with TXRF for ultratrace Cd determination in different types of environmental waters is shown. Parameters affecting the extraction procedure and TXRF measurement conditions have been carefully evaluated to ensure the highest sensitivity for Cd determination. Using the best analytical conditions, it was found that the minimum cadmium content that could be detected in an aqueous solution was 0.04 μg L−1. This value is more than two orders of magnitude lower compared with the direct TXRF analysis of Cd in aqueous samples. The precision of the methodology was evaluated in terms of relative standard deviation (RSD) of six replicate analyses of a standard solution containing 3 μg L−1. The precision of the method was determined to be approximately 5% RSD. In order to test the suitability of the method when dealing with complex matrices as well as the influence of interfering ions, the determination of Cd in spiked water samples (sea water, estuarine water and river water) at the levels of 1 μg L−1 and 5 μg L−1 was undertaken and Cd added to the samples was quantitatively determined. Our results give insight into the possibilities of the combination of DLLME and TXRF for ultratrace Cd determination in different types of environmental waters. [ABSTRACT FROM AUTHOR]

A dispersive solid-phase microextraction (DSPME) with multiwalled carbon nanotubes (MWCNTs) as solid sorbent and ammonium pyrrolidinedithiocarbamate (APDC) as chelating agent was developed for determination of selenium. In the proposed procedure, the Se(iv)–APDC complex is adsorbed on MWCNTs dispersed in aqueous samples. After the adsorption process, the aqueous samples are filtered and MWCNTs with selenium chelate are collected onto a filter. The loaded filters are directly measured using X-ray fluorescence (XRF) spectrometry. In order to obtain high recovery of the Se ions on MWCNTs, the proposed procedure was optimized for various analytical parameters such as pH, amounts of MWCNTs and APDC, sample volume and time of the sorption process. Under optimized conditions Se ions can be determined with very good recovery (97 ± 3%), precision (RSD = 3.2%) and detection limits (from 0.06 to 0.2 ng mL−1, depending on counting time and XRF equipment). The effect of common coexisting ions was also investigated. Se(iv) can be determined in the presence of heavy metal ions and alkali metals. The chemical interferences observed for high concentrations of Cu(ii), Fe(iii), and Zn(ii) can be completely eliminated using precipitation with NaOH. The proposed method was applied for the determination of Se in mineral water and biological samples (Lobster Hepatopancreas). The proposed method can also be applied for selenium speciation. The concentration of selenate can be obtained as the difference between the concentration of selenite after and before prereduction of selenate to selenite. [ABSTRACT FROM AUTHOR]