Trace and ultratrace analysis of liquid samples by X-ray fluorescence spectrometry

Facilitating inorganic arsenic speciation and quantification in waters: Polymer inclusion membrane preconcentration and X-ray fluorescence detection

BACKGROUND

Arsenic, classified as a priority pollutant and human carcinogen by the IARC, is subject to stringent regulatory limits in food and water. Among various arsenic species found in water samples, arsenite (As(III)) is identified as the most toxic form. Given the limitations of conventional spectroscopic techniques in speciation analysis, there is a crucial need for innovative and sustainable methodologies that enable arsenic speciation. Simplifying these methodologies is essential for widespread applicability and effective environmental monitoring.

RESULTS

This study proposes a simple and cost-effective analytical methodology for speciating inorganic arsenic in water samples. The method involves extracting As(III) into a polymer inclusion membrane (PIM) containing the extractant Cyanex 301 (bis(2,4,4-trimethylpentyl) dithiophosphinic acid), followed by analysis using energy dispersive X-ray fluorescence (EDXRF) spectrometry. The concentration of arsenate was measured after a reduction step using a thiosulfate/iodide mixture. This simple methodology allows a limit of quantification for trivalent arsenic (2 μg L-1), which is well below the World Health Organization's recommended maximum permissible level of As in drinking water (10 μg L-1). The method that is developed allows the determination of As at trace levels in waters with naturally occurring arsenic.

SIGNIFICANCE AND NOVELTY

This study represents a significant advance in the field, providing a novel and efficient methodology for arsenic speciation analysis in water samples. By combining the advantages of polymer inclusion membrane (PIM) extraction with energy dispersive X-ray fluorescence (EDXRF) spectrometry, this study offers a cost-effective and environmentally friendly approach to address the critical issue of arsenic contamination in water sources, thereby contributing to enhanced environmental monitoring and public health protection.

A novel organic chromo-fluorogenic optical sensor for detecting chromium ions

Sensing trivalent chromium ion (Cr(III)) is widely applied in different areas, such as clinical analysis, marine, environmental monitoring, or even chemical industry applications. Cr(III) has a significant role in the physiological process of human life. It is classified as an essential micronutrient for living organisms. Herein, we developed and designed a novel optical Cr(III) ions sensor film. The investigated sensor has a relatively small dynamic range of 1.24 × 10-3 to 0.5 μM. We report a highly sensitive optical sensor film for Cr(III) ions based on diethyl 3,4-diaminothieno[2,3-b]thiophene-2,5-dicarboxylate (3D) probe. The optical characteristics of the chemical probe exhibit substantial emission at 460 nm under 354 nm excitation. Besides, the interaction of the Cr(III) ions with 3D involves a complex formation with a 2:1 (metal: ligand) ratio, which is convoyed by the main peak enhancement that centered at 460 nm of 3D, and the main peak is red-shifted to 480 nm. The easily discernible fluorescence enhancement effect is a defining characteristic of the complexation reaction between the 3D probe and Cr(III). On the basis of the substantial fluorescence mechanism caused by the formation of a (Cr(III)-3D complex, which inhibits the photo-induced electron transfer (PET) process, the devised optical sensor was proposed. This film exhibits exceptional sensitivity and selectivity due to its notable fluorescence properties, stock shift of less than 106 nm, and detection capabilities at a significantly low detection limit of 0.37 × 10-3 μM. The detection procedure is executed by utilizing a physiological pH medium (pH = 7.4) with a relative standard deviation RSDr (1 %, n = 3). In addition, the 3D sensor demonstrates a high degree of affinity for Cr(III), as determined by the calculation of its binding constant to be 1.40 × 106. We present an impressive optical sensor that is constructed upon a three-dimensional molecule.

Development of a spectrofluorometric method for selective and sensitive determination of zinc in human Plasma: Implications for olfactory function

The relationship between zinc levels and olfactory function is an area of active research due to the role of zinc-dependent metalloenzyme, carbonic anhydrase, in maintaining olfactory function. In this study a spectrofluorometric method was developed for determining zinc levels in the human plasma of healthy participants and patients with olfactory dysfunction. The method relies on the fluorescence property changes of 4-Methylesculetin, which interacts with zinc. In this interaction, the oxygen atom of hydroxyl groups serves as a ligand, coordinating with zinc as a Lewis acid. As a result, the formed complex exhibits significant fluorescence enhancement attributed to the rigid chelate structure, thereby enhancing quantum yield. The resulting complex displays emission peak at 520 nm, which is distinct from the emission peak of 4-Methylesculetin at 460 nm. This bathochromic shift indicates heightened excited-state energy, attributed to zinc coordination and complex formation. The reaction conditions were carefully optimized to ensure selective zinc determination in plasma samples. The developed method demonstrates linearity over a concentration range of 200-4000 ng/mL, with a lower limit of quantification of 115 ng/mL. When applied to quantify plasma zinc levels, the method revealed significantly decreased zinc levels in patients with olfactory dysfunction compared to healthy individuals. These results suggest a potential link between olfactory dysfunction and zinc levels (normal vs. patient; 1150 ± 19 ng/mL vs. 940 ± 14 ng/mL, p < 0.05). The developed method was validated following the ICH M10 guidelines and provided a feasible investigative link between zinc and olfactory function.

A Facile Method to Fabricate an Enclosed Paper-Based Analytical Device via Double-Sided Patterning for Ionic Contaminant Detection

Microfluidic paper-based analytical devices (μPADs) have been developed for use in a variety of diagnosis and analysis fields. However, conventional μPADs with an open-channel system have limitations for application as analytical platforms mainly because of the evaporation and contamination of the sample solution. This study demonstrates the design and fabrication of an enclosed three-dimensional(3D)-μPAD and its application as a primary early analysis platform for ionic contaminants. To generate the hydrophobic PDMS barrier, double-sided patterning is carried out using a PDMS blade-coated stamp mold that is fabricated using 3D printing. The selective PDMS patterning can be achieved with controlled PDMS permeation of the cellulose substrate using 3D-designed stamp molds. We find the optimal conditions enabling the formation of enclosed channels, including round shape pattern and inter-pattern distance of 10 mm of stamp design, contact time of 0.5 min, and spacer height of 300 µm of double-sided patterning procedure. As a proof of concept, this enclosed 3D-μPAD is used for the simultaneous colorimetric detection of heavy metal ions in a concentration range of 0.1-2000 ppm, including nickel (Ni2+), copper (Cu2+), mercury (Hg2+), and radioactive isotope cesium-137 ions (Cs+). We confirm that qualitative analysis and image-based quantitative analysis with high reliability are possible through rapid color changes within 3 min. The limits of detection (LOD) for 0.55 ppm of Ni2+, 5.05 ppm of Cu2+, 0.188 ppm of Hg2+, and 0.016 ppm of Cs+ are observed, respectively. In addition, we confirm that the analysis is highly reliable in a wide range of ion concentrations with CV values below 3% for Ni2+ (0.56%), Cu2+ (0.45%), Hg2+ (1.35%), and Cs+ (2.18%). This method could be a promising technique to develop a 3D-μPAD with various applications as a primary early analysis device in the environmental and biological industries.

Investigating the Potential Use of Date Kernel Ash (DKA) as a Partial Cement Replacement in Concrete

The palm and date sector is one of the most important sectors in Saudi Arabia. The total number of fertile palm trees in Saudi Arabia is about 31 million. In the production of pitted dates, date molasses, date paste, and date confectionery, a considerable number of date kernels are usually discarded as waste. This study reports experimental investigations conducted to evaluate the potential of waste date kernel ash (DKA), obtained by the calcination of date pits at 800 °C, as a partial cement replacement in concrete. DKA has low silica oxide and does not qualify as a pozzolanic material. The effect of DKA partially replacing the cement and acting as a filler material in concrete was investigated, and its properties were compared with two pozzolanic materials, fly ash (FA) and natural pozzolan (NP). Twelve concrete mixes in which cement was replaced with different proportions of calcined DKA (5%, 10%, 15%, 20%, and 30%), NP (10%, 20%, and 30%), and FA (10%, 20%, and 30%) were investigated in the experimental program. The properties of DKA, FA, and NP concrete mixes were evaluated in fresh and hardened states, including the heat of hydration, mechanical characteristics, and thermal properties. The results show that replacing cement with 5% date kernel ash increases the compressive strength by 0.42%, 3.2%, and 2.5% at 3, 7, and 28 days, respectively, while the 28-day compressive strength decreases by 2.4%, 5.4%, 16.3%, and 26.69% when the cement is replaced with 10%, 15%, 20%, and 30% DKA, respectively. Date kernel ash concrete mixes with 10%, 20%, and 30% replacement levels demonstrated higher compressive and tensile strengths and lower thermal conductivity, density, and workability when compared to natural pozzolan and fly ash. DKA is a promising partial cement replacement material; nevertheless, additional research is required to assess the durability of DKA in concrete.

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.

Real-Time On-Site Multielement Analysis of Environmental Waters with a Portable X-ray Fluorescence (pXRF) System

Strict regulations are in place to control the effluents of mining sites and other industries. Heavy metal contamination of aquatic systems caused by leakages is difficult to mitigate as it takes time to detect and localize the leak. Dynamic sampling would drastically reduce the time to locate leakages and allow faster actions to reduce the impact on the environment. The present study introduces a novel portable multielement water analysis system to simultaneously measure Mn, Ni, Cu, Zn, Pb, and U in water samples from natural sources within 15 min from the sampling. The metals are preconcentrated from a 10 mL water sample into a nanoporous filter based on bisphosphonate-modified thermally carbonized porous silicon. The metals can be conveniently analyzed from the filter with a portable XRF analyzer in field conditions. The system was empirically calibrated for a lake water matrix with neutral pH and low alkaline metal concentration. A strong correlation between the XRF intensities and the ICP-MS results was obtained in a concentration range from 50 to 10 000 μg/L. With a DPO-2000C XRF analyzer, the detection limits were 103, 86, 92, 35, 44, and 43 μg/L for Mn, Ni, Cu, Zn, Pb, and U, respectively. The corresponding values with X-MET8000 Expert Geo were 137, 46, 62, 38, 29, and 54. The system was successfully validated with simulated multielement lake water samples and piloted in field conditions. The system provides an efficient way to monitor metals in environmental waters in cases where quick on-site results are needed.

Occurrence of Silver-containing Particles in Rat Brains upon Intranasal Exposure of Silver Nanoparticles

The widespread application of silver nanomaterials raises health concerns due to the adverse effects that can be associated with silver nanoparticles (AgNPs) exposure. AgNPs can be introduced into human bodies via inhalation, either intentionally (intranasal administration of AgNPs) or unintentionally (environmental pollution, accidental release, or occupational exposure). Recent studies have shown that intranasal exposure of experimental animals to AgNPs can lead to the accumulation of silver (Ag) in brain tissues. However, there is little information available concerning what forms of Ag (particulate and ionic) exist in brain tissues. This study aimed to investigate whether particulate Ag exists in rat brains following intranasal exposure of AgNPs at 1 mg/kg/day using multiple analytical techniques. The results demonstrated that Ag-containing particles were presented in AgNPs-exposed rat brains, accounting for 20.2%- 68.1% of the total Ag. The mass concentrations of Ag-containing particles in brain tissues increased with exposure time but only decreased by 37.5% after elimination for 4 weeks upon exposure cessation. The size of Ag-containing particles identified in rat brains was larger than the original AgNPs. The Ag-containing particles identified in the rat brain were composed of multiple elements, including Ag, sulfur (S), selenium (Se) with atomic percentages of 45.8%, 37.5%, 16.7% respectively. The finding highlighted the occurrence and accumulation of transformed AgNPs containing S and Se in rat brains after intranasal exposure to AgNPs, implying potential risks for brain health.

Determination of Chlorides in Ionic Liquids by Wavelength Dispersive X-ray Fluorescence Spectrometry

The synthesis of ionic liquids (ILs) usually involves two steps: (i) quaternization of a precursor followed by (ii) a salt metathesis reaction to introduce the desired anion. A consequence of the second step is that most ILs still contain some amount of the initial anion, often chloride. In this work, wavelength dispersive X-ray fluorescence (WDXRF) spectrometry is presented for the direct measurement of chlorides in ILs. The WDXRF settings were optimized, and the system was calibrated for the detection of chloride in several analogues of the commercially available IL Aliquat 336, [A336][X] (with X = I-, Br-, NO3 -, or SCN-). The Cl Kα intensity showed excellent linearity for samples with a conversion >0.80 (approximately Cl < 8000 ppm). Synthetic quality control samples showed that the instrumental error and deviations induced by the calibration procedure were small with maximum values of 1 and 5%, respectively. Detection and quantification limits depended strongly on the matrix (i.e., anion system and dilution) but were relatively low: 42-191 and 127-578 ppm Cl, respectively. Compared with other analytical techniques used for this purpose, the strengths of WDXRF include its ease of use, rapid measurements, the near absence of sample preparation steps, and versatility in terms of anion systems and chloride concentration range.

Hierarchical Porous Carbon Electrodes with Sponge-Like Edge Structures for the Sensitive Electrochemical Detection of Heavy Metals

This article presents the development of a highly sensitive electrochemical heavy metal sensor based on hierarchical porous carbon electrodes with sponge-like edge structures. Micrometer-scale hierarchical nanoporous carbon electrodes were fabricated at a wafer-scale using cost-effective batch microfabrication technologies, including the carbon microelectromechanical systems technology and oxygen plasma etching. The sponge-like hierarchical porous structure and sub-micrometer edges of the nanoporous carbon electrodes facilitate fast electron transfer rate and large active sites, leading to the efficient formation of dense heavy metal alloy particles of small sizes during the preconcentration step. This enhanced the peak current response during the square wave anodic stripping voltammetry, enabling the detection of Cd(II) and Pb(II) at concentrations as low as 0.41 and 0.7 μg L⁻¹, respectively, with high sensitivity per unit sensing area (Cd: 109.45 nA μg⁻¹ L mm⁻², Pb: 100.37 nA μg⁻¹ L mm⁻²).

Disposable and Low-Cost Colorimetric Sensors for Environmental Analysis

Environmental contamination affects human health and reduces the quality of life. Therefore, the monitoring of water and air quality is important, ensuring that all areas are acquiescent with the current legislation. Colorimetric sensors deliver quick, naked-eye detection, low-cost, and adequate determination of environmental analytes. In particular, disposable sensors are cheap and easy-to-use devices for single-shot measurements. Due to increasing requests for in situ analysis or resource-limited zones, disposable sensors’ development has increased. This review provides a brief insight into low-cost and disposable colorimetric sensors currently used for environmental analysis. The advantages and disadvantages of different colorimetric devices for environmental analysis are discussed.

Use of elemental profiles to verify geographical origin and botanical variety of Spanish honeys with a protected denomination of origin

Honey with Protected Denomination of Origin (PDO) could be an attractive target for fraudsters. Elemental profiles by Energy Dispersive-X Ray Fluorescence were processed by multivariate methods to classify 183 PDO honeys produced in three regions of Spain (Liébana, Granada, Tenerife). Additional honey samples (18) produced in a fourth region without PDO (El Bierzo) separated well from the PDO clusters. The manganese content was a discriminant marker of Liébana PDO and El Bierzo, that could also be differentiated from each other. Within each region, distinct clusters revealed differences between dark vs light varieties, multi- vs uni-floral honey and producers of the same PDO. The developed models were validated with 131 samples produced outside the PDO regions and El Bierzo. The proposed classification approach could be implemented as a fast screening tool to support pollen analysis in honey authentication. The reduced number of observations in some light honey models affected their performance.

Rapid direct determination of tin in beverages using energy dispersive X-ray fluorescence

This article presents a new method for the simpler and faster determination of tin in beverages using EDXRF. Absorption coefficients for aqueous calibration samples were calculated and shown to be nearly identical to those of the beverage samples, thus permitting the use of aqueous standard solutions for external calibration. Beverage samples could then be measured directly using the external calibration. Determination of tin using this method takes 4 min. The LOD and LOQ were 4 mg L^-1 and 15 mg L^-1 respectively, and the precision was 3.89%. Different canned beverages (cold coffee, various fruit juices) were measured and the results compared to the concentrations obtained using ICP-OES after digestion. The two methods showed good compatibility, thus establishing the newly developed method as a rapid, simple, and accurate method for the determination of tin in beverages.

Comprehensive approach to the validation of the standard method for total reflection X-ray fluorescence analysis of water

In this work, we present the validation of the chemical method for total reflection X-ray fluorescence (TXRF) analysis of water, proposed as a standard to the International Standard Organization. The complete experimental procedure to define the linear calibration range, elements sensitivities, limits of detection and quantification, precision and accuracy is presented for a commercial TXRF spectrometer equipped with Mo X-ray tube. Least squares linear regression, including all statistical tests is performed separately for each element of interest to extract sensitivities. Relative sensitivities with respect to Ga, as internal standard, are calculated. Accuracy and precision of the quantification procedure using Ga as internal standard is evaluated with reference water samples. A detailed discussion on the calibration procedure and the limitation of the use of this method for quantitative analysis of water is presented.

Bioimaging of isosteric osmium and ruthenium anticancer agents by LA-ICP-MS

Two isosteric organometallic drug candidates revealed distinct in vivo antitumour activities and spatial distributions in mouse tissues.

Preconcentration of Zn, Cu, and Ni Ions from Coffee Infusions via 8-Hydroxyquinoline Complexes on Graphene Prior to Energy Dispersive X-ray Fluorescence Spectrometry Determination

A simple and effective preconcentration procedure based on dispersive micro solid-phase extraction prior to energy dispersive X-ray fluorescence spectrometric (EDXRF) determination of trace amounts of Ni, Cu, and Zn in coffee infusions was proposed. The method is based on the adsorption of 8-hydroxyquinoline metal complexes on micro amounts of graphene nanoparticles. In order to optimize adsorption process, the influence of some parameters such as pH, graphene mass, concentration of 8-hydroxyquinoline (8-HQ) and Triton X-100, sample volume, and sorption time were examined. At optimal preconcentration conditions, calibration curves were linear from 1 to 150 ng mL^-1 for Ni and Cu and from 1 to 200 ng mL^-1 for Zn. The recoveries of the metal ions were in the 95-98% range with the precision lower than 4.6%. The obtained detection limits were 0.08 ng mL^-1 for Ni and 0.09 ng mL^-1 for Cu and Zn. The proposed method was successfully applied to determination of Ni, Cu, and Zn in coffee infusions. Accuracy and repeatability of the proposed procedure were confirmed by the standard addition method and compared to the results obtained by ICP-OES technique.

Green approach for ultratrace determination of divalent metal ions and arsenic species using total-reflection X-ray fluorescence spectrometry and mercapto-modified graphene oxide nanosheets as a novel adsorbent

A new method based on dispersive microsolid phase extraction (DMSPE) and total-reflection X-ray fluorescence spectrometry (TXRF) is proposed for multielemental ultratrace determination of heavy metal ions and arsenic species. In the developed methodology, the crucial issue is a novel adsorbent synthesized by grafting 3-mercaptopropyl trimethoxysilane on a graphene oxide (GO) surface. Mercapto-modified graphene oxide (GO-SH) can be applied in quantitative adsorption of cobalt, nickel, copper, cadmium, and lead ions. Moreover, GO-SH demonstrates selectivity toward arsenite in the presence of arsenate. Due to such features of GO-SH nanosheets as wrinkled structure and excellent dispersibility in water, GO-SH seems to be ideal for fast and simple preconcentration and determination of heavy metal ions using methodology based on DMSPE and TXRF measurement. The suspension of GO-SH was injected into an analyzed water sample; after filtration, the GO-SH nanosheets with adsorbed metal ions were redispersed in a small volume of internal standard solution and deposited onto a quartz reflector. The high enrichment factor of 150 allows obtaining detection limits of 0.11, 0.078, 0.079, 0.064, 0.054, and 0.083 ng mL(-1) for Co(II), Ni(II), Cu(II), As(III), Cd(II), and Pb(II), respectively. Such low detection limits can be obtained using a benchtop TXRF system without cooling media and gas consumption. The method is suitable for the analysis of water, including high salinity samples difficult to analyze using other spectroscopy techniques. Moreover, GO-SH can be applied to the arsenic speciation due to its selectivity toward arsenite.