Simultaneous determination and speciation analysis of arsenic and chromium in iron supplements used for iron-deficiency anemia treatment by HPLC-ICP-MS

Capillary Flow-Driven Microfluidics Combined with a Paper Device for Fast User-Friendly Detection of Heavy Metals in Water

Human exposure to heavy metals is a concerning global problem because of its detrimental effect on our health and ecosystem. Assessing the levels of these metals is cost- and labor-intensive and nonuser friendly because current analysis approaches typically rely on heavy instrumentations like inductively coupled plasma-mass spectrometry, which is only possible in centralized labs. Hence, simple economical detection methods are in high demand in developing countries and areas with insufficient infrastructure, professional experts, and appropriate environmental treatment. Several microfluidic paper-based analytical devices have been reported as promising alternatives to conventional testing methods for on-site heavy metal detection. Paper-based microfluidics are advantageous because of their simple fabrication, biodegradability, low cost, and ability to operate without pumps. However, typical assay times for current platforms are slow, and they typically rely on pipetting a fixed volume into the assay cards. This adds complexity in actual field scenarios. Here, we report a novel, inexpensive, and straightforward capillary-driven microfluidic device combined with paper for rapid and user-friendly detection of Ni(II), Cu(II), and Fe(III) in water. A colorimetric approach was adopted to quantify these metals. The device was able to produce a homogeneous color signal within 8 s of sample insertion. The limit of detection and limit of quantification were calculated to be 2 and 6.67 ppm for nickel, 0.3 and 1 ppm for Cu, and 1.1 and 3.67 ppm for Fe, respectively. The majority (>90%) of the collected samples showed recovery in the 80-110% range with acceptable accuracy and precision (<15% RSD) for a colorimetric device. This technique can be beneficial for rapidly assessing heavy metal exposure in drinking and surface water at drastically reduced assay time and is the first example of capillary flow-driven microfluidic devices as a transport medium for heavy metal detection.

Smartphone-based microfluidic chip modified using pyrrolidine-1-dithiocarboxylic acid for simultaneous colorimetric determination of Cr3+ and Al3+ ions

A portable µ-chip-based colorimetric device was developed for the determination of Cr³⁺ and Al³⁺ ions. The silver nanoparticles were modified with pyrrolidine-1-dithiocarboxylic acid ammonium salt as a novel ligand for the first time. The color of modified AgNPs in the test zone immediately changes after the addition of Cr³⁺ and Al³⁺ ions. The resulting color changes were detected by the naked eye or were taken by a smartphone camera. The obtained images were analyzed by RGB software to assay the Cr³⁺ and Al³⁺ ions concentration. Under optimized experimental conditions, the linear ranges are 0.1-220 and 0.01-250 µM for Cr³⁺ and Al³⁺ ions, respectively. The probe has a limit of detections of 10.66 and 3.55 nM for Cr³⁺ and Al³⁺ in an aqueous solution. In the case of µ-chip, the concentration ranges are 0.1-200 μM and 0.01-220 μM for Cr³⁺ and Al³⁺ ions, with detection limits of 9.18 and 2.30 nM, respectively. The µ-chip showed great potential as a fast detection tool for the monitoring of Cr³⁺ and Al³⁺ ions in real samples such as river water samples.

Application of Liquid Chromatography Coupled to Mass Spectrometry in Quality Assessment of Dietary Supplements—A Case Study of Tryptophan Supplements: Release Assay, Targeted and Untargeted Studies

Dietary supplements are widely consumed in the EU and the USA. Based on their similarity to pharmaceuticals, consumers mistakenly believe that dietary supplements have also been approved for safety and efficacy. However, in the absence of mandatory testing, data on supplement quality is scarce. Thus, we applied liquid chromatography coupled with tandem mass spectrometry to analyse the quality of dietary supplements containing tryptophan (Trp). We examined 22 supplements in tablets or capsules, produced in the USA, Great Britain, Germany, France, Czech Republic, and Poland. Trp release, crucial for bioavailability and efficiency, was assessed. Additionally, we performed a qualitative analysis of the main ingredient and screened for contaminants. Among the contaminants, we detected Trp’s metabolites, condensation products of Trp and carbonyl compounds, Trp degradation products, degradation products of kynurenine, and other contaminants such as glucosamine and melatonin. The main ingredient content was in the range of 55–100% in capsules and 69–87% in tablets. Surprisingly, almost no Trp release was noted from some supplements. Our study confirms the need to advance research on supplements. We believe that the high-quality analysis of supplements based on reliable analytical techniques will be an important contribution to the discussion on the regulatory framework of these products.

Cationic Metal–Organic Framework-Based Mixed-Matrix Membranes for Fast Sensing and Removal of Cr2O72− Within Water

Considering that metal–organic framework (MOF)-polymer mixed-matrix membranes (MMMs) can overcome the drawbacks of intrinsic fragility and poor processability of pure-MOF membranes, we designed MOF-based MMMs for efficient removal and fast fluorescence sensing of heavily toxic ions within water systems simultaneously. In this work, a series of MOF-based MMMs are prepared by mixing a hydrolytically stable cationic [Eu₇ (mtb)₅(H₂O)₁₆]·NO₃ 8DMA·18H₂O (denoted as Eu-mtb) MOF material into poly (vinylidene fluoride) with high loadings up to 70%. The free volume at the interface between the polymer and Eu-mtb particles, combined with the permanent porosity and uniform distribution of Eu-mtb particles, enables these MMMs to show fast enrichment of Cr₂O₇^2- from solutions and consequently have a full contact between the analyte and MOFs. The developed Eu-mtb MMM (70wt% loading) thus shows both efficient removal and exceptional fluorescence sensing of Cr₂O₇^2- in aqueous media. The overall adsorption capacity of the Eu-mtb MMM (70 wt% loading) for Cr₂O₇^2- reaches up to 33.34 mg/g, which is 3.4 times that of powder-form Eu-mtb. The detection limit of the Eu-mtb MMM (70 wt% loading) for Cr₂O₇^2- is around 5.73 nM, which is lower than that of the reported powder-form Eu-mtb. This work demonstrates that it is feasible to develop flexible luminescent MOF-based MMMs as a significant platform for efficient removal and sensitive sensing of pollutants from water systems simultaneously.

Influence of cations on As(III) removal from simulated groundwaters by double potential step chronoamperometry (DPSC) employing polyvinylferrocene (PVF) functionalized electrodes

As(III) removal from groundwaters is challenging because of its neutral charge and low surface affinity under circumneutral pH conditions. In this work, we investigate the influence of Ca²⁺ and Mg²⁺ on the removal of As(III) by a redox active polyvinylferrocene (PVF) functionalized electrode in a modified double potential step chronoamperometry (DPSC) setup. In the absence of divalent cations, nearly 90% As(III) removal is achieved over ten continuous cycles by single-pass DPSC, even in the presence of competing anions, however the presence of divalent cations at concentrations ≥ 1.25 mM significantly inhibits As(III) removal. The divalent cations enhance arsenic removal in the first (removal) step but suppress electrode regeneration in the 2^nd step. Our results suggest that Ca²⁺/Mg²⁺ either acts as a bridge between the electrode surface and As anions or the sorption of Ca²⁺/Mg²⁺ increases the positive charge on the electrode surface thereby facilitating As(V) sorption. We show that effective electrode regeneration can be achieved using an NaOH wash however the overall complexity of the process increases. Overall, we conclude that the influence of divalent cations on As removal by electro-sorption processes needs to be taken into consideration for application of this technology for real groundwater treatment.

A new method for highly efficient separation and determination of arsenic species in natural water using silica modified with polyamines

A simple and highly efficient method for the determination of highly toxic arsenic species using non-covalently aminated silica is proposed. The polyamines including poly(hexamethyleneguanidine), poly(4,9-dioxadodecane-1,12-guanidine), hexadimethrine, and poly(diallyldimethylammonium) were tested as silica modifiers. The prepared adsorbents allow effective preconcentration of anionic species of arsenic from aqueous solutions. It was found that As(V) can be quantitatively extracted from solutions at pH 4.5-7.0 by the anion exchange mechanism in less than 5 min, while neutral at this pH As(III) was not adsorbed at these conditions. A reaction with 2,3-dimercapto-1-propanesulphonic acid, which resulted in the formation of the negatively charged complex of As(III) with adsorbents was used for its quantitative extraction from solutions with a pH of 3.5-6.5. A system of two cartridges filled with poly(diallyldimethylammonium) modified silica and the on-line reaction of As(III) with 2,3-dimercapto-1-propanesulphonic acid proceeding between the cartridges was used for separate preconcentration and determination of As(V) and As(III) at pH 5. The proposed method was used for four-year monitoring of natural water pollution by arsenic in the area of residence of the indigenous peoples of Tyva Republic (Russia).

AF4-UV-ICP-MS for detection and quantification of silver nanoparticles in seafood after enzymatic hydrolysis

A method based on asymmetric flow field-flow fractionation (AF4) coupled to ultraviolet-visible (UV-vis) spectroscopy and inductively coupled plasma mass spectrometry (ICP-MS) has been developed for silver nanoparticles (Ag NPs) detection and quantification in bivalve molluscs. Samples were pre-treated using a conventional enzymatic (pancreatin and lipase) hydrolysis procedure (37 °C, 12 h). AF4 was performed using a regenerated cellulose (RC) membrane (10 kDa, 350 μm spacer) and aqueous 5 mM Tris-HCl pH = 7.4 as carrier. AF4 separation was achieved with a program that included a focusing step with tip and focus flows of 0.20 and 3.0 mL min^-1, respectively, and an injection time of 4.0 min. Elution of different size fractions was performed using a cross flow of 3.0 mL min^-1 for 15 min, followed by linear cross flow decrease for 7.5 min, and a washing step for 9.4 min with no cross flow. Several bivalve molluscs (clams, oysters and variegated scallops) were analysed for total Ag content (ICP-MS after microwave assisted acid digestion), and for Ag NPs by the method presented here. Results show that Ag NPs are detected at the same elution time than proteins (UV monitoring at 280 and 405 nm), which suggests a certain interaction occurred between Ag NPs with proteins in the enzymatic extracts. AF4-UV-ICP-MS fractograms also suggest different Ag NPs size distributions for selected samples. Membrane recoveries, determined by peak area comparison of fractograms with and without application of cross flow, were within the 49-121% range. Confirmation of the presence Ag NPs in the investigated enzymatic extracts was demonstrated by SEM after an oxidative pre-treatment based on hydrogen peroxide and microwave irradiation.

Chromium Determination in Leather and Other Matrices: A Review

Leather industry plays an essential role in the world's economy; however, it also has a negative environmental impact due to the generation of significant quantities of wastes, some of which are classified as hazardous chemicals. Chrome tanning, the most popular tanning process, employs chromium salts, acids, and some other chemicals. Some dyes can be also a source of chromium. As a result, hexavalent chromium, a known carcinogenic and mutagenic, can be found in leather products and cause allergic dermatitis or trigger other diseases. For this reason, it is important to quantify the total amount of chromium in final leather goods, as well as the oxidation state in which this element is found. This paper aims to summarize chromium contamination due to the leather production processes, and to review the analytical methods that have been used to determine chromium's most abundant species: Cr(III) and Cr(VI) in leather and other matrices (foodstuffs, cosmetic products, environmental, and pharmaceutical samples). The international and European regulations are presented as well as the last academic developments to extract and quantify chromium species. The future outlook of pretreatment and quantification techniques are also discussed in this work, with a special focus on chromium interconversions.

Ammonium acetate as a novel buffer for highly selective robust urinary HPLC-ICP-MS arsenic speciation methodology

Ammonium acetate is employed in order to develop a novel HPLC-ICP-MS arsenic speciation methodology applicable to six arsenic species, i.e, AC, AB, As^III, As^V, DMA and MMA. The most predominant species in the toxicological field are covered in a 30-min chromatogram with reproducible and repeatability peak area ratio. Moreover, typical problems from traditional methods are sorted out by using a robust, high-selective and ⁷⁵ArCl⁺ interference-free methodology. Chromatographic and detector optimization ensures low LOQs for each species with acceptable precision and accuracy values obtained using four urinary arsenic speciation PTS enabling to be useful for sub ng mL^-1 arsenic exposure assessments.

Selective Arsenic Removal from Groundwaters Using Redox-Active Polyvinylferrocene-Functionalized Electrodes: Role of Oxygen

In this work, we investigate selective sorption of arsenic from simulated groundwaters at pH 8 by a redox-active polyvinylferrocene (PVF)-functionalized electrode using a modified double potential step chronoamperometry (DPSC) method. Our results show that effective and sustainable As(III) removal can be achieved at 0 V once the electrode is activated via anodic polarization. During activation, ferrocene (Fc) in PVF is oxidized to the ferrocenium ion (Fc⁺) with the latter facilitating As(III) sorption and subsequent oxidation as well as As(V) sorption. The high affinity of Fc⁺ to As and weak attraction to competing anions at 0 V ensure high selectivity of As over Cl^-, SO₄^2-, and NO₃^- at concentrations typical of groundwaters. Following the removal process, efficient regeneration of the electrode is achieved at -1.2 V wherein Fc⁺ is reduced to Fc thereby facilitating As desorption from the electrode surface. Our results further show that O₂ and associated generation of hydrogen peroxide during the regeneration step drive the oxidation of Fc to Fc⁺, thereby maintaining the constant generation of Fc⁺ required to achieve As(III) removal in subsequent cycles. Our results show that 91.8 ± 0.6% of As(III) could be selectively removed from simulated groundwater over 10 cycles at an ultralow energy consumption of 0.12 kWh m^-3.

Quantitative X-ray fluorescence analysis: Trace level detection of toxic elemental impurities in drug product by ED-XRF spectrometer

Inorganic impurity analysis of pharmaceutical drug products is of paramount importance at trace levels due to the availability of toxic metals. The existing techniques require extensive development and chemical treatment to evaluate the presence of class I (Pb, Cd, Hg and As) and class II (Co, V and Ni) heavy metal elements which are harmful to the environment. To overcome these issues, a cost and time effective wavelength dispersive X-ray fluorescence spectrometry (XRF) was introduced to determine the concentration of trace elements in one of the angiotensin receptor blocker (ARB) (tablet sample 300 mg) according to guidelines addressed in ICH Q3D and USP. The validation study focused on class I and class II elements are also in accordance with regulatory guidelines. Overall it includes the comprehensive characterization of analytical method which is compliant with the requirement of USP. The novelty of this work includes the application of EDXRF in routine analysis of trace elements (especially volatile Hg) present in the pharmaceutical product beyond the previously published studies for the limited number of the non-pharmaceutical regime. Apart from this it also requires minimal sample preparation and method development and is able to quantify toxic impurities which are present in the sample in less than 20 ppm concentration, with the lowest level of detection up to 0.1 ppm.

Structural diversity, magnetic properties, and luminescence sensing based Ni(ii)/Zn(ii) coordination polymers of the semirigid 3,3′-((5-carboxy-1,3-phenylene)bis(oxy))dibenzate ligand

Four novel CPs were synthesized and two Zn(ii)-CPs can be used as fluorescent probes for the detection of CrO₄²⁻/Cr₂O₇²⁻.

Contaminants: a dark side of food supplements?

Food supplements (FS) are often consumed as one of the strategies to fight ageing-associated pathologies, especially in the case of oxidative stress-related diseases. Despite the popularity of FS, some concerns about their quality and safety have been raised, especially regarding the presence of contaminants. This paper reviews and discusses the occurrence of contaminants in marketed samples of FS in the last two decades, considering both scientific literature and notifications registered on RASFF portal. The most relevant classes of contaminants were included namely metals, toxins, pesticides, dioxins and PCBs, as well as pharmacologically active ingredients. Variable amounts of contaminants were reported in a significant number of commercially available FS. Although the presence of contaminants does not necessarily mean that their levels exceed the regulatory limits or that the FS intake constitutes a risk to human health, it alerts for the need to further monitor FS safety. The evaluation of the risk associated to the consumption of FS, especially in the elderly population, is particularly challenging due to the frequent exposure to multiple toxicants and to different exposure sources, as well as due to possible pre-existing diseases and respective therapeutics. Therefore, improved quality control procedures and monitoring programs should be pursued in order to avoid undesirable products and assure the safety of FS.

Modified Double Potential Step Chronoamperometry (DPSC) Method for As(III) Electro-oxidation and Concomitant As(V) Adsorption from Groundwaters

Constrained by low energy efficiency and ineffectiveness in As(III) removal under circumneutral pH conditions by many exsiting technologies, As(III) removal has become an issue. In this work we present proof of concept of a modified double potential step chronoamperometry (DPSC) method of As(III) oxidation and concomitant As(V) electro-sorption from aqueous solution. Results show that in situ anodic As(III) oxidation, As(V) electro-sorption, and As(V) electro-desorption are affected by aqueous pH with high oxidation and sorption/desorption rates observed at the elevated pH. We particularly show that effective As(III) oxidation and concomitant As(V) adsorption are related to (i) the rapid oxidation of the deprotonated species compared to the protonated species and (ii) stronger electrochemical interaction between the multicharged As(V) species and the electrodes. At 1.2 V and an electric energy consumption of 0.06 kWh m^-3, the total As concentration can be reduced from 150 to 15 μg L^-1 using an electrochemical cell with electrode area of 10 × 8 cm² and electro-sorption time of 120 min. On the basis of the experimental results, we have developed a mathematical model to describe the kinetics and mechanism of arsenic removal by the modified DPSC method with this model of use in predicting, and potentially optimizing, process performance under various conditions.

Development of a New Kinetic Spectrophotometric Method for the Determination of Chromium with an Optical Probe

The aim of this work is the development, optimization, and validation of a new spectrophotometric kinetic method for the determination of dissolved chromium species in water samples with the use of the polymethine dye Astra Phloxine FF. The progress of the chemical reaction was simple, effective, and precisely monitored from the start of the reaction using an optical probe. The method is based on the impact of Cr(VI) concentration on the rate of decrease in the Astra Phloxine FF concentration. The experimental data were evaluated using four experimental data analysis methods, namely with the initial rate method, the average rate method, the fixed time method, and the absorption peak volume change method. Under the optimal reaction conditions, the best results were achieved using the method of the average rate constant for evaluating the experimental data. Using this data evaluation method for the determination of Cr(VI), the LoD was found to be 1.87 µg L^-1 and RSD ( n = 6; 0.2 mg L^-1 Cr) 3.59%. The presented work was used for the determination of chromium in model samples-CRM material and tap and waste water-and with the calibration line method and the standard additions method.

Pharmacokinetic Properties of Arsenic Species after Intravenous and Intragastrical Administration of Arsenic Trioxide Solution in Cynomolgus Macaques Using HPLC-ICP-MS

A rapid and sensitive method was established for arsenic (As) speciation based on high performance liquid chromatography coupled to inductively coupled plasma mass spectrometry (HPLC-ICP-MS). This method was validated for the quantification of four arsenic species, including arsenite (AsIII), arsenate (AsV), monomethylarsonic acid (MMAV) and dimethylarsinic acid (DMAV) in cynomolgus macaque plasma. Separation was achieved in just 3.7 min with an alkyl reverse phase column and highly aqueous mobile phase containing 20 mM citric acid and 5 mM sodium hexanesulfonate (pH = 4.3). The calibration curves were linear over the range of 5⁻500 ng·mL-1 (measured as As), with r > 0.99. The above method was validated for selectivity, precision, accuracy, matrix effect, recovery, carryover effect and stability, and applied in a comparative pharmacokinetic study of arsenic species in cynomolgus macaque samples following intravenous and intragastrical administration of arsenic trioxide solution (0.80 mg·kg-1; 0.61 mg·kg-1 of arsenic); in addition, the absolute oral bioavailability of the active ingredient AsIII of arsenic trioxide in cynomolgus macaque samples was derived as 60.9 ± 16.1%.

Potential Point-of-Care Microfluidic Devices to Diagnose Iron Deficiency Anemia

Over the past 20 years, rapid technological advancement in the field of microfluidics has produced a wide array of microfluidic point-of-care (POC) diagnostic devices for the healthcare industry. However, potential microfluidic applications in the field of nutrition, specifically to diagnose iron deficiency anemia (IDA) detection, remain scarce. Iron deficiency anemia is the most common form of anemia, which affects billions of people globally, especially the elderly, women, and children. This review comprehensively analyzes the current diagnosis technologies that address anemia-related IDA-POC microfluidic devices in the future. This review briefly highlights various microfluidics devices that have the potential to detect IDA and discusses some commercially available devices for blood plasma separation mechanisms. Reagent deposition and integration into microfluidic devices are also explored. Finally, we discuss the challenges of insights into potential portable microfluidic systems, especially for remote IDA detection.

Determination and speciation of ultratrace arsenic and chromium species using aluminium oxide supported on graphene oxide

Alumina supported on graphene oxide (Al₂O₃/GO) nanocomposite as new nanosorbent in dispersive micro-solid phase extraction (DMSPE) for As(V) and Cr(III) preconcentration is described. The crucial issue of the study is synthesis of novel nanocomposite suitable for sorption of selected species of arsenic and chromium. Al₂O₃/GO demonstrates selectivity toward arsenates in the presence of arsenites at pH 5 and chromium(III) ions in the presence of chromate anions at pH 6. The Al₂O₃/GO nanocomposite was characterized by scanning electron microscopy (SEM) transmission electron microscopy (TEM), powder X-ray diffraction (XRD) and the Raman spectroscopy. The maximum adsorption capacity calculated based on the Langmuir adsorption model were 43.9 mg g^-1 and 53.9 mg g^-1 for As(V) and Cr(III), respectively. The nanocomposite was used as solid sorbent in preconcentration of As(V) and Cr(III)_ions from water samples and their determination using energy dispersive X-ray fluorescence spectrometry (EDXRF). The As(V) and Cr(III) ions can be quantitatively preconcentrated from 25 to 100 mL aqueous samples within 5 min using DMSPE procedure and 1 mg of Al₂O₃/GO. The nanocomposite was also used for preparation of Al₂O₃/GO membrane. Then, As(V) and Cr(III)_ions can be retained under flow condition by passing analyzed solution through Al₂O₃/GO membrane. Under the optimized conditions, As(V) and Cr(III) ions can be determined with very good recovery (92-108%), precision (RSD 2.7-4.0%) and excellent limit of detection (0.02 ng mL^-1 As and 0.11 ng mL^-1 Cr). The accuracy of the method was studied by analyzing certified reference materials (NIST 1640a) and spiked real water samples.

A Water-Stable Luminescent ZnII Metal-Organic Framework as Chemosensor for High-Efficiency Detection of CrVI -Anions (Cr2 O72- and CrO42- ) in Aqueous Solution

A new luminescent Zn^II -MOF with 1D triangular channels along the b axis, namely NUM-5, has been successfully assembled and well characterized, which features good stability, especially in aqueous solution. Interestingly, this compound exhibits a fast, sensitive and selective luminescence quenching response towards Cr^VI (Cr₂ O₇^2- /CrO₄^2- ) in aqueous solution. The detection limits towards Cr₂ O₇^2- and CrO₄^2- ions are estimated to be 0.7 and 0.3 ppm, respectively, which are among the lowest detection limits reported for the MOF-based fluorescent probes that can simultaneously detect Cr₂ O₇^2- and CrO₄^2- in aqueous environment. The possible detection mechanism has been discussed in detail. Moreover, it can be easily regenerated after detection experiments, indicative of excellent recyclability. All these results suggest NUM-5 to be a highly selective and recyclable luminescent sensing material for the quantitative detection of Cr^VI anions in aqueous solution.

A Review on Recent Applications of High-Performance Liquid Chromatography in Metal Determination and Speciation Analysis

High-performance liquid chromatography (HPLC) has several advantages over the conventional methods due to their operational simplicity. It is a vital tool to determine metal ions having same mass but different electronic configuration, to separate complex mixtures and to resolve ions that may be indistinguishable by mass spectrometry alone. Metal ions play vital role in many biological processes and involved in setting up of many diseases. Therefore, the development of simple methods for the detection and quantification of metals in real samples might serve as diagnostic tools for various diseases. This review article focuses on the recent main feature of this technique, i.e. speciation of metal ions and their applications to series of problem of metal ion chemistry in different environmental matrixes. Speciation of metals is of increasing interest and has a great importance because of bioavailability, environmental mobility, toxicity and potential risk of metals. With the capability of partitioning the complex species of different metal ions, HPLC is an efficient technique for this task. This review summarizes recent advances in the development of HPLC to the fundamental understanding of metal ion chemistry in the environment and discusses all the issues that still need a lot of consideration. It has been classified into different sections depending on the role of HPLC in separation used and metal speciation; furthermore, the underlying sample preconcentration techniques and detection systems involved for the determination of metal ions and their applications were discussed.