Determination of total inorganic arsenic in water samples by cadmium ion assisted photochemical vapor generation-atomic fluorescence spectrometry

Heavy metal ion sensing strategies using fluorophores for environmental remediation

The main aim of this review is to provide an extensive summary of the latest advances within the emerging research area focused on detecting heavy metal ion pollution, particularly sensing strategies. The review explores various heavy metal ion detection approaches, encompassing spectrometry, electrochemical methods, and optical techniques. Numerous initiatives have been undertaken in recent times in response to the increasing demand for fast, sensitive, and selective sensors. Notably, fluorescent sensors have acquired prominence owing to the numerous advantages such as outstanding specificity, reversibility, and sensitivity. Further, it also explores the discussion of various nanomaterials employed in sensing heavy metal ions. In this regard, the exclusive emphasis is placed on fluorescent nanomaterials based on organic dyes, quantum dots, and fluorescent aptasensors for metal ion removal from aqueous systems to identify the destiny of dangerous heavy metal ions in clean circumstances.

Integrated microfluidic platforms for heavy metal sensing: a comprehensive review

Heavy metals are found naturally; however, anthropogenic activities such as mining, inappropriate disposal of industrial waste, and the use of pesticides and fertilizers containing heavy metals can cause their unwanted release into the environment. Conventionally, detection of heavy metals is performed using atomic absorption spectrometry, electrochemical methods and inductively coupled plasma-mass spectrometry; however, they involve expensive and sophisticated instruments and multistep sample preparation that require expertise for accurate results. In contrast, microfluidic devices involve rapid, cost-efficient, simple, and reliable approaches for in-laboratory and real-time monitoring of heavy metals. The use of inexpensive and environment friendly materials for fabrication of microfluidic devices has increased the manufacturing efficiency of the devices. Different types of techniques used in heavy metal detection include colorimetry, absorbance-based, and electrochemical detection. This review provides insight into the detection of toxic heavy metals such as mercury (Hg), cadmium (Cd), lead (Pb), and arsenic (As). Importance is given to colorimetry, optical, and electrochemical techniques applied for the detection of heavy metals using microfluidics and their modifications to improve the limit of detection (LOD).

Efficient Photochemical Vapor Generation from Low Concentration Formic Acid Media

Herein, we report on surprisingly efficient photochemical vapor generation (PVG) of Ru, Re, and especially Ir, achieved from very dilute HCOOH media employing a thin-film flow-through photoreactor operated in flow injection mode. In the absence of added metal ion sensitizers, efficiencies near 20% for Ir and approximately 0.06% for Ru and Re occur in a narrow range of HCOOH concentrations (around 0.01 M), significantly higher than previously reported from conventionally optimized HCOOH concentrations (1-20 M). A substantial enhancement in efficiency, to around 9 and 1.5%, could be realized for Ru and Re, respectively, when 0.005 M HCOONa served as the PVG medium. The addition of metal ion sensitizers (particularly Cd2+ and Co2+) to 0.01 M HCOOH significantly enhanced PVG efficiencies to 17, 2.2, and 81% for Ru, Re, and Ir, respectively. Possible mechanistic aspects occurring in dilute HCOOH media are discussed, wherein this phenomenon is attributed to the action of 185 nm radiation available in the thin-film flow-through photoreactor. An extended study of PVG of Fe, Co, Ni, As, Se, Mo, Rh, Te, W, and Bi from both dilute HCOOH and CH3COOH was undertaken, and several elements for which a similar phenomenon appears were identified (i.e., Co, As, Se, Te, and Bi). Although use of dilute HCOOH media is attractive for practical analytical applications employing PVG, it is less tolerant toward dissolved gases and interferents in the liquid phase due to the likely lower concentrations of free radicals and aquated electrons required for analyte ion reduction and product synthesis.

Sensitive Determination of Arsenic by Photochemical Vapor Generation with Inductively Coupled Plasma Mass Spectrometry: Synergistic Effect from Antimony and Cadmium

A novel method for the determination of trace arsenic (As) by photochemical vapor generation (PVG) with inductively coupled plasma mass spectrometry measurement was developed in this study. The synergistic effect from antimony (Sb) and cadmium (Cd) was found for the photochemical reduction of As for the first time. Effective photochemical reduction of As was obtained in the system containing 10% (v/v) acetic acid, 5.0 mg L-1 Sb(III), and 20.0 mg L-1 Cd(II) with 100 s UV irradiation. Analytical sensitivity of As(III) was comparable with that of As(V) under the tested conditions, making direct determination of total As feasible. Compared to the pneumatic nebulization method, analytical sensitivity of the developed method was enhanced about 50 folds. The PVG efficiency was estimated up to be 99 ± 3%. The limit of detection (LOD) (3σ) was found to be 2.1 ng L-1 for As, which was improved about 30-fold compared to that using direct sample introduction solution nebulization. Considering the sample dilution prior to analysis (usually one-fold), the LOD was actually enhanced about 15 folds. The relative standard deviations of seven replicate measurements of 1.0 μg L-1 As(III) and As (V) standard solutions were 2.3 and 2.9% for As(III) and As(V), respectively. The proposed method was successfully applied for the detection of As in certified reference materials of sediments (GBW07303a and GBW07305a), as well as three water samples. The mechanism of the PVG system was investigated by using gas chromatography mass spectrometry, electron paramagnetic resonance, and X-ray photoelectron spectroscopy. (CH3)3As along with (CH3)3Sb were synthesized under UV irradiation. Besides, volatile species of Cd were also found. The result obtained in this study is useful for developing efficient "sensitizers" in PVG and understanding the transformation of As in the presence of hydride/cold vapor forming elements in the photochemical process.

Shipboard determination of arsenite and total dissolved inorganic arsenic in estuarine and coastal waters with an automated on-site-applicable atomic fluorescence spectrometer

The speciation of trace level arsenic (As) in estuarine and coastal waters is crucial for both biogeochemical and toxicological studies of this toxic metalloid. However, the accurate and on-site determination of As in complex seawater matrices is challenging because of the low concentration of As, the easy conversion of arsenite (As(III)) to arsenate (As(V)), and the considerable effect of salinity on the determination of As via conventional methods. In this study, a custom-made shipboard atomic fluorescence spectrometer (AFS) is reported for the on-site speciation of inorganic As in estuarine and coastal waters. After comprehensive optimization of the instrumental and chemical parameters, the method demonstrated high sensitivity (limits of detection: 0.02 μg L-1), good linearity (R2 > 0.999 for all calibration curves up to 8 μg L-1), high precision (relative standard deviations (RSDs) of less than 2% at 1 μg L-1 over a year-long evaluation), and excellent performance for sample analysis for different matrices with varying salinities (recoveries: 96.3%-105.3%). The portable and field-applicable AFS was successfully applied to the on-site and shipboard simultaneous determination of As(III) and total dissolved inorganic arsenic (TDIAs) in the coastal waters of Shandong, Jiangsu, Zhejiang, Fujian, and Guangdong province of China, demonstrating its robustness and applicability in harsh conditions.

Chemical vapor generation of tungsten for atomic spectrometric determination: Homogeneous sensitizer and mechanism study

BACKGROUND

Inductively coupled plasma-mass spectrometry (ICP-MS) is one of the most powerful instrumental techniques for the determination of tungsten for its low detection limit and wide linear range, while it remains challenging since the analytical performance can be affected by complicated sample matrix. Chemical vapor generation (CVG) harbors the potential to be an alternative to conventional solution nebulization for sample introduction to reduce matrix effect. However, the CVG of tungsten was low in efficiency. It is clear that green and homogeneous enhancement for CVG of tungsten is desired and the mechanism is worth in-depth investigation.

RESULTS

Two green and homogeneous enhancement systems for CVG of tungsten were studied, including photochemical vapor generation (PVG) and hydride generation (HG) with sensitizers, Fe3+ and DDTC, respectively. Under optimal conditions, the limits of detection (LODs) were 0.02 μg L-1 for the PVG and 0.003 μg L-1 for the HG, respectively. For PVG, the Fe3+/Fe2+ cycling, free radical species, gaseous product, and the chemical speciation evolution of W in the PVG process were studied in detail. Photo-Fenton effect, generated reductive radical ·CO2-, gaseous product Fe(CO)5, and the mixed valence of W5+/W6+ in the PVG process were found to be crucial for the enhancement. As for HG, the complexation between W(VI) and DDTC might be conducive to the enhanced HG efficiency.

SIGNIFICANCE

This work not only in-depth expands the element scope of CVG, but also investigates the enhancement mechanisms experimentally, which might render a deep insight into the CVG processes and foreshadow new guidelines for screening green and efficient homogeneous sensitizers for CVGs of more elements in the future.

Ultraviolet assisted liquid spray dielectric barrier discharge plasma-induced vapor generation for sensitive determination of arsenic by atomic fluorescence spectrometry

In this study, a novel sensitive method for As determination by atomic fluorescence spectrometry was developed based on UV-assisted liquid spray dielectric barrier discharge (UV-LSDBD) plasma-induced vapor generation. It was found that prior-UV irradiation greatly facilitates As vapor generation in LSDBD likely because of the increased generation of active substances and the formation of As intermediates with UV irradiation. The experimental conditions affecting the UV and LSDBD processes (such as formic acid concentration, irradiation time, the flow rates of sample, argon and hydrogen) were optimized in detail. Under the optimum conditions, As signal measured by LSDBD can be enhanced by about 16 times with UV irradiation. Furthermore, UV-LSDBD also offers much better tolerance to coexisting ions. The limit of detection was calculated to be 0.13 μg L^-1 for As, and the relative standard deviation of the repeated measurements was 3.2% (n = 7). The accuracy and effectiveness of this new method were further verified by the analysis of simulated natural water reference sample and real water samples. In this work, UV irradiation was utilized for the first time as an enhancement strategy for PIVG, which opens a new approach for developing green and efficient vapor generation methods.

Detection of trace antimony by vanadium (IV) ion assisted photochemical vapor generation with inductively coupled plasma mass spectrometry measurement

In this work, a method for sensitive detection of trace antimony (Sb) was developed by inductively coupled plasma mass spectrometry (ICP MS) coupled with photochemical vapor generation (PVG). V(IV) ions were used as new "sensitizers" for improving the PVG efficiency of Sb. Factors influenced the PVG and the detection of Sb by ICP MS were investigated, including the type and concentration of low molecular weight organic acids, the UV irradiation time, the concentration of V(IV) ions, the air-liquid interface, the flow rate of Ar carrier gas, and interferences from co-existing ions. It was found that efficient reduction of Sb was obtained in the medium of 10% (v/v) formic acid (FA), 10% (v/v) acetic acid (AA), and 80 mg L^-1 of V(IV) with 100 s UV irradiation. Under the selected conditions, there was no significant difference in analytical sensitivity between Sb(III) and Sb(V). The limit of detection (LOD, 3σ) was 4.7 ng L^-1 for Sb with ICP MS measurement. Compared to traditional direct solution nebulization, the analytical sensitivity obtained in this work was enhanced about 19-fold. Relative standard deviations (RSDs, n = 7) were 1.9% and 2.3% for replicate measurement of 0.5 μg L^-1 Sb(III) and Sb(V) standard solutions, respectively. The proposed method was applied for the determination of trace Sb in water samples and two certified reference materials (CRMs) of sediments with satisfactory results. Moreover, the generated volatile species of Sb in this work was found to be (CH₃)₃Sb.

An integrated supervision framework to safeguard the urban river water quality supported by ICT and models

Models and information and communication technology (ICT) can assist in the effective supervision of urban receiving water bodies and drainage systems. Single model-based decision tools, e.g., water quality models and the pollution source identification (PSI) method, have been widely reported in this field. However, a systematic pathway for environmental decision support system (EDSS) construction by integrating advanced single techniques has rarely been reported, impeding engineering applications. This paper presents an integrated supervision framework (UrbanWQEWIS) involving monitoring-early warning-source identification-emergency disposal to safeguard the urban water quality, where the data, model, equipment and knowledge are smoothly and logically linked. The generic architecture, all-in-one equipment and three key model components are introduced. A pilot EDSS is developed and deployed in the Maozhou River, China, with the assistance of environmental Internet of Things (IoT) technology. These key model components are successfully validated via in situ monitoring data and dye tracing experiments. In particular, fluorescence fingerprint-based qualitative PSI and Bayesian-based quantitative PSI methods are effectively coupled, which can largely reduce system costs and enhance flexibility. The presented supervision framework delivers a state-of-the-art management tool in the digital water era. The proposed technical pathway of EDSS development provides a valuable reference for other regions.

Highly Efficient Photochemical Vapor Generation for Sensitive Determination of Iridium by Inductively Coupled Plasma Mass Spectrometry

Herein, we describe the highly efficient photochemical vapor generation (PVG) of a volatile species of Ir (presumably iridium tetracarbonyl hydride) for subsequent detection by inductively coupled plasma mass spectrometry (ICPMS). A thin-film flow-through photoreactor, operated in flow injection mode, provided high efficiency following optimization of identified key PVG parameters, notably, irradiation time, pH of the reaction medium, and the presence of metal sensitizers. For routine use and analytical application, PVG conditions comprising 4 M formic acid as the reaction medium, the presence of 10 mg L^-1 Co²⁺ and 25 mg L^-1 Cd²⁺ as added sensitizers, and an irradiation time of 29 s were chosen. An almost 90% overall PVG efficiency for both Ir³⁺ and Ir⁴⁺ oxidation states was accompanied by excellent repeatability of 1.0% (n = 15) of the peak area response from a 50 ng L^-1 Ir standard. Limits of detection ranged from 3 to 6 pg L^-1 (1.5-3 fg absolute), dependent on use of the ICPMS reaction/collision cell. Interferences from several transition metals and metalloids as well as inorganic acids and their anions were investigated, and outstanding tolerance toward chloride was found. Accuracy of the developed methodology was verified by analysis of NIST SRM 2556 (Used Auto Catalyst) following peroxide fusion for sample preparation. Practical application was further demonstrated by the direct analysis of spring water, river water, lake water, and two seawater samples with around 100% spike recovery and no sample preparation except the addition of formic acid and the sensitizers.

Frontier Materials for Adsorption of Antimony and Arsenic in Aqueous Environments: A Review

As highly toxic and carcinogenic substances, antimony and arsenic often coexist and cause compound pollution. Heavy metal pollution in water significantly threatens human health and the ecological environment. This article elaborates on the sources and hazards of compound antimony and arsenic contamination and systematically discusses the research progress of treatment technology to remove antimony and arsenic in water. Due to the advantages of simple operation, high removal efficiency, low economic cost, and renewable solid and sustainable utilization, adsorption technology for removing antimony and arsenic from sewage stand out among many treatment technologies. The adsorption performance of adsorbent materials is the key to removing antimony and arsenic in water. Therefore, this article focused on summarizing frontier adsorption materials' characteristics, adsorption mechanism, and performance, including MOFs, COFs, graphene, and biomass materials. Then, the research and application progress of antimony and arsenic removal by frontier materials were described. The adsorption effects of various frontier adsorption materials were objectively analyzed and comparatively evaluated. Finally, the characteristics, advantages, and disadvantages of various frontier adsorption materials in removing antimony and arsenic from water were summarized to provide ideas for improving and innovating adsorption materials for water pollution treatment.

Simultaneous Detection of Ruthenium and Osmium by Photochemical Vapor Generation-Inductively Coupled Plasma-Mass Spectrometry

Efficient simultaneous photochemical vapor generation (PVG) of ruthenium (Ru) and osmium (Os) in the medium of formic acid was demonstrated. A flow-through photoreactor hyphenated to an inductively coupled plasma-mass spectrometer (ICP-MS) was used for the PVG and subsequent detection of the two elements. A similar synergistic enhancement from cobalt and cadmium ions on the PVG efficiency of both Ru and Os was discovered. Following the critical evaluation of the impacts of various transition metal ions, the concentrations of formic acid, cobalt, and cadmium ions, the flow rate of carrier gas, and the UV irradiation time, impressive limits of detection (LODs) of 5 and 0.5 ng L^-1 were achieved for Ru and Os, respectively. The accuracy of the proposed PVG-ICP-MS method was validated by the analysis of several water samples with desirable spike recoveries obtained. Furthermore, the volatile compounds of Ru were directed and cryogenically trapped in acetonitrile and generation of carbonyls of Ru was verified by high-resolution electrospray ionization-mass spectra (ESI-MS).

Ultrasensitive determination and non-chromatographic speciation of inorganic arsenic in foods and water by photochemical vapor generation-ICPMS using CdS/MIL-100(Fe) as adsorbent and photocatalyst

The determination of inorganic arsenic species in real samples can be particularly challenging due to their trace levels and the interferences arising from sample matrix. Normally, the speciation analysis necessitates chromatographic separation. Herein, we report a novel method for the ultrasensitive detection and non-chromatographic speciation of inorganic arsenic by inductively coupled plasma mass spectrometry (ICP-MS), utilizing CdS/MIL-100(Fe) composites as an adsorbent and photocatalyst. The synthesized CdS/MIL-100(Fe) could completely adsorb As(V) and As(III) within 5 and 105 min, respectively. Following filtration and re-suspension in formic acid, the adsorbed As(III)/As(V) were reduced to arsine (AsH₃) under UV irradiation and swept to ICP-MS for detection. The limits of detection were found to be 1.7 ng L^-1 (without preconcentration) and 0.11 ng L^-1 (after 20-fold preconcentration). The method was successfully applied to the determination of trace inorganic arsenic in various food and water samples.

Health risks from groundwater arsenic on residents in northern China coal-rich region

Shanxi Province of northern China is a typical mining concentration and arsenism area. Years of mining activities have resulted in serious regional groundwater problems in Shanxi. Therefore, it is of great significance to know the health risk of groundwater arsenic on residents under the background of mining activities. Kriging interpolation was used to illustrate the spatio-temporal dynamics of the health risks on groundwater arsenic based on a ten-year investigation. The groundwater arsenic concentrations decreased over time and the distribution of high arsenic concentrations shrank. High arsenic concentrations were mainly distributed in the northern and middle basin areas. The forecasted area of high risks in coal mining areas was 5623 km², which was larger than that in non-coal mining areas. The residents living around mining areas were more vulnerable to exposure to groundwater arsenic. Further, the output map outlines the high-risk zones in order to protect the safety of drinking water for residents. This study may be helpful for the policy-makers to adopt a lower limit for groundwater arsenic to the worst affected regions and groups.

Rapid and Low Cost Determination of Total Mercury in Cat Foods by Photochemical Vapor Generation Coupled to Atomic Absorption Spectrometry

A rapid and low-cost method for determination of total mercury (THg) in cat food was developed based on photochemical vapor generation (PVG) coupled to cold vapor atomic absorption spectrometry (CVAAS). Cat food samples with ingredients based on tuna fish and other seafood were investigated. Organic acid precursor and concentration for radical generation and Hg photoreduction, sample UV irradiation time, and carrier gas flow were optimized. Highest PVG efficiency was achieved using 10% v v^-1 formic acid, 4-s UV irradiation time, and a carrier gas flow of 50 mL min^-1. The calibration function presented a correlation coefficient of 0.99. Accuracy was confirmed by analysis of Certified Reference Materials with recoveries of 93-110% and relative standard deviation lower than 6%. Under optimized conditions, a procedural detection limit of 0.28 μg kg^-1 was obtained. Determination of THg in 10 samples of cat food purchased in local markets revealed a concentration range of 0.035-0.388 mg kg^-1. Highest concentrations were found in cat foods. Only one sample presented a concentration close to the regulatory limit of the European Commission Directive. Assuming the estimated daily food intake (EDI) calculated in a range of 0.0021 to 0.023 mg of THg per day per kg body weight, it is concluded that it remains below that considered lethal for cats. The methodology is efficient, simple, low cost, and fit for purpose.

Impact of Gas-Liquid Interface on Photochemical Vapor Generation

Interfacial effect has attracted increasing interest as the inherent asymmetric environment of a gas-liquid interface leads to different chemical and physical properties between this region and the bulk phase, resulting in enhanced chemical processes, specific reactions, and mass transfer at the interface. Photochemical vapor generation (PVG) is regarded as a simple and green sample introduction method in atomic spectrometry. However, the photochemical behavior of elements with the interface is not known. Herein, we report the PVG of elements at the gas-liquid interface along with a possible mechanism investigated for the first time. Enhancement and/or suppression effects from the gas-liquid interface were observed on the PVG of 17 elements, which was correlated with the properties of analytes and the generated intermediate substances/products of PVG and the applied conditions. Enhancement from 1.1- to 7.3-fold in analytical sensitivity was found for 12 elements in the system with gas-liquid interface(s) compared to the results obtained in previous reports of PVG using traditional flow injection with inductively coupled plasma mass spectrometry measurement. The introduction of gas-liquid interface(s) and the resultant elevated temperature inside the PVG reactor likely facilitated the generation of radicals, the subsequent radical-based reactions, and the separation/transport/detection of volatile species of elements. In contrast, intermediate substances/products generated in PVG with poor thermostability will readily decompose at elevated temperatures, leading to a decreased signal response of analytes. The finding is helpful to understand the transport of elements under UV irradiation in the environment and has potential for analysis of trace elements in environmental and biological samples.

Cadmium Assisted Photochemical Vapor Generation of Tungsten for Detection by Inductively Coupled Plasma Mass Spectrometry

Efficient photochemical vapor generation (PVG) of tungsten has been achieved for the first time using a 19 W thin film flow-through photoreactor. The volatile product (most probably tungsten hexacarbonyl) was generated using a flow injection mode and 40% (v/v) formic acid as the reaction medium. An inductively coupled plasma mass spectrometer was utilized for ultrasensitive detection. The addition of Cd²⁺ as a sensitizer was critical, enhancing the overall PVG efficiency some 30 000-fold. At an optimal irradiation time of 19 s, a 6.1-fold enhancement factor and an overall PVG efficiency of 43% were determined from a comparison of the response to direct solution nebulization when using a sample flow rate of 2 mL min^-1 and 500 mg L^-1 Cd²⁺ as a sensitizer. A limit of detection of 0.9 ng L^-1 and repeatability (RSD) of 2% at 100 ng L^-1 were achieved. Interference from inorganic acids (HNO₃, HCl, H₂SO₄, and HF) was investigated with respect to analytical application to real samples. The accuracy and practical feasibility of this ultrasensitive methodology was successfully verified by analysis of Certified Reference Material CTA-FFA-1 (Fine Fly Ash) and six natural water samples with low W concentrations.