Enzyme-assisted extraction and liquid chromatography-inductively coupled plasma mass spectrometry for the determination of arsenic species in fish

Arsenic speciation in freshwater fish: challenges and research needs

Food and water are the main sources of human exposure to arsenic. It is important to determine arsenic species in food because the toxicities of arsenic vary greatly with its chemical speciation. Extensive research has focused on high concentrations of arsenic species in marine organisms. The concentrations of arsenic species in freshwater fish are much lower, and their determination presents analytical challenges. In this review, we summarize the current state of knowledge on arsenic speciation in freshwater fish and discuss challenges and research needs. Fish samples are typically homogenized, and arsenic species are extracted using water/methanol with the assistance of sonication and enzyme treatment. Arsenic species in the extracts are commonly separated using high-performance liquid chromatography (HPLC) and detected using inductively coupled plasma mass spectrometry (ICPMS). Electrospray ionization tandem mass spectrometry, used in combination with HPLC and ICPMS, provides complementary information for the identification and characterization of arsenic species. The methods and perspectives discussed in this review, covering sample preparation, chromatography separation, and mass spectrometry detection, are directed to arsenic speciation in freshwater fish and applicable to studies of other food items. Despite progress made in arsenic speciation analysis, a large fraction of the total arsenic in freshwater fish remains unidentified. It is challenging to identify and quantify arsenic species present in complex sample matrices at very low concentrations. Further research is needed to improve the extraction efficiency, chromatographic resolution, detection sensitivity, and characterization capability.

The relevance of arsenic speciation analysis in health & medicine

Long term exposure to arsenic through consumption of contaminated groundwater has been a global issue since the last five decades; while from an alternate standpoint, arsenic compounds have emerged as unparallel chemotherapeutic drugs. This review highlights the contribution from arsenic speciation studies that have played a pivotal role in the progression of our understanding of the biological behaviour of arsenic in humans. We also discuss the limitations of the speciation studies and their association with the interpretation of arsenic metabolism. Chromatographic separation followed by spectroscopic detection as well as the utilization of biotinylated pull-down assays, protein microarray and radiolabelled arsenic have been instrumental in identifying hundreds of metabolic arsenic conjugates, while, computational modelling has predicted thousands of them. However, these species exhibit a variegated pattern, which supports more than one hypothesis for the metabolic pathway of arsenic. Thus, the arsenic species are yet to be integrated into a coherent mechanistic pathway depicting its chemicobiological fate. Novel biorelevant arsenic species have been identified due to significant evolution in experimental methodologies. However, these methods are specific for the identification of only a group of arsenicals sharing similar physiochemical properties; and may not be applicable to other constituents of the vast spectrum of arsenic species. Consequently, the identity of arsenic binding partners in vivo and the sequence of events in arsenic metabolism are still elusive. This resonates the need for additional focus on the extraction and characterization of both low and high molecular weight arsenicals in a combinative manner.

In vitro bio-accessibility and distribution characteristic of each arsenic species in different fishes and shellfishes/shrimps collected from Fujian of China

It is very important to consider the bio-accessibilities and concentrations of each arsenic species, not total arsenic, in seafood in order to accurately assess internal exposure level and health risk of arsenic from seafood. Herein, the concentrations and in vitro bio-accessibilities of each arsenic species in various fishes and shellfishes/shrimps were extensively investigated. Experimental results showed that arsenic species and contents in shellfishes/fishes remarkably varied with the difference of fish/shellfish species or individuals and sampling area, and arsenobetaine (AsB) is dominant arsenic species for fishes and shellfishes/shrimps. Different arsenic species in the same fish/shellfish have quite different bio-accessibilities, and the bio-accessibilities of each arsenic species also varied with fish/shellfish species or individuals. As³⁺ in fishes/shellfishes was partly oxidized to form As⁵⁺ during gastrointestinal digestion, and thus it is more reasonable and practicable to evaluate the bio-accessibilities of inorganic arsenic (iAs, total As³⁺ and As⁵⁺), not individual As³⁺ and As⁵⁺. Fishes and shellfishes/shrimps have similar bio-accessibilities of iAs, AsB and total arsenic, whereas have different bio-accessibilities of MMA (monomethylarsonic acid), DMA (dimethylarsinic acid), and two un-identified arsenic (Ui-As1 and Ui-As2). The results of this study provided a valuable knowledge for accurately assessing the health risk of arsenic in seafood.

Hydrolytic enzyme modified magnetic nanoparticles: An innovative and green microextraction system for inorganic species in food samples

In the presented study, the usability of hydrolytic enzyme immobilized magnetic nanoparticles as an extraction agent for the microextraction of metal ions from food samples was investigated. α-amylase modified magnetic carbon nanotubes (α-amylase-Fe₃O₄/MWCNTs) was used as an extraction agent for direct microextraction of trace arsenic from food sample phase into liquid phase medium prior to its ICP-MS determination. In extraction studies using hydrolytic enzymes, it is impossible to recover the free soluble enzyme after extraction without losing its activity. In our study, this problem was overcome by immobilizing the hydrolytic enzyme on magnetic support. In this way, α-amylase-Fe₃O₄/MWCNTs as an extraction agent with a reuse property of at least six times was used. α-amylase-Fe₃O₄/MWCNTs was characterized by FT-IR, XRD, SEM, SEM-EDX, VSM, TGA, and DTG techniques. Optimization of the presented method was performed using 1568 A rice flour certified reference material. Analytical parameters such as type of hydrolytic enzyme, pH and volume of the aqueous phase, extraction temperature and ultrasonic irridation time were optimized. The microextraction step was performed in ultrasonic water bath within only ∼15 min. Limit of detection (LOD), limit of quantification (LOQ) and relative standard deviation (RSD %) values for the developed method were found to be 14.3 μg kg^-1, 47.3 μg kg^-1 and 7.5%, respectively. The method was successfully applied to the analysis of arsenic contents of different rice and flour samples.

Simultaneous Species Analysis of Arsenic, Selenium, Bromine, and Iodine in Bottled Drinking Water and Fruit Juice by High-Performance Liquid Chromatography-Inductively Coupled Plasma Mass Spectrometry

A method for the simultaneous determination of arsenobetaine, arsenite, arsenate, dimethylarsinic acid, monomethylarsonic acid, selenite, selenate, bromate, bromide, iodate, and iodide in bottled drinking water and fruit juice samples was established by using high-performance liquid chromatography-inductively coupled plasma mass spectrometry. The separation of eleven compounds was performed on an ion exchange chromatography column (Dionex IonPac AS14) with 20 mmol L^-1 (NH₄)₂CO₃ (pH 10) and 50 mmol L^-1 (NH₄)₂CO₃ (pH 10) as a mobile phase. The limits of quantification of the method were 0.17 - 1.2 μg L^-1 for the test compounds in bottled drinking water and 0.34 - 2.4 μg L^-1 in fruit juice. The average recoveries ranged from 85.8 to 102.2%, and the relative standard deviations (RSDs) obtained in fortification recovery studies were generally <4.2% for bottled drinking water samples. The average recoveries ranged from 88.1 to 118.0% (except for iodate) for fruit juice sample.

Quantitative selenium speciation in feed by enzymatic probe sonication and ion chromatography-inductively coupled plasma mass spectrometry

A rapid, sensitive and species preservative analytical method for the simultaneous determination of six selenium (Se) species has been developed. Enzymatic probe sonication (EPS) was investigated as a novel and alternative technology for the extraction of Se species from feed matrices and the results were compared with the conventional hot water extraction, enzymatic hydrolysis and sequential extraction. The critical parameters of EPS such as enzyme types, extraction time, temperature, ultrasonic power and sample/enzyme ratio were varied with control. The Se species were separated and quantitatively determined by ion chromatography-inductively coupled plasma mass spectrometry (IC-ICP-MS). Under current optimised conditions, six inorganic and organic Se species were completely separated within 15 min in a single chromatographic run. The spectral interferences from the argon plasma ⁴⁰Ar₂, ⁴⁰Ar³⁷Cl or ¹H⁷⁹Br were effectively removed by employing the kinetic energy discrimination (KED) mode. Quantitative extraction for total Se (>94.8%) and more than 89.0% for the sum of different Se chemical forms without species transformation were obtained in only 60 s by applying the EPS treatment using aqueous protease XIV. The limits of detection (LODs) and quantification (LOQs) for Se species were in the ranges of 0.21-0.56 µg kg^-1 and 0.69-1.87 µg kg^-1, respectively. The proposed method was successfully applied to the speciation of Se in several reference materials and feed samples collected from the markets and local farms.

Speciation Analysis of Trace Arsenic, Mercury, Selenium and Antimony in Environmental and Biological Samples Based on Hyphenated Techniques

In order to obtain a well understanding of the toxicity and ecological effects of trace elements in the environment, it is necessary to determine not only the total amount, but also their existing species. Speciation analysis has become increasingly important in making risk assessments of toxic elements since the toxicity and bioavailability strongly depend on their chemical forms. Effective separation of different species in combination with highly sensitive detectors to quantify these particular species is indispensable to meet this requirement. In this paper, we present the recent progresses on the speciation analysis of trace arsenic, mercury, selenium and antimony in environmental and biological samples with an emphasis on the separation and detection techniques, especially the recent applications of high performance liquid chromatography (HPLC) hyphenated to atomic spectrometry or mass spectrometry.

Total Arsenic and Arsenic Species Determination in Freshwater Fish by ICP-DRC-MS and HPLC/ICP-DRC-MS Techniques

Analytical methods for the determination of total arsenic (TAs) and arsenic species (arsenite-As(III), arsenate-As(V), monomethylarsenic acid-MMA, dimethylarsenic acid-DMA and arsenobetaine-AsB) in freshwater fish samples were developed. Inductively coupled plasma mass spectrometry with dynamic reaction cell (ICP-DRC-MS) and high-performance liquid chromatography hyphenated to ICP-DRC-MS were used for TAs and arsenic species determination, respectively. The DRC with oxygen as a reaction gas was used. Sample preparation, digestion, and extraction were optimized. Microwave assisted digestion and extraction provided good recovery and extraction efficiency. Arsenic species were fully separated in 8 min using 10 mmol L-1 of ammonium dihydrogen phosphate and 10 mmol L-1 of ammonium nitrate. Overlapping of AsB and As(III) of arsenic species in the presence of a high concentration of AsB and trace amounts of As(III) were studied. Detailed validation of analytical procedures proved the reliability of analytical measurements. Both procedures were characterized by short-term and long-term precision: 2.2% (TAs) up to 4.2% (AsB), and 3.6% (TAs) up to 7.2% (DMA), respectively. Limits of detection (LD) were in the range from 0.056 µg L-1 for TAs to 0.15 µg L-1 for As(V). Obtained recoveries were in the range of 85%⁻116%. Developed methods were applied to freshwater fish samples analysis.