Speciation analysis of mercury in seawater from the lagoon of Venice by on-line pre-concentration HPLC–ICP-MS

The present and potential future of aqueous mercury preservation: a review

Mercury is considered to be one of the most toxic elements to humans. Due to pollution from industry and artisanal gold mining, mercury species are present globally in waters used for agriculture, aquaculture, and drinking water. This review summarises methods reported for preserving mercury species in water samples and highlights the associated hazards and issues with each. This includes the handling of acids in an uncontrolled environment, breakage of sample containers, and the collection and transport of sample volumes in excess of 1 L, all of which pose difficulties for both in situ collection and transportation. Literature related to aqueous mercury preservation from 2000-2021 was reviewed, as well as any commonly cited and relevant references. Amongst others, solid-phase extraction techniques were explored for preservation and preconcentration of total and speciated mercury in water samples. Additionally, the potential as a safe, in situ preservation and storage method for mercury species were summarised. The review highlighted that the stability of mercury is increased when adsorbed on a solid-phase and therefore the metal and its species can be preserved without the need for hazardous reagents or materials in the field. The mercury species can then be eluted upon return to a laboratory, where sensitive analytical detection and speciation methods can be better applied. Developments in solid phase extraction as a preservation method for unstable metals such as mercury will improve the quality of representative environmental data, and further improve toxicology and environmental monitoring studies.

Dielectric barrier discharge-assisted determination of methylmercury in particulate matter by atomic absorption spectrometry

Particulate matter (PM) impregnated with methlymercury (MeHg⁺) was analyzed using atomic absorption spectrometry coupled to a customized dielectric barrier discharge (DBD) device. Chemical vapor generation (CVG) was applied to generate methylmercury hydride and the DBD device promoted bond cleavage with subsequent release of free Hg atoms to the gas phase. Hydride generation was carried out using a lab-made syringe-based device in batch mode using argon as a carrier gas. Optimized conditions included the use of 1.0 mL of a 0.05% m/v NaBH₄ solution and 1.0 mL of a 10% v/v HCl solution. This system was coupled to the DBD device, designed to operate in "plasma jet" configuration. Assessment of the designed device for methylmercury detection was established based on an on-off switch, which promptly demonstrated that Hg signals could only be detected upon activation of the plasma discharge. In parallel, adsorption of MeHg⁺ to PM-loaded glass fiber filters was investigated. Direct analysis of methylmercury-impregnated PM resulted in significant signal suppression compared to the same mass of analyte from an aqueous standard, which suggests that methylmercury is efficiently adsorbed on PM. This was later confirmed by repeating the same experiment with "blank" (PM-free) glass fiber filters. Hence, extraction of methylmercury to a liquid phase was required for quantification. In order to demonstrate the feasibility of the proposed setup to carry out methylmercury detection in the presence oh Hg²⁺, recovery tests were conducted by mixing MeHg⁺ with Hg²⁺ at three distinct concentration levels (100 : 1, 10 : 1 and 1 : 1 MeHg⁺ : Hg²⁺). Recoveries better than 91% were obtained for MeHg⁺ under these conditions, which demonstrates that the device is efficient for MeHg⁺ determination by simply modulating the plasma (switching on-off). Limits of detection and quantification were established as 6 ng and 19 ng, respectively.

DNA-templated fluorescent silver nanoclusters on-off switch for specific and sensitive determination of organic mercury in seafood

Organic mercury including methyl-mercury and ethyl-mercury (CH₃Hg⁺ and C₂H₅Hg⁺) has high toxicity and bio-accumulation, and thus is easy to generate bio-amplification in food chain. Hence, the specific detection of organic mercury has great significance for objectively assessing the health risk of mercury in seafood. We herein designed an aptamer (A_S-T7), which consists of a silver nanoclusters (AgNCs) scaffold sequence (A_S) and a T-rich sequence (A_T7), for simultaneously synthetizing DNA-templated AgNCs and recognizing organic mercury, and further developed a label-free fluorescent method for the sensitive and specific determination of organic mercury (CH₃Hg⁺ and C₂H₅Hg⁺ total concentration) by using DNA-templated AgNCs as signal. Without organic mercury, Ag⁺ in the mixture of aptamer and Ag⁺ was bond on A_S of aptamer to form A_S-templated AgNCs after reduction, and thus emitted strong fluorescence. Whereas, in the presence of organic mercury, CH₃Hg⁺/C₂H₅Hg⁺ was bond on A_T7 of aptamer to generate photoinduced electron transfer (PET) between CH₃Hg⁺/C₂H₅Hg⁺ and A_S-templated AgNCs, and thus results in fluorescence quenching of A_S-templated AgNCs. The fluorescent method could be used to rapidly detect organic mercury with a detection limit of 5.0 nM (i.e. 1.01 ng Hg/g), which meets the U.S. EPA standard of 0.3 mg/kg (wet). The method was successfully used to detect organic mercury in water and fish muscle with a recovery of 96%-104% and an inter-days RSD (n = 5) < 7%. The success of the study promised a reliable method for rapid and specific detection of organic mercury in environmental and biological samples.

Simultaneous enrichment of inorganic and organic species of lead and mercury in pg L-1 levels by solid phase extraction online combined with high performance liquid chromatography and inductively coupled plasma mass spectrometry

Quantification of ultra-trace inorganic and organic species of lead and mercury in unpolluted environmental water is crucial to estimate the mobility, toxicity and bioavailability and interactions. Simultaneous pre-concentration of Pb and Hg species in pg L^-1 levels followed by multi-elemental speciation analysis makes great sense to a large set of unstable samples because of time advantages. Herein simultaneous enrichment and speciation analysis of ultra-trace lead and mercury in water was developed by online solid-phase extraction coupled with high performance liquid chromatography and inductively coupled plasma mass spectrometry (SPE-HPLC-ICP-MS) for this aim. Pb(II), trimethyl lead (TML), triethyl lead (TEL), Hg(II), methylmercury (MeHg) and ethylmercury (EtHg) were baseline separated in 11 min under gradient elution using 5 mM l-cysteine (Cys) at pH 2.5 in the 0-1 and 4-15 min and 5 mM Cys + 0.5 mM tetrabutyl ammonium hydroxide solution at pH 2.5 in the 1-4 min. Lead and mercury species in 10 mL intact water samples were adsorbed on a 1 cm C₁₈ enrichment column pre-conditioned with 10 mL of 1 mM 2-mercaptoethanol at 10 mL min^-1, and then directly desorbed by the mobile phases. High enrichment factors (459 for Pb(II), 1248 for TML, 1627 for TEL, 2485 for Hg(II), 1984 for MeHg and 1866 for EtHg) were obtained with good relative standard deviations (<5%), leading to low LODs (0.001-0.011 ng L^-1) and LOQs (0.004-0.036 ng L^-1). Good accuracy of this method was validated by two certified reference materials of total lead in water (GBW08601) and total mercury in water (GBW08603) along with spiked recoveries (89-93%). The method was applied to analyze trace lead and mercury species in river, lake, tap and rain water, and purified and mineral water. Inorganic lead of 13-68 ng L^-1 and inorganic mercury of 21-49 ng L^-1 were measured in the nine water samples whereas TML, TEL and MeHg were not detected with 2-5 ng L^-1 EtHg presented only in one river water and tap water.

Ultra-trace determination of total mercury in Italian bottled waters

Mercury (Hg) is a widespread, highly toxic persistent pollutant with adverse health effects on humans. So far, concentrations below the method detection limit have always been reported by studies on the concentration of mercury in bottled water when determined using instrumental analytical methods. These are often very expensive and are unaffordable for many laboratories. In this work, a less expensive method based on cold vapour atomic fluorescence spectrometry has been employed to determine total mercury (Hg_T) concentrations in bottled natural mineral waters. In all, 255 waters representing 164 different typologies were analysed. They came from 136 springs located in 18 Italian regions. In all samples, Hg_T concentrations were found in the range of sub-nanogram to a few nanograms per litre, well below the National and European regulatory limit (1 μg L^-1). Differences in Hg_T concentrations were related not only to the environmental characteristics of the springs but also to the extent and impact of human activities. Higher concentrations were found in waters coming from regions with former mining and/or natural thermal and volcanic activity. These data allowed us to estimate the mercury intake by population (adults, children and toddlers) from drinkable mineral waters consumption. The mean mercury daily intake was found to be remarkably lower, not only than the provisional tolerable value (1 μg L^-1 according to European and Italian legislation) but also than the estimated provisional tolerable weekly intake (PTWI) value (4 μg kg^-1 body weight) recommended by the Joint FAO/WHO Expert Committee on Food Additives (JECFA).

Hg(2+) detection using a disposable and miniaturized screen-printed electrode modified with nanocomposite carbon black and gold nanoparticles

A miniaturized screen-printed electrode (SPE) modified with a carbon black-gold nanoparticle (CBNP-AuNP) nanocomposite has been developed as an electrochemical sensor for the detection of inorganic mercury ions (Hg(2+)). The working electrode surface has been modified with nanocomposite constituted of CBNPs and AuNPs by an easy drop casting procedure that makes this approach extendible to an automatable mass production of modified SPEs. Square wave anodic stripping voltammetry (SWASV) was adopted to perform Hg(2+) detection, revealing satisfactory sensitivity and detection limit, equal to 14 μA ppb(-1) cm(-2) and 3 ppb, respectively. The applicability of the CBNP-AuNP-SPE for the determination of inorganic mercury has been assessed in river water by a simple filtration and acidification of the sample as well as in soil by means of a facile acidic extraction procedure assisted by ultrasound.

A novel ion imprinted SiO2 microsphere for the specific and rapid extraction and pre-concentration of ultra-trace methyl mercury

A novel MeHg ion imprinted silica microsphere was designed and synthesized for the specific, cost-effective and rapid pre-concentration of ultra-trace MeHg from natural water.

Thiol-functionalized silica microspheres for online preconcentration and determination of mercury species in seawater by high performance liquid chromatography and inductively coupled plasma mass spectrometry

Thiol-functionalized silica microspheres were synthesized from aminosilica for online mercury preconcentration, followed by high performance liquid chromatographic separation and inductively coupled plasma mass spectrometry detection.

Gold nanorods-based FRET assay for ultrasensitive detection of Hg2+

A fluorescence method for detecting mercury ion in a homogeneous medium is proposed with gold nanorods (GNRs) as a fluorescence quencher on the basis of the fluorescence resonance energy transfer (FRET). Under the optimum conditions, the method exhibits a dynamic response range from 10 pM to 5 nM with a detection limit of 2.4 pM.