Advances in the analysis methods of inorganic elements in foods

Inorganic elements in food are very important to human body both2o2n nutrition and health safety. The study and analysis of inorganic elements in food can help to evaluate the nutritional value of food and avoid toxic and harmful foods, and understand the situation and extent of food contamination in order to identify and control pollution sources. It is also beneficial to guide the production and development of fortified foods and to improve food processing technology and food quality. Therefore, the content of inorganic elements should be monitored and detected in the food production process. In order to provide a reference for the analysis of inorganic elements in food, the main methods and characteristics of inorganic elements analysis in food and its quality control at home and abroad were reviewed, and the development trend of inorganic elements analysis methods in food were clarified, including traditional chemical and physical methods, as well as covered nanotechnology and biotechnology in recent years. The practical application of these analytical methods in recent years was enumerated

Investigations on the development of a novel hybrid sensor for environmental monitoring applications.

Heavy metal toxicity is a major environmental problem world-wide. Increased spreading and high concentration levels of the toxic heavy metals in water environments have posed a severe threat to human health and the ecosystem. Over the years, to improve the drinking water quality standards, safe threshold concentrations of these highly toxic pollutants are constantly being lowered by the governmental and environmental bodies. Current instrumental techniques used to detect these low levels of heavy metal ions are laboratory based, use sophisticated instruments, expensive, time consuming and require trained personnel. There is a constant need for the development of in-situ, rapid, highly sensitive and selective sensors to monitor the very low concentration levels. Various approaches for improving sensitivity and selectivity have been investigated over the years involving multiple detection techniques. In general, optical approaches provide higher sensitivity along with simplicity while electrochemical sensors provide better selectivity. In the last decade, nanomaterials have emerged as a key element in their sensitivity improvement. Combining all these advantages, a novel hybrid sensor has been envisaged integrating optical and electrical fields in addition to nanomaterials. This thesis reports investigations on enhancing the sensitivity/selectivity through optical, nanomaterials and electrochemical routes, and then integrating these to realise a hybrid sensor. A novel optical sensor has been developed using the phenomena of evanescent waves in optical fibre with dithizone to detect heavy metal ions. A U-bent sensor geometry has been investigated to enhance the optical sensitivity of the sensor through higher evanescent field near the surface. Further, optical field confinement to the surface has been investigated through thin film coating to improve the sensitivity. A new inverted trench design based sensor has been developed, and sensitivity enhancement has been achieved through this novel design and confirmed using modelling work accompanied by experimental results. Large surface to volume ratio of nanomaterials, such as ZnO nanowires, on the sensor surface can provide enhanced surface interactions leading to higher sensitivity. But, surfaces modified with ZnO nanostructures tend to be hydrophobic in nature. A new remote and non-contact method to tune the wettability of the ZnO nanostructures using LEDs has been developed. Higher sensitivity has been achieved by tuning the wettability of ZnO nanowires using the developed method. An electrochemical sensor has been developed in order to understand the potential effects of the electric field on the near surface molecular dynamics and thereby, effects on the optical detection. Effects of parameters such as deposition time, scan frequency, concentration, electrode materials and their surface area have been investigated to improve the sensitivity and selectivity. Multi-ions selectivity has been achieved by simultaneous detection of copper, mercury and lead ions in buffer solution. Higher sensitivity has been obtained by modifying the gold electrode using graphene flakes. Further, to integrate the optical field with this sensor to realize the hybrid sensor, thickness of the gold electrode has been optimised to allow the penetration of evanescent field onto the electrode surface. Under optimised conditions evanescent field resonantly couples to the surface plasmons of the gold electrode. Computational investigations have been carried out to study the effect of number of graphene layers on the sensitivity of the surface plasmon resonance (SPR) based optical sensor integrated with the electrochemical sensor. Preliminary investigations on the developed hybrid sensor show that the electric field complements the optical field. Investigations have shown that application of electric field enhances the sensitivity for optical detection by attracting more ions on the electrode and also, provides the multi-ion selectivity. These investigations have opened up new possibilities for the real-time monitoring of highly sensitive and selective molecular interactions, showing strong potential in a range of applications areas such as environmental sensing, biosensing and agricultural sensing

Sensory polymeric foams as a tool for improving sensing performance of sensory polymers

Microcellular sensory polymers prepared from solid sensory polymeric films were tested in an aqueous Hg(II) detection process to analyze their sensory behavior. First, solid acrylic-based polymeric films of 100 µm thickness were obtained via radical copolymerization process. Secondly, dithizone sensoring motifs were anchored in a simple five-step route, obtaining handleable colorimetric sensory films. To create the microporous structure, films were foamed in a ScCO2 batch process, carried out at 350 bar and 60 °C, resulting in homogeneous morphologies with cell sizes around 5 µm. The comparative behavior of the solid and foamed sensory films was tested in the detection of mercury in pure water media at 2.2 pH, resulting in a reduction of the response time (RT) around 25% and limits of detection and quantification (LOD and LOQ) four times lower when using foamed films, due to the increase of the specific surface associated to the microcellular structure.Fondo Europeo de Desarrollo Regional) and both the Spanish Agencia Estatal de Investigación (MAT2017-84501-R) and the Consejeria de Educación-Junta de Castilla y León (BU306P18

Identification of heavy metal ions from aqueous environment through gold, Silver and Copper Nanoparticles: An excellent colorimetric approach

Heavy metal pollution has become a severe threat to human health and the environment for many years. Their extensive release can severely damage the environment and promote the generation of many harmful diseases of public health concerns. These toxic heavy metals can cause many health problems such as brain damage, kidney failure, immune system disorder, muscle weakness, paralysis of the limbs, cardio complaint, nervous system. For many years, researchers focus on developing specific reliable analytical methods for the determination of heavy metal ions and preventing their acute toxicity to a significant extent. The modern researchers intended to utilize efficient and discerning materials, e.g. nanomaterials, especially the metal nanoparticles to detect heavy metal ions from different real sources rapidly. The metal nanoparticles have been broadly utilized as a sensing material for the colorimetric detection of toxic metal ions. The metal nanoparticles such as Gold (Au), Silver (Ag), and Copper (Cu) exhibited localized plasmon surface resonance (LPSR) properties which adds an outstanding contribution to the colorimetric sensing field. Though, the stability of metal nanoparticles was major issue to be exploited colorimetric sensing of heavy emtal ions, but from last decade different capping and stabilizing agents such as amino acids, vitmains, acids and ploymers were used to functionalize the metal surface of metal nanoparticles. These capping agents prevent the agglomeration of nanoparticles and make them more active for prolong period of time. This review covers a comprehensive work carried out for colorimetric detection of heavy metals based on metal nanoparticles from the year 2014 to onwards. © 202

Uso de polímeros de impronta molecular para la simplificación del análisis de mercurio total y metilmercurio

El objetivo de la realización de esta tesis y desarrollar métodos de análisis de mercurio y metilmercurio rápidos, sencillos y asequibles a la maioria de los laboratorios de rutina, que sean de aplicación en el ámbito medioambiental, alimentario y de salud pública. El mercurio está considerado un contaminante prioritario en el marco de la política europea de aguas, con valores límite en aguas superficiales de entre 0,05-0,07 µg/L. La especie metilmercurio y una de las especies mas tóxicas y causa daño en el sistema nervioso, cardiovascular e inmunolóxico. Por otra parte, el límite legal que fija la Unión Europea para lo metilmercurio en pescado y de 1 mg/Kg (Regulación (CE) En el 629/2008). Por lo tanto, es necesario desarrollar métodos sencillos y rápidos de análisis para controlar la concentración de mercurio en muestras de interés medioambiental y la especie metilmercurio en productos pesqueros destinados al consumo humano. Para esto, se desarrollarán polímeros de impronta molecular, sintetizados habida cuenta la estructura del analito que se quiere determinar

Ligands for Complexation, Extraction, and Sensing of Mercury(II) for Application to High-Level Waste (HLW) at the Savannah River Site (SRS)

Mercury (Hg) separation and sensing is of high significance due to Hg(II) environmental mobility and toxicity. Furthermore, the use of Hg in nuclear applications has resulted in its accumulation in several DOE sites, such as in Oak Ridge and Savannah River reservations. Organic mercury species have been found in low activity waste (LAW) streams resulting from high-level waste (HLW) processing at the Savannah River Site (SRS), therefore posing a threat to humans and the environment. Mercury, being a soft Lewis acid, has a strong affinity for softer Lewis bases, such as S- or N-donor ligands. Therefore, we focus on synthesizing and studying soft-donor organic ligands, such as thioamides and sulfonamides, as effective complexants, extractants or chemosensors for inorganic mercury. We studied the interaction of Hg(II) with bis-arylsulfonamide ligand derivatives derived from substituted o-phenylenediamine and several sulfonyl chlorides. Successful extraction of Hg(II) from alkaline aqueous phases into dichloroethane was observed, with extraction efficiency and recovery as high as 97.4 % and 81.5 %, respectively, at pH 12.0 by the disulfonamide ligand L4. The influence of pH, ligand concentration, and the presence of the organic base (triethylamine) was studied in detail. The crystal structure of the isolated Hg(II) complex with the disulfonamide analog L2 shows a 1:2 Hg(II):L2 stoichiometry with two triethylammonium countercations (Et3NH+) coordinating in the outer sphere. The bis-dansylsulfonamide (LD) derivative was shown to be an effective Hg(II) sensor, as fluorescence quenching was observed upon gradual addition of HgCl2 solution with complete quenching occurring at Hg(II):LD molar ratio of 1:1. Thioamide ligands derived from 2,6-diaminopyridine were also studied. The pyridine N atom and the thiocarbonyl moiety on these ligands result in strong Hg(II) binding (log K = 7.43). The lipophilic derivative of this thioamide ligand (PDT) is a potential extractant for industrial solvent extraction processes. PDT extracts Hg(II) with an extraction efficiency of 99.7% and discriminates the presence of mercury over various competing metal ions, which are present in higher concentrations at HLW. We also carried out a spectroscopic and structural study on a Hg(II)-mediated cyclization reaction of a dithioamide ligand derived from o-phenylenediamine to a benzimidazole derivative, which has led to a potentially new paradigm for Hg(II) sensing. Overall, with high observed recovery for extracted Hg(II), strong binding, and high selectivity for several of our studied ligands, this research has demonstrated new pathways for application of Hg(II) sensing, complexation, and recovery from alkaline high-level tank waste

Speciation Studies of Biologically Active Compounds (Atomic Absorption, Ultrasonic Nebulization, Hplc, Organoleads, Aminoglycosides-Metal Complexes).

Part I. Development of a new nebulizer-flame atomizer atomic absorption system designed for metal speciation. A new flame atomic absorption system has been designed and developed. A new, highly efficient ultrasonic nebulizer was used for sample introduction and aerosol generation. Extensive evaluations and modifications of commercially available atomic absorption spray chambers and burner heads were conducted. Observations made during these studies centered on some of the fundamental properties of aerosol transport within the atomic absorption nebulization system. The new flame atomic absorption system consisted of the ultrasonic nebulizer incorporated into a modified spray chamber. The aerodynamic properties of the chamber were designed to given maximal aerosol transport. Burner extensions were incorporated into the chamber and could be resistively heated to aid in desolvation of the aerosol. This system exhibited an increase in sensitivity, depending on the conditions and flow rates, of approximately 5 to 7 fold, and an increase in detection limits of approximately 2 to 4 fold over that reported for commercial flame atomizers. Part II. The speciation of organoleads, mercury compounds, and metal complexes of aminoglycosides. A number of physiologically and environmentally important organoleads and mercurials were speciated by high performance liquid chromatography-atomic absorption (HPLC-AA). HPLC systems were developed to separate these compounds by using complementary thin layer chromatographic (TLC) methods with colorimetry detection. These systems were used to study the conversion of tetraethyllead in seawater over a long period of time and the decomposition of diethyllead dichloride. Results showed that the triethyllead chloride was stable in seawater for at least one year, and that diethyllead chloride decomposes into triethyllead chloride and lead(2+) compounds. Metal complexation with a class antibiotics, aminoglycosides, was investigated both by HPLC-AA and TLC-colorimetry. New HPLC and TLC systems were developed to separate the metal/complexes or the uncomplexed aminoglycoside. The formation of the copper and cobalt complexes was shown to be a function of the ratio of metal to aminoglycoside

Spectrophotometric methods of analysis

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A REAL-TIME MONITORING IONIC LIQUID CHEMICAL SENSOR FOR HEAVY METALS AND TOXIC POLLUTANTS

Heavy metal and toxic pollutants in water samples cause severe health risks. Current methods used are time consuming; costly, and involve toxic organic solvents: Areal-time, ionic liquid monitoring chemical sensor is needed for instantaneous analysis of samples. Ionic liquids, ion compounds with low melting point, have become popular subject ofstudy because ofthenproperties especially non-toxicity, no vapor pressure and electrochemical properties. Recent studies suggest that ionic liquids can be used as solvents, reaction media or electrolyte, substituting volatile organic solvents, for heavy metals and toxic pollutant electrochemical activity. This research focuses on the use of ionic liquid for the development of a chemical sensor to detect and determine toxic analytes especially lead; Lead was chosen as the metal ion for this study due to its effects on children. [HMIM][TFSI] was chosen for this study due to its electrochemical and environmental properties and anodic stripping voltammetry (ASY* was chosen as analysis method due to its sensitivity range, convenience and cost effectiveness. Due to its simplicity and convenience, carbon paste method was chosen to incorporate the ionic liquid into the electrode design. Results show that the ionic liquid modified carbon paste electrodes measure higher current compared to the simple carbon paste electrodes. It is assumed that the modified electrodes are more sensitive to change in measured current compared to the simple ones. However, since [H3vHM][TFSI] is a hydrophobic ionic liquid, it alone is not capable of interacting with lead ion since metal ions are always hydrated in a solution. Metal ions were not depositing on the electrode surface and there were no peaks registered in the plot. Through research, it was known that ligands and other types of co-solvents can be used to aid metal ion penetration into the hydrophobic ionic liquid phase. Thus, it is hoped that the project can be expanded by incorporating these ligands into the electrode design in the near future. As a conclusion, the ionic liquid modified carbon paste electrodes shows promising signs to be used as chemical sensors for lead detections due their electrochemical and environmental aspects