Analytical Techniques for Arsenic - Assignment Example

ANALYTICAL TECHNIQUES FOR ARSENIC Prepared by Date University Professor’s Name Course Name Background of Arsenic Element Arsenic is one of the most notable chemical elements 33. This element is mainly found in minerals that are mostly a combination of both sulphur and metals. The first isolator of arsenic is not well-known but much of the credit is shown to Albert Magnus, who first isolated the chemical element in the year-1250 (Mandal & Suzuki, 2002). The element is named after Latin arsenicum and, also Greek arsenickon that are both names of pigment and yellow orpiment respectively. In early identification phase; arsenic played a significant role within the Bronze Age where it was used to add to bronze as a distinct straightener. For most cases, it is found within the earth’s crust in a form commonly identified as Iron Arsenide Sulfide; it is further found within the atmosphere as arsenic trioxide dusts, which is indeed a by-product of industrial smelting operations (Mandal & Suzuki, 2002). Considering the fact that the element undergoes a distinctive set of reactions with water, food among others, it is encountered in numerous phases of both organic and inorganic compounds (World Health Organisation, 2011). In other cases, it occurs as pure elemental crystal and is metalloid in nature. The element has a great number of allotropes however; the most popular and distinguished one is the gray for that is deemed to be very crucial in numerous industrial processes. Arsenic atomic symbol-As is always in a solid state. Despite the many forms of arsenic allotropes, the white arsenic is known to be a more dangerous form that emanates as a by-product of copper refining (Mandal & Suzuki, 2002). In today’s world, the chemical element is highly adopted within the semi-conductor industry for purpose of developing light emitting diodes (LEDs) and, also used in generation of semiconductor for transistors as well as other electronic devices. In the natural environment, arsenic exists mostly in the +3 and +5 oxidation states. As (III) is mostly identified as being the most dangerous and toxic in comparison to As (V) (Dixit & Hering, 2003). This is especially since it mostly occurs under such suppressed environmental condition as in the case of over-flooded soils. On the other hand, As (V) mostly occurs under an oxidised environmental setting like in the case of drained soils. It is however; important to understand that both of these oxidation states of arsenic are popularly perceived to be occurring together with these soil structures due to lower levels of transformation that is always noted between oxidation states (Dixit & Hering, 2003). Arsines are organic arsenic species that are generated from microbial actions in such platforms as landfills and hot-water springs. They are indeed acutely toxic in the event that there is the presence of As-H bond (Cullen, N.d). On the contrary however; Me3As, Gosio gas is deemed to be even less toxic in the event that there is the historical connection with illness and a much recent hypothesis for which it is associated with the causes of Sudden Infant Death Syndrome. In addition to this, the methylation of arsenic undergoes a step-by-step oxidation/reduction process that first involves oxidative addition of a methyl group from S-adenosylmethanionine to arsenic (III) species that further transforms to a methylarsenic (V) product (Cullen, N.d). Consequently, the next phase involves a two-step electron reduction process that also involves thiol groups; with the immediate product being the methylarsenic(III) organic species that is deemed far much ready for a next oxidation process (Cullen, N.d). In natural and drinking water, the level of arsenic is positioned between 1 and 2 µg/l (Szkoda, Zmudzki, & Grzebalska, 2006). It is crucial to note that the level might increase in such cases as areas with volcanic rock and Sulfide mineral deposits; areas that mostly contain natural resources where the level of as high as 12 mg/l can be reported; areas that are deemed to be very near to anthropogenic sources like in the mining and agrochemical manufacture as well as in geothermal waters where the maximum level can be established to be 25mg/l (Szkoda, Zmudzki, & Grzebalska, 2006). Notably, the overall mean arsenic concentrations within waters from sedimentary rocks would range between 5 and 3000 mg/l while highest levels of arsenic concentration would occur in contaminated waters. In relation to food, it is noted that the overall estimations of daily dietary intake of arsenic-infiltrated products could vary due to a wider variations within the consumption of fish and shellfish mostly. Research indicates that there are approximately 25% of arsenic-related infiltrations in food that is mostly present as inorganic state (Szkoda, Zmudzki, & Grzebalska, 2006). For most cases, both fish and meat are the main sources of dietary intake of arsenic and their levels might range from 0.4 to 118mg/kg as reported in marine fish that is sold for purpose of human consumption while in meat and poultry-related products; the concentration might reach 0.44 mg/kg (Szkoda, Zmudzki, & Grzebalska, 2006). The overall mean of day-to-day partake of arsenic in food products for adults is approximated to range between 16.7 to 129 µg while for infants, the degree ranges from 1.26 to 15.5 µg (Szkoda, Zmudzki, & Grzebalska, 2006). In regards to arsenic levels in biological samples like blood, a preparation technique that involves digestion with nitric acid and hydrogen peroxide and using the HGAAS as the sole analytical model, a level of 0.5 µg/l is identified; for hair, the preparation technique involves wet ash that is combined with nitric acid/per chloric acids and reduced using sodium borohydride using HGAAS analytical technique the sample detection limit is identified to be 0.1 µg/l; and in the case of urine that is subjected to irradiation epithermally and using NAA analytical model results to a sample detection range of between 40-100ng/g or 0.5 µg/sample. (Szkoda, Zmudzki, & Grzebalska, 2006) For the case of nails that are subjected to a preparation methodology involving wet ashing and hydrogen peroxide and using HGAAS analytical approach results to a sample detection of 1.5 µg/g (Szkoda, Zmudzki, & Grzebalska, 2006). In regards to such foreign samples as soft tissue; the measurement of arsenic levels adopts a preparation technique that focuses on digestion with nitric acid/sulphuric acids and in the extraction with chloroform using GFAAS analytical approach, with the sample detection levels established to be 0.2 ppm. In nails, a wet ashing preparation model that integrates nitric acids and hydrogen peroxide and later subjected to HGAAS analytical approach results to a sample detection limit of 1.5 µg/g (Szkoda, Zmudzki, & Grzebalska, 2006). Analytical Technique used in Determination of Arsenic in; i) Drinking Water & Groundwater The most common methods for determining arsenic in drinking and groundwater are through EPA Method 1632: Hydride Generation Atomic Absorption Spectrophotometry (HGAAS) as well as inductively coupled plasma mass spectrometry (ICP-MS) (Chatterjee, et al. 2000). The methods involve a preparation technique that involves digestion with 6M HCI that allows a reduction to arise with sodium borohydride and later subjected to cold trap and desorption into quartz furnace (Chatterjee, et al. 2000). Other notable methods for analysis arsenic in water include; EPA Method 206.4: SDDC colorimetric spectrophotometry at 510nm; EPA Methods 206.2 and 7060A: GFAAS with Ni(NO3)2 modifier and EPA Method 206.3 that are mostly used for determining arsenic levels in water that is mixed with solid wastes (Chatterjee, et al. 2000). ii) Food In relation to foods, two common analytical methods are used; Graphite Furnace Atomic Absorption Spectrometry (GFAAS) and Hydride Generation atomic Absorption Spectrometry (HGAAS). In using the GFAAS technique, the preparation technique would involve immediate digestion with nitric acid; dry ashing with magnesium oxide as well as reduction with ascorbic acid (Chatterjee, et al. 2000). On the other hand, the preparation method for HGAAS involves immediate digestion with nitric/sulphuric acid and a subsequent reduction to its trivalent arsenic state with the addition of potassium iodide and later, a reduction that would encompass arsine with sodium borohydride (Chatterjee, et al. 2000). iii) Rice For rice, the most viable analytical approach would be the adoption of Inductively Couple Plasma-Mass Spectrometry (ICP-MS) with a speciation using High Performance Liquid Chromatography (HPLC) (Bruno, et al. 2016). The technique adopts an ion source with a distinctive mass analyser like the quadrupole mass filters. The method is deemed to be unique and effective since it is EPA-approved for arsenic detection with a limit of 0.1µg/L (Bruno, et al. 2016). The sensitivity of the method can be further enhanced using a hydride generation (HG) approach that would result to a more efficient sample introduction as well as a matrix removal (Bruno, et al. 2016). iv) Biological Material Biological materials are best assessed and analysed using the Atomic Absorption Spectrometry (AAS). The most notable approaches for this technique include; AAS (FAAS), electro-thermal AAS (ET-AAS) as well as Hydride Generation (HG)-AAS. GF-AAS is directly deposited in a distinctive graphite furnace and entirely dissolved as well as mineralised in situ (Chatterjee, et al. 2000). The next phase involves vaporisation process that would later results to a volatile set of hybrids. The process also involves the use of such matrix modifiers as a distinct mixture of palladium and magnesium that protects the underlying analyte from possible premature volatilisation immediately prior to the vaporisation process that can result to loss of arsenic altogether. v) Hair The most adopted analytical method for determining arsenic in hair is Hydride Generation Atomic Absorption Spectrometry (HGAAS). The preparation model for this technique involves intensive wet ashing with nitric or sulphuric acids as well as hydrogen peroxide (Chatterjee, et al. 2000). The next step involves a reduction process to arsine that involves sodium borohydride. The method has a sample detection limit of 0.06µg/g under a 93% confidence level (Chatterjee, et al. 2000). In other cases, hair is also analysed using the Neutron Activation Analysis (NAA) method since it has the capacity to measure arsenic detection limit of 0.001µg/g and, also since hair is perceived to be a relatively small biological sample that is sensitive to analysis and detection process. vi) Urine There are different known analytical methods for determining arsenic level in urine. These are; first, Neutron Activation Analysis (NAA) where the preparation method involves irradiate epithermally with a detection sample limit of between 40-100ng/g and a confidence level of between 93-109%; Colorithmetric photometry analytical method whose preparation process involves immediate digestion with nitric and perchloric acid and a reduction with tin chloride-the method has a detection sample limit of 0.5μg/sample and confidence level of between 90-110%; and also, a flow injection HGAAS analytical method whose preparation technique involves majorly pre-treatment with L-cysteine and a reduction with potassium iodide (Chatterjee, et al. 2000). The method has a sample detection limit of 0.1μg/L and a 95% confidence level. vii) Soil The analytical method for determining arsenic levels in soil include; x-ray fluorescence backscatter (XRF); the preparation involves pellets and has a sample detection limit of 4mg/kg; Colorimetric spectrometry at 712nm whose preparation method involves selective complexation of As+5 with ammonium molybdate and, also HG-HCT/GC-MID that greatly involves extraction of sodium bicarbonate with a sample detection limit of between 0.2 and 0.4 μg/L and a 97% confidence level (Chatterjee, et al. 2000). viii) Environmental Materials Atomic Absorption Spectrometry (AAS) is one of the most notable analytical methods used for the purpose of measuring environmental materials. It encompassed of such methodologies as AAS (FAAS), Electro-thermal AAS (ET-AAS) and HG-AAS. FAAS possesses a sample detection limit of (~1 mg/L) (Chatterjee, et al. 2000). GF-AAS adopts a deposition within a graphite furnace for which there is full dissolution and mineralisation. The resultant analyte is then subjected to vaporisation to come up with volatile hybrids. It is US-approved EPA analytical methods for arsenic in water and other notable environmental samples (Chatterjee, et al. 2000). HG-AAS utilises a hydride production methodology that can be easily linked to numerous detection systems while still improving the detection limit aspects. Arsenic Analysis Techniques Inductively Couple Plasma Mass Spectrometry (ICP-MS); some of the advantages of this analytical technique include; it is approved by US EPA, it possess a multi-element capacities as well as a linear dynamic range (Helaluddin, 2016). However, it is fond of spectral and matrix interferences. The methodology however could not accommodate sensitivity improvisation hence the formulation of another technique. Absorption Spectrometry (AAS); like graphite furnace atomic absorption spectrometry (GF-AAS) sole advantage rests with the fact that it is approved by the US EPA. On the contrary, however, it results to pre-atomisation deficits and also, it requires the adoption of matrix modifiers (Helaluddin, 2016). Considering the fact that there are far too many AAS techniques that portray different means and forms of presentation and atomisation of a sample; a much definite technique was required altogether. Spectrometry, Atomic-Fluorescence (AFS); is an ideal arsenic detection model for speciation duties related to hydride forming elements and Hg. It has a detection limit set below µg L−1 as well as a relatively broader linear calibration level that extends to mg L−1, this fosters its application to a great deal of environmental, biological and food samples (Helaluddin, 2016). However, it requires a great set of vapour generation and optical designs for purpose of achieving full benefits. High-Performance Liquid Chromatography (HPLC); method like HPLC-ICP-MS was formulated to test the total arsenic level of water, urine and hair; the advantage of this technique lies in the fact that it does not require any form of sample pre-treatment while some of its drawbacks indicates that it is very expensive and mostly time consuming and also, it can further results to spectral and matrix interferences at all costs (Helaluddin, 2016). It was devised for the purpose of covering for shortcomings related to liquid chromatography. Solid-Phase Extraction(SPE); is analytical technique formulated for the purpose of executing rapid; selective sample preparation as well as purification before chromatography analysis has been done (Helaluddin, 2016). It allows for an immediate sample clean-up, recovery process and concentration of proper elements for accurate analysis. The only challenge related to this technique rest with efficient selection process for the most viable and suitable product for application process. Fluorimetry; is an analytical technique that seeks to achieve the immediate function of high sensitivity while at the same time ensure to prevent possible loss of specificity. It is simple and speedy in nature; a factor that ensures to eliminate the degree of sample preparation procedures that is faced whenever removing possible interferences from samples (Helaluddin, 2016). It however; suffers from a low analytical ranges for detection sample limits, which resulted to the formulation of tandem mass spectrometry (tandem MS). Tandem Mass Spectrometry (Tandem MS); is an analytical technique that was derived from Fluorimetry. It is used for the purpose of breaking down possible predetermined ions into fragments (Helaluddin, 2016). It is also beneficial in the process of conducting diastereomeric procedures as well as enantioselective quantification. Atomic-emission spectrometry (AES); is an analytical technique that fosters a higher level of energy that fosters the atoms into electronic phases, which consequently results to emission of light whenever they are allowed to return to their electronic state. It is however not frequently used in the course of determining arsenic levels in biological samples and ICP-AES was recently withdrawn from US EPA since it was inadequate; resulting to multi-element analysis (Helaluddin, 2016). Multi-element analysis; is an analytical technique that is used for analysing mineral processes samples that portray a set of distinct dissolution techniques. It is considered to be relevant and reliable since it encompasses other instrumental analytical techniques like ICP-OES, ICP-MS and XRF (Helaluddin, 2016). However, the technique is deemed to be very tedious and time-consuming since it requires graphical representations as well as adoption of such multivariate statistics as Analysis of Variance (ANOVA) thereby restricting the capacity to differentiate between different local background variations resulting to the formulation of colometric/spectrometric technique. Colometric/Spectrometric technique; is a method that takes cognizant of the fact that there is always the formation of volatile arsine gas to aid with the separation of arsenic from possible spectral and matrix interferences (Helaluddin, 2016). The method is easy to use and relatively cheaper in relation to the set of equipment and operational costs. However, it is only reliable in determining semi-quantitative and not holistic quantities of high concentrations of arsenic in water; a factor that prompted the formulation of gas chromatography (GC). Gas Chromatography (GC); is an analytical technique that is adopted for the purpose of analysing volatile substances within their gaseous state. Samples are dissolved in a solvent and later vaporised for purposes of separating them from between stationary and mobile phases (Helaluddin, 2016). However, it is not considered to be suitable for detection of semi-volatile compounds as well as results to a higher concentration hence methane is sorted for purposes of achieving high performances. Flow-Injection Analysis (FIA); is a technique that allows for the injection of a liquid sample into shifting stream of suitable liquid. It is considered to be very controlled and reproducible since most of the underlying conditions are reproduced (Helaluddin, 2016). The methodology is highly sophisticated and thus, poses a difficulty to use since it focuses on a high number of attributes like dead time; sample loop, dispersion among others. Chemometrics; is an analytical technique that is adopted for the extraction of information from measurement that are derived from chemical systems with the use of both mathematical and statistical processes. It is quite accurate and definite in its application. However; the technique is tedious and requires lots of skilled knowledge. Potentiometry; is the most current analytical technique that is used to measure the potential of a given electrochemical cell that has been subjected under distinctive static conditions. It is deemed reliable and useful since it does not allow for current flow through the electrochemical cell hence a fully quantitative methodology (Helaluddin, 2016). It is however a sophisticated method since it requires the measurement of the differences between two potential electrodes. References List Bruno, E, S et al. 2016. Analytical strategies for the determination of arsenic in rice. Journal of Chemistry, vol.2016, pp. 1-11 Cullen, W, R. N.d Arsenic species in the environment. Environmental Chemistry Group. University of British Columbia. Accessed from https://wwwbrr.cr.usgs.gov/projects/GWC_chemtherm/FinalAbsPDF/cullen.pdf Chatterjee, A., Shibata, Y., Yoshinaga, J. & Morita, M. (2000) Determination of arsenic compounds by high-performance liquid chromatography-ultrasonic nebulizer-high power nitrogen-microwave-induced plasma mass spectrometry: An accepted coupling. Analysis Chemistry, vol. 72, pp. 4402–4412 Dixit, S. & Hering, J.G., 2003. Comparison of arsenic (V) and arsenic (III) sorption onto iron oxide minerals: implications for arsenic mobility. Environmental Science & Technology, 37(18), pp.4182-4189 Helaluddin, ABM.2016. Main analytical techniques used for elemental analysis in various matrices, Tropical Journal of Pharmaceutical Research, vol.15.no.2, pp.427-434. Mandal, B.K. & Suzuki, K.T., 2002. Arsenic round the world: a review. Talanta, 58(1), pp.201-235 Szkoda, J, Zmudzki, J & Grzebalska, A. 2006. Determination of arsenic in biological material by hydride generation atomic absorption spectrometry method. Bulletin for Veterinary Institution Pulaway, vol.50. 269-272 World Health Organisation. 2011. Arsenic in drinking water. WHO/SDE/WSH/03.04/75/Rev/1 Accessed from http://www.who.int/water_sanitation_health/dwq/chemicals/arsenic.pdf?ua=1 Read More

It is however; important to understand that both of these oxidation states of arsenic are popularly perceived to be occurring together with these soil structures due to lower levels of transformation that is always noted between oxidation states (Dixit & Hering, 2003). Arsines are organic arsenic species that are generated from microbial actions in such platforms as landfills and hot-water springs. They are indeed acutely toxic in the event that there is the presence of As-H bond (Cullen, N.d). On the contrary however; Me3As, Gosio gas is deemed to be even less toxic in the event that there is the historical connection with illness and a much recent hypothesis for which it is associated with the causes of Sudden Infant Death Syndrome.

In addition to this, the methylation of arsenic undergoes a step-by-step oxidation/reduction process that first involves oxidative addition of a methyl group from S-adenosylmethanionine to arsenic (III) species that further transforms to a methylarsenic (V) product (Cullen, N.d). Consequently, the next phase involves a two-step electron reduction process that also involves thiol groups; with the immediate product being the methylarsenic(III) organic species that is deemed far much ready for a next oxidation process (Cullen, N.d). In natural and drinking water, the level of arsenic is positioned between 1 and 2 µg/l (Szkoda, Zmudzki, & Grzebalska, 2006).

It is crucial to note that the level might increase in such cases as areas with volcanic rock and Sulfide mineral deposits; areas that mostly contain natural resources where the level of as high as 12 mg/l can be reported; areas that are deemed to be very near to anthropogenic sources like in the mining and agrochemical manufacture as well as in geothermal waters where the maximum level can be established to be 25mg/l (Szkoda, Zmudzki, & Grzebalska, 2006). Notably, the overall mean arsenic concentrations within waters from sedimentary rocks would range between 5 and 3000 mg/l while highest levels of arsenic concentration would occur in contaminated waters.

In relation to food, it is noted that the overall estimations of daily dietary intake of arsenic-infiltrated products could vary due to a wider variations within the consumption of fish and shellfish mostly. Research indicates that there are approximately 25% of arsenic-related infiltrations in food that is mostly present as inorganic state (Szkoda, Zmudzki, & Grzebalska, 2006). For most cases, both fish and meat are the main sources of dietary intake of arsenic and their levels might range from 0.

4 to 118mg/kg as reported in marine fish that is sold for purpose of human consumption while in meat and poultry-related products; the concentration might reach 0.44 mg/kg (Szkoda, Zmudzki, & Grzebalska, 2006). The overall mean of day-to-day partake of arsenic in food products for adults is approximated to range between 16.7 to 129 µg while for infants, the degree ranges from 1.26 to 15.5 µg (Szkoda, Zmudzki, & Grzebalska, 2006). In regards to arsenic levels in biological samples like blood, a preparation technique that involves digestion with nitric acid and hydrogen peroxide and using the HGAAS as the sole analytical model, a level of 0.

5 µg/l is identified; for hair, the preparation technique involves wet ash that is combined with nitric acid/per chloric acids and reduced using sodium borohydride using HGAAS analytical technique the sample detection limit is identified to be 0.1 µg/l; and in the case of urine that is subjected to irradiation epithermally and using NAA analytical model results to a sample detection range of between 40-100ng/g or 0.5 µg/sample. (Szkoda, Zmudzki, & Grzebalska, 2006) For the case of nails that are subjected to a preparation methodology involving wet ashing and hydrogen peroxide and using HGAAS analytical approach results to a sample detection of 1.

5 µg/g (Szkoda, Zmudzki, & Grzebalska, 2006). In regards to such foreign samples as soft tissue; the measurement of arsenic levels adopts a preparation technique that focuses on digestion with nitric acid/sulphuric acids and in the extraction with chloroform using GFAAS analytical approach, with the sample detection levels established to be 0.2 ppm.

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