Arsenic analytical methods

This book contains conttibutions from world-renowned international scientists on topics that include toxicity of arsenic, analytical methods for determination of arsenic compounds in the environment, health and risk exposure of arsenic, biogeochemical conttols of arsenic, Peatment of arsenic-contaminated water, and microbial ttansformations of arsenic that may be useful in bioremediation. 

The following procedure has been recommended by the Analytical Methods Committee of the Society for Analytical Chemistry for the determination of small amounts of arsenic in organic matter.20 Organic matter is destroyed by wet oxidation, and the arsenic, after extraction with diethylammonium diethyldithiocarbamate in chloroform, is converted into the arsenomolybdate complex the latter is reduced by means of hydrazinium sulphate to a molybdenum blue complex and determined spectrophotometrically at 840 nm and referred to a calibration graph in the usual manner. 

Analytical Methods Committee, Determination of Arsenic in Organic Materials, Society for Analytical Chemistry, London, 1960... 

Multivariate chemometric techniques have subsequently broadened the arsenal of tools that can be applied in QSAR. These include, among others. Multivariate ANOVA [9], Simplex optimization (Section 26.2.2), cluster analysis (Chapter 30) and various factor analytic methods such as principal components analysis (Chapter 31), discriminant analysis (Section 33.2.2) and canonical correlation analysis (Section 35.3). An advantage of multivariate methods is that they can be applied in... 

A review of the analytic chemistry of arsenic in the sea, including occurrence, analytical methods, and the establishment of analytical standards, has been published [3]. 

The simplest analytical method is direct measurement of arsenic in volatile methylated arsenicals by atomic absorption [ 11 ]. A slightly more complicated system, but one that permits differentiation of the various forms of arsenic, uses reduction of the arsenic compounds to their respective arsines by treatment with sodium borohydride. The arsines are collected in a cold trap (liquid nitrogen), then vaporised separately by slow warming, and the arsenic is measured by monitoring the intensity of an arsenic spectral line, as produced by a direct current electrical discharge [1,12,13]. Essentially the same method was proposed by Talmi and Bostick [10] except that they collected the arsines in cold toluene (-5 °C), separated them on a gas chromatography column, and used a mass spectrometer as the detector. Their method had a sensitivity of 0.25 xg/l for water samples. 

Modern analytical methods are so sensitive that low levels of many elements that would be toxic at higher levels can be found, e.g. arsenic. At one time some US states had laws banning any food with measurable quantities of arsenic. At this time, lead arsenate was used as an insecticide - if arsenic was present in measurable quantities then insecticide residues were present. However, such low levels of arsenic are not a health problem. 

The aim of this work was to investigate the arsenic mobilization from the tailings material (200 - 500 pg/g As) into the seepage water (up to 3.5 mg/L As) and the process of seepage water effluent forming an immobilized precipitate (up to 8 % As) in the creek. Different analytical methods for the determination of total concentrations and different sequential extraction methods as well as hyphenated techniques for speciation analysis were applied to follow the way of the arsenic in this environment. 

The analytical methods described were found to be suitable for the investigation of the fate of arsenic in this environmental system. 

Table 12.15 Comparison of arsenic determination in sediments by different analytical methods (pg/g dry weight)...

The accuracy of the analytical method was established hy independent analysis of the three additional filters from each of the 5 10 and 20 yg/m3 generation runs using both NAA and XRF analyses. Because NAA and XRF analysis techniques provide only a total arsenic measurement, the IC-AAS speciation results obtained for MMA, DMA and p-APA were used to estimate the total amount of arsenic. Table X presents the total arsenic obtained by the three techniques. The accuracy ranged from 90-120 of the values obtained by NAA and XRF. 

The most useful chemical species in the analysis of arsenic is the volatile hydride, namely arsine (AsH3, bp -55°C). Analytical methods based on the formation of volatile arsines are generally referred to as hydride, or arsine, generation techniques. Arsenite is readily reduced to arsine, which is easily separated from complex sample matrices before its detection, usually by atomic absorption spectrometry (33). A solution of sodium borohydride is the most commonly used reductant. Because arsenate does not form a hydride directly, arsenite can be analyzed selectively in its presence (34). Specific analysis of As(III) in the presence of As(V) can also be effected by selective extraction methods (35). 

In general, agreement between the two analytical methods is reasonable. There is a consistent negative imbalance, averaging —26% and —16% for NAA and SSMS results, respectively, for the major elements and —1% and —18% for the minor elements. We excluded the results for mercury and arsenic in the averages for minor elements. In view of the necessary assumptions and the difficulty of obtaining truly representative samples, the balance is satisfactory for most elements. Notable exceptions are elements which can be present in a gaseous form. One may be arsenic (Table III), and another is mercury which is discussed... 

The action of arsine on silver and mercury salts has attracted much attention owing to the important application to analytical methods for arsenic (p. 319). The action of arsine on a dilute aqueous solution of silver nitrate has long been known to yield metallic silver, arsenious acid and nitric acid.9 With more concentrated solutions the introduction of a few bubbles of arsine produces a deep lemon-yellow coloration, the liquid also acquiring an acid reaction. The coloration disappears after one or two days, silver is precipitated and the colourless solution contains arsenious and arsenic acids.10 If a rapid stream of arsine be passed into a concentrated solution of silver nitrate at 0° C. the whole liquid solidifies to a yellow crystalline mass which rapidly blackens with separation of silver. Lassaigne represented the reaction with the dilute solution by the equation... 

The application of the foregoing analytical methods to the detection, separation and estimation of arsenic in a great variety of materials is the subject of an extensive literature, and a list of references to some useful papers of recent date is appended.2... 

Arsenical or mercury compounds are detected by evaporating a quarter of a litre of the ink and heating the extract with 1-2 c.c. of concentrated sulphuric acid and 5-10 c.c. of fuming nitric acid until nitrous vapours are eliminated, the addition of nitric acid and the heating being repeated until a perfectly colourless liquid is obtained (Rothe). The sulphuric add is then expelled and the residue tested for arsenic and mercury by the ordinary analytical methods. 

Methylarsenic usually represents less than 10% of the total arsenic in seawater (Le, 2002), 97. The principal methylarsenic species in seawater are MMA(V) and DMA(V) (Francesconi and Edmonds, 1994), 222. Several other organoarsenicals may also be present. However, analytical methods are not always available to identify every organoarsenical in seawater and other materials. In some circumstances, unidentified organoarsenicals may represent a significant portion of the total arsenic in coastal marine waters, perhaps >25 % (Francesconi and Edmonds, 1994), 224. 

In 1836, James Marsh developed an analytical method for detecting low concentrations of arsenic in various materials (Nriagu, 2002), 9. The technique allowed investigators to identify arsenic in autopsies and increase the number of murder convictions. Nevertheless, the Marsh and subsequent analytical techniques have often not been used unless physicians or other investigators first suspect arsenic poisoning. Even... 

Goessler, W. and Kuehnelt, D.D. (2002) Analytical methods for the determination of arsenic and arsenic compounds in the environment, in Environmental Chemistry of Arsenic (ed. W.T. Frankenberger Jr., Marcel Dekker, New York, 27-50. 

Fourier transform infrared (FTIR) spectroscopy An analytical method that uses infrared radiation to investigate the chemical characteristics of a sample. This method may be used to identify the valence states of arsenic on adsorbents and bonds between arsenic and other elements (e.g. (Goldberg and Johnston, 2001)) (compare with Raman spectroscopy). 

Speciation (chemistry) The chemical species in a sample, which includes information on its valence state and specific chemistry. For example, the speciation of arsenic in a groundwater sample may include arsenic fluoride species, such as AsCbF2-. Also, an analytical method that identifies the valence state of a chemical species in a sample. 

New Hampshire Developing public-health laboratory capacity to biomonitor for arsenic, mercury, phthalates, poly-brominated diphenyl ethers and planning pilot studies to estimate body burden of environmental toxicants using newly developed biomonitoring analytic methods (CDC 2005). 

With the detection and introduction of titration (more general volumetry) into the arsenal of analytical methods, an increasing need arose for means which allowed the end-point of such an analysis to be detected. This need stimulated the search for indicator dyes, and consequently the methods of dye synthesis were also used for this purpose. Asa result, most indicator dyes are now synthetic. 

Huang, D.Q., O. Nekrassova, and R.G. Compton. 2004. Analytical methods for inorganic arsenic in water A review. Talanta 64 269-277. 

The most generally applied method for determination of an arsenical is by atomic absorption spectrometry (AAS) after reduction of the compound to AsH3. However, this only provides an indication of the presence of the element as against a natural background. Lewisite rapidly hydrolyzes to 2-chlorovinylarsonous acid (CVAA see Figure 7) in an aqueous environment such as blood plasma, and analytical methods have focused mainly on the determination of CVAA (see Chapter 16). 

Arsine has been determined colorimetrically or by collection on activated charcoal and flameless AAS analysis by S-229 (12). Nitric acid desorption of the charcoal offers a safe method of handling the arsenic analyte than arsine generation. This method does not specify use of an EDL as does S-309, however, it is advisable if an EDL source is available. 

Once incorporated, unbound lewisite is quickly hydrolyzed. Its predominant metabolite is 2-chlorovinylarsonous acid, CVAA (Figure 50.8). Analytical methods to confinn lewisite exposure have, at least in the past, focused on the detection and quantification of CVAA. However, Noort et al. (2002) also pointed out that due to the high affinity of arsenic towards sulfhydryl groups, adducts of lewisite/ CVAA and cysteine residues of proteins are formed. In an in vitro study, incubating " C-labeled lewisite with human blood samples, 90% of lewisite was found in erythrocytes, whereas 25 to 50% of arsenic was bound to globin. From these protein adducts, CVAA can be released to form an adduct with the antidote British Anti-Lewisite (BAL) (Fidder et al, 2000). The authors were also able to identify a specific protein adduct of lewisite formed with the cysteine residues 93 and 112 of P-globin. See Detection of DNA and protein adducts of vesicants, below, for analytical... 

Ultrasonic nebulizers have also been employed in continuous flow systems as interfaces between sample preparation steps in the analytical process and detection by virtue of their suitability for operating in a continuous mode. Thus, preconcentration devices have commonly been coupled to atomic spectrometers in order to increase the sensitivity of some analytical methods. An enhancement factor of 100 (10 due to USNn and 10 due to preconcentration) was obtained in the determination of platinum in water using a column packed with polyurethane foam loaded with thiocyanate to form a platinum-thiocyanate complex [51]. An enhancement factor of 216 (12 with USNn and 18 with preconcentration) was obtained in the determination of low cadmium concentrations in wine by sorption of metallic complexes with pyridylazo reagents on the inner walls of a PTFE knotted reactor [52]. One special example is the sequential determination of As(lll) and As(V) in water by coupling a preconcentration system to an ICP-AES instrument equipped with a USN. For this purpose, two columns packed with two different resins selective for each arsenic species were connected via a 16-port valve in order to concentrate them for their subsequent sequential elution to the spectrometer [53]. 

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