Arsenic , detection with conducting

Arsenous acid is a veiy weak acid and cannot be detected at low levels by the conductivity detector. However, like sulphide, it is easily detected with the ultraviolet detector. The simultaneous determination of arsenite and arsenate is possible. 

Molecular substances such as solvents (water and methanol) and solutions of nonionized organic acids and carbohydrates do not conduct electricity and are not detected by conductivity. The portion of a weak acid that does ionize will contribute to the conductivity signal. The ionic form of the weak acid depends on pH. A weak acid with a pKa larger than about 6 camiot be detected with suppressed conductivity detection because aU anions are converted to the acid form by the suppressor. So while it is possible to separate both arsenite and arsenate on the... 

Figure 3 Gradient separation of anions using suppressed conductivity detection. Column 0.4 x 15 cm AS5A, 5 p latex-coated resin (Dionex). Eluent 750 pM NaOH, 0-5 min., then to 85 mM NaOH in 30 min. Flow 1 ml/min. 1 fluoride, 2 a-hydrox-ybutyrate, 3 acetate, 4 glycolate, 5 butyrate, 6 gluconate, 7 a-hydroxyvalerate, 8 formate, 9 valerate, 10 pyruvate, 11 monochloroacetate, 12 bromate, 13 chloride, 14 galacturonate, 15 nitrite, 16 glucuronate, 17 dichloroacetate, 18 trifluoroacetate, 19 phosphite, 20 selenite, 21 bromide, 22 nitrate, 23 sulfate, 24 oxalate, 25 selenate, 26 a-ketoglutarate, 27 fumarate, 28 phthalate, 29 oxalacetate, 30 phosphate, 31 arsenate, 32 chromate, 33 citrate, 34 isocitrate, 35 ds-aconitate, 36 trans-aconitate. (Reproduced with permission of Elsevier Science from Rocklin, R. D., Pohl, C. A., and Schibler, J. A., /. Chromatogr., 411, 107, 1987.)...

Prest, J.E., Baldock, SJ., Fielden, P.R., Goddard, N.J., Brown, B.J.T., Miniaturised isotachophoretic analysis of inorganic arsenic speciation using a planar polymer chip with integrated conductivity detection. J. Chromatogr. A 2003,990, 325-334. 

A New Bedford Harbor Sawyer Street site in Massachusetts has been designated as a superfund site due to PCB contamination of river sediments. Commodore was one of three companies chosen to conduct demonstration studies on-site under contract to Foster Wheeler Environmental Company. The river sediment was first washed with diisopropylamine by the Ionics RCC B.E.S.T process [35], producing an oil concentrate. The PCB level in the B.E.S.T concentrate was approximately 32,800 ppm. Dioxins/furans (TEFs) were also present at 47 ppm. This concentrate was reacted with SET in the SoLV process to destroy the PCBs and dioxins (Table 4). After treatment, the PCB level was 1.3 ppm, well below regulatory requirements for disposal in nonhazardous waste landfills. Dioxins were also readily remediated. This study also illustrates that the SoLV process can remove metals from substrates. The concentrate received was found to have lead, arsenic, and selenium in high parts-per-billion levels. After treatment with the SoLV process, the levels were below detection limits. The metals were... 

Conductivity detection performed with a contactless conductivity detector through the packed bed was shown to be a more versatile and sensitive method than indirect UV detection [77]. Chen et al. employed inductively couple plasma mass spectrometry (ICP MS) as a detection tool for the simultaneous analysis of various ionic species of arsenic, chromium, and selenium [79]. The separation was achieved on an OT CEC column prepared by bonding a macrocyclic polyamine medium on the walls of the capillary. 

Covello et have described a procedure in which arsenic in toxicological samples is reduced to arsine, which is then swept out of the reaction flask with helium to a column of silica gel. Detection is achieved by thermal conductivity at levels down to 2 fig arsenic. 

For this study, we consider four types of water non-impacted (arsenic below detection limit), low (greater than the detection limit and less than 10 pg/l As), moderate (10-100 p.g/1 As), and high (greater than 100 pg/1 As). Typical of water quality data, the data set is censored and as such, the concentrations reported for most constituents are not normally distributed (Gibbons, 1994). Because of this limitation, box plots (Fig. 6) are used to evaluate and compare the water quality results. The distributions of concentrations were compared for iron, sulfate, pH, alkalinity, nickel, zinc, manganese and specific conductance (SC). The box plots should be viewed with consideration of sample size, which is indicated on Fig. 6. 

Johann Heinrich Biltz (Berlin, 26 May 1865-Breslau, 29 October or 2 November 1943), a pupil of Victor Meyer, professor in Breslau (1911), determined the vapour densities of stannous chloride, cuprous and silver chlorides, phosphorus, sulphur, selenium, tin, arsenic, antimony and bismuth, detecting the molecule Sg. His later work was largely on organic chemistry. His brother Eugen Wilhelm Biltz (Berlin, 8 March 1877-Heidelberg, 13 November 1943) was professor in Gottingen (1900), Clausthal (1908), and Hannover. He published an immense number of papers, on colloids, the conductivities of fused salts, the compounds of ammonia with salts, compounds of beryllium and other rarer metals, sulphides, phosphides and tellurides, etc., and the molecular volumes of solid compounds. ... 

The familiar principle that binary reactions can frequently be used for the detection of either of the reactants is not limited to reactions conducted in liquid media. Recently it has been found that AsgSg or AsgSg are produced when a mixture of elemental arsenic and sulfur is heated at 110° C. The sulfur melts and then reacts. This synthesis of arsenic sulfides followed by treatment with ammonia (formation of ammonium sulfo salts) permits the detection of As or S (see pages 111 and 436). 

---