University of Massachusetts at Amherst Department of Chemistry James Kearns Tyson Research Group Department of Chemistry, University of Massachusetts 701 Lederle Graduate Research Tower 710 North Pleasant Street, Amherst, MA , USA Field Portable Methods for the Determination of Arsenic in Environmental Samples

2 University of Massachusetts at Amherst Department of Chemistry Presentation Outline  1. Research Goals, the Arsenic Problem, and Field Kits.  2. The Chemical Methods The Gutzeit Method: Hydride Generation of Arsenic. The Molybdenum Blue Method.  3. Experimental Project 1: 24 Hour Field Kit Sensitivity Project 2: Measuring Arsenic in Soils with the Gutzeit Method Project 3: Silver Nitrate as a Detection Reagent for the Gutzeit Method Project 4: Molybdenum Blue and the Detection of Arsenic with Cameras Project 5: Flow Injection and the Determination of Arsenic Project 6: The Stoichiometry of Heteropolyacids  4. SNPs Research  5. Future Work  6. Questions

3 University of Massachusetts at Amherst Department of Chemistry What is the Size of the Arsenic Problem? Millions of people worldwide are chronically exposed to arsenic through drinking water, including 35—77 million people in Bangladesh. Argos, M. et al. The Lancet, Early Online Publication, 2010

4 University of Massachusetts at Amherst Department of Chemistry The Goals of this PhD. Research Project Goal: To develop a more reliable field portable chemical method to measure arsenic in environmental samples at, or below, 10 µg L -1 (ppb). Areas of investigation: (1) Improvement in Gutzeit methodology for water and soil testing with digital image analysis and use of silver nitrate as a reagent (2) Optimization of the molybdenum blue chemistry (3) The single nucleotide polymorphism study to understand the health consequences of arsenic exposure.

5 University of Massachusetts at Amherst Department of Chemistry The Challenges of Laboratory Instruments: (1) High Cost (2) Materials and Maintenance (3) Trained Technician Is There a Need for Field Portable Instruments? The Current Reliability of Field Portable Methods: “Accurate, fast measurement of arsenic in the field remains a technical challenge. Technological advances in a variety of instruments have met with varying success. However, the central goal of developing field assays that reliably and reproducibly quantify arsenic has not been achieved” Melamed, D. Anal. Chim. Acta, 2005, 532, Kinniburgh, D.G.; Kosmus,W. Talanta, 2002, 58, The Need for Field Kits: “The only feasible approach (for the measurement of the tube wells, which are estimated to be more than 10 million) is through the use of field kits.”

6 University of Massachusetts at Amherst Department of Chemistry The Gutzeit Test Reaction 1 (aq): arsenite + zinc + acid produces AsH 3,which rises into head space of reaction container. Reaction 2 (g): AsH 3 reacts with mercuric bromide impregnated test strip. Measurement: Yellow-brown color produced after set time is compared with preprinted chart.

7 University of Massachusetts at Amherst Department of Chemistry The Gutzeit Method Chemistry Zn(0)  Zn e - The Formation of Arsine (AsH 3 ) 2H + + 2e -  H 2 As(III) + 3e -  As(0) As(0) + 3e - +3H +  AsH 3 AsH 3 (g) + 3HgBr 2 (aq)  As(HgBr) 3 (aq) + 3HBr AsH 3 (g) + 3AgNO 3 (s)  AsAg 3 (s) + 3HNO 3 The reaction of Arsine Brindle, I. D. “Vapour-generation analytical chemistry: from Marsh to multimode sample-introduction system” Analytical Bioanalytical Chemistry 388, 2007,

8 University of Massachusetts at Amherst Department of Chemistry Molybdenum Blue Method Ammonium molybdate, sulfuric acid, a reducing agent and a catalyst are combined; the molybdate forms an inorganic polymer, which is then reduced and turns from yellow to blue.

9 University of Massachusetts at Amherst Department of Chemistry Molybdenum Blue Chemistry Molybdate reacts with the +5 species of P, As, Sb, and Bi. 12 MoO AsO H + → AsMo 12 O H 2 O Chemical Reaction: for formation of molybdenum blue Matsunaga, H.; Kanno, C.; Toshishige, M. Suzuki, T.M. Talanta, 2005, 66, Analytes which react with the molybdenum blue chemistry The Stages: of molybdenum blue formation 1. Complex only reacts in a solution containing arsenic (V). 2. After reduction, the complex’s Max is near 850nm.

10 University of Massachusetts at Amherst Department of Chemistry The “Molybdenum” Blue Complex 1. Arsenate + molybdate + acid + reducing agent gives blue color due to formation of heteropoly species containing both Mo (IV) and Mo (VI). 2. Octahedral subunits form the structure. 3. Arsenic substitutes for a molybdenum or trapped in the interior of the larger polymer. Gouzerh, P.; Proust, A. Main-group element, organic, and organometallic derivatives of polyoxometalates. Chem. Rev. 1998, 98, 77.

11 University of Massachusetts at Amherst Department of Chemistry Color Measurement and Tristimulus Colorimetry  Photons come in different wavelengths  According to tristimulus colorimetry theory, the human eye interacts with three regions of the electromagnetic spectrum  Detection methods measure light using tristimulus theories Konica Minolta, the essentials of imaging web site (accessed August, 2010)

12 University of Massachusetts at Amherst Department of Chemistry Reflectance Spectroscopy  I = I 0 *e -kx  Reflectance spectroscopy operates according to Beer’s Law  Where I is observed light  I 0 is the original light intensity  The value k is the absorption coefficient specific for that substance at a specific wavelength.  The value x is the distance the photons travel through the substance USGS, about reflectance spectroscopy website, (accessed August, 2010)

13 University of Massachusetts at Amherst Department of Chemistry Quantification of Molecules Using Reflectance Spectroscopy  I = I 0 *e -kx  These methods used a tristimulus scanner  I and I o are known, the precision of the emission of incident wavelengths and their detection have to be further established  The value k is the absorption coefficient specific for that substance at a specific wavelength. The k value is not known because the reaction products are not homogeneous or characterized  The value x is the distance the photons travel through the substance because the thickness of the mercuric bromide is not known and are not uniform  The USGS reflectance spectroscopy places samples on glass, this experiment uses white plastic

14 University of Massachusetts at Amherst Department of Chemistry Project 1: Improving Field Kit Sensitivity using Digital Image Analysis  Time: five replicate measurements at 20, 30, 40 minutes and 24 hours at the concentrations of 10, 25, 50, 100, 250, 500 µg L -1 (ppb).  Temperature: five replicate measurements at 35° C and the concentrations of 10, 25, 50, 100, 250, 500 µg L -1 (ppb).  Determinations of (1) s ( standard deviation of field kit measurements), (2) S 0 (Standard deviation at zero concentration), (3) k ( constant relative error) with time and temperature variations plus scanner use.  The Red, Green and Blue values were measured using computer software.

15 University of Massachusetts at Amherst Department of Chemistry The Research or Kinniburgh and Kosmus Kinniburgh, D.G., Kosmus, W. Talanta, 2002, 58, Thompson, M. Howarth, R.J. Analyst, 1976, 690

16 University of Massachusetts at Amherst Department of Chemistry Current Analytical Precision with the Gutzeit Method Kinniburgh, D.G., Kosmus, W. Talanta, 2002, 58,

17 University of Massachusetts at Amherst Department of Chemistry Results: Tables of Standard Deviation Values and Mean Blue Values at Different Times

18 University of Massachusetts at Amherst Department of Chemistry The Standard Plot of Color Versus Concentration Concentration of As(III)  g L -1 Blue Pixel Count

19 University of Massachusetts at Amherst Department of Chemistry The Determination of Standard Deviation in Concentration Concentration of As (III) Blue Pixel Value

20 University of Massachusetts at Amherst Department of Chemistry The Values s o and k at 24 Hours of Reaction Time Concentration As (III) g L -1 Standard Deviation in Concentration As(III)  g L -1 Standard Deviation of Concentration

21 University of Massachusetts at Amherst Department of Chemistry Results: Table of S o and K Values at Different Times

22 University of Massachusetts at Amherst Department of Chemistry Results: Graphs Comparing Time and Temperature Concentration of As (III)  g L -1 Blue Pixel Value

23 University of Massachusetts at Amherst Department of Chemistry Conclusions of DIA Experiment  1. Scanning improves precision compared to naked eye determination at 20 minutes. Naked eye (Kinniburg) k = 0.3 and S o = 7. This method produced k = 0.2 and S o = 2.6.  2. Increasing the reaction time from 20 minutes to 40 minutes also decreases k (for 20, 30, and 40 minutes) and increases S o (for 20,30, and 40 minutes).  3. Running the reaction at 35°C produces results similar to 40 minutes and 24 Hours.

24 University of Massachusetts at Amherst Department of Chemistry Conclusions of DIA Experiment Table of s Values at 10 and 50  g L -1