Sequential extraction of phosphorous from soil
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1) Fifty soil samples from Fayetteville, NC were sequentially extracted to quantify phosphorus fractions that can reveal historical land use. 2) Phosphorus was extracted into three fractions and analyzed using both Murphy-Riley colorimetry and ICP-OES. 3) Quality control measures showed inconsistencies between duplicate extractions for colorimetry and differences from standard reference values, indicating issues with the extraction or analysis methods. Further work is needed to determine the best method for analyzing phosphorus fractions in soil.
Sequential extraction of phosphorous from soil
- 1. Sequential Extraction of Phosphorus from Soil: A Geoarcheology Application Ariel Atkinson, A.R. Smith Department of Chemistry, Appalachian State University, Boone, NC 28607, Senior Research Final Presentation under the supervision of Carol M. Babyak
- 2. Why? -50 soil samples from Fayetteville, NC -New I-95 loop will be built -Surfer contour plot will be constructed -Historical land use will be recorded http://www.ssg-surfer.com/ssg/detailed_description.php?products_id=135 Surfer Contour Plot
- 3. Inorganic phosphorus in soil can be extracted in three different fractions The amount of phosphorus in each fraction is expressed as a percent of total phosphorus in the soil Used to determine what the land was used for historically Quantified either through colorimetry or ICP-OES Overview
- 4. Phosphorus Abundant in the environment Comes from a variety of human activities: -farming -cleaning -food preparation -medical care -waste Stable in soil can reveal the historical land use patterns.
- 5. Forms of P
- 6. Operational Definition of Phosphate Fractions in Soil Fraction I Non-occluded Fraction II Occluded Fraction III Bound to calcium Al Al OH crystal surface O O P O OH Eidt, Science 1977, 197, 1327; Holliday, V.T. J. Archeological Science 2007, 34, 301. Ca10(PO4)6F2 Ca10(PO4)6(OH)2 Al Al OH O O P O O Al Al OH Phosphate is part of an iron or aluminum hydroxide mineral Phosphate is part of a calcium mineralPO4 3- is weakly adsorbed
- 7. Correlation Between Fractionation of Phosphorus and Land Use Source FrI % FrII % FrIII % Total (ppm) Land Use Norway 84 7 9 1256 Mixed veg. farming Germany 82 10 8 78 Mixed veg. farming Colombia 85 11 4 206 Mixed veg. farming Germany 44 49 7 43 Forest (pine) Wisconsin 34 54 12 315 Forest (maple) Argentina 38 28 34 2324 Residential (abnd) Wisconsin 40 20 40 1393 Residential(modern) (Eidt, 1974)
- 8. Goals Extract inorganic phosphorus from soil samples Quantify phosphorus fractions in Fayetteville soil using Murphy-Riley colorimetry Quantify fractions in soil using ICP-OES Compare colorimetry to ICP-OES Possibly decide which method is superior
- 9. Soil Preparation and Extraction Fraction Extraction Solvent Fraction 1- Loosely Bound Phosphorus NaOH/NaCl-shake 12 hrs Na3Cit/HCO3- heat 30 mins. Fraction 2- Occluded Phosphorus Na3Cit/HCO3-heat Na-dithionite-let oxidize for 8 days Fraction 3-Calcium Phosphorus HCl-shake 4 hrs 1) Air dry overnight 2) Cone and Quarter 3) Sieve 4) Extraction on 2 g of soil http://www.bridgewater.edu/~ koverway/courses/CHEM320/ ppts/Section2Sampling.pdf Cone and Quartering Extraction Solvents for each Fraction
- 10. Methods of Quality Control 1) A sample duplicate every ten samples 2) A standard reference soil purchased from NIST 3) A calibration curve is produced using prepared phosphate standards every time colorimetry or ICP-OES is performed
- 11. Murphy-Riley Colorimetry Molybdenum is added to the extract A Molybdophosphoric acid is formed, and then reduced by sodium citrate or ascorbic acid to form a blue color The more intense the blue color, the more phosphorus present Immediately quantified using a spectrophotometer http://www.umaine.edu/SECRL/photos.htm
- 12. y = 0.2479x + 0.0004 R2 = 1 0 0.05 0.1 0.15 0.2 0.25 0.3 0 0.2 0.4 0.6 0.8 1 1.2 y = 0.0411x - 0.0057 R2 = 0.9979 -0.005 0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0 0.2 0.4 0.6 0.8 1 y = 0.2429x + 0.0018 R2 = 0.9986 0 0.05 0.1 0.15 0.2 0.25 0.3 0 0.2 0.4 0.6 0.8 1 1.2 Frac.IA: June 20, 2007 Frac. IB: July 6, 2007 Frac. 2: July 30, 2007 Frac. 3: July 17, 2007 y = 0.0317x - 0.004 R2 = 0.9984 0 0.005 0.01 0.015 0.02 0.025 0.03 0 0.2 0.4 0.6 0.8 1 Colorimetry Standard Curves
- 13. Colorimetry Results %Fraction1 %Fraction 2 %Fraction 3 average % 38.32 57.12 4.57 stnd dev. 16.90 17.59 4.25 min 11.49 16.21 0.75 max 79.21 85.86 29.23 All extractions and colorimetry of soil samples were performed successfully from May to July 2007. The results are highly variable
- 14. Quality Control Results A rigorous quality control was followed May to July: 1) Percent differences for the duplicates ranges widely: Fr1:24.4% Fr2:17.5%, Fr3:38.2%. 2)The SRM, certified by NIST to contain 860 mg of phosphate per kg of soil, measured to contain an average of 612 mg/kg. 28.8% difference 3) The average R-squared value, for the calibration curves, was 0.9932
- 15. Colorimetry Pros and Cons -Inconsistencies between duplicates inhomogeneous soil or non-reproducible extraction -Requires a lot of preparation -Time Consuming -Fairly Good Calibration Curves -Few Interferences
- 16. ICP-OES Inductively coupled plasma- optical emission spectroscopy Extract is aspirated into the torch of the ICP, where it is atomized Atoms become excitedemitting photons at a characteristic wavelength Intensity of the emission is correlated with the concentration of the phosphorus in the sample http://www.icp-oes.net/images/torche2.jpg
- 17. ICP results Standard Calibration y = 598.18x +1.0436 R2 = 0.999 0 50 100 150 200 250 300 350 0 0.2 0.4 0.6 Concentration of P (ppm) Intensity(CPU) LOD=0.007 ppm Sample Fraction Conc. w/ ICP-OES (ppm) Conc. w/ Colorim. (ppm) 13 3 0.143 4.794 61 2 0.822 287.764 55 2 0.659 355.491 55 3 0.128 7.893 27 1b 0.809 174.810 Standard Calibration Curve
- 18. What Happened? Interferences -unlikely:ICP should atomize completely -matrix spike Bind to colloidal soil particles in solution -heating -nitric acid digestion Bind to walls of container
- 19. Further Work Storage Time Study Method development to determine phosphorus bonded to bottle walls Running fresh extracts on ICP-OES and colorimetry Construction of surfer plots
- 20. Summary - > 50 samples from Fayetteville were sequentially extracted. - > 200 extracts were analyzed using M-R colorimetry. -Colorimetry data will be used to construct Surfer plots. -Due to sample storage, it is impossible to say whether ICP-OES or colorimetry is the best method.
- 21. Acknowledgements I would like to acknowledge the following people for their help: -Dr. Carol M Babyak -Dr. Keith Seramur -Dr. Shea Tuberty -Dr. Lynn Siefferman -The A.R. Smith Department of Chemistry
- 22. References Eidt, Robert C. 1977.Detection and Examination of Anthrosols by Phosphate Analysis. Science. 197. 4311: p. 30-34 Eidt, Robert. Woods. 1974. Theoretical and Practical Considerations in the Analysis of Anthrosols. Abandoned Settlement Analysis. 1st ed, p.155-189. Murphy, J. Riley,J.P.1962. A MODIFIED SINGLE SOLUTION METHOD FOR THE DETERMINATION OF PHOSPHATE IN NATURAL WATERS. Anal.Chim.Acta, 27: 31-36. Sobeck, Ebeling.2007. “Mass Spectrometric Analysis for Phosphate in Soil Extracts.”Analytical Sciences Digital Library E-UGR. <http://www.asdlib.org/articles.php?type=eUGH> Standard Methods for the Examination of Water and Wastewater. 1999. p.4-139 – 4-147.