Sequential extraction of phosphorous from soil
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Transcript of Sequential extraction of phosphorous from soil
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
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
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
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.
Forms of P
Operational Definition of Phosphate Fractions in Soil
Fraction INon-occluded
Fraction IIOccluded
Fraction IIIBound 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
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)
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
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
Methods of Quality Control1) 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
Murphy-Riley ColorimetryMolybdenum 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
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
Colorimetry Results
%Fraction1 %Fraction 2 %Fraction 3average % 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
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
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
ICP-OESInductively 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
ICP results
Standard Calibration
y = 598.18x + 1.0436R2 = 0.999
0
50100
150
200
250300
350
0 0.2 0.4 0.6
Concentration of P (ppm)
Inte
nsity
(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 0.809 174.810Standard Calibration Curve
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
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
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.
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
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.