Introduction Determination of Phosphate Levels in Soil by a Semi-Quantitative, Portable Method Catherine O'Dell Chemistry 362, Davidson College Introduction Archaeologists use levels of phosphate found in soil to locate areas of previous human occupation. Results from this study will be applied to choosing a method for on-site analysis at the Athienou Archaeological Project in Cypress by students with minimal chemistry background. The method chosen must be easily transportable, have a relatively simple procedure and be semi-quantitative. 20-22 cm deep soil from undisturbed wooded area Soil samples were run through three methods for determining the level of phosphate. Examples of filter paper used in the spot test method.
Color spreads and darkens over time.
Figure 3 Plot of absorbance vs. wavelength data from UV-Vis spectrophotometry measurements of treated soil solutions, showing the highest absorbance for fertilized soil. The UV-Vis method was followed, except that absorbances at 889 nm were used for a comparative analysis. Because the absorbances were so low for these samples, some even negative, the aliquot size was increased to 1.0 mL from 0.1 mL in subsequent procedures, as shown below. Figure 4 Figure 5 Plots of absorbance vs. wavelength data from UV-Vis spectrophotometry measurements of treated soil solutions, showing the highest absorbance for heated, fertilized soil. The UV-Vis method was followed, but altered slightly by mixing a 1.0 mL aliquot of a solution of 0.1 g soil in 5 mL 2 M HCl with an acidic molybdenum reagent.