# 3.1: Analysis

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### Phosphate Analysis of Data

Measure the absorbance of five unknowns and the standards. Using Microsoft Excel plot the concentration of your standards on the x-axis in µM versus the absorbance. Make sure to take the blank into account and include the zero point on your graph. Eliminate any outliers using statistical analysis of the five unknown results.

Find the regression line for your standard curve and choose a linear fit with the equation and R2 value displayed on your graph.

Include a copy of your graph in the Appendix of your lab report.

Use the LINEST function in the worksheet of Excel to calculate the errors of your slope intercept and y values.

Find the average and standard deviation of the five-absorbance measurements for your sample. Also, calculate the 95% confidence interval for your answer. For the sample, find the concentration of phosphate from the regression line that you calculated.

No error propagation for this part of the lab.

Report the final concentration as mg/L or ppm for total phosphorous (P) and (PO4)3-

Compare your phosphate concentrations with others in the literature and comment on what your numbers mean in terms of pollution and how they might relate to your DO measurements.

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