both the NA and NB concentrations resulted in an inequalities that did not hold true, meaning a difference in their known concentrations and their experimental means is not statistically significant and it can be said that validation standards are equivalent to the known concentrations of the validation standards. A percent relative standard deviation was also performed for NA and NB. The %RSD for NA was 0% and the %RSD for NB was 1.73% indicating strong precision in the triplicate measurements made. The results for the environmental samples collected do not fully support the original hypothesis. Based on the original hypothesis it was expected that the Western Stream would have the lowest concentration of nitrate when in fact it had the highest measured average concentration of 16.6 mg/L N. The Formal Gardens that was expected to have the highest concentration of the three locations had the second highest measured average concentration of 12.3 mg/L N. Finally, the Western Pond that was expected to have the second highest concentration of the three locations actually had the lowest measured average concentration of 7.53 mg/L N. A Q-test was performed on one of the measured concentrations from the Western Stream to ensure that it was not outlier. The Q-test proved the data point was not an outlier. A Q-test was also performed on one of the measured concentrations from the Formal Gardens to ensure that it was not an outlier. The Q-test again proved the data point was not an outlier. The nitrate concentrations collected for the three locations is suspicious, because nitrate levels in natural water rarely ever exceeds 10 mg/L N ( 2 ). Also, in the city of Oxford’s Water Quality Report in 2011, the highest nitrate level detected was only 1.06 ppm ( 1 ). Two of the locations did exceed the value of 10 mg/L N, which is surprising. Because the validation sample results were sufficiently accurate and precise, it is safe to say that the method of analyzing all samples with the ISE was done correctly and is not at fault for the experimental nitrate concentration values that were very high and varied so much from the hypothesis. None of the environmental measurements were outliers as indicated by the Q-test, again indicating that the 10
method of analyzing with the ISE was not done incorrectly. It is possible that the values were high because the glassware was not cleaned sufficiently beforehand or the ISA was not calibrated properly thus causing it to display higher nitrate concentration values than actually present in the water. It would be difficult to propose a new hypothesis without further researching the environmental sample locations and determining if they are in fact treated with fertilizer or not. Because the Western Stream ended up having the highest concentration of nitrate in the water, it could be assumed that some type of outside factor is affecting the high concentration, whether it is fertilizer or not. It is possible that the stream is near areas that are treated with fertilizer and
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- Spring '12
- Nitrate, mg/L, environmental samples