Validation Samples Correspondingly during week two, validation samples were obtained in the forms of NA and NB, in volumes of ~350 mL. These validation samples were then transferred to six Erlenmeyer flask (100 mL per flask), three flasks containing NA and three flasks containing NB for triplicate measurements. Analyzing the Samples Once all 11 solutions were ready, 2.0 mL of the ISA solution was added each of the six volumetric flasks containing the calibration standards, and the five Erlenmeyer flasks containing the validation samples. Once each of the samples was thoroughly mixed, 40 mL of all 11 solutions were transferred to 11 large test tubes and mixed thoroughly. To analyze the solutions, each solution was tested using an ion-selective electrode (ISE). The ISE was rinsed with deionized water, and blotted dry between each test. The solutions were tested lowest to highest concentrations. Once all solutions were tested and voltage (in mV) was recorded, a calibration curve was created by taking the logarithm of the nitrate concentrations (mg/L N) on the X-axis vs. the measured potential (mV) on the Y-axis. A linear least squares analysis was done and the concentrations were found by interpolation, using the equation of a line. After measurement and analysis was completed on all 11 4
solutions, the solutions were discarded and the probe was rinsed. Glassware was then cleaned and supplies were put away, including the remaining stock solution. Environmental Analysis Environmental samples were obtained from the Level 27 pond, the lake at Hueston Woods, and the stream behind Yager Stadium. These samples were tested and analyzed the same way as the validation solutions and calibration standards described above. However, the environmental samples were first filtered, by gravity filtration, with fluted filter paper before the analyses. New calibration standards were created for this week of the experiment, and three filtered samples of each environmental sample were used for triplicate measurement (9 total). A calibration curve was made from the new calibration standards so that nitrate concentrations could be determined from the environmental samples through interpolation. These environmental samples were tested to determine whether the nitrate levels were within government regulations, which is less than or equal to 10 mg/L N. These samples were also tested to determine whether the group’s hypothesis was supported. Calculation of Stock Solution A series of conversions were used to determine the mass (in grams) needed to make the stock solution with KNO 3 . The specific conversion steps used for this lab was: ( 100 mg 1 L N 1 g 1000 mg 1 mol 14.01 g N 1 mol KN O 3 1 mol N 101.10 g KN O 3 1 mol KN O 3 ) = 0.722 g L KN O 3 . Calculation of Calibration Standards The equation M 1 V 1 = M 2 V 2 was used to calculate the dilutions from the stock solution needed to create the calibration curve for week two of the experiment.
- Spring '12
- Standard Deviation, Water supply, Nitrate, Hueston Woods