Discussion

Element concentration yields from the EPA method were typically higher than element concentration yields from the collision reaction cell method. The percent difference between the collision reaction cell method and the EPA method generally decreased as element concentrations increased. Copper had a higher mean concentration than Arsenic or Chromium, and Copper had the lowest percent difference of the three. Arsenic’s high percent differences might be attributable to small concentrations, some below the limit of detection. With such small numbers, .1 ppb difference can be a 200% difference. 

Cadmium’s highest limit of detection (1.36 * 10 = 13.6 ppb) was higher than the EPA’s regulated upper limit (5.0 ppb).  We cannot report whether cadmium concentrations were below EPA limits, but we can report that none of the samples had a concentration above the limit of detection. To be confident that cadmium concentrations are below the EPA upper limit, the samples may need to be run undiluted. All other limits of detection were below the EPA concentration limit. 

Concentrations below the limit of detection were a clear limitation of this experiment. The EPA’s method 200.8 recommends 10x dilution, but based on the concentrations we found, dilution might not be necessary for measuring metal concentrations in drinking water. Rivers, streams, lakes, and groundwater typically call for dilutions, but drinking water is filtered. Large concentrations of toxins are removed before the water reaches the tap.

While estimating concentrations is difficult when they are at or near the limit of detection, low concentrations show the robustness of the EPA’s method. If concentrations of toxins above the EPA’s upper limit were present, we would have detected them and reported the values accordingly. 

Using both interference equations and collision reaction cell technology, we found no metal concentrations exceeding EPA limits. The water at the UT Austin campus is safe to drink!

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Table 7: UT Building Information – Year Occupied

The table above shows the occupation year of each building where we analyzed water samples. The oldest building is the PAR, and the newest building is the GLT. It is important to note that this data does not contain renovation years. There does not appear to be a correlation between the building occupation year and the amount of contaminants present in the water; the GLT, despite being the newest building, contains the most Zinc and Chromium.

Some limitations of our experiment include user error and possible contamination of samples. For future work, testing more buildings and several water fountains on the same floor would encompass more data and results, hopefully accounting for possible contamination. More elements could also be added to the analyte list to expand the research. Thanks for reading!