We decided to prepare a new standard gas since the old standard gas was giving us variable, inaccurate results.  We decided to target a standard gas with CF₃SF₅, SF₆, and N₂O concentrations of 119 ppmv, 476 ppmv, and 4% respectively. We used the same serial dilution method to prepare the gas.

We found the concentrations of CF₃SF₅ and SF₆ in the standard gas to be 1817 and 816 ppbv respectively.  We were not sure why the actually concentrations were so much higher than the targeted concentrations.  The concentration of CF₃SF₅ was particularly alarming.  Nevertheless, we decided that the gas could still potentially provide accurate data.

We used the same experimental method to diffuse the gas across a water membrane. and to measure the resulting diffused gas concentration.   We found the diffusion coefficients in pure over a temperature range of 3.0 ^oC to 30.0 ^oC  and we found the diffusion coefficients in seawater over a temperature range of 15 ^oC to 30.0^oC.  We found the following results with this gas standard:

 

The results for SF₆ matched previous work quite well, validating the results for CF₃SF_5. More trials should be conducted to ensure that the diffusion coefficients yield a low standard deviation.

The diffusion coefficients for SF₆ were 6-19% lower in sea water than in pure water.  Likewise, the diffusion coefficients for CF₃SF₅ were 5-7% lower in sea water.  It is not clear whether diffusivity decreases due to the sea water or the variability in the experimental method.  In previous studies, the diffusion coefficient for SF₆ did not change between pure water and sea water; however it would make sense physically for diffusivity to decrease in salt water. \

It is recommended to better determine the solubility of CF₃SF₅ in both pure and salt water to determine a more accurate diffusion coefficient.