Determing Sulfite Detection as a Viable Method:
UV-Vis
Team Chocolate was able to run samples of sulfite, PEG and cobalt chloride catalyst throught the HPLC. Results suggested that both sulfite and PEG had a strong absorbance at both 265 and 275 nm. LEDs at both of these wavelengths were ordered.
To follow up, samples were run through the UV-Vis Spectrophotometer in the Yates Lab. At very dilute concentrations, sulfite started absorbing below 250 nm. The same was true for much more concentrated solutions of PEG.
Sulfite Test Kit
A sulfite test kit was used over the course of the reaction by taking out samples every 30 seconds once the sodium sulfite was added. The color change would indicate the ppm of sulfite in the sample.
The sulfite test kit also worked when PEG was present. Two different concentrations of PEG was used for the following trials: one that modified the viscosity to 10 cp and one that modified it to 13.5 cp. These values were obtained by using a viscometer on a sample of the reaction fluid. When 8.3 grams of sodium sulfite was added to 16.6 L of water and 0.02 g of cobalt chloride catalyst, the OTR was calculated from the slope of the test kit data. The results are summarized below:
A T-Test was performed on the average OTR determined by the test kit and the actual OTR determined by the O2 sensor (or sulfite sensor in trials with PEG).
Null Hypothesis: The OTR result from the oxygen/sulfite sensor is the same as the OTR result from the sulfite test kit.
| Trial # | Mean Test Kit OTR(mol/L*s) | Actual OTR(mol/L*s) | P-Value |
| 45 – Water | 4.01 E-6 | 4.96 E-6 | 0.511 |
| 71 – PEG (10 cp) | 2.78 E-6 | 3.24 E-6 | 0.694 |
| 75 – PEG (13.5 cp) | 2.84 E-6 | 2.84 E-6 | 0.997 |
In trials with water, the high p-value indicates that the test kit OTR is not statistically different from the actual OTR. In trials with PEG, the high p-values indicate that the sulfite sensor prototype measures the concentration of sulfite to give an OTR similar to the test kit.
This indicates that monitoring the sulfite concentration can yield accurate OTR results.