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Literature Article Analysis: Electrochemistry (Scott)

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    Out-of-Class Questions

    Article: Soleymanpour and Rezvani. Development of a novel carbon paste sensor for determination of micromolar amounts of sulfaquinoxaline in pharmaceutical and biological samples, Materials Science and Engineering C, 58, 504-509, 2016.

    Suggestions: read the article individually first (potentially multiple times) and make notes of items you do not understand, then re-read the article with your group.

    1. Look up and define any terms you were unfamiliar with, but are important for the comprehension of the paper. List the terms and definitions below.

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

    1. a. We did not directly discuss carbon past electrodes but they are most similar to which type of electrodes we did discuss? Be as specific as possible.

       

       

       

      1. The composition of the carbon paste electrode (CPE) is also listed in Table 1. Briefly describe the purpose and importance of each component.

     

     

     

     

     

     

     

    1. On page 505 under 2.3 Emf measurements there is the shorthand (line) notation for the electrochemical cell assembly. Draw what this electrochemical cell would look like. Include as much detail as possible (i.e. include filling solutions when necessary) and clearly label each part. What is the working electrode and reference electrode?

     

     

     

     

     

     

     

    1. The response of the CPE under optimal conditions is shown in Figure 2 with the line fitting y=-58.4x-76.8.
      1. Theoretically what would you have expected Ecell to equal for this CPE (Ecell= _____)? What is included in K?

         

         

         

         

      2. Based on Figure 2 and the line of best fit how did the Ecell actually correlate?

         

         

         

         

      3. When testing the “real samples” the authors used standard additions instead of the external calibration curve. Briefly describe what standard additions are, how they work, and why the authors chose to use this method.

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

    1. Table 2 lists the selectivity coefficients with various interfering species.
      1. Which species listed interfered the most with the CPE response? Explain your choice.

         

         

         

         

         

         

      2. You are using the CPE from the paper to determine the amount of SQX in a sample of milk being sold at the Danville Farmers Market. Using the external calibration curve in Figure 2 (y=-58.4x-76.8) you measure a potential of 121.3 mV. What is the measured concentration (in mM) of SQX in the milk sample.

         

         

         

         

         

         

         

         

         

      3. After additional analysis with the Benedict’s Assay (an assay used for the identification of reducing sugars) you realized there is also 115 mM of the milk sugar and interfering species lactose. What is the act SQX concentration (in mM) in the milk assuming no other interfering species? Does your new answer make sense given your recent discovery?

     

     

     

     

     

     

     

     

     

     

     

     

    In-Class Questions

    Article: Soleymanpour and Rezvani. Development of a novel carbon paste sensor for determination of micromolar amounts of sulfaquinoxaline in pharmaceutical and biological samples, Materials Science and Engineering C, 58, 504-509, 2016.

    1. On page 506 in Table 1 the authors list 12 different sensor “cocktails” and their respective responses to the analyte.
      1. Rank the three sensors cocktails that showed the best performance with 1 being the best overall, 2 being the second best and 3 being the third best overall (the number of the composition is fine). Justify your choices and why these three are the best cocktails.

         

         

         

         

         

         

         

      2. The authors make the statement in the middle of section 3.1 that “… the absence of the ion-exchanger in the CPE composition caused a negligible [response]…”. Based on Table 1, do you agree with the authors claim? Explain.

     

     

     

     

     

     

    1. In section 3.3 and with Figure 3 the authors discuss the effect of pH on the CPE. The authors state that the working pH range of the sensor suitable for SQX determination was pH 8.0-10.0
      1. Why did the authors choose this pH range as the working range?

         

         

         

         

      2. If you attempted to quantify SQX at a pH of 5 would the actual [SQX] be greater than, less than, or consistent with the measured [SQX]? Explain your answer and explicitly state why the sensor response would stay the same or move in the direction you chose.

         

         

         

         

         



         

      3. If you attempted to quantify SQX at a pH of 12 would the actual [SQX] be greater than, less than, or consistent with the measured [SQX]? Explain your answer and explicitly state why the sensor response would stay the same or move in the direction you chose.

     

     

     

     

     

     

     

     

     

    1. You have developed an ionophore, SQX ionophore 1, for SQX- and want to create a liquid membrane ISE to replace CPE discussed in the paper.
      1. What would your membrane need to consist of (you don’t have to know specific chemicals but general type and anything key about the chemical for it to function, i.e charge) and what is the purpose of each component.

         

         

         

         

         

         

         

         

         

         

         

      2. Draw a diagram of the working electrode and label it completely (include any filling solutions that are necessary).

     

     

     

     

     

     

     

     

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