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Research Question:
Research Question:
What experimental conditions are necessary to reproducibly make quantitative electrochemical measurements with microfluidic technology?
What experimental conditions are necessary to reproducibly make quantitative electrochemical measurements with microfluidic technology?
Learning Objectives:
Learning Objectives:
- Determine the details and constraints of making an electrochemical measurement, particularly in a microfluidic format, and make appropriate experimental adjustments
- Use the Nernst equation to relate concentrations and measured electrochemical potentials.
- Make serial dilutions
- Explain the difference between the analytical results of logarithmic relationships and linear relationships in analytical measurements.
To Do List:
To Do List:
Step 1: Read lab background, watch videos, and visit links provided on this page about the experimental context
Step 1: Read lab background, watch videos, and visit links provided on this page about the experimental context
Step 2: Read procedure
Step 2: Read procedure
Step 3: Watch corresponding lab tutorials:
Step 3: Watch corresponding lab tutorials:
Step 4: Answer pre-lab questions
Step 4: Answer pre-lab questions
Step 5: Perform lab experiment
Step 5: Perform lab experiment
Step 6: Answer post-lab questions
Step 6: Answer post-lab questions
Figure 1. Contaminated water from the Flint River4
Flint Water Crisis
Flint Water Crisis
Flint, Michigan is a prime example of how water pollution and elevated copper levels can cause lethal damages in communities and aquatic life who consume it. In 2014, the city decided to switch the water source for the community from Lake Huron to the Flint River to save money. The new water source had high levels of corrosive metals and dangerous contaminants.1 The Flint River has become a waste site for many businesses in the area. Pollution like sewage, car parts, meatpacking waste, and paper waste all have been dumped into this river.2 In the time the water source switched, 12 people died and 79 people became ill from Legionnaires’ disease. It was later recorded that 80% of these cases were related to the contamination of the Flint River.3
Copper is an important and abundant transition metal that naturally occurs in multiple forms in the environment. Common sources of copper include geological deposits, volcanic rocks, and the erosion of sedimentary rock. Traces of copper can be found in aquatic environments in low concentrations, normally less than 10 ppb.5 Copper levels can be toxic at levels as low as 10-20 ppb or µg/L (less than a speck of dust), and these levels are elevated because aquatic habitats and ecosystems are the main receptor of industrial and urban wastewater, storm water run off, and atmospheric deposition.5
When the water in Flint was tested for high levels of lead and copper, extremely unsafe levels of each were found in the water. One of the studies that has now become regularly repeated to find unsafe drinking water was tested in 2016. Copper was found in major abundance- with levels as high as 11,650 ppb at one site.6 Even though this problem was identified and tested, it hasn’t gone away. A lead and copper rule test was run in 2018 and the highest copper content was measured as 2,920 ppb.7 While the overall copper levels decreased, they are still far above what would be considered safe to ingest. The EPA has put a rule in place called the Lead and Copper Rule, which will regulate the amount of lead and copper in drinking water. These two metals are often found together in contaminated water and increase the risk from ingestion when together. They can cause several issues from gastrointestinal distress to brain damage.8 Many places across the entire United States violated this rule when it was first put in effect.
Figure 2. Violations against the lead and copper rule in 20159
Copper Contamination of Aquatic Systems and Drinking Water
Copper Contamination of Aquatic Systems and Drinking Water
Copper is both essential and toxic to life; at low concentrations it is considered an essential nutrient, but can become toxic to aquatic organisms and humans at higher concentrations.5 While copper deficiencies are rare in both humans and aquatic species, overdoses of copper can cause severe harm for both.10 For humans, copper overdoses occur with an intake of 44 mg Cu/L and can cause gastrointestinal distress, vomiting, headache, nausea and more.10 Concentrations of copper ranging from 10-20 ppb are acutely toxic (lethal) to freshwater fish, and chronic exposure can lead to effects on survival, growth, reproduction, brain function, enzyme activity, blood chemistry, and metabolism.5,10 Though copper is not commonly thought of as a harmful metal, surprisingly low concentrations are needed to go from essential to toxic in both humans and aquatic life. To best control levels of copper in freshwater systems and therefore in aquatic and human life, cleanup of urban rivers and other freshwater bodies needs to be a priority.
Humans who ingest high amounts of copper can be at extreme risk for health complications. Infants and people with chronic liver disease are especially at risk for complications from copper ingestion. Another issue in relation to high copper ingestion can severely affect about 1% of the US population who have polymorphisms which makes them store extra copper. This can make them more at risk for organ failure and death related to high levels of copper in the body.11 High amounts of copper in water mostly affects people who live in more northern areas of the US. These areas are most likely near copper plants or large industrial plants which utilize copper.12
Figure 3. Effects of high copper levels in the body13
Microfluidic Electrochemical Devices
Microfluidic Electrochemical Devices
Electrochemical cells typically use volumes of solution on the mL scale to generate electricity, such as household batteries and electrolysis apparatuses. Scaling the cell down to the microfluidic level drastically reduces the amount of reagents used and waste produced. Recent research has focused on developing microfluidic electrochemical cells to create on-site detection methods for chemical pollutants.11 The devices require very small sample sizes and reagent volumes, allowing many tests to be carried out rapidly. Paper microfluidic devices are simple and cost-effective to produce and electrochemical devices show high sensitivity to analytes.
Concentration Cells
Concentration Cells
Copper concentrations in aqueous samples can be determined using an electrochemical cell and a known standard solution of copper. The reaction shown between ionic and neutral copper generates an electric potential when a concentration cell is formed with aqueous copper solutions. This lab will measure the potential between two copper solutions in a dogbone chip with a salt bridge connecting the cells instead of beakers filled with solution. Using a microfluidic device eliminates the need for the solutions to be in beakers with a huge salt bridge connecting them. The dogbone chips have the concentration cells and the salt bridge all on one device.
Watch this video on Isiah Warner and how he grew up to be a tremendous chemist and researcher!
Watch this video on Isiah Warner and how he grew up to be a tremendous chemist and researcher!
References
References
United States Environmental Protection Agency Aquatic Life Criteria - Copper. https://www.epa.gov/wqc/aquatic-life-criteria-copper (accessed June 29, 2020).
Water Quality Association Copper in Drinking Water. https://www.wqa.org/learn-about-water/common-contaminants/copper (accessed July 1, 2020).
Centers for Disease Control and Prevention Copper and Drinking Water from Private Wells. https://www.cdc.gov/healthywater/drinking/private/wells/disease/copper.html (accessed July 1, 2020).
Garbarino, J. R.; Hayes, H. C.; Roth, D. A.; Antweiler, R. C.; Brinton, T. I.; Taylor, H. E. Heavy Metals in the Mississippi River. 1995.
Hamline University Graduate School of Education Mississippi River. https://cgee.hamline.edu/rivers/Resources/river_days/info.html#:~:text=The%20Mississippi%20River%20serves%20as,million%20people%20in%20central%20U.S. (accessed July 1, 2020).
By Shannon1 - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=47308146
Center for Biological Diversity Freshwater Protection. https://www.biologicaldiversity.org/campaigns/freshwater_protection/index.html (accessed June 29, 2020).
Jones, M. G26 Project. https://ic.arc.losrios.edu/~veiszep/08fall2002/Jones/G26_JonesM_Project.htm (accessed Jul 23, 2020).
United States Environmental Protection Agency History of the Clean Water Act. https://www.epa.gov/laws-regulations/history-clean-water-act (accessed June 30, 2020).
Water, N. Risk Characterization. https://www.ncbi.nlm.nih.gov/books/NBK225399/ (accessed Jul 23, 2020).
Zheng, T.; Liu, Y.; Xu, C.; Lu, H.; Wang, C. Focusing surface acoustic waves assisted electrochemical detector in microfluidics. Electrophoresis 2020, 41, 860-866.
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