Trace Metals Analysis using Digital Microscopes

Project Title: Trace Metals Analysis using Digital Microscopes

Long Title (if desired): Trace Metals Analysis using Digital Microscopes and High Energy (Hydrophobic) Surfaces

Project Lead's Name: Andre J. Sommer

Project Lead's Email:

Project Lead's Phone: 513-529-2874

Project Lead's Division: CAS

Primary Department: Chemistry and Biochemistry

Other Team Members and their emails:

  • Neil D. Danielson,
  • Hang Ren,

List Departments Benefiting or Affected by this proposal: Chemistry and Biochemistry

Estimated Number of Under-Graduate students affected per year (should be number who will actually use solution, not just who is it available to): 200

Estimated Number of Graduate students affected per year (should be number who will actually use solution, not just who is it available to): 6

Describe the problem you are attempting to solve and your approach for solving that problem: The attractiveness of using cellphones for chemistry experiments at the undergraduate level is that most students have a cell phone and have experience using them to collect images (take photos). They are a part of the students ever day life and they are familiar with them. Recently, several reports have been published in which cell phones have been used as detectors in spectrophotometers and microscopes. Further, the images collected with the cell phones can be further analyzed to identify and quantify chemical components. One such very recent report employed a cellphone with a modified lens to detect lead in aqueous solutions down to the part per billion levels by measuring the amount of lead chromate precipitate formed. With the nation focused on lead in drinking water and its adverse health effects the addition of such an experiment to an undergraduate analytical laboratory would not only be timely but garner the student’s interest in analytical chemistry for solving real world problems. In addition, the students would learn fundamental concepts of analytical and physical chemistry, microscopy, image analysis and physics. In this proposal we plan to use inexpensive (~$250) digital microscopes to detect metals and other ions down to the part per billion level. In fact, the magnification capable of these microscopes is markedly more powerful that the home-made lens described for the cell phone, meaning that such low levels of metal detection should be facile.

A fundamental experiment in analytical chemistry is the quantitative determination of a metal by precipitation analysis. In this analysis an aqueous metal ion is precipitated by complexing it with an anion. For example lead can be precipitated out of solution using the chromate ion via the following chemical reaction: Pb2+(aq) + CrO42-(aq) <=> PbCrO4 (s)

The precipitate on the right is bright yellow solid. In the typical procedure, a solution containing lead is mixed with a solution containing excess chromate producing the precipitate. The precipitate is then isolated, dried and weighed such that the concentration in the original lead solution can be determined. An issue arises however when the amount of solution or the concentration of lead is low. The formed precipitate could be invisible to the unaided eye or two small to be handled. Here however is where microscopy and a little bit of physical chemistry come in. A small droplet of the lead solution that has been mixed with the complexing anion is placed on a hydrophobic surface like Teflon. Because the solution does not wet the surface, it beads up and as the water evaporates, the droplet gets smaller and the concentration of the ions increase promoting precipitation. After the water has evaporated, the precipitate remains on the surface distributed over a microscopic area at which time it can be analyzed with the microscope. Once the precipitate is formed, an image can be taken and analyzed with open source software to determine the amount of lead or other ion in the original liquid sample.

Qualitative analysis using precipitation chemistry is a standard first year chemistry experiment done at virtually all universities and colleges for many decades. However, it is badly in need of an update and this proposal using digital microscopes describes just that.

How would you describe the innovation and/or the significance of your project: We envision the use of these microscopes to detect and quantitate ions by precipitation chemistry in at least two courses, CHM 145M and CHM 375. Impact to a potentially new physical/analytical chemistry laboratory course is very possible.

CHM 145M is the second semester general chemistry laboratory course taken by chemistry/biochemistry majors (about 120 students). This course is usually taught by an analytical chemistry professor, currently A. J. Sommer, and in the past by N. D. Danielson. H. Ren is a new analytical chemistry faculty member, just starting this Fall, and will likely become involved in teaching this course.

One of the experiments in CHM 145M (and also CHM 145, taken by science majors) is entitled “Qualitative Analysis” and was developed by N. D. Danielson. In that experiment, students gain exposure to some simple chemical reactions of common cations and anions such as precipitation reactions and complex ion formation, use these observations of simple chemical reactions to identify the cations and anions in an “unknown” solution mixtures, and gain an understanding of solubility product constants Ksp. The metal ions Ca2+, Mg2+, Ba2+, and Zn2+ as well as the anions Cl-, Br-, I-, SO42-can all be distinguished qualitatively in various mixtures by precipitation. However, quantitative determination of these precipitates is not currently done due to a lack of suitable detection instruments such as a digital microscope. We envision students would first practice microscope detection of precipitates generated from known standard solutions of each of these ions. Then real applications such as water hardness (Ca and Mg in water) and Zn in supplements could be selected by the student. All various levels of water hardness (Soft- less than 17.1 mg/L, Slightly hard-17.1-60 mg/L, Moderately Hard-60-120 mg/L, Hard-120-180 mg/L, Very Hard- Over 180 mg/L) should be easily determined through precipitation and separation of first Ca2+ with oxalate and Mg2+ with hydroxide. Zinc is found in supplements at usually a 30 mg level and through precipitation with ferrocyanide, quantitation should be easy. The precipitation of halides with silver ion can distinguish between all three ions Cl-, Br-, and I-. The indirect determination of Na+ in various products such as onion salt or meat tenderizer through precipitation of Cl- should be feasible. Iodized salt contains about 0.006-0.01% as potassium iodide. Upon addition of Ag+ to a solution of this salt, the AgI will be yellow in color and the AgCl white. Determination of iodide using the color resolution of the camera should be possible. If not, the AgCl can be dissolved with thiosulfate leaving the unchanged AgI. Showing the application of precipitation chemistry for the analysis of real products should be meaningful to the students. CHM 375, analytical chemistry, teaches the use of modern instrumentation (molecular spectroscopy, atomic spectroscopy, chromatography, mass spectrometry, and electrochemistry) for the determination of both organic compounds such as quinine and caffeine and ions such as potassium, manganese, and fluoride. This course was developed by N. D. Danielson about five years ago and he has been the only instructor. It is a required course for all chemistry/biochemistry majors and is usually taken by juniors or seniors. Students majoring in science education with an emphasis in chemistry are also required to take this course and chemical engineering students will also occasionally elect this course. This course is offered both semesters with a yearly enrollment of about 70 students. The following experiment involving electrochemistry with digital microscope detection is envisioned.

The detection of metal ions via particle formation can be also achieved by metal particle deposition on a transparent indium tin oxide (ITO) electrode. Instead of using a precipitation agent, the metal ions, e.g., Pb2+, will be deposited onto the ITO electrode a constant voltage. The formation of metal particles at ITO surface can be imaged simultaneously using the USB digital microscope. The kinetics of formation can be also tracked simultaneously during the deposition by taking a video of this process and analyzed with open source software Image J. The number, size, as well as the kinetics of particle formation can be used to quantify the metal ion species in solution.

For the last two weeks of CHM 375, students elect a special project which is more open-ended in nature. We envision the digital microscopes could be used for these special projects to follow precipitation chemistry not done in CHM 145M detection of thin layer chromatography spots.

How will you assess the success of the project: Qualitative analysis using precipitation chemistry is a standard first year chemistry experiment done at virtually all universities and colleges for many decades. However, it is badly in need of an update and this proposal using digital microscopes describes just that. The CHM 145 qualitative analysis experiment described in this proposal is new in design compared to most and has not been previously published. We are confident that this experiment with the digital microscope quantitation approach would be an important addition to the chemical education literature and we plan to submit such a manuscript to the Journal of Chemical Education.

Student learning of analysis through digital microscopy will be tracked based on quality of the lab reports and answers to corresponding exam questions.

Total Amount Requested: $4,782

Budget Details: Sixteen 40X-2500X LED digital binocular compound microscopes with USB cameras are requested (see photo of the microscope in Budget Details below). These will be used by students working in groups of three in two separate lab sections of 24 students each. The microscopes have six wide-field magnification settings (40X, 100X, 250X, 400X, 1000X, 2500X) with 360 OC swiveling binocular head. The digital camera comes with advanced editing, processing, and measuring software for Windows XP/Vista/7/8/10. The price below is quoted from the web site.

16 AmScope 2500X Digital Microscopes @ $252 $4032 1 Miscellaneous Lab Supplies (Teflon tape, chemicals, ITO electrodes) $750

Is this a multi-year request: No

Please address how, if at all, this project impacts any of Miami's BCSAE, 2020, or divisional plans: No impact envisioned at this time.