Dr. Christopher Fenk

"Development of Introductory and Advanced Applications of Digital Camera Colorimetry"

Research in my group focuses on the development of pedagogical laboratory methods for use in secondary and post-secondary educational settings. In addition, these methods have significant potential to bring the basic theories of advanced instrumentation to developing countries both in education and in field applications. We are currently developing a number of laboratory methods focused on extending the applications of digital camera colorimetry (DCC). DCC is a spectroscopic method that uses modern hand-held devices (phones, cameras, notebook computers, etc.) as both light source and detector. Using mobile phones as analytical instruments is particularly appealing due to the ubiquity of mobile devices worldwide. We are currently developing DCC protocols for use in introductory laboratory courses along with a number of relevant field applications.

Red, green and blue detection channels of modern CMOS sensors provide for a range of data handling techniques based upon the sample of interest. Mathematical merging of data derived from these color channels also provides for gray channel analysis. A basis set of sample and data handling techniques has already been developed and is now being extended to include other analyses. To date, we have developed analytical methods for the colorimetric determination of food coloring solutions as well as the analytical determination of aspartame in tabletop sweetener. A sample of an image from this project is shown below. We have extended this technology to optimize the experimental conditions and to include other first-year chemistry laboratory experiments.

Our best results were obtained when experimental samples were photographed in a standard 96-well plate at an optimum distance from the sample.  The mathematics of this sample optimization may be readily summarized and extracted from the graphic shown below.

Although determining the optimal focal length, x, is a complex trigonometric function, it may be approximated using the following equation based upon an infinite Taylor series:

Where; x is the focal length, y is the sample cell width and φis the desired level of precision.  This equation allows us to determine the optimum focal length for our determinations based upon the level of precision desired.  For most of our experiments the desired level of precision is set so that the focal length, x , is less than 0.5% (φ= 0.005) greater than the distance to the outermost sample cell, w.

Using this mathematical relationship, we were able to use DCC to determine aspartame concentration in tabletop sweeteners in a manner analogous to that previously published.  Quite remarkably the results of this assay were on par with those obtained using a traditional spectrophotometer (see below).

More recently, DCC was used to determine the rate law for the classical crystal violet-sodium hydroxide (CV/NaOH) reaction. Results obtained using DCC were virtually identical to those obtained with a Beckman model DU-520 research grade instrument! Finally, we were able to use DCC to determine the equilibrium constant of the iron(III)-thiocyanate equilibrium. The equilibrium constant found using DCC is within 3% of the value obtained with a laboratory grade spectrometer, however further refinements are required to make the method more accurate. Both the CV/NaOH experiment and the [Fe(SCN)]2+ equilibrium constant experiments are classic undergraduate spectroscopy experiments that may be readily incorporated into the undergraduate curriculum.

REU students working on this project will work on new applications of DCC and collect data for publication in the Journal of Chemical Education.

1. Christopher J. Fenk and Donald G. Gerbig, Jr. “Digital Camera Colorimetry: An Advanced Undergraduate Laboratory Experiment.” J. Chem. Educ. 2017 Manuscript in preparation.
2. Christopher J. Fenk, Donald G. Gerbig, Jr. and Joshua R. Menefee “Digital Camera Colorimetry: Basic Concepts and Introductory Experiments.” J. Chem. Educ. 2017 Manuscript in preparation.
3. Christopher J. Fenk, Douglas H. Motry, Nicole M. Hickman, Melissa A. Fincke, Barry Lavine “Identification and Quantitative Determination of Caffeine, Acetaminophen, and Acetylsalicylic Acid in Commercial Analgesic Tablets by LC-MS” J. Chem. Educ. 2010, 87(8), 838-841. DOI: 10.1021/ed100280y (Cited as one of the “top ten most read” JCE articles of 2011)
4. Claudia Khourey-Bowers and Christopher J. Fenk "Influence of Constructivist Professional Development on Chemistry Content Knowledge and Scientific Model Development" J. Sci. Teacher Educ. [Online] 2009, DOI: 10.1007/s10972-009-9140‑0, [Print] J. Sci. Teacher Educ. 2009, (20) 437–457.
5. Christopher J. Fenk, Donald G. Gerbig, Jr. and Nathan Kaufman “A New Colorimetric Assay of Tabletop Sweeteners Using a Modified Biuret Reagent” J. Chem. Educ. 2007, 84 (10), 1676-1678.
6. Donald G. Gerbig, Jr., Christopher J. Fenk and Amy S. Goodhart “The Dot Blot ELISA: A Rapid and Simple Experiment to Demonstrate Antibody-Antigen Interactions” Am. Biol. Teach. 2000, 62(8), 583-587.
7. Christopher J. Fenk, Donald G. Gerbig, Jr. and Stephanie Y. Grooms “A Rapid and Highly Specific Western Blot Experiment for Introductory Biochemistry” J. Chem. Educ. 2000, 77 (3), 373-374.