Is open-access tap water monitoring possible using the coffee-ring effect?

Academic Research Topics in Environmental Measurement and Monitoring
Oral Presentation

Prepared by R. Lahr, X. Li, S. Allen, A. Sanderson
Michigan State University, 1449 Engineering Research Ct, A111 Engineering Research Complex, East Lansing, Michigan, 48824, United States


Contact Information: rlahr@msu.edu; 517-884-8460


ABSTRACT

Few low-cost and low-tech tools exist for citizen scientists and resource-limited organizations to accurately measure tap water quality (e.g., presence/absence paper or dipstick tests, colorimetric tests with pillow packets of reagents, low-cost spectrometers). Herein a new method was developed and evaluated for water testing that can be conducted using commonly available and reusable materials (aluminum sheet, dropper, 30x triplet jeweler’s loupe ($18), and a cell phone camera). This method harnesses the coffee-ring effect to provide nano-scale chromatography of solute particles within an aqueous droplet on a solid substrate. Each aqueous sample leaves a distinguishable “fingerprint” residue pattern after water evaporates, reflecting the solubility and size of solute particles that exist in the sample or form as water leaves the droplet. Droplets of various tap water samples and synthetic tap waters were dried on aluminum substrates and photographs of the residue patterns were captured with a cell phone camera and jeweler’s loupe. Unique and reproducible residue patterns were obtained for tap waters from communities across southern Michigan. Synthetic tap water solutions were created to mimic community tap waters with varied amounts of hardness, alkalinity, sodium, chloride, sulfate, total dissolved solids, iron, and copper. Features of residue patterns that correlated to concentration were identified for each tap water component. Microscope images and chemical analyses were also collected to confirm identities if residue features. The coffee-ring effect was also partnered with in-syringe solid-phase extractions to concentrate heavy metals before analysis. Methods were applied by three groups of minimally trained students to evaluate the data quality achieved by new users and the potential of the method for open-access water testing. Data suggests the coffee-ring effect will be a valuable tool for laboratory water analyses, citizen science programs, and hands on tap water education.