Characterization of Pieces of Paper That Form Reagent Containers for Use as Portable Analytical Devices

Reagent-deposited pieces of paper were characterized by the use of a compact conductometer, a compact pH sensor, and a conventional spectrophotometer to assess their suitability for use as reagent containers. The pieces of paper were fabricated by wax printing to form a limited hydrophilic area to which a consistent volume of an aqueous reagent could be added. The pieces of paper without the reagent increased the conductivity of water gradually because of the release of sodium salts, whereas pH of NaOH decreased because of the acidity of the functional groups in the paper. Three reagents, sulfamic acid as an acid, Na₂CO₃ as a base, and BaCl₂ as a metal salt, were deposited on the pieces of paper to evaluate their ability to release from the pieces of paper. Sulfamic acid and Na₂CO₃ were released in quantities of 58 and 73% into water after 420 s, whereas 100% of BaCl₂ was released after 480 s. The conductometric titrations of NaOH, HCl, and Na₂SO₄, and the spectrophotometry of Fe²⁺ were examined using the pieces of paper that contained sulfamic acid, Na₂CO₃, BaCl₂, and 1,10-phenanthroline. Titrations using the pieces of paper suggested that the reagents were quantitatively released into the titrant, which resulted in a linear relationship between the endpoints and the equivalent points. In 120 s of soaking time, 60-70% of the reagents were released. The spectrophotometric measurements of Fe²⁺ indicated that when an excess amount of the reagents was deposited onto the pieces of paper, they nonetheless sufficiently fulfilled the role of a reagent container.