Abstract: Methods, apparatuses, and systems for determining a concentration of a target gas in a sample gas. An example method of preparing a replaceable testing material for detecting a target gas in a sample gas may include preparing a solution comprising a solute and a solvent, wherein the solute comprises o-tolidine; introducing a testing material substrate to the prepared solution for a period of time; and removing at least a portion of the solvent from the testing material substrate such that the testing material substrate comprises at least a portion of the o-tolidine, and thereby forming the replaceable testing material for detecting the target gas in the sample gas.

Abstract: Systems, apparatus, and methods for detecting air breathed by a user and/or one or more gases are provided herein. In some embodiments, an apparatus may include a test material adapted to reduce in size when exposed to one or more stimuli. In some embodiments, one or more chemicals may be disposed on the test material and, when exposed to the air breathed by the user, the one or more chemicals are adapted to transform from a first color to a second color. In some embodiments, when the test material reduces in size an intensity of the second color increases. The apparatus may further include a face mask. In this regard, the test material may be removably attached to the face mask. The apparatus may further include a spectrophotometer configured to determine if the one or more chemicals have transformed from the first color to the second color.