New Methods for the Optical Detection of Trace Compounds and the Delivery of a Chemical Oxidant

Biogenic amines are known indicators of spoilage in food. Indole in particular is a chemical used extensively to indicate seafood freshness. Levels higher than 25 μg [micrograms]/100 g shrimp mark early decomposition, according to the US Food and Drug Administration. We developed an optical probe based on an Ehrlich-type reaction to detect indole in shrimp. The probe is based on the reaction of p-dimethylaminobenzaldhyde (DMAB) with indole, generating red β[beta]-bis(indolyl)methane (BIM). Color development is observed by the naked eye after exposure to indole. When using UV-Visible spectroscopy as a detection method, the limits of detection and quantification are of 0.05 and 0.16 μg mL^-1 [per milliliter], respectively. These limits lead to quantification of less than 25 μg [micrograms] indole/100 g shrimp, when recovery is accounted for. Moreover, an inexpensive handheld colorimeter can be used to perform optical measurements of indole by the probe with similar sensitivity. In addition, studies to confirm the structure of BIM were conducted. The β-position of two indole molecules is involved in the reaction with one DMAB molecule, yielding the product β[beta]-bis(indolyl)methane (BIM).Determination of amines in aviation fuels is of interest as these species reduce fuel stability when present in higher concentrations. Since anilines and indoles are species of major presence in fuels, we have explored their simultaneous determination by the probe using a chemometric calibration with Classical Least Squares and Principal Component Regression.In-situ chemical oxidation (ISCO) is an approach for remediation of polluted groundwater by the release of oxidants directly into the contaminated zone. We have developed a system for the controlled release of potassium persulfate from pellets of diatomaceous earth for the oxidation of organic contaminants, obtaining a continuous delivery for up to 21 h. In addition, this approach was used to release Fe²⁺ [iron two plus] ions for in-situ activation of persulfate. Controlled-released persulfate and Fe²⁺ ions from the pellets have been used for batch treatment of 15 mg L^-1 [per liter] trichloroethylene (TCE) aqueous solution, giving residual TCE concentration of < [less than] 0.06 mg L^-1 after 6 h and degradation of 93% TCE after 2 h.