Quantitative headspace analysis of selected odorants from latrines in Africa and India.

Abstract

This analytical investigation focuses on the quantification of odorant molecules in the headspace of latrines. Hydrogen sulfide and methyl mercaptan were derivatized under a more stable N-ethyl maleimide conjugate. Since the amount of odorant molecules is very low in the gas phase, we developed a method that had two steps of concentration. The first step consisted of the accumulation of volatiles in buffered water by bubbling 350 L of air in a bottle. The second step consisted of loading the water on a 1 g solid-phase extraction cartridge, shipping it to our laboratories, and desorbing with Et2O, which achieved a total concentration factor of 3.5 × 10(6). The acidification of the water phase gave us access to the acids, and an additional bottle containing an acidic ion-exchange resin gave us access to trimethyl amine. The limits of quantification in the gas phase were 8.7 × 10(-4) μg/L air for hydrogen sulfide, 1 × 10(-4) μg/L air for methyl mercaptan, 1 × 10(-3) μg/L air for butyric acid, 1 × 10(-4) μg/L air for p-cresol, 1 × 10(-5) μg/L air for indole, and 1 × 10(-5) μg/L air for skatole. The system was calibrated by using olfactometers, which can deliver a precisely known quantity of volatiles into the air. We were able to quantify all compounds near their odor detection thresholds (ODTs). All ODTs were measured in our laboratory with the same olfactometry method. This allowed accurate and comparable ODT values for malodorant compounds from toilets.