Net Weights: Visualizing and Quantifying their Contribution to Drug Background Levels in Forensic Laboratories.

While the drug background in forensic laboratories has been quantified, the processes that most contribute to the background have not been extensively researched. This work presents both qualitative visualization and quantitative analysis of the spread of simulant drug particulate during the process of taking net weights. The process was modeled using three masses of powder (0.2 g, 2 g, and 100 g). The net weight process, in which the mixture was poured onto weighing paper, was mimicked and the resulting aerosolized particulate was allowed to settle. Wetted cotton swabs were then used to sample 6.45 cm2 (1 in2) squares extending up to 61 cm (24 in) away from the weigh paper. The swabs were then extracted and quantified using LC-MS/MS and two-dimensional color plots were created to visualize the magnitude of particulate spread. Qualitative flow visualization of the process, accomplished using laser light sheet videography, was also completed to support the quantitative extraction experiments and provide a visual representation of the mechanism of particulate spread. Surface concentrations were found to be highest in the area immediately surrounding the weigh paper, though transport as far as 61 cm (24 in) was observed with all mass loadings. The amount of the material aerosolized and transported on the bench surrounding the weigh paper was dependent upon the mass of material being poured. These results highlight that weighing activities encountered in forensic labs may be a primary contributor to drug background and may be a potential source of inhalation exposure for chemists.