Investigation of practical in-situ methods to determine airborne and surface iodine species in clandestine methamphetamine laboratories

Abstract

Suspected illicit methamphetamine (MA) clandestine laboratories ‘clan labs’ are routinely tested for methamphetamine residues; however, this does not indicate whether the contamination has occurred from ‘smoking’ or illicit MA manufacturing. The use of iodine (I₂ ) to synthesise MA can expose residents of current or former ‘clan labs’ to potential toxic I₂ residue contamination on surfaces and in the air. A positive result for methamphetamine and I₂ is highly suggestive that manufacturing has occurred. This thesis focused on developing an in-situ colorimetric indicator to detect and quantify I₂ and iodide (I-) residues on non-porous and porous surfaces and in the air. The developed colorimetric indicator is a ~0.9 mm dia. gel disc produced from agarose containing a gold colloid stabilised with polyethyleneimine (PEI) that changes from clear light-yellow to pink/purple when exposed to I₂ or I-. Discs were exposed to I₂ and I- surface residues in an enclosed environment or subjected to a dynamic airflow of iodine vapour and photographs were taken to capture colour responses and pattern formations. ImageJ software was used to process and analyse the characteristics observed in the images by converting the colour to greyscale pixel values providing qualitative and semi-quantitative results. Surface I₂ residues of 4.75 μg, spread over a non-porous surface area of 23.8 cm², are proportional to the recommended surface I₂ exposure level of 20.0 μg/100 cm² in New Zealand, and displayed a visible colour response by 15 min with repeatable results. The sensor discs showed a detection limit of 0.5 μg after 30 min sensing time for I₂ and showed selectivity for I₂ and I-. The disc had a lower limit of detection for iodine than the currently used starch spray indicator method. A colour response occurred for the discs exposed to 4.75 μg I₂ residues on selected common household non-porous and porous surfaces within 30 min. However, discs suspended above 4.75 μg I₂ residues on porous painted GIB® plaster board did not change colour within 30 min, suggesting a longer sensing interval would be required for this surface type. Discs exposed for 30 min to I₂ vapour could detect an airborne iodine concentration of 0.15 ppm I₂ per 7.5 L air with a visible colour response and this is comparable to the NIOSH and OSHA recommended exposure guideline level of 0.1 ppm. The Gold-PEI gel sensor disc could be stored for 15 days with no spontaneous colour response in the blank discs, and with minimal or no difference compared to freshly prepared discs when placed on I- and I₂ residues. This developed method provides a novel in-situ colorimetric indicator to detect and semi-quantify iodine species residues within 30 min on surfaces and in the air that are above the I₂ recommended exposure level guidelines in New Zealand.