A comparison of spectrophotometric and denuder based approaches for the determination of gaseous molecular iodine

Abstract. The presence of molecular iodine in the atmosphere is thought to have implications for both climate and human nutritional health, but measurement of the gas at low concentrations requires technically demanding techniques that are not widely accessible. Here, amylose coated denuder tubes and solvent traps coupled with spectrophotometric detection are evaluated and compared as relatively cheap and straightforward methods to measure gaseous molecular iodine at environmentally relevant concentrations. Denuder tubes were found to give unacceptably low and highly variable recoveries of molecular iodine from a test gas source, with values ranging from 1 to 62%. Blank concentrations were also high, being equivalent to a gas phase concentration of 5 pptv under typical operating conditions. Ethanol and hexane solvent traps gave much better performance. Optimisation of the hexane solvent trap method gave 100% recovery and an atmospheric limit of detection of 70 pptv, which is within the range of concentrations observed in the coastal marine atmosphere.