A new method for sampling fumarolic gases: Analysis of major, minor and metallic trace elements with ammonia solutions

A new method using ammonia solutions in pre-evacuated quartz bottles has been experimented for volcanic gas sampling and analysing. Various tests (reproducibility, variability and comparison with known methods such as NaOH pre-evacuated bottles and acid condensates) have been performed to check for their efficiency. By using ammonia solutions, acid gases (St, HCl, HF), carbon dioxide, noncondensible gases (N2, Ar, …) and metallic trace elements (MTE) can be measured with standard methods (HPLC, GC, titrimetry, ICP-MS).Results show that acid gases, CO2 and noncondensible gases are sampled and analysed with similar efficiency in NH4OH bottles than by using the known and accurate NaOH method. Moreover, a key point is that NH4OH solutions, after undergoing adequate processing (oxidation and acidification) allow also precise MTE measurements by using standard ICP-MS methods. Such MTE measurements appear much more reliable than those performed on acid condensates.Pre-evacuated ammonia bottles appear therefore as an optimum tool to collect volcanic gases and to obtain their complete chemical composition.