Rapid determination of Gold in MIBK extracts using Okamoto-cavity microwave-induced plasma atomic emission spectrometry

An Okamoto-cavity microwave-induced plasma (MIP) with a nitrogen-oxygen gas mixture was employed as an excitation source for emission analysis to observe the behavior of gold in a sol-vent extraction method using 4-methyl-2-pentanone (MIBK). The MIBK extracts were directly aspirated to conduct direct and rapid analysis. The mixed gas plasma could be maintained with a high robustness against the loading of a MIBK solvent. This is probably because the organic solvent can be easily removed due to reactions with active oxygen species in the MIP. The observed emission lines of gold, Au I 242.795 nm and Au I 267.595 nm, were not free from self-absorption especially when the MIBK solution was introduced, because they were atomic reso-nance lines. The Au I 242.795-nm line, which was less sensitive but had a larger dynamic range compared to the Au I 267.595-nm, was employed for the actual application. The detection limit of gold in the MIBK solution was estimated to be 0.0008 g/dm³, based on five-times the standard deviation of the emission intensity in the blank solution. After the MIBK extraction using a 2 M hydrochloric acid solution, the distribution ratio of gold from the aqueous phase to the organic phase could be determined to be more than 200.