Chloroplatinate Method Development and Quantification of Chloroplatinates in New and Used Catalyst Materials and Urban Atmospheric Aerosols
In order to specifically measure levels of chloroplatinates in Vehicle Exhaust Catalysts (VEC) and urban atmospheric aerosols, an extraction and analysis protocol that would enable accurate quantification of major chloroplatinate species was developed and validated by the University of Wisconsin (USA).
The analytical challenges of quantification and speciation of chloroplatinates in catalyst materials and particularly environmental materials at native, background concentrations are many. Though available information was extremely limited (there exists little or no data on environmental concentrations of chloroplatinates), reasonable estimates suggested low ng/g concentrations. Effective extraction, isolation, and quantification at these very low concentrations without altering the chemical form (speciation) of the chloroplatinate target species has, to a large degree, eluded the analytical community. A significant and very detailed method development project was therefore undertaken, which resulted in an acceptable procedure for analysing selected chloroplatinates in extracted solutions from substrate materials.
The method developed was then used to measure concentrations of chloroplatinate within eight different VEC and also atmospheric particulate matter collected from roadside canyons and/or roadside motorways as well as background urban sites from six climatically diverse European cities.
For three-way automotive catalysts (TWC), concentrations of tetrachloroplatinate were nearly identical in marine and Midwest aged catalysts at 2.9 ± 1.2 ng/g. This represents just 1.3% and 1.2% respectively of extractable platinum and a vanishingly small percentage (0.00036 and 0.00023% respectively) of total platinum contained in the catalyst. Concentrations of hexachloroplatinate were greater than tetrachloroplatinate and slightly higher in the marine aged catalyst (5.3 ± 2.9 ng/g) than in the Midwest aged catalyst (3.8 ± 1.4 ng/g). As a percentage of bulk platinum these concentrations represent 0.00066 and 0.0003% of total platinum respectively. For diesel catalysts the results were generally higher than observed in the TWC. As a percentage of total platinum, though, the levels were even lower than in the TWC, typically less than 0.0001% (except around 0.0004% for the Light Duty Diesel aged catalyst).
PM3 (fine particulate matter <3 µm) air concentrations (mass per volume of air) of tetrachloroplatinate averaged 0.022 pg/m3 from roadside aerosol sampling, excluding the higher levels measured at the urban canyon sites of Stockholm (0.051 pg/m3) and Thessaloniki (0.11 pg/m3). PM3 air concentrations of hexachloroplatinate averaged 0.066 pg/m3, excluding the higher levels measured at the urban canyon sites of Stockholm (0.11 pg/m3) and Thessaloniki (0.22 pg/m3). Chloroplatinate levels in the coarse PM fraction were at or below the detection limit (<0.01 pg/m3).
Unidentified anionic platinum species were observed in extracts of most the samples characterized in this study. These species are not parent hexa- or tetra- chloroplatinate structures. Their prevalence is significantly greater in samples with complex ligands; e.g. in natural organic matter such as present in both the surrogate soils and "gulley-pot" matrices examined in this study. It was recommended that future work should address the identification of these species.
A copy of the full University of Wisconsin report can be obtained by contacting IPA (science@ipa-news.com). This research is also being written up for publication in the peer-reviewed scientific literature.