IP10 Emerging Issues in Analytical Chemistry
B115 & B116
1:20 PM - 4:40 PM, Wednesday
(IP079) effects of different extraction and analysis techniques on the determination of arsenic species in sediments.
Gurleyuk, H1, Garcia, J1, Meyer, J1, 1 Frontier Geosciences, Seattle, WA, USA
ABSTRACT- Speciation data is usually accepted only by some regulators but there seems to be no set laws or regulations on this matter. The lack of species-specific regulations is mostly due to the absence of methods that can reliably measure the analytes of interest at the regulatory levels. The most common method for the extraction of As species from soils and sediments is the use of phosphate-based solutions. In this method, a 0.1 M phosphoric acid solution is used to extract As(III) and a 0.1 M Sodium phosphate solution for As(V) and methylated arsenic species. After extraction, the first extract is analyzed for As(III), while the second is analyzed for total inorganic arsenic and methylated arsenic species by hydride generation - cryo-trapping - atomic absorption spectrometry (HG-CT-AAS) which provides detection limits below 0.001 mg/Kg. It is very important to use a method that can differentiate between As(III), As(V) and organic arsenic species in the extracts instead of total inorganic As analysis. Time after time, we have seen that other As species are also extracted in each step that can not be distinguished from the target species by total inorganic arsenic analyses. For instance, during extraction of As(III), we have seen that 8 times more As(V) was extracted in addition to various other organo-arsenic species. This means that if total inorganic arsenic was determined instead of As(III), a false and significantly high concentration for As(III) would be obtained. This could cause costly wrong decisions in risk assessment, treatment and remediation studies. Another alternative to HG-CT-AAS is using ion chromatography coupled to an ICP-MS (IC-ICP-MS). This technique can determine each As species in a single run and allows determination of arsenosugars that are present in fish tissue. Various cases will be presented where the use of different analytical techniques resulted in unreliable data.
Key words: extraction , arsenic, sediments, speciation