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Application of Selenium Speciation Analysis to Elucidate Limitations with Accepted Total Selenium Methods
Oral Presentation
Prepared by R. Gerads, H. Gurleyuk
Applied Speciation and Consulting, LLC, 18804 Northcreek Parkway, Bothell, WA, 98011
Contact Information: russ@appliedspeciation.com; 425-483-3300
ABSTRACT
Current accepted methods for total selenium quantification are known to produce bias results depending on the selenium species and other compounds present in solution. The issues with the current methodologies are holistic including: selection of sample vessels, preservation techniques, applied digestion procedures, and analytical methods. Certain selenium species are known to form insoluble precipitates and colloidal elemental selenium in the presence of nitric acid which either adsorb onto the walls of the container or deposit to the container floor. With the remaining selenium species present in solution most analytical methods exacerbate the bias with chemical and spectral interferences. Selenium speciation analytical methods, using various ion chromatography method coupled to inductively coupled plasma collision reaction cell mass spectrometry (IC-ICP-CRC-MS), was applied to quantify and track which selenium species are not supported by existing preparatory and analytical approaches.
The most prevalent selenium species in industrial and natural aquatic systems are selenite, selenate, selenocyanate, and methyl seleninic acid. Scientific publications have confirmed that naturally occurring microbes (Pseudomonas fluorescens) were identified to generate selenocyanate as a metabolic byproduct confirming that selenocyanate is a naturally occurring selenium species. Selenocyanate has been proven to convert to elemental selenium in the presence of 1% nitric acid, which is recommended by all current EPA methods for total recoverable metals analysis of surface and groundwater matrices. Selenite, which has been accepted to be stable in solution, has also been documented to become destabilized in complex matrices resulting in precipitation from solution upon preservation following EPA protocols. As much as a 47% loss of selenium was reported when EPA methods were applied to specific matrices.
The situation is further complicated by the biases associated with the accepted analytical platforms specified in EPA Methods 6020, 200.8, and 1638. Although most of the limitations and interferences associated with the suggested analytical platforms are known they cannot be accounted for on an absolute basis.
Comparison between various hyphenated techniques for selenium speciation analyses will be presented alongside the corresponding total selenium results which have been analyzed in conformance to EPA protocols.
Oral Presentation
Prepared by R. Gerads, H. Gurleyuk
Applied Speciation and Consulting, LLC, 18804 Northcreek Parkway, Bothell, WA, 98011
Contact Information: russ@appliedspeciation.com; 425-483-3300
ABSTRACT
Current accepted methods for total selenium quantification are known to produce bias results depending on the selenium species and other compounds present in solution. The issues with the current methodologies are holistic including: selection of sample vessels, preservation techniques, applied digestion procedures, and analytical methods. Certain selenium species are known to form insoluble precipitates and colloidal elemental selenium in the presence of nitric acid which either adsorb onto the walls of the container or deposit to the container floor. With the remaining selenium species present in solution most analytical methods exacerbate the bias with chemical and spectral interferences. Selenium speciation analytical methods, using various ion chromatography method coupled to inductively coupled plasma collision reaction cell mass spectrometry (IC-ICP-CRC-MS), was applied to quantify and track which selenium species are not supported by existing preparatory and analytical approaches.
The most prevalent selenium species in industrial and natural aquatic systems are selenite, selenate, selenocyanate, and methyl seleninic acid. Scientific publications have confirmed that naturally occurring microbes (Pseudomonas fluorescens) were identified to generate selenocyanate as a metabolic byproduct confirming that selenocyanate is a naturally occurring selenium species. Selenocyanate has been proven to convert to elemental selenium in the presence of 1% nitric acid, which is recommended by all current EPA methods for total recoverable metals analysis of surface and groundwater matrices. Selenite, which has been accepted to be stable in solution, has also been documented to become destabilized in complex matrices resulting in precipitation from solution upon preservation following EPA protocols. As much as a 47% loss of selenium was reported when EPA methods were applied to specific matrices.
The situation is further complicated by the biases associated with the accepted analytical platforms specified in EPA Methods 6020, 200.8, and 1638. Although most of the limitations and interferences associated with the suggested analytical platforms are known they cannot be accounted for on an absolute basis.
Comparison between various hyphenated techniques for selenium speciation analyses will be presented alongside the corresponding total selenium results which have been analyzed in conformance to EPA protocols.