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Extracting Metallic Nanoparticles from Soils for Quantitative Analysis: Method Development Using Engineered Silver Nanoparticles and SP-ICP-MS
journal contribution
posted on 2017-01-12, 00:00 authored by D. M. Schwertfeger, Jessica R. Velicogna, Alexander H. Jesmer, Selin Saatcioglu, Heather McShane, Richard P. Scroggins, Juliska I. PrinczThe
lack of an efficient and standardized method to disperse soil
particles and quantitatively subsample the nanoparticulate fraction
for characterization analyses is hindering progress in assessing the
fate and toxicity of metallic engineered nanomaterials in the soil
environment. This study investigates various soil extraction and extract
preparation techniques for their ability to remove nanoparticulate
Ag from a field soil amended with biosolids contaminated with engineered
silver nanoparticles (AgNPs), while presenting a suitable suspension
for quantitative single-particle inductively coupled plasma mass
spectroscopy (SP-ICP-MS) analysis. Extraction parameters
investigated included reagent type (water, NaNO3, KNO3, tetrasodium pyrophosphate (TSPP), tetramethylammonium hydroxide
(TMAH)), soil-to-reagent ratio, homogenization techniques as well
as procedures commonly used to separate nanoparticles from larger
colloids prior to analysis (filtration, centrifugation, and sedimentation).
We assessed the efficacy of the extraction procedure by testing for
the occurrence of potential procedural artifacts (dissolution, agglomeration)
using a dissolved/particulate Ag mass ratio and by monitoring the
amount of Ag mass in discrete particles. The optimal method employed
2.5 mM TSPP used in a 1:100 (m/v) soil-to-reagent ratio, with ultrasonication
to enhance particle dispersion and sedimentation to settle out the
micrometer-sized particles. A spiked-sample recovery analysis shows
that 96% ± 2% of the total Ag mass added as engineered AgNP is
recovered, which includes the recovery of 84.1% of the particles added,
while particle recovery in a spiked method blank is ∼100%,
indicating that both the extraction and settling procedure have a
minimal effect on driving transformation processes. A soil dilution
experiment showed that the method extracted a consistent proportion
of nanoparticulate Ag (9.2% ± 1.4% of the total Ag) in samples
containing 100%, 50%, 25%, and 10% portions of the AgNP-contaminated
test soil. The nanoparticulate Ag extracted by this method represents
the upper limit of the potentially dispersible nanoparticulate fraction,
thus providing a benchmark with which to make quantitative comparisons,
while presenting a suspension suitable for a myriad of other characterization
analyses.
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ratioKNOExtracting Metallic Nanoparticlesmethoddispersible nanoparticulate fractionsoil dilution experimentAg massSP-ICP-MSAgNP-contaminated test soilextractionprocedurespiked-sample recovery analysisnanoparticulate Ag2.5 mM TSPPplasma mass spectroscopycharacterization analysesEngineered Silver NanoparticlesTMAH
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