Determination of As species distribution and variation with time in extracted groundwater samples by on-site species separation method

Large Quantity EDTA Addition and Cold Storage in Dark Recommended for Preserving Inorganic Arsenic Speciation in Reducing Groundwater

“…First was the precipitation of Fe (oxyhydr)­oxides, especially in Fe­(II)-rich reducing groundwaters (Table S2). The Fe (oxyhydr)­oxide phases formed from Fe­(II) oxidation and Fe­(III) hydrolysis during the freezing and thawing processes have been shown to sorb As from solution, changing the total concentration and the species distribution. , This was consistent with the observation of high As species transformation rate and loss of As species in Fe-rich waters, , even though storage at −20 °C (freezing) was reported to be useful for Fe-poor samples . A further problem with Fe­(II) in reducing groundwaters is that, in the presence of air, Fe­(III) formed by the rapid oxidation of Fe­(II) at circum-neutral pH is able to covert iAs­(III) to iAs­(V) rapidly .…”

“…Both the water treatment and hydrogeochemical communities are interested in reliable methods to preserve iAs­(III) and iAs­(V) species in reducing groundwater samples for subsequent laboratory analysis. Recently, thio-As and organothio-As species have been observed in sulfide-rich geothermal waters , and groundwaters; , organo-As (methylated As) has also been detected in very reducing groundwaters containing methane. , Thio-As species are expected at circumneutral or higher pH if appreciable amounts of sulfide (>1 mg/L) are present . It is worth noting that iAs, especially iAs­(III), still accounts for the majority of As found in domestic well waters which are frequently associated with Fe-reducing conditions ,,− and remain the target of water treatment. , …”

“…To prevent iAs species in reducing groundwater from interconversions and coprecipitation with Fe- or Mn- oxides upon exposure to air ,, during sampling, on-site measurement, , separation, , and various sample preservation techniques , have all been investigated. On-site preservation of the iAs­(III) and iAs­(V) for laboratory speciation analysis is easier to perform than on-site measurement or separation.…”

“…In establishing these standard methods, most tests have been conducted in the laboratory with spiked synthetic solutions (Table S1), including deionized water, distilled water, tap water, and bottled drinking water. ,,,, Clearly, they do not fully capture the chemical and microbiological variabilities in natural groundwater that will impact the performance. More concerning is that studies have reported oxidation of iAs­(III) when HCl and/or HNO 3 are used for groundwater samples , or spiked surface water samples ,, (Table S1).…”

Atomic spectrometry update – a review of advances in environmental analysis

“…It should be noted that chromatographic separations typically separate chloride from As species and that most ICP-MS instruments these days have collision cells that successfully remove the ArCl + interference so HCl can in fact be used without the risk of species oxidation by HNO 3 . A different approach was adopted 64 for groundwater samples with To overcome the problem of a >60% reduction in As III concentrations that occurred aer 36 h of collection, samples were preconcentrated on-site onto strong cation-and anionexchange cartridges. Recoveries of As species were quantitative when the Fe 2+ concentrations were <10 mg L −1 .…”