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Research articles

ScienceAsia 41 (2015): 187-197 |doi: 10.2306/scienceasia1513-1874.2015.41.187

Determination of inorganic arsenic species by hydride generation atomic absorption spectrophotometry and cathodic stripping voltammetry

Pipat Chootoa,*, Puchong Wararattananuraka, Tawatchai Kangkamanoa, Chalermpol Innuphata, Waraporn Sirinawinb

ABSTRACT:     Flow injection-hydride generation-atomic absorption spectrophotometry (FI-HG-AAS) and square wave cathodic stripping voltammetry (SWCSV) were compared to detect inorganic arsenic species in lemongrass and turmeric. Two species, arsenite (AsIII) and arsenate (AsV), were considered as they are known to occur in most terrestrial plants. AsIII and total water-soluble inorganic arsenic (TAsinorg) were determined under different conditions. AsIII was selectively determined by using a soft generation condition, i.e., low HCl concentration, whereas TAsinorg was determined after pre-reduction of AsV to AsIII with a KI/ascorbic acid mixture. The AsV content was estimated as the difference between both measurements. Under optimal conditions, the limits of detection (LOD) by FI-HG-AAS were 0.02 and 0.03 µg/l for AsIII and TAsinorg, respectively. Relative standard deviations (n=9) of less than 4% were obtained for both inorganic arsenic species. The accuracy was also verified by analysing spiked samples and certified reference material: CTA-VTL-2 (Virginia Tobacco leaves). The recoveries of both species were found to be between 90 and 115%. The determination of inorganic arsenic species by SWCSV in the samples is based on the formation of a copper-arsenic intermetallic compound at the hanging mercury drop electrode (HDME) during the preconcentration step. Only AsIII was deposited on the Hg electrode when Cu was present in the HCl medium. TAsinorg can be determined by reducing AsV to AsIII with sodium thiosulphate. AsV is quantified as the difference. At optimum conditions, the LOD for AsIII and AsV were 0.5 and 0.4 µg/l, respectively. Relative standard deviations (n=10) of less than 5% were obtained and the method was validated by analysing the spiked samples and certified reference material. FI-HG-AAS showed better LOD than SWCSV for both inorganic arsenic species. There was, however, a strong agreement between TAs values obtained by using FI-HG-AAS and SWCSV technique in lemongrass, turmeric, and the certified reference material (CTA-VTL-2). AsV was the main inorganic arsenic species found in lemongrass and turmeric. The results confirm that the As content of both samples do not exceed the food safety limits for Thailand and several countries.

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a Department of Chemistry, Analytical Chemistry Division, Faculty of Science, Prince of Songkla University, Hatyai, Songkhla 90112 Thailand
b Division of Environmental Science, Faculty of Science, Ramkhamhaeng University, Bangkok 10240 Thailand

* Corresponding author, E-mail: pipat.c@psu.ac.th

Received 4 Aug 2014, Accepted 7 Jul 2015