in Natural Waters

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ofarse·nic wnst:attied out byGF~A$A. Ascau be seen in Table 4- the recovenesof both As(tll) and As(V) are.saUsfndory. Table 4. Reoovetyof AS(HI) and As{V} ...
Chem. Anal. (Warsaw), 41, 45 (1996)

Application of a Chelating Resin Loaded with Thionalide to Speciation Analysis of As (III,V) in Natural Waters by J. Chwastowska *, E. Sterlhiska, W. Zmijewska and J. Dudek Department ofAnalytical Chemistry, Institute ofNuclear Chemistry and Technology, ul.Dorodna 16, 03-195 Warsaw, Poland

Key words: arsenic(III), arsenic(V), speciation, preconcentration, thionalide-Ioaded resin, natural waters, GF-AAS Thionalide loaded acrylic resin (Bio Beads SM-7) was used for separation of As(III) from As(V) and their preconcentration from natural waters. At pH 8.0 As(III) was retained on the column bed while As(V) passed to the effluent. As(V), after reduction to As(III), was then retained on another column from 4 mol 1-1 hydrochloric acid solution. The retained arsenic was eluted with concentrated nitric acid and determined by GF AAS. As(III) and As(V) were determined in samples of river, well and mine waters. Do rozdzielania As(III) od As(V) i ich za tc;zania z wad naturalnych zastosowano sorbent z tionalidem osadzonym na zywicy poliakrylowej (Bio Beads SM-7). Przy pH 8.0 As(III) sorbuje siC; na ztozu kolumny natomiast As(V) przechodzi do wycieku. Po redukcji do As(III) arsen sorbowany jest na ztozu drugiej kolumny z roztworu kwasu solnego 0 stc;zeni u 4 moll-I. Zasorbowany arsen wymywa sic;ze ztoza stc;zonym kwasem azotowym i oznacza metod arsenate > monomethyl arsonic acid (MMA) > dimethyl arsinic acid (OMA) [1].

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J. Chwastowska, E. Sterlinska et at.

It has been shown that in natural systems arsenic occurs mainly as As(V), As(III), MMA and DMA [2-5]. The concentration of arsenic in natural waters depends on the geological composition and the degree of pollution of the environment. In majority of natural waters it varies in the range 0.1-1 0 ~g 1-1, in this 90-95% is inorganic As. The ratio of As(III) to As(V) varies widely [2,6-7] reflecting the oxidation-reduction potential of the particular system from which the sample was taken. Oxidation of As(III) and biochemical processes of methylation are possible [8-11]. Numerous analytical techniques such as spectrophotometry [12,13], anodic stripping voltammetry [14-16], differential pulse polarography [17,18], NAA [8,9, 1921], GF-AAS [1,4,22,23], HG-AAS [4,24-27], ICP [28,29],I~P-MS [30,31], often coupled with selective methods of separation an,d preconcentration such as extraction [8,9,20] coprecipitation [20-29], iOn,-excha,nge [18,32] and various chromatographic methods [33,34], have been used for the determination of various arsenic species in natural waters. In this work speciation of As(III) and As(V) in natural waters is carried out by separation and preconcentration of the above species on achelating sorbent thionalide-loaded acrylic resin, followed by the determination by GF-AAS. The preparation and properties of the sorbent and its application to the determination of total antimony and its speciation in natural waters have been described in our earlier works [35-37]. Terada and co-workers [38] first prepared a sorbent withthionalide (thionalide loaded silica gel) and applied it to the separation of As(III) from As(V) and their preconcentrationfrom sea water followed by spectrophotometric determination. The same sorbent was applied to the preconcentration of Sb(III) from natural waters followed by the detennination by GF-AAS [39].

EXPERIMENTAL Reagents, solutions and apparatus Thionalide (puriss.p.(l.) was obtained from Fhika & Buchs. Bio~Beads SM~7 resin (2~50 mesh) was purchased from Bio~Rad.Arsenic trioxide (s.p.) was obtained from Koch& Light. All other reagents used in this. work were analytical-reagent grade. Doubly distilled water (quartz still) was used throughout. Concentrated hydrochloric acid was purified from As by 6..,fold extraction with CCI4. Concentrated nitric acid (Merck) was purified by distillation from quartz apparatus. A standard solution of As(II1) of a concentration of 1.00 mg ml-1 was prepared by dissolving 0.1320 g of ASZ03 in 6 nioll-1 HCI upon heating under a reflux condenser and diluting to 100 ml with 6 mol 1-1 HCI. .Astandard solution of As(V) of a concentration of 1.00mgml-1 was prepared by dissolving 0.4165g of NazHAs04'7HzO in 15 ml of 0.2 mol 1-1 NaOHanddiluting to 100mi with distilled water. A borate buffer solution was prepared by adding 3.9 ml of,0.s,moll-1 KOH to 50 ml ofa !,oluti.on 0.5 mol 1-1 in H3B03 andKCI and diluting to 100 ml with water. The pH of the buffer solution was adjusted to 8.0with a KOH solution: A synthetic water solution of the following composition (mg ml-1): Na+ (i5), K+ (4), Mg z+(20), Ca z+ (55), CI- (124), sot (80). The solution was prepared by dissolving 0.0380 g of NaCI, 0.0076 g of KCI, 0.100 g of MgS0 4 and 0.1530 g of CaClz in water and diluting to 1 I with water. .