1

Literature Study on Speciation Analysis of Inorganic Arsenic in

Aqueous Samples Using Inductively Coupled Plasma Mass

Spectrometry

Assefa Yimer, 2011

Degree project in chemistry, 15hp

Department of chemistry

Umeå University

Sweden

Supervisor: Solomon Tesfalidet

Examiner: Erik Björn

2

Abstract

The oxidation state of arsenic plays an important role in its behavior and toxicity. As(III) and As(v) are

the most toxic forms and known to be carcinogens. This literature study covers speciation analysis of

inorganic arsenic species in water samples using high performance liquid chromatography inductively

coupled plasma mass spectrometry (HPLC-ICP-MS). Moreover, species stability, factors affecting

arsenic speciation and sample preservation techniques are also discussed.

3

Table of contents

1. Introduction ......................................................................................................................................... 4

2. Common Analytical Methods Used for Speciation Analysis of Arsenic ........................................ 5

2.1 High Performance Liquid Chromatography (HPLC) ................................................................... 5

2.1.1 Ion Exchange HPLC ...................................................................................................................... 5

2.1.2 Ion Pair HPLC ............................................................................................................................... 5

2.2 HPLC-ICP-MS .................................................................................................................................. 5

2.3 GC-ICP-MS ....................................................................................................................................... 6

3. Detection Limit .................................................................................................................................... 7

4. Species Stability ................................................................................................................................... 7

4.1 Factors Affecting Arsenic Speciation .............................................................................................. 7

4.1.1 pH ................................................................................................................................................... 7

4.1.2 Redox Potential (Eh) ...................................................................................................................... 9

4.1.3 Natural Organic Matter (NOM) ................................................................................................... 9

4.1.4 Iron (Fe2+

/Fe3+

) ............................................................................................................................. 10

4.1.5 Microbial Activities ...................................................................................................................... 10

5. Preservation of Arsenic Species ....................................................................................................... 10

5.1 Filtration .......................................................................................................................................... 10

5.2 Acidification..................................................................................................................................... 10

5.3 Storage and Type of Container Used for Storage ....................................................................... 10

5.4 Stabilization Using EDTA ............................................................................................................. 11

6. Conclusion ......................................................................................................................................... 15

7. Acknowledgement ............................................................................................................................. 16

8. References .......................................................................................................................................... 17

9. Appendix ............................................................................................................................................ 20

4

1. Introduction Natural sources and anthropogenic activities are encountered for the introduction of several metals in to

the environment. Among these, arsenic, the 20th most abundant element in the earth´s crust is widely

distributed in soil, sediments, water, air and in biological system. Most problems related to arsenic are due

to mobilization under natural conditions. There are also additional man made impacts through combustion

of fossil fuels, mining activities, the use of arsenic as an additive to livestock feed, the use of arsenical

herbicides, pesticides and crop dessicants. Though there are studies suggesting consumption of arsenical

pesticides and herbicides has fallen dramatically, recent uses on wood preservation is common [1].

Manufacturing semiconductor at industrial level is also accountable for the release of arsenic. The main

source of human exposure is due to its accumulation in food. Compounds like aryloarsenicals has been

used as additive for animal feed which can find its way easy to human diet [2]; The use of 4-hydroxy-3-

nitrophenyl arsenic acid in chicken feed for promoting growth [3].

Geological sources from surface weathering or underground deposits contribute much for the aquatic

environment. The biggest threat for human health is water since it can easily get in to human body. The

concentration of arsenic in water ranges from µg/L (ppb) to mg/L (ppm) level[4].

Arsenic exists in the environment in four oxidation states (As0, As

3-, As

3+ & As

5+) for both organic and

inorganic forms. There is great variation in toxicity between different arsenic compounds. Due to

chemical similarity of arsenic with phosphate, it might interfere to the phosphate transport system and yet

replaces phosphate in energy transfer phosphorylation reactions [5]. Some studies have shown that

enzyme inactivation may take place due to the high affinity of arsenic for thiol(-SH) groups in

proteins[5]. The toxicity, bioavailability and transport properties of arsenic depends highly in its chemical

form[12]. The most acutely toxic types are inorganic forms [6]. In reducing conditions, the inorganic

forms exist as trivalent arsenate (H3AsO3), and the pentavalent arsenite (H2AsO4-) is favored under

oxidizing condition [7]. Inorganic arsenite [As(III)], is extensively metabolized in humans. Arsenate

[As(v)] is less toxic than arsenite[As(III)] [8]. The organic forms like monomethyl arsonic acid [MMA(v),

CH3AsO(OH)2] and dimethyarsenic acid [DMA(v), (CH3)2AsO(OH)] show a toxicity factor of one in

four hundred when compared to inorganic types[9]. The inorganic forms are known to be carcinogens.

With an increase in the degree of methylation, toxicity generally decreases. The order of toxicity is :

arsenite > arsenate > monomethylarsonate > Dimethylarsinate [10].

Many countries in the world are suffering from a contaminated arsenic ground water. Among these;

Hungary, Finland, USA, Argentina, China, Taiwan, India, Bangladish, Japan and Vietenam are noticeable

ones[see appendix 1]. Contamination of water with arsenic is believed to bring diseases on long term

basis like gangrene, skin cancer, splenomegaly, hepatomegaly, nonpitting swelling, leucomelonsis,

cardiovascular diseases, conjunctivitis, hyperkeratosis and hypopigmentation [10]. According to

EPA(U.S) and WHO, 10µgl-1

is the recommended value for drinking water and 50 µgl-1

, the maximum

permissible concentration[46,11]. Due to these regulations sensitive and reliable analytical methods are

needed. Total quantification of an element is not sufficient but it is also mandatory to determine the

species within which the elements are found. Analyzing a sample to identify/or quantify one or more

chemical species is called speciation analysis [13]. The aim of this project is to make a literature study on

the speciation analysis of inorganic arsenic in water samples using chromatographic separation technique

coupled to inductively coupled plasma mass spectrometry. Moreover, sampling, storage conditions,

stability of the inorganic species and detection limits are also included.

5

2. Common Analytical Methods Used for Speciation Analysis of Arsenic

2.1 High Performance Liquid Chromatography (HPLC) Most compounds which are not sufficiently volatile for gas chromatography can be separated through the

use of high performance liquid chromatography. HPLC applies high pressure to force a solvent through

closed columns containing very fine particles that yields good resolution separations. The system in

HPLC consists of a solvent delivery route, a sample injection valve, a high pressure column, a detector

and a computer to control the system and display results. Below are types of HPLC in connection to ICP-

MS.

2.1.1 Ion Exchange HPLC It employs a mechanism of exchange equilibria between the mobile phase containing oppositely charged

ions and stationary phase of the surface ions [3]. It operates in two separation modes, cation exchange or

anion exchange. The most commonly used column in anion exchange chromatography is Hamilton

PRPx100. DionexAS7, ION120 and LC-SAX were also used. These columns use polar stationary phases.

Malonates, acetates, phosphates, carbonates and a small percentage of methanol were components of the

different mobile phases used at different pH (table 1). Retention of analytes and separation in ion

exchange HPLC can be affected by standard variables like flow rate and introduction of organic modifiers

in to the mobile phase. Furthermore, the PH of the mobile phase, the ionic strength of the solute,

concentration of the ionic strength of the buffer and temperature can influence the technique. For

separation of arsenic compounds, Isocratic or gradient ion exchange are applied.

2.1.2 Ion Pair HPLC Ion pair HPLC involves either anion pairing or cation pairing technique. In such a separation, surface of a

stationary phase is kept less polar than the mobile phase. Addition of a counter ion to the mobile phase in

reversed phase ion-pair chromatography is important and a secondary chemical equilibrium of the ion pair

is established to monitor retention and selectivity. Ion pair separates ionic species and uncharged

molecular species as well. Long chain alkyl ions can be used as ion pair reagents. The mobile phases in a

simple reversed phase HPLC are aqueous solutions which may partly contain organic modifiers. With a

significant change in the organic content of the mobile phase, a signal drift is possibly noticed in the

ICPMS detector [3]. Reversed phase columns like Capcell C18 pak, ODS-3 and Devilsol C30-UG-5 were

used. The mobile phase compositions and the optimization parameters are given in table 2.

2.2 HPLC-ICP-MS The big merit of liquid chromatography is the use of different mobile phases and stationary phases that

would allow suitable condition for speciation analysis. High sensitivity, wide linear dynamic range, multi

element capability, isotope ratio measurement capability are the advantages that an ICPMS can offer.

However, an optimal solvent composition should be attained when ICPMS is coupled to HPLC. Plasma

instability and accumulation of carbon residue on sampling cone may arise due to high concentration of

some organic solvents [15]. Signal suppression would occur in the ICP if there is much salt concentration

thereby increasing space-charge effects where the ion beam is defocused [16]. In using ICP-MS as a

detector, spectral interferences may arise due to the formation of 40

Ar35

Cl+

which has the same mass as 75

As. Other interferences can also originate from samples having a complicated matrix. However, such

6

problems can be solved by applying mathematical equations, using dynamic reaction cells or high

resolution ICP-MS [4].

Fig 1. HPLC-ICP-MS Coupling [50].

2.3 GC-ICP-MS Gas chromatography is applicable for the separation of volatile and semi-volatile compounds and

possesses a high resolving power. Properly derivatized compounds having high boiling and polarity can

also be separated i.e The arsenic species need to be derivatized prior to separation by GC. Compared to

HPLC-ICP-MS, GC-ICP-MS offers 100% introduction efficiency to the ICP and significant

chromatographic resolution [14]. Moreover, the stable and dry plasma conditions allow only fewer

spectral interferences.

7

Fig 2. Schematic Diagram of GC-ICP-MS [42].

3. Detection Limit In most of the cases, detection limits are calculated as three times the standard deviation of the

background signal or replicate analysis of deionized spiked water samples. Below are datas on limit of

detection obtained with LC-ICP-MS. The LOD results obtained from Duarte et.al[54] are 0.02µgL-1

for

As(III) and 0.10 µgL-1

for As(V). However, Ronkarrt et. al [44] achieved 0.017 µgL-1

for As(III) and

0.026 for As(V). Day et.al [55] conduced arsenic speciation methods on drinking water with LOD 0.067

µgL-1

for As(III) and 0.089 µgL-1

for As(V). Better detection limits than Day et. al was obtained by Roig-

Navaro et. al [47] with values 0.046 µgL-1

for As(III) and 0.03 for As(V). Worse detection limits were

obtained by Milstein et.al [48], 0.09 µgL-1

for As(III) and 0.3 µgL-1

As(V). Robust and sensitive method

for the determination of arsenic species in sea water was conducted by Nakazato et. al [56] using hydride

generation techniques coupled to ICP-MS where detection limit for As(III) was 0.0028 µgL-1

in pure

water, 0.0034 µgL-1

in 2% Cl-1

solution. For As(V), 0.0045 µgL-1

in pure water and 0.0042 µgL-1

in 2%

Cl- solution.(see Table 3)

4. Species Stability Maintaining the integrity of the original chemical species in the sample is very important to obtain

reliable speciation information. Among species of arsenic, As(III) and As(v) are the dominant forms in

water. Stability of arsenic species can be affected by several factors during the different steps in the

analytical chain.

Fig 1.Changes or processes affecting stability of arsenic speciation during different steps of sampling to

analysis [18].

4.1 Factors Affecting Arsenic Speciation

4.1.1 pH Among the different forms of arsenic, As(III), As(v), MMA(v) and DMA(v) exhibit acid base equilibria

that results various major and minor species along changes with pH. There are no analytical techniques

that allow quantification of these type of individual complexes illustrated in fig 2 and fig 3 at typical

natural concentration.

8

Fig 2. A graph showing distribution of As(III), As(v), MMA(v) and DMA(v) hydroxide species as a

function of pH at 25oC[17].

Dissociation of As(OH)3 in water follows the following (a) to (c) (Pierce and Moore,1982 cited in[17])

As(OH)3 As(OH)2O- + H

+ Pka1=9.2(a)

As(OH)2O-

As(OH)O22-

+ H+ Pka2=12.1(b)

As(OH)O22-

AsO33-

+ H+ Pka3=12.7(c)

From the figure above, As(OH)3 dominates over the others at pH=7

As(v) undergoes the dissociation below (d) to (F) (Goldberg and Johnston, 2001 cited in[17])

AsO(OH)3 AsO2(OH)2- + H

+ Pka1=2.3 (d)

AsO2(OH)2- AsO3(OH)

2- + H

+ Pka2=6.8(e)

AsO3(OH)2-

AsO43-

+ H+

Pka3=11.6(f)

Almost the same amounts of AsO2(OH)2- and AsO3(OH)

2- exist at neutral pH.

The monoprotic acid (MMA) and the Diprotic acid (DMA) undergo (g) to (i) (Cox and Ghosh, 1994 cited

in[17])

9

CH3AsO(OH)2 CH3AsO2(OH)- + H

+ Pka1=4.1(g)

CH3AsO2(OH)- CH3AsO3

2- + H

+ Pka2=8.7(h)

(CH3)2AsO(OH) (CH3)2AsO2- + H+ Pka1=6.2(i)

At pH=7, major species of MMA(v) is CH3AsO2(OH)-, minor species is CH3AsO3

2- but for DMA(v)

both (CH3)2AsO(OH) and (CH3)2AsO2- are present.

4.1.2 Redox Potential (Eh) Considering pH and Eh, it is possible to model arsenic speciation. The figure below illustrates the

relationship between redox potential and pH for inorganic arsenic compounds in the natural environment.

Fig 3.The Eh-pH diagram for arsenic at 250C,1

atm and total arsenic 10-5

mol/L, total sulfur 10-3

mol/L. Parenthesis is for solid species in the cross

hatched area with a solubility of less than 10-5.3

mol/L (Source: Fergusson and Gavis, 1972 cited and

reproduced in [17])

In oxidizing conditions, H3AsO4 is likely to exist at pH<2. For a pH range 2-11, both H2AsO4- and

HAsO42-

do sufficiently exist under the same environment (oxidizing). However, at low Eh values,

inorganic arsenic species [As(III)], H3AsO3 predominantly exists.

4.1.3 Natural Organic Matter (NOM) In aqueous systems, NOM is ubiquitous and has a number of functional groups like phenolic, carboxylic,

esteric, amino, quinine, sulfhydryl, hydroxyl, nitroso and other moieties[19]. NOM rich waters

dominantly contain As(III) since it has a reducing property[20]. NOM can form complexes with Fe(II)

thereby retarding the Fe(III) oxidation of As(III) [21]. A report has shown that As(v) is reduced because

of NOM in rain water and soil-pore water samples preserved by EDTA[22].

10

4.1.4 Iron (Fe2+/Fe3+) Iron exists as Fe(II) or Fe(III) depending on PH and Eh. When atmospheric oxygen reacts with a

dissolved iron (Fe(II)), precipitation of iron as HFOs (hydrated ferric oxides) is formed that offers

sorption sites for dissolved arsenic species. Preferential co-precipitation of As(v) occurs since it is anionic

species [23]. In the presence of Fe(III), light exposure and preservation by HCl, Fast oxidation of As(III)

to As(V) was noticed in synthetic solution [24]. With the addition of of Fe(II) on iron rich ground water

samples having PH<2, an excellent preservation of As(III) is obtained [25].

4.1.5 Microbial Activities Conversion of arsenic species by micro-organisms include redox, methylation and demethylation [26].

Reduction of As(V) and oxidation of As(III) was found using mixed microbial cultures [27]. Microbes

that reduce As(V) were obtained in oxic water samples [28].

5. Preservation of Arsenic Species

5.1 Filtration It is useful for separating particulate bound and dissolved fraction of an element. It inhibits changes in

speciation partly through removal of micro-organisms and partly through the removal hydrated ferric

oxides. During some field speciation method, loss of arsenic occurs as a result of the deposited HFOs on

filters [22]. For a sample containing dissolved iron with PH>8, filtration should be done fast (~<10

minutes) [29]. Filters of size 0.1 - 0.2µm improves stability since many of the bacteria have dimensions

less than 0.45 µm [30]. However, concentration of the dissolved arsenic obtained using filter 0.45 µm is

much higher than 0.2 µm filtered sample [31].

5.2 Acidification During acidification, precipitation of iron is suppressed by increasing its solubility. Furthermore, the

method reduces microbial activities. For preserving arsenic species, HCl is widely used [32]. Hydrogen

chloride alone could not preserve As(III) in Fe(III)) containing samples[25]. Using HNO3 as a

preservative enables oxidation of As(III) to As(V) due to photo-reduction of HNO2. The use of H2SO4 as a

preservative is noted, but not recommended for it is difficult to purify and may lead to BaSO4

precipitation. H3PO4 preserves by lowering PH and complexing Fe[34]. However, high acid

concentration may destroy chromatographic columns. In samples containing higher amount of iron (AMD

waters), insoluble phosphate, strengite [Fe3(PO4)2] is formed[35]. Redox potential (Eh) of a solution

might increase by the use of H2SO4 and H3PO4, especially in oxic water samples (Eh~>400mv), where

oxidation of As(III) is favored [36].

5.3 Storage and Type of Container Used for Storage Different types of plastics (polypropylene, polyethylene, polycarbonate) and glass containers can be used

for storing samples. Leaching of species from the material and adsorption losses should be controlled.

Containers made of glass that are rinsed with HNO3 exhibited to leach out arsenic [37]. Photochemical

reactions do also contribute for the loss of species. Opaque glass sample storage are preferred than plastic

containers which in most of the cases are translucent [38]. However, Community bureau of reference,

measurements and testing programme (BCR study) revealed that glass and plastic containers are equally

11

good at storing samples for arsenic speciation [18]. Refrigeration minimizes biotic and abiotic processes

that alter arsenic species. Many authors do agree that, 40C is recommendable for stabilizing arsenic

species[39]. Increasing temperature leads to an increase in biotic and abiotic oxidation rates of As (III),

thus stabilization period minimizes for samples at room temperature [42]. For iron deficient samples, -

200C is considered good but alternations in arsenic species were detected in iron rich samples [34].

5.4 Stabilization Using EDTA In acid-mine-drainage (AMD ) samples , the redox activities of the two iron species, Fe(II)and Fe(III),

should be lowered to stabilize the arsenic species. EDTA can form stable complexes with the iron species

thereby decreasing the free metal ion concentration. However, the chelating agent, EDTA, can also form

stable metal complexes with Ca and Mg. Thus, higher concentration of EDTA is needed to make arsenic

species stable [40]. But, PH increment is favored while using higher EDTA concentration (10mmoL/L)

due to formation of protonated metal-EDTA complex[41]. There are studies showing an adjustment of PH

to 3.2 when using EDTA to preserve arsenic speciation, this suppresses oxidation of Fe(II) [36].

Successful preservation could not be obtained if lower EDTA concentration (1.25mmoL/L) is used for

ground water samples having high Fe(II), Ca and Mg[41].

Table 1.Application of ion exchange(anion exchange) HPLC with ICP-MS for speciation analysis.

Species

matrix Column Mobile phase Optimization Retention

time(minutes)

Literatu

re cited

As(III)

As(V)

MMA(V)

DMA(V)

AsB

Well

water

Anion exchange

Dionex AS7

(250mmx4mm,10µm)

Gradient

elution

a.2.5 mM

ammonium

dihydrogen

phosphate

b.50mM

ammonium

dihydrogen

phosphate

PH=10

F.R=1ml/min

1.35,AsB

2.0, DMA(V)

3.0, As(III)

8.7, MMA(V)

14.8, As(V)

[44]

As(III)

As(V)

MMA(V)

DMA(V)

Natural

water

Anion exchange

Hamilton PRP-x100

(250mmx4.1mm)

Gradient

elution

38-75mM

phosphate

buffer

PH=5.7

F.R=1mL/min

C.T=330C

3.1, As(III)

3.6, DMA(V)

4.7, MMA(V)

6.1, As(V)

[45]

As(III)

As(V)

MMA(V)

DMA(V)

Surface

water

Anion exchange

Hamilton PRP-x100

(250mmx4.1mm,10

µm)

Isocratic

elution

20mmolL-

1NH4H2PO4

PH=5.6

F.R=1.5

mL/min

1.7, As(III)

2.5, DMA(V)

5.0, MMA(V)

9.7, As(V)

[46]

As(III)

As(V)

MMA(V)

DMA(V)

Surface

water

Anion exchange:

ION

120(120mmx4.6mm,1

0 µm)

Gradient

elution

4mM-0.3M

ammonium

hydrogen

carbonate/2%

PH=10.3

F.R=1ml/min

2.5, DMA(V)

3.5, As(III)

7.0, MMA(V)

8.5, As(V)

[47]

12

methanol

Anion exchange

Hamilton PRP-x100

(250mmx4.1mm,10

µm)

Gradient

elution

10mM-

100mM

Ammonium

dihydrogen

phosphate/2

% methanol

pH=6

F.R=1ml/min

2.5, As(III)

3.7, DMA(V)

4.7, MMA(V)

5.8, As(V)

Anion exchange

Hamilton PRP x100

(250mmx4.1mm,1 0

µm)

Gradient

elution

4mM-0.3M

ammonium

hydrogen

carbonate/2%

methanol

PH=8

F.R=1ml/min

2.5, As(III)

4.25, DMA(V)

5.5, MMA(V)

7.0, As(V)

As(III)

As(V)

MMA(V)

DMA(V)

roxarsone

Natural

water

Anion exchange

Dionex AS7

(4mmx250mm)

Gradient

elution

2.5-50mM

nitric acid in

0.5%

methanol

F.R=1ml/min

C.T=330C

1.7, As(III)

2.3, MMA(V)

4.4, DMA(V)

5.6, As(V)

6.7,Roxarsone

[45]

As(III)

As(V)

Anion exchange

LC-SAX

(4mmx50mm)

Isocratic

elution

12.5mM

malonate

And 17.5

mM acetate

PH=4.8

F.R=1ml/min

C.T=330C

0.9, As(III)

1.5, As(V)

As(III)

As(V)

MMA(V)

DMA(V)

Drinki

ng

water

Anion exchange

Hamilton PRP x100

(250mmx4.1mm,10

µm)

Isocratic

elution

14mM

phosphate

buffer

PH=6

F.R=1.5ml/mi

n

C.T=250C

2, As(III)

4.7, DMA(V)

6.5, MMA(V)

11.5, As(V)

[48]

Anion exchange

Hamilton PRP x100

(250mmx4.1mm,10

µm)

Gradient

elution

30ml-100mM

TRIS acetate

buffer

PH=7

F.R=1.5ml/mi

n

C.T=250C

2, As(III)

4.7, DMA(V)

6.5, MMA(V)

11.5, As(V)

Table 2.Application of ion pairing HPLC with ICPMS for arsenic speciation

species Matrix column Mobile phase optimization Retention

time(minutes)

Literatu

re cited

As(III)

As(V)

River

Water

Reversed

phase

Capcell C18

pak

Isocratic elution

5mM butane sulfonic

acid,2mM malonic

acid,0.3mM hexane

PH=2.5

F.R=1mL/mi

n

2.4, As(V)

3.0, As(III)

[51]

13

(250mmx4.6

mm)

sulfonic acid,0.5%

methanol

As(III)

As(V)

MMA(V)

DMA(V)

Well

water

Reversed

phase

ODS-

3(150mmx4.

6,3µM)

Isocratic elution , 5mM

TBAH,3mM malonic

acid,5%methanol

F.R=1.5mL/

min

C.T=500C

1.5, As(III)

2.4, DMA(V)

3.2, MMA(V)

4.7, As(V)

[52]

As(III)

As(V)

MMA(V)

DMA(V)

AsB

AsC

TMAO

TeMA

Hot

spring

water

Reversed

phase

Devilsol

C30-UG-5

(250mmx4.6

mm,5µM)

Isocratic elution,10mM

sodium butane

sulfonate,4mM

malonic acid,4mM

tetramethyl ammonium

hydroxide,0.1(v/v)%m

ethanol,20mM

ammonium

tartarate(pH=2.0)

mixed solution.

PH=2

F.R=0.75ml/

min

Column

temperature

is same as

room

temperature.

5.2, As(V)

5.5, As(III)

5.75,

MMA(V)

7.0, DMA(V)

8.5, AsB

9.7, TMAO

10.4, TeMA

10.8, AsC

[53]

C.T=column temperature MMA(V) = Mononethylarsonic acid

F.R= Flow rate DMA(V) = Dimethylarsinic acid

HPLC= High performance liquid chromatography AsB = arsenobetaine

ICP-MS=Inductively coupled plasma mass spectrometry AsC = Arsenocholine

As(III)=Arsenic(III) TMAO = Trimethylarsenic oxide

As(V)=Arsenic(V) TeMA = Tetra methylarsonium ion

Table 3 – summary for the work done on speciation of inorganic arsenic species.

Type of

sample

containers

used

Sample

storage

Sample preparation Type of

matrix

Analytica

l method

Detection limit Refe

renc

e As(III)

(µgL-1

)

As(V)

(µgL-1

)

Polyethylene

bottles

<40C Manually shaken,

centrifuged (10,000rpm

for 10 minutes) and

filtered through 0.45µm

filter

Water from

industrial

shale

processing

LC-ICP-

MS

0.02 0.1 [54]

Polyethylene

flasks

40C - Well Water LC-ICP-

MS

0.017 0.026 [44]

Opaque, clean,

high density

propylene

bottle

EDTA - Drinking

water

LC-ICP-

MS

0.067 0.089 [55]

Polyethylene

flasks

40C Filtered through

0.45µm membrane

Filter

Surface

water

LC-ICP-

MS

0.046 0.03 [47]

Polypropylene -200C Filtered through Drinking LC-ICP- 0.09 0.3 [48]

14

bottles 0.45µm filter water MS

Polypropylene

bottles

Stored

in

darkne

ss at

40C

- Sea water LC-ICP-

MS

[56]

For pure

water

0.015 0.057

For 2%

Cl-

solution

0.057 0.116

LC-ICP-

ORS-MS

For pure

water

0.025 0.020

For 2%

Cl-

solution

0.022 0.021

LC-HG-

ICP-MS

For pure

water

0.0028 0.0045

For 2%

Cl-

solution

0.0034 0.0042

LC-ICP-MS=Liquid chromatography inductively coupled plasma mass spectrometry

LC-ICP-ORS-MS=Liquid chromatography inductively coupled plasma mass spectrometry using reaction

cell

LC-HG-ICP-MS=Liquid chromatography inductively coupled plasma mass spectrometry using hydride

EDTA=Ethylene diamine tetra acetic acid

Table 4. Some studies showing stability durations of inorganic arsenic species [As(III) and As(V)]

No Observations made Reference cited

1 No change of As(III) and As(V)was observed in pure water for 24 hours both

in light and dark conditions(no additives were used)

As(III) and As(V) species up to five days were preserved by the addition of

EDTA to experimental solutions(both in light and dark conditions)

[57]

2 At 40C, 20

0C, 40

0C with PH=1.6 and 7.3, As(V) was stable for at least 4

months in waste water.

4 months stability period was attained for As(III) in treated waste water at

PH=7.3 However, at PH=1.6,complete conversion of As(III) to As(V) was

noticed within two months at 400C.

At PH=7.6,complete transformation of As(III) to As(V) was achieved in raw

waste waters within 50 days ,even at 40C

[58]

3 As(V) in surface waters did not show show alternations during 15 day storage

at 40C.

[59]

4 At room temperature, reduction of As(V) to As(III) within few days was [60]

15

observed in Otawa river and deionized water samples spiked with As(III) and

As(V)[0.5-20µg/L]

A natural water sample filtered with 0.45µm and a total concentration of 21

µg/L, stored in a filled bottle at about 50C preserved As(III) and As(V)

concentration for about 30 days.

5 Slow transformation of As(III) to As(V) was noticed during the 8 day

observation period in spiked natural water samples with ascorbic acid.

As(V) was reduced to As(III) within 3 days in rain water in the presence of

ascorbic acid.

[61]

6 Less than 1 µg/L change in As(III) in 16 days was noticed in reagent water

containing As(III),Fe(III) and EDTA.

Capability of EDTA for preserving original As(III)+ As(V) in three well

waters for ten days has been noted.However,2-3 µg/L of As(III) changed to

As(V) after 14-27 days.

[62]

7 Stability period of 1 week for As(III) with the addition of HCl (PH<2) and

excess Fe(III)) to groundwater samples.

[25]

8 At 40C, Samples containing As(III) and As(V) at concentration levels of 0.5

µg/ml or 1 µg/ attained stability for 21 days. However, some alternations were

noted after 29 days of storage.

[63]

9 Different tests on aqueous mixtures at -200C, +3

0C and +20

0C were conducted

for storing arsenic species. Excellent storage temperature was +30C but species

transformations occurred at -200C.

[64]

6. Conclusion Speciation of arsenic in water is vital to assess toxicity, transport and bioavailability. The type of

analytical method used and the knowledge of the different processes that affect inter-conversion of

arsenic species is important to reach to a representative data. Depending on the type of the sample matrix,

preservation by EDTA and acids help in As(III)/As(v) stabilization. Furthermore, filtration, optimum

storage conditions and suitable sample containers play significant role in maintaining integrity of arsenic

species. HPLC-ICP-MS is the most commonly used hyphenated system for speciation analysis of arsenic.

HPLC is a versatile separation technique since it uses different types of stationary phases (Normal,

reversed) and various mobile phases. Separation can also be enhanced by adding ion pair reagents to the

mobile phase. Changing mobile phase during analysis (gradient elution) is also another merit of liquid

chromatography. ICP-MS can serve as an element specific detector and offers better sensitivity. During

speciation analysis of arsenic using ICP-MS, polyatomic interferences like 40

Ar35

Cl+

(the same mass as 75

As) occur due to the presence of chloride in the water samples and the gaseous argon plasma. To

overcome this problem, reaction cells, mathematical equations or high resolution ICP-Ms can be applied.

16

7. Acknowledgement

I would like to thank my supervisor, Dr. Solomon Tesfalidet for providing me valuable

comments, good instruction, proper guidance and encouragement. Moreover I would like to

extend my gratitude to my examiner, Dr. Erik Björn for his constructive comments.

17

8. References 1. P.L.Smedley, D.G. Kinniburgh, Appl. Geochem. 17 (2002) 517-568.

2. Z.Gong, X. Lu, M. Ma, C.Watt, X.C. Le, Talanta 58 (2002) 77-96.

3. C. B'Hymer, J.A. Caruso, Journal of Chromatography A, 1045 (2004) 1-13.

4. I. Komorowicz, D. Baralkiewicz, Talanta 84 (2011) 247-261.

5. Eaton. A, Wang HC, Northington J, Analytical Chemistry of Arsenic in Drinking Water. Denver, Co:

AWWARF Research foundation; 1997. p. 2.

6. P.J. Craig (Ed), Organometallic Compounds in the Environment: Principles and Reactions, Longman,

London, 1986, pp. 198-228.

7. R. Cornelis, H. Crews, J.Caruso, K.G. Heumann (Eds) , Handbook of Elemental Speciation II. Species

in the Environment, Food, Medicine and Occupational Health, John Wiley and Sons, New York, 2005.

8. B. Venupopal, T.D. Luckey, Metal Toxicity in Mammals, vol 2. Plenum Press, New York, 1978.

9. W.R. Penrose, Crit. Rev. Environ. Control 5 (2000) 465.

10. C.K. Jain, I. Ali, Water Res. 34 (2001) 4304-4312.

11. WHO Arsenic compounds, Environmental Health Criteria 224, 2nd

ed., World Health Organization,

Geneva, 2001.

12. A.L. Rosen, G.M. Hieftje, Acta. B 59 (2004) 135-146.

13. D.M. Templaton, F. Ariese, R. Cornelis, L.-G. Danielsson, H. Munatu, H.P. Vanleeween, R.

Lobinski, Pure Appl. Chem 72 (2000) 1453-1470.

14. M. Popp, S. Hann, G. Kollensperger, Analytica. Chemica. Acta 688 (2010) 114-129.

15. A. Montaster (Ed.), Inductively Coupled Plasma Mass Spectrometry, Wiley-VCH, New York, NY,

1998, pp. 711-712.

16. A. Montaster (Ed.), Inductively Coupled Plasma Mass Spectrometry, Wiley-VCH, New York, NY,

1998, pp. 543-547.

17. V.K. Sharma, M. Sohn, Environment International 35 (2009) 743-759.

18. A.R. Kumar, P. Riyazuddin, Trends in Analytical Chem. 29 (2010) 1212-1223.

19. G.J. Liu, X.R. Zhang, J. Jain, J.W. Talley, C.R. Neal, Water Sci. Technol. Water Supply 6 (2006) 175.

20. M. Rassler, B. Michalke, P. Schramel, S. Schulte-Hostede, A. Kettrup, Sci. Tot. Environ. 258 (2000)

171.

21. A.D. Redman, D.L. Macalady, D. Ahman, Environ. Sci. Technol. 36 (2002) 2889.

18

22. M. Edwards, S. Patel, L. McNeill, H. Chen, A.D. Eaton, R.C. Antweiler, H.E. Taylor, Am. Water

Works Assoc. 90 (1998) 103.

23. S.J. Hug, L. Canonica, M. Wegelin, D. Gechter, U.V. Gunten, Environ. Sci. Technol. 35 (2001) 2114.

24. M.T. Emett, G.H. Khoe, Water Res. 35 (2001) 649.

25. M. Borho, P. Wilderer, Aqua 46 (1997) 138.

26. R. Bentley, T.G. Chasteen, Microbiol. Mol. Biol. Rev. 66 (2002) 250.

27. W.R. Cullen, K.J. Reimer, Chem. Rev. 89 (1989) 713.

28. C.A. Jones, H.W. Langner, K. Andersson, T.R. McDermott, W.P. Inskeep, Soil. Sci. Soc. Am. J. 64

(2000) 600.

29. P.A. Gallagheer, C.A. Schwegel, A. Parks, B.M. Gamble, Environ. Sci. Technol. 38 (2004) 2919.

30. J.R. Scudlark, D.L. Johnson, Estuarine Coast. Shelf sci. 14 (1982) 693.

31. Y.T. Kim, H. Yoon, C. Yoon, N.C. Woo, Environ. Geochem. Health 29 (2007) 337.

32. R.B. McClesskey, D.K. Nordstron, A.S. Maest, Appl. Geochem. 19 (2004) 995.

33. V. Cheam, H. Agemian, Analyst (Cambridge, UK) 105 (1980) 737.

34. B. Dauss, J. Mattush, R. Wennrich, H. Weiss, Talanta 58 (2002) 57.

35. B. Dauss, H. Weiss, J. Mattush, R. Wennrich, Talanta 69 (2006) 430.

36. G. Samantha, D.A. Clifford, Environ. Sci. Technol. 39 (2005) 8877.

37. J.H. Huang, G. Ilgen, Anal. Chim. Acta 512 (2004) 1.

38. V. Oliveria, A.M. Sarmiento, J.L. Gomez-Ariza, J.M. Nieto, D. Sanchez-rodas, Talanta 69 (2006)

1182.

39. P. Quevauviller, M.B. de la calle-Guntinas, E.A. Maier, C. Camara, Microchim. Acta 118 (1995) 131.

40. G.E.M. Hall, J.E. Valve, M.B. Parsons, Chinese J. Geochem. 25 (2006) 197.

41. A.G. Gault, J. Jana, S. Chakraborty, P. Mukherjee, M. Sarkar, B. Nath, D.A. Polya, D. Chatterjee,

Anal. Bioanal. Chem. 381 (2005) 347.

42. www.speciation.net/public/document/2007/08/11/2930.html

43. U. S. Environmental Protection Agency, Interim Primary Drinking Water Standards, Fed. Reg. 40

(1975) 11, 990.

44. S.N. Ronkart, V. Laurent, P. Carbonnele, N. Mabon, A. Copia, J-P. Barthelemy, Chemosphere 66

(2007) 738-745.

19

45. A.J. Bednar, J.R. Garbarino, M.R. Burkhardt, J.F. Ranville, T.R. Wildman, Water Research 38 (2004)

355-364.

46. J. Zheng, H. Hintelmann, B. Dimock, M.S. Dzurko, Anal. Bioanal. Chem. 377 (2003) 14-24.

47. A.F. R-Navarro, Y.M. Bravo, F.J. Lopez, F. Hernandez, Journal of Chromatography A,912 (2001)

319-327.

48. L.S. Milstein, A. Essader, E.D. Pellizzari, R.A. Fernando, O. Akinbo, Environment International 28

(2002) 277-283.

49. W.D. James, T. Ragharn, T.J. Gentry, G. Shan, R.H. Loeppert, J. Radioanal. Nucl. Chem. 278 (2)

(2008) 267-270.

50. http://www.chem-agilent.com/cimg/00000124.pdf

51. K. Sathrugnan, S. Hirta, Talanta 64 (2004) 237-243.

52. A. Shraim, N. Chandraserkarn, C.D. Anurandha, S. Hirano, Appl. Organometal. Chem. 16 (2002)

202-209.

53. Y. Morita, T. Kobayashi, T. Kuroiwa, T. Narukawa, Talanta 73 (2007) 81-86.

54. F.A. Duarte, J.S.F. Pereira, M.F. Mesko, F. Goldschmidt, E.M.D.M. Flores, V.L. Dressler,

Spectrochemica. Acta part B 62 (2007) 978-984.

55. J.A. Day, M. Montes-Bayon, A.P. Vounderheide, J.A. Caruso, Anal. Bioanal. Chem. 373 (2002) 664-

668.

56. T. Nakazato, H. Tao, T. Tanguchi, K. Isshiki, Talanta 58 (2002) 121-132.

57. A.J. Bendnar, J.R. Garbarino, J.F. Ranville, T.R. Wildeman, Environ. Sci. Technol. 36 (2002) 2213-

2218.

58. M. Segura, J. Munoz, Y. Madrid, C. Camara, Anal. Bioanal. Chem. 374 (2002) 513-519.

59. A.F. Roig-Navaro, Y. Martinez-Bravo, F.J. Lopez, F. Hernendaz, J. Chromatogr. A 912 (2001) 319-

327

60. G.E.M. Hall, J.C. Pelchat, J. Anal. At. Spectrom. 14 (1999) 205.

61. M. Edwards, S. Patel, L. McNeil, H. Chim, M. Frey, A.D. Eaton, R.C. Antweller, H.E. Taylor, J. Am.

Water Works Assoc. 90 (1998) 103.

62. P.A. Gallagher, C.A. Schwegel, X. Wei, J.T. Creed, J. Environ. Monit. 3 (2001) 371-376.

63. Z. Jokai, J.Hegoczki, P. Fodor, Microchem. J. 59 (1998) 117.

64. T. Lindeeman, A. Prange, W. Dannecker, B. Neidhart, J. Anal. Chem. 368 (2000) 214.

20

9. Appendix