Inorganic arsenic speciation in water samples by miniaturized solid
phase microextraction using a new polystyrene polydimethyl siloxane
polymer in micropipette tip of syringe system
Jamshed Ali
a,b, Mustafa Tuzen
a,n, Tasneem G. Kazi
b, Baki Hazer
c aGaziosmanpaşa University, Faculty of Science and Arts, Chemistry Department, Tokat 60250, Turkey bNational Centre of Excellence in Analytical Chemistry, University of Sindh, Jamshoro 76080, Pakistan cBulent Ecevit University, Chemistry Department, Zonguldak 67100, Turkey
a r t i c l e i n f o
Article history: Received 30 June 2016 Received in revised form 24 August 2016 Accepted 28 August 2016 Available online 29 August 2016 Keywords:
Inorganic arsenic speciation Natural water
Polystyrene polydimethyl siloxane Syringe system
Electrothermal atomic absorption spectrometry
a b s t r a c t
The polymer, polystyrene polydimethyl siloxane was loaded into the micropipette tip of the syringe system as an adsorbent to developed miniaturized solid phase microextraction. Standard solutions of arsenate and arsenite were passed through the adsorbent loaded in micropipette tip to check the ad-sorption behaviors. It was observed that arsenate adsorbed on the polystyrene polydimethyl siloxane in the pH rang of 6–8, while arsenite was directly passed through the micropipette tip of syringe system. The adsorbed arsenate in micropipette tip of syringe system were eluted by 1.0 M hydrochloric acid. The total inorganic arsenic contents were obtained by the addition of oxidizing agent potassium perman-ganate into the studied samples before passing to the micropipette tip of syringe system. Arsenite concentration in water samples were measured by subtracting arsenate from total inorganic arsenic concentration. Different characteristics which effect the determination of arsenate specie like amount of adsorbent, adsorption capacity, pH, pulled and pushed cycles for adsorption and desorption, volume of sample, eluent type and it volume were also studied in detail. Enrichment factor and detection limit of arsenate by desired method were 218 and 6.9 ng L1respectively. The relative standard deviation was 4.1% (n¼10, C¼0.12 mg L1). Accuracy of the desired technique was confirmed by analysis of the CRMs
(Lake Ontario Water TM-28.3 and Riverine Water NRCC-SLRS-4). Desired technique was significantly useful for determination of the total arsenic, arsenate, and arsenite contents in different natural water samples.
& 2016 Elsevier B.V. All rights reserved.
1. Introduction
The arsenic (As) has occurrence in the environmental at a trace level in the forms of organic/inorganic compounds. Measurement of total inorganic arsenic (tAs), arsenate and arsenite in the en-vironmental samples is very important for risk assessment of life and it toxicity[1]. The toxicity of As depends on its species, like arsenite is more toxic than arsenate and inorganic As compounds are much more hazardous than its organic forms can be persisted in the environmental samples at ultra-trace levels[2]. Arsenic is very toxic metalloid for human being to cause different diseases like skin lesions, keratosis (skin hardening) and carcinogenic effect (lung cancer, liver tumors, and bladder cancer), when it exposure to body even at a trace level, that way it become an important issue in the world to affecting the life[3]. Contamination of As in
different environmental water and other human being consump-tion samples have affect 4100 million people across the world [4,5]. In developing countries contamination of As in water system like surface water and ground water where higher than the per-missible level of As for drinking water [6]. The recommended permissible level of As in drinking water according to the world health organization (WHO) is 10mg L1[7]. Occurrence of As in
the water samples due to the leaching of As from different natural sources as well as human activities like industrial effluents, pes-ticides, wood preservative agents, combustion of fossil fuels, and mining activity[8]. Industrial waste water mostly contains differ-ent toxic elemdiffer-ents and created environmdiffer-ental pollution and harmful for living things. Minerals are the main sources of arsenic occurrence in the earth crest and released into the environment through water leaching[9,10]. Arsenopyrite is the most abundant mineral which is frequently occurred in the soil and sediments of the mining area[11]. Explaining the leaching mechanisms of As from arsenopyrite has been a great interest to numerous re-searchers of the world [12]. Contamination of As in soil and Contents lists available atScienceDirect
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Talanta
http://dx.doi.org/10.1016/j.talanta.2016.08.075 0039-9140/& 2016 Elsevier B.V. All rights reserved.
nCorresponding author.
different natural water samples may be affected crops and pose hazards to human health through food chain transfer[13]. Stability of inorganic As species in water samples is a major concern due to inter conversion of As species like arsenate into arsenite [14]. Stability of As species were achieved by maintaining the following parameter like pH, light, microbial activity, sampling container material, storage in refrigerator at 4°C and analysis was done as soon as possible within one day[15].
In the light of above mention fact andfigures, it is necessary to accurately measure of As species in different natural water sam-ples. Many analytical methods like co-precipitation was presented in the literature for inorganic As speciation in environmental water samples by graphite furnace atomic absorption spectro-metry (GF-AAS)[16]. Various instrumental techniques including hydride generation atomic absorption spectrometry (HG-AAS), hydride generation-atomic fluorescence spectrometry (HG-AFS) [17], inductively coupled plasma optical emission spectrometry OES), inductively coupled plasma mass spectrometry (ICP-MS)[18]and high performance liquid chromatography–microwave digestion–hydride generation–atomic absorption spectrometry (HPLC–MW–HG–AAS)[19]after some modification steps to sample preparation and separation process[20–23]are used for the de-termination of arsenic. Disadvantages of the above mention ana-lytical instrumental technique are very expensive running cost due to high price of accessories and also not available in each and every analytical laboratory especially in the developing countries. Therefore, some methods developed for the separation and pre-concentration of the target analyte from environmental samples according the need of the laboratory setting and low costs in-struments[24]. Arsenic measurementfield kits are also available in the market but it generally consists of As gas which create As pollution in the environment [8]. Accurately assessments of As species in the natural water samples is an ongoing requirement to developed a simple and effective method. Some of the reported method in the literature has been address these requirements. Direct analysis of As species by ET-AAS is much more difficult [25,26], due to the low LOD and interference of coexistence ions in the studied samples. Therefore, some methods were developed to preconcentration and separation to enhance LOD and reduced the interferences like liquid-liquid extraction, cloud point extraction, electro deposition, co-precipitation, membranefiltration and solid phase extraction (SPE)[27,28]. In the above methods, SPE is one of the best choices for samples preparation due to its simplicity, easy methodology, high EF, and sensitivity[29,30]. Maximum recovery of hydrophobic As species by using SPE method due to the solid support of hydrophobic functionality of adsorbents [31]. Many adsorbents have been reported in the literature to develop SPE method for analysis of As species likes solvent-impregnated resins, polyurethane foam, amberlite resins, modified clinoptilolite zeolite etc[32–34].
The basic principle of the current study is to introduce a min-iaturized solid phase microextraction (MSPME) method for se-paration and preconcentration of inorganic As species, including total inorganic arsenic and arsenate in mineral water, tap water, ground water, lake water, river water and sea water. The devel-oped MSPME wasfirst time used for speciation and quantification of inorganic As species in the studied water samples coupled to analysis by ET-AAS. In thefirst MSPME step, a micropipette tip of the syringe system packed with polystyrene polydimethyl siloxane as adsorbent was used for the preconcentration of arsenate and the removal of matrix, especially organic compounds from natural water samples. The elution solution from MSPME was buffered and employed for further preconcentration and separation of the analyte with pulled and pushed cycles by using the plunger of the syringe. Various factors influencing separation, preconcentration and determination of the analyte was investigated in detail. The
proposed MSPME method for quantification of low level As species in natural water samples of different ecosystem and open a door for their application in different environmental samples.
2. Experimental 2.1. Instrumentations
The extracted species of As from water samples were analysis by ET-AAS (Perkin Elmer model A Analyst 700, Norwalk, CT, USA), coupled with a graphite furnace HGA-400, autosampler AS-800, and deuterium lamp for background correction[35]. The experi-mental conditions of ET-AAS are electrodeless discharge lamp was used as light source for measurement of As species. Recommended current for analysis of As by electrodeless discharge lamp was set at 380 mA at wavelength at 193.7 nm, spectral bandwidth of 0.7 nm. Recommended furnace program for arsenic analysis have five steps: cooling, drying, ashing, atomization, cleaning set as [temperature (°C)/ramp time/hold time(s)/internal flow/gas type] for all steps such as [100/5/20/250/normal], [140/15/15/250/nor-mal], [1300/10/20/250/Nor[140/15/15/250/nor-mal], [2300/0/5/0/nor[140/15/15/250/nor-mal], [2600/1/3/ 250/normal] respectively. The pH of the studied samples was measured by a pH meter (Sartorius professional, meter pp-15). FT-IR spectra of 4000–400 cm1(Thermo Electron Corporation,
Ni-colet avatar 5700) was used for the characterization of the pre-pared materials.
2.2. Standard solution and reagents
The stock solutions (1000 mg L1) of arsenate and arsenite were prepared in high purity deionised water by dissolving ap-propriate amounts of potassium arsenate monobasic (KH2AsO4)
and arsenic oxide (As2O3) which were obtained from Merck
(Darmstadt, Germany). Potassium permanganate (KMnO4) was
obtained from the Sigma-Aldrich. Linoleic acid was supplied from Fluka. Specific amount of acetic acid salt was dissolved by deio-nised water to prepared stock buffer solution and used for re-quired pH control. HCl (purity 37%, Sp.gr:1.19) and HNO3 (purity
65%, Sp.gr:1.41) were obtained from Merck (Darmstadt, Germany). Throughout the experimental work we used high purity deionised water taken from a Milli-Qs water system (ELGA Laboratory, Bucks, UK). Plastic bottles for fresh water sampling were dipped into 10% HNO3for one day, after one day it should be washing with
deionised water, and then dried.
2.3. Synthesis of polystyrene-g-linoleic acid-g-polydimethyl siloxane Linoleic acid was autoxidized by exposing to air oxygen ac-cording to the procedure described in the cited reference in order to prepare polymeric linoleic acid peroxide[36]. Polymeric linoleic acid peroxide can be used as a macroperoxide initiator in order to obtain block/graft copolymer [37]. Styrene polymerization was initiated by polymeric linoleic acid peroxide to obtain polystyrene-g-polylinoleic acid. Terminal carboxylic ends of the graft copoly-mer were reacted with polydimethyl siloxane with amine end groups according to the procedure described in the cited literature [38]. For the condensation reaction procedure, dissolved 1.1 g of poly(linoleic acid) peroxide macro initiator and 3.0 g of poly di-methyl siloxane in 10 mL toluene under the argon gas by flask with glass stopper. The temperature and time maintained for condensation reaction was at 95°C for 5.0 h respectively. After the condensation reaction, the required polymer of polystyrene poly-dimethyl siloxane was precipitated because solvent partially eva-porated. The mixture of above solution wasfiltered, separated the polystyrene polydimethyl siloxane material and dried in room
temperature for 24 h. For increase the purity of synthesis desired copolymer, dried material of polystyrene polydimethyl siloxane was dipped into petroleum ether for one day in order to complete removal of unreacted poly dimethyl siloxane. The condensation reaction of poly(linoleic acid) peroxide macro initiator with poly dimethyl siloxane for synthesis of the copolymer polystyrene polydimethyl siloxane is shown inFig. 1.
2.4. Sampling
The real water samples were collected from different location and different sampling point such as mineral water from local market, tap water samples from Gaziosmanpasa University, Lake water samples from Almus lake, river water samples from Yesi-lirmak river, Tokat. Sea water samples were collected from Black sea, Samsun city of Turkey. Ground water samples were collected from Tharparkar, Pakistan. All water samples were preserved by stored in an ice box and getting to laboratory as soon as possible for avoids the contamination. Water samples from each sampling point were mixed into a washed plastic bucket to make five composite sample of each sampling point. The composite water samples werefiltered with Whatman 0.45 mm filter paper with the help of vacuum pump. These composite water samples are kept at 4°C temperature until analysis of As species[39,40]. 2.5. Design of syringe system
In syringe system, a micropipette tip (250mL, capacity) was washed and rinsed with distilled water and then dried at room temperature. The amount of 5.0 mg of synthesis polymer as ad-sorbent was added into a micropipette tip plugged with a small portion of cotton at both ends of tip. After loaded of adsorbent and cotton materials into the micropipette tip was tightly connected to syringe system. The possible impurities were removed by passing 2.0 mL HCl (1.0 mol L1) through the syringe system. The cleaning with deionized water was performing until it becomes neutral. The syringe system was each time conditioned to the desired pH value with appropriate buffer solution before use. After every elution, the polymer in tip was also washed with a 5.0 mL of water.
2.6. Procedure of desired method
The procedure of MSPME method by using syringe system was simple and easy to operate for preconcentration and separation of arsenic species from water samples. 10.0 mL of each standard (125 ng L1) arsenate, arsenite solutions and real water samples were taken by syringe system after the maintenances of desired pH values by the addition of 100mL of borate buffer. Then these samples were passed through the adsorbent by slowly pushing the plunger of syringe by hand. The complete adsorption of the ar-senate onto the polymer was performed by 5.0 cycles of pulling and pushing by hand slowly in specific time of 0.5–1.0 min. Finally, arsenate retained on the synthesized polymer of polystyrene polydimethyl siloxane was eluted with (1.0 mol L1, 1 mL) of HCl into a small volumetricflask was performed by 2 cycles of pulling or pushing by hand slowly. Total inorganic As was measured after the oxidation of arsenite into arsenate by addition of 0.05 mol L1 KMnO4, reported by Gong et al.[40], then preconcentration and
separation as same procedure of above. The concentration of senite in real water samples were estimated by subtracting ar-senate from total inorganic arsenic. The blank values for arar-senate and total inorganic As were determined after the deionized water subjected to the same procedures mention in above. The actual concentrations of the arsenic species were obtained after blank subtraction.
2.7. Optimised parameters
Optimisation parameters play an important role for the max-imum recovery of the arsenate by using proposed method in syringe system. The effecting parameters in the proposed method such as loading amount of polymer, adsorbing capacity of polymer, samples volume and pH, concentration of elution solvent and pushing/pulling cycles by the syringe were studied in detail.
3. Results and discussion 3.1. Characterization
A novel adsorbent, polystyrene-g-polylinoleic acid-g-poly-dimethyl siloxane was synthesized and characterized by FT-IR technique to identify the functional groups (Fig. 2a). The brush type of configuration and enhanced hydrophobicity coming from polydimethyl siloxane groups enhance the adsorption capability of the novel multigraft copolymer[41,42]. We also get the informa-tion about interacinforma-tion of arsenate with adsorbent material of polystyrene polydimethyl siloxane in the micropipette tip of syr-inge system was shown in Fig. 2b. The strong and broad picks appeared at 3368–3250 cm1 after the passing of As standard solution through the micropipette that may be bounded hydroxyl (-OH) or amine (-NH) groups of the adsorbent. The permit peaks shown at 2923 cm1, in both spectra due to the aliphatic C–H bond of the polymer. The N–H bending at 1674 cm1, the COO2
asymmetric stretching vibration at 1612 cm1 and the NH+ 3
bending at 1478 cm1[43,44]. These spectral results show that this polymer can be used as adsorbent for inorganic As speciation analysis in the natural water samples.
3.1.1. Amount of adsorbent
In the proposed method the amount of loading adsorbent into the micropipette tip of the syringe system is one of the critical parameter. The loading polymer has large surface area, micro-porous structures and not soluble in aqueous solution have im-proved its overall adsorption capabilities. Effect of loading amount of polymer for maximum extraction of arsenate was studies in the range of 2.0–8.0 mg. The maximum recovery of arsenate was observed495%, when the amount of adsorbent 5.0 mg used. So, this amount of adsorbent was used for proposed method. The higher amount of adsorbent from this value has no significant effect on the recovery of arsenate by developed method.
3.1.2. Adsorption capacity
The adsorption capability of the polymer polystyrene poly-dimethyl siloxane was carried out by using optimum procedure; 10 mL model solution of arsenate (100 mg L1) was passed
through the syringe system containing 0.05 g polymer polystyrene polydimethyl siloxane as adsorbent at pH 7. Afterfive cycles the effluent solution was analysis by ET-AAS and remaining con-centration of arsenate (41.5 mg L1) was found in the model so-lution. The adsorption capacity was measured by using the fol-lowing formula:
= ( − )
Ac V Ci Cf W
where; Ac is shown the adsorption capacity, Ciand Cfis the initial
andfinal arsenate concentrations after five cycle through the mi-cropipette tip of syringe system. W is indicated the weight of adsorbent loaded into the micropipette tip and V is the volume of model solution of arsenate. The calculated Ac of the polymer polystyrene polydimethyl siloxane as adsorbent was found to be 11.7 mg g1,as compared to the literature reported data[45,46]. The adsorption capacity of our polymer, polystyrene polydimethyl siloxane for arsenate is significantly higher than the literature reported adsorbents for arsenate determination.
3.1.3. Effect of pH
The pH of studied samples solution plays a vital role in the separation and preconcentration of arsenic species by adsorption material of polymer. In aqueous solution, pH effect on the ad-sorption capability of arsenate and arsenite species in the micro-pipette tip of syringe system loaded with polystyrene poly-dimethyl siloxane as adsorbent was shown inFig. 3. The effect of pH the adsorption material of polystyrene polydimethyl siloxane showed different adsorption characteristics towards arsenate and arsenite species in the ranged of 2.0–9.0 pH. The species of ar-senate was quantitatively adsorbed by the new used polymer in the pH range of 6.0–8.0, while arsenite was not retained at any pH of the studied samples. It is also observed that the adsorption of arsenate on polymer increases with increases the pH of studied samples. The different adsorption behavior of arsenate and ar-senite on polystyrene polydimethyl siloxane adsorbent can be explained by their pKa values. The pKa values of arsenate and arsenite species in compound forms like H3AsO4 (pKa1¼2.3),
−
H AsO2 4 (pKa2¼6.8), and HAsO42− (pKa3¼11.6), while for arsenite
species H3AsO3(pKa1¼9.2),H AsO2 −3(pKa2¼12.1) and also reported
Fig. 2. The FT-IR spectra of (a) polystyrene polydimethyl siloxane and (b) after pulling and pushing cycles of arsenate solution through micropipette tip of by syringe system.
in literature[47–49]. According to the pKa values of arsenate and arsenite, when pH was above 6.0, arsenate exists as negatively charged ions, whereas, arsenite exists mainly as uncharged species in the whole studied pH range[50,51]. Thus, arsenate was ad-sorbed by adsorbent when pH46.0 and arsenite was not adsorbed in the whole studied pH range. It seems that the functional groups of polystyrene polydimethyl siloxane in syringe system are be-having more selective towards the species carrying higher charges. Thus, the arsenate could be separated from total inorganic As at high acidic medium. The possible reactions of arsenate with the polymer of polystyrene polydimethyl siloxane might be described as follows:
HAsO42þ2[R2RʹN]þ-[HAsO4]2-[R2RʹN]þ 2
In the experiments, pH 7.0 was selected for the separation of arsenate from arsenite in water samples.
3.1.4. Pulled/pushed cycles for adsorption and desorption
The number of cycles for pulled and pushed the studied sam-ples through the adsorbent by syringe system is an important parameter for the separation/preconcentration of arsenate. The repeated pulling and pushing of the studied samples through the adsorbent for the separation and preconcentration of arsenate was investigated in the range of 1–10 inFig. 4. The maximum recovery of arsenate was observed after 5 pulling and pushing of standard
Fig. 3. Effect of pH on the recovery of (a) arsenate (b) arsenite by the proposed method of MSPME.
solution through the micropipette tip of syringe system. So, the optimum values for number of pulling/pushing cycles for separa-tion and preconcentrasepara-tion of arsenate could be 5.0 atflow rate of (10 mL min1). Desorption of enriched arsenate from the ad-sorbent in the micropipette tip by 1.0 mol L1 HCl solution. Complete extraction of arsenate by pulling/pushing of 1.0 mL of 1.0 mol L1 of HCl at flow rate of (5 mL min1) for each cycle,
however, to achieve sufficient recovery within a short period of time.
3.1.5. Effect of sample volume
The volume of sample is an important parameter for separation and preconcentration of arsenate from studied samples by using proposed method. So, the volume effect for adsorption on the polymer in the micropipette tip of syringe system were in-vestigated by passing 5–15 mL containing 0.125 mg L1 arsenate solution. The adsorption of the arsenate was observed maximum at 10 mL of the studied samples. This means that the adsorption capability of the polystyrene polydimethyl siloxane as adsorbent is excellent for arsenate. However, the recovery of arsenate adsorp-tion reduced when the volume of sample was higher than this amount. The recovery of arsenate was reduced may be due to the excess amount of arsenate loaded over the adsorbent capacity. So, 10 mL of sample volume was selected as optimised volume for proposed method.
3.1.6. Effect of the type and volume of eluent
A suitable eluent has ability to completely elution of the ad-sorbed arsenate with small volume, which is necessary to obtained high preconcentration factor. Desorption of arsenate from the adsorbing material of polymer in micropipette tip of syringe sys-tem was depend on the eluent types, concentration and its volume for completely extraction. We used HNO3and HCl as eluent and
HCl is good eluent type due to high extraction efficiency.
Maximum recoveries (495%) were observed for the arsenate with 1.0 mL of 1.0 mol L1HCl.
3.2. Oxidation of arsenic
The specific amount of KMnO4was used as an oxidizing agent
to convert the arsenite into the arsenate for determination of total inorganic arsenic concentration in the studied samples [50,52]. The reaction of arsenite with KMnO4was shown as follows:
2MnO4þ3H3AsO3-2MnO2(S)þ3HAsO42þH2Oþ4Hþ
Concentration of the oxidizing agent KMnO4and reaction time
to convert the arsenite into arsenate completely have been studied in detail. Therefore, 0.05 mol L1KMnO4in studied samples were
sufficient for conversion of arsenite into arsenate. After the in-vestigation of KMnO4concentration the reaction time of KMnO4
with arsenite was observed and noted that it reaction is very ra-pidly within 2.0 min. Immediately analysis of the real water samples according to the desired procedure to reduce the chance of co-precipitation of target metal with MnO2during the course of
oxidation[52].
3.3. Analyticalfigure of merits
The analytical figures of merits of the proposed method for determination of arsenate at trace level in the real water samples by preconcentration and separation from different matrices was investigated: the linear range of calibration graphs of the proposed method for arsenate at pH 7.0 were 0.025–0.50 mg L1. Limit of
detection (LOD) was calculated as LOD¼3 SD/m, where SD is the standard deviation corresponding to 10 blank analysis and m is the slope of calibration graph. So, the LOD of our method was found to be 6.9 ng L1that is lower as compared to the cited references in Table 1for arsenate. The enrichment factor (EF) was calculated by
Table 1
Comparison of analytical parameters of the MSPME with literature reported methods for arsenic speciation in water samples. Adsorbent materials Methods Techniques Linear range (mg L1) LODa
(ng L1) E.Fb RSDc (%) Ref SWCNTsd SPEl HG-DC-AFSm 0.01–2.00 3.80 25.4 4.20 [2] CTAB-ACMNPse SPE UV–visn 90.0–4000 28,000 175 2.80 [53]
HSBNZrO2BOf SPE HG-AAS° 0.03–40.0 9250 20.0 5.61 [54]
Fe3O4/Mg-Al LDHg SPE CLp 0.005–5.00 2.00 80.0 2.17 [55]
PTFE-turningsh SPE HG-AAS 0.04–5.00 20.0 10.0 2.80 [21]
C-18i SPE ICP-MSq 20.0–60.0 90.0 50.0 6.02 [56]
Eggshell SPE HG-AFSr
0.005–2.0 1.00 33.3 5.00 [57]
Activated carbon SPE ET-AASs
0.27–5.25 50.0 50.0 4.10 [15]
AAPTSj
SPE ICP-EOSt 0.30–30.0
50.0 100 7.50 [58]
PSPDMSk
MSPME ET-AAS 0.025–0.50 6.9 218 4.1 This study
Key:
a
Limit of detection calculated as three times standard deviation of the blank signal.
b
Enrichment factor calculated as the ratio of slopes of calibration graphs obtained by with and without preconcentrated methods for determination of arsenic.
c
Relative standard deviation calculated as the ratio of sample mean and it standard deviation of ten time repeated analysis (0.125mg/L, As).
d
Single walls carbon nanotube.
e
Cetyltrimethyl ammonium bromide immobilized on alumina-coated magnetite nanoparticles.
fHybrid sorbent based on nano zirconium dioxide boron oxide. gFe O−
3 4doped Mg-Al layered double hydroxide.
h Polytetrafluoroethylene- turnings. i Non-polar (C18) sorbent. j Aminoethylamino propyltrimethoxysilane. k
Polystyrene polydimethyl siloxane.
l
Solid phase extraction.
mHydride generation double channel atomicfluorescence spectrometry. n
Ultra violet-visible spectrophotometer .
°Hydride generation atomic absorption spectrometry. p
Chemiluminescence.
q
Inductively couple plasma mass spectrometry.
r
Hydride generation atomicfluorescence spectrometry.
sElectrothermal atomic absorption spectrometry. tInductively coupled plasma optical emission spectrometry.
the ratio of the slope of calibration curves with and without pre-concentration by the proposed method and the values of EF was found to be 218 which is higher than as compared to literature reported preconcentration methods (Table 1). The relative stan-dard deviation (RSD) for the analysis of arsenate by this method was observed 4.1% at (C¼0.12 mg L1, n¼10). The comparison of the analyticalfigures of merits of the proposed preconcentration method for inorganic As speciation in water samples by using a new adsorbent of polystyrene polydimethyl siloxane with litera-ture reported methods[53–58]are given inTable 1. All parameters like liner calibration range, LOD, EF, and RSD by proposed method is comparable with all reported adsorbents but EF of our new used adsorbent is very higher than in reported methods. The speciation analysis of inorganic arsenic species in water samples can be easily determined by using this proposed syringe system method. 3.4. Interference of coexisting ions
To check the effect of coexisting ions in water samples for se-paration and preconcentration of arsenate was measured under the optimised experimental conditions by proposed method. Various coexisting ions were added individually to the model so-lutions containing 100mg L1 arsenate, respectively. Effect of
in-terference of coexisting ions was investigated by measuring the concentration of arsenate after the addition of specific amount of cations, anions and alkali and alkaline earth metals. An ion was considered as interfering when it caused a variation in the con-centration of the analyte greater than 5%. Some metal ions are more interfered as compared to other metal ions. It was observed that in the presence of 10000 mg L1 Naþ, 3000 mg L1 Kþ, 2000 mg L1 Ca2þ, 1000 mg L1 Mg2þ, Mn2þ, Zn2þ, Cu2þ, 250 mg L1As3þ, 200 mg L1 Al3þ and Fe3þ, 50 mg L1, Pb2þ,
Cd2þ, Cr3þ, Ni2þ, 1000 mg L1 F, 10000 mg L1 Cl,
5000 mg L1 I, 500 mg L1 NO3, 2000 mg L1 SO42,PO43,
the desired arsenate recovery still could be occurred. The resulted data indicated that the % recovery of arsenate was496% (Table 2) for all studied matrix ions by this syringe system for pre-concentration. Therefore, metal ions interference can be mini-mized by controlling of optimum parameters of proposed method.
So, we concluded that our proposed method was free from the interference of coexisting ions were found in natural water sam-ples. It was also observed that 30 mg L1Mn7þ as KMnO
4 was
added for oxidizing of arsenite into arsenate did not interfere with the determination of arsenate by syringe system.
3.5. Application of real water samples
For validity and accuracy of the proposed MSPME method was confirmed by the analysis of various CRMs of (Lake Ontario water-TM-28.3 and Riverine water-NRCC-SLRS-4) for inorganic As spe-ciation in water (Table 3). The measured values of total As in CRM are much closed to the certified values and percentage recoveries 497%. Present method was also compared with the literature reported methods as shown inTable 1. Highly selective and sen-sitive proposed MSPME method was successfully used for de-termination of low level arsenic species in different environmental water samples. Spiking addition was used to check the proposed method accuracy and reliability, to spiked standard concentration of total arsenic and arsenate in different real water samples at two known concentration levels, 3.0 and 6.0
μ
g L1. A good agreement was obtained between the added and measured concentrations of total As and arsenate in each samples. The proposed MSPME method by using syringe system was used to the assessment of low level of total As, arsenate and arsenite in different water samples such as mineral water, tap water, ground water, lake water, river water, sea water (Table 4). It was observed that the % recoveries by spiking addition method in real water samples was found496% for total As and arsenate species determination. The recommended values of As is 10mg L1 for drinking water byWorld Health Organization (WHO)[59]and the US Environmental Protection Agency (USEPA) [60]. Resulted data of Table 4 was shown that the level of arsenic species like total As, arsenate and arsenite concentration in all studied water samples except of Tharparkar ground water were below the WHO and USEPA re-commended limit and were safe andfit for consumption. In these natural water samples, arsenate was predominant among the in-organic As species as reported in literatures[51,52]. Concentration of arsenate and arsenite measured by this method were found higher concentrations as compared to the literature reported, may be due to the different geographical locations[59]. Unpredictably, high levels of arsenate and arsenite were obtained in Tharparakar ground water and the total As was higher than the recommended values for drinking water by WHO and USEPA.
4. Conclusions
The new polymer, polystyrene polydimethyl siloxane was synthesized and used as adsorbent material in the micropipette tip of the syringe system for determination of As species by ET-AAS.
Table 2
The tolerance limits of interfering ions for arsenate analysis by proposed method. Ions Added compounds (Studied
ranged) Tolerance limitsa (mg L1) Recovery (%) Naþ NaCl (5000–12,000) 10000 9675b Kþ KCl (1000–4000) 3000 9873 Ca2þ CaCl2(1000–3000) 2000 9972 Mg2þ Mg(NO3)2(500–1200) 1000 9772 Mn2þ MnSO4(500–1200) 1000 9872 Zn2þ ZnSO4(500–1200) 1000 9773 Cu2þ CuSO4(500–1200) 1000 9673 As3þ As 2O3(50–300) 250 9772 Al3þ Al(NO 3)3(50–250) 200 9972 Fe3þ FeCl3(50–250) 200 9772 Pb2þ Pb(NO 3)2(20–60) 50 9971 Cd2þ CdSO4(20–60) 50 9872 Cr3þ Cr(NO3)3(20–60) 50 9772 Ni2þ NiSO4(20–60) 50 9972 F NaF (500–1200) 1000 9772 Cl NaCl (5000–12,000) 10000 9874 I NaI (1000–6000) 5000 9973 − NO3 KNO3(100–600) 500 9872 − SO42 Na2SO4(500–2500) 2000 9673 − PO43 Na3PO4(500–2500) 2000 9873 Key: a Concentration of arsenate: 100mg L1. b Mean7Standard deviation. Table 3
Arsenic speciation in certified reference materials.
CRMs Arsenic
species
Certified
va-lues (mg L1) Measured va-lues (mg L1) R (%)
Lake ontario water (TM28.3) Total As 6.270.8 6.270.6 99 Arsenate NCa 5.270.3 NC Arsenite NC 1.070.1 NC Riverine water (NRCC-SLRS4) Total As 0.770.1 0.770.1 100 Arsenate NC 0.670.1 NC Arsenite NC 0.170.1 NC
Key: Mean7Standard deviation.
This new adsorbent is free of chemical interference with high adsorption property/adsorption capacity; it is an ideal adsorbent for determination of total As, arsenite and arsenate in different water samples. The prepared micropipette tip connected to syr-inge system is an ideal technique for separation and pre-concentration of As species. The proposed MSPME method is ex-cellence technique, due to the low cost, simple and less amount of sample and elution reagent requirements. Our proposed MSPME method by micropipette tip of syringe system was excellently used for inorganic As species in real water samples from different lo-cation of Turkey and Pakistan. Sample preparation by using this method is more affected as compared to conventional SPE due to the faster extraction at a short time. The proposed method was optimised by excellent accuracy and precision. The results show that the total As concentration in all studied samples were found lower than WHO recommended values for drinking water except ground water from district Tharparkar, Pakistan.
Acknowledgments
The author Jamshed Ali thanks to the Scientific and Technolo-gical Research Council of Turkey (TUBITAK) for awarding me“2216 Research Fellowship Program for Foreign Citizens” and providing financial support. The author also would like to thank to Ga-ziosmanpasa University for providing excellent research labora-tory facilities to carry out this research work.
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Mineral water 0.0 0.0 0.770.1a NCb 0.670.1 NC 0.170.01 3.0 3.0 3.770.2 98 3.570.2 97 0.270.01 6.0 6.0 6.770.3 99 6.570.3 98 0.270.1 Tap water 0.0 0.0 0.970.1 NC 0.670.1 NC 0.370.1 3.0 3.0 3.870.2 99 3.670.2 98 0.270.1 6.0 6.0 6.970.3 99 6.670.3 98 0.370.1 Ground water 0.0 0.0 1170.5 NC 9.570.4 NC 1.570.1 3.0 3.0 1471.1 96 1271.1 97 2.070.1 6.0 6.0 1772.2 98 1672.2 99 1.070.0 Lake Water 0.0 0.0 1.870.1 NC 1.270.1 NC 0.670.01 3.0 3.0 4.871.2 98 4.271.2 98 0.670.1 6.0 6.0 7.872.4 100 7.272.8 99 0.670.1 River water 0.0 0.0 2.270.3 NC 2.170.3 NC 0.170.01 3.0 3.0 5.271.4 98 5.172.3 98 0.170.01 6.0 6.0 8.272.9 99 8.173.9 99 0.170.1 Sea water 0.0 0.0 1.670.1 NC 1.470.1 NC 0.270.1 3.0 3.0 4.571.4 96 4.471.3 100 0.170.01 6.0 6.0 7.673.2 100 7.473.5 99 0.270.1 Key: aMean7Standard deviation. bNot calculated, n¼3.
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