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I nternational Journal of Scientifi c Research i n Knowledge (I JSRK), 1(6), pp. 163-174, 2013Available online at http://www.ijsrpub.com/ijsrk

ISSN: 2322-4541; 2013 IJSRPUB

http://dx.doi.org/10.12983/ijsrk-2013-p163-174

163

Full Length Research Paper

Preconcentration of Trace Copper (II) Using octadecyl Silica Membrane DisksModified Functionalized Graphene with Octadecylamine (ODAGO) in Water and

Paraffin-Embedded Tissues from Liver Loggerhead Turtles Specimens by FAAS

Ali Moghimi

Department of Chemistry, Varamin (Pishva) Branch, Islamic Azad University Varamin, Iran

E- mail:[email protected]; [email protected]

Received 10 April 2013; Accepted 14 May 2013

Abstract. A simple and reproducible method for the rapid extraction and determination of trace amounts of copper (II) ions

using octadecyl-bonded silica membrane disks modified by Functionalized Graphene with octadecylamine (ODAGO) and

Atomic Absorption Spectrometry is presented. The method is based on complex formation on the surface of the ENVI-18

DISKTM

disks followed by stripping of the retained species by minimum amounts of appropriate organic solvents. The elution

is efficient and quantitative. The effect of potential interfering ions, pH, ligand amount, stripping solvent, and sample flow rate

were also investigated. Under the optimal experimental conditions, the break-through volume was found to about 1000mL

providing a preconcentration factor of 500. In the present study, we report the application of preconcentration techniques stillcontinues increasingly for trace metal determinations by flame atomic absorption spectrometry (FAAS) for quantification of

Cu in Formalin-fixed paraffin-embedded (FFPE) tissues from Liver loggerhead turtles. The maximum capacity of the disks

was found to be 389 4 g for Cu2+

.The limit of detection of the proposed method is 3ng per 1000mL.The method was applied

to the extraction and recovery of copper in different water samples.

Key words: Copper (II), SPE;Octadecyl slica disks; AAS, Functionalized Graphene with octadecylamine (ODAGO),Formalin-fixed paraffin-embedded (FFPE)

1. INTRODUCTION

Graphenes are attracting renewed interests owing to

recent advances in micromechanical exfoliation andepitaxial growth methods that make macroscopic 2Dsheets of sp2-carbon atoms available (Geim et al.,2007). A variety of simple yet elegant physics relatingto its zero-gap semiconductor character has thus beendemonstrated (Meyer et al., 2007). It would be verydesirable to make these materials solution (or more

accurately, dispersion) processable by coating or

printing, which will open applications for large and/orflexible substrates. Graphite oxide (GO) is a possiblecandidate for this because it is a precursor to graphenethrough deoxidation either thermally or by chemicalreduction (Wood et al., 1983). Although GO itself hasbeen studied for over a century,(Brodie, Philos et al.,

1859). Its structure and properties remain elusive, andprogress has been made only recently to givematerials with limited dispersability and electronicquality (Shuai Wang et al., 2008; Schniepp et al.,2005).

The Direct determination of trace metals especially

toxic metal ions such as copper, tin, lead andmetalloids arsenic, antimony and selenium fromvarious samples requires mostly an initial and efficientpre-concentration step (Leyden et al., 1976). This pre-

concentration is required to meet the detection limitsas well as to determine the lower concentration levelsof the analyte of interest (Jones et al., 1983). This can

be performed simply in many ways including liquidand solid phase extraction techniques (Nambiar et al.,1998; Caroli et al., 1991). The application of solidphase extraction technique for preconcentration oftrace metals from different samples results in severaladvantages such as the minimal waste generation,reduction of sample matrix effects as well as

adsorption of the target species on the solid surface in

a more stable chemical form (Alexandrova et al.,1993).

The normal and selective solid phase extractors arethose derived from the immobilization of the organiccompounds on the surface of solid supports which aremainly nano polyurethane forms, filter paper (Leyden

et al., 1975), cellulose ( Gennaro et al., 1983) and ionexchange resins (Shamsipur et al., 2005). Silica gel,alumina, magnesia and zirconia are the majorinorganic solid matrices used to immobilize the targetorganic modifiers on their surfaces (Unger et al.,

1979) of which silica gel is the most widely used solid

support due to the well documented thermal, chemicaland mechanical stability properties compared to otherorganic and inorganic solid supports (Boudreau et al.,1989).
mailto:[email protected]:[email protected]:[email protected]


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Preconcentration of Trace Copper (II) Using octadecyl Silica Membrane Disks Modified Functionalized Graphene with

Octadecylamine (ODAGO) in Water and Paraffin-Embedded Tissues from Liver Loggerhead Turtles Specimens by

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The surface of silica gel is characterized by thepresence of silanol groups, which are known as weakion exchangers, causing low interaction, binding andextraction of the target analytes (Kvitek et al., 1982).

For this reason, modification of the silica gel surfacewith certain functional groups has successfully beenemployed to produce the solid phase with certainselectivity characters (Bruening et al., 1991). Twoapproaches are known for loading the surface of solidphases with certain organic compounds and these aredefined as the chemical immobilization which is basedon chemical bond formation between the silica gelsurface groups and those of the organic modifier, andthe other approach is known as the physicaladsorption in which direct adsorption of the organicmodifier with the active silanol groups takes place

(Unger et al., 1979).Selective solid phase extractors and pre-

concentrators are mainly based on impregnation of thesolid surface with certain donor atoms such as oxygen,nitrogen and sulfur containing compounds (Mahmoud,1979; Mahmoud et al., 1997; Tong et al., 1990; Dadleret al., 1987).

The most successful selective solid phases for softmetal ions are sulfur-containing compounds, which

are widely used in different analytical fields. Amongstthese sulfur-containing compounds aredithiocarbamate derivatives for selective extraction of

copper(II) (Mahmoud 1999; Mahmoud 1998) and pre-concentration of various cations (Leyden et al., 1976;

Moghimi et al., 2009; Tehrani et al., 2005) and 2-mercaptobenzothiazol-modified silica gel for on-line

pre-concentration and separation of silver for atomicabsorption spectrometric determinations (Moghimi etal., 2009). Ammonium hexa-hydroazepin-1-dithiocarboxylate (HMDC)-loaded on silica gel assolid phase pre-concentration column for atomic

absorption spectrometry (AAS) and inductivelycoupled plasma atomic emission spectrometry (ICP-AES) was reported (Alexandrova et al., 1993).Mercapto-modified silica gel phase was used in pre-concentration of some trace metals from seawater

(Moghimi et al., 2009). Sorption of copper (II) bysome sulfur containing complexing agents loaded onvarious solid supports (Moghimi et al., 2011) was alsoreported. 2-Amino-1- cyclopentene-1-dithiocaboxylicacid (ACDA) for the extraction of silver(I), copper(II)and palladium(II) (Moghimi 2009), 2-[2-triethoxysilyl-ethylthio] aniline for the selectiveextraction and separation of palladium from otherinterfering metal ions (Tehrani et al., 2005) as well as

thiosemicarbazide for sorption of different metal ions(Moghimi et al., 2011) and thioanilide loaded on silicagel for pre-concentration of palladium(II) from water(Tehrani et al., 2005) are also sulfur contaning silicagel phases.

Ion adsorption onto solid chelating nano polymermaterials is now considered as one of the mostpromising techniques for selective concentration,removal and recovery of metal ions from a wide

variety of sources. Among different types of polymeradsorbent, polymer fibers have attracted great interestin recent years (Tahaei et al., 2008; Moghimi, 2006).This can be related to their structure andcharacteristics, like high specific surface, small cross-section, uniformity in diameter (in macroscopic scale)and long length of fiber to diameter (Abdouss et al.,2012).

In our previous attempts, we modified SPEmembrane disks with suitable compounds forselective determination of copper (Tuzen et al.,2009).Meanwhile, other investigators have

successfully utilized these sorbents for quantitativeextraction and monitoring trace amounts of lead

(Tahaei et al., 2008).The optimized method was applied to Cu

2+

determinations in different natural waters. The secondaim of this study was the selection of an appropriatemethod for the analysis of FFPE tissues were based on

present work with atomic absorptionspectrophotometric determination of Cu.

2. Experimental

2.1. Reagents

All acids were of the highest purity available fromMerck and were used as received. Methanol and

Chlorofom were of HPLC grade from Merck.Analytical grade nitrate salts of litium, sodium,potassium, magnesium, calcium, strontium, barium,zinc, cadmium, lead, nickel, cobalt(II), and copper(II)were of the highest purity. Ultra pure organic solvents

were obtained from E.Merck, Darmstat, Germany, andHigh Purity double distilled deionized water was usedthroughout the experiments.

The stock standard solution of Cu2+

was preparedby dissolving 0.1000g of the copper powder in 10mL

concentrated nitric acid and diluted to 1000mL withwater in a calibrated flask. Working solutions wereprepared by appropriate dilution of the stock solution.

2.2. Apparatus

Determination of Cu2+

contents in working sampleswere carried out by a Varian spectra A.200 modelatomic absorption spectrometerequipped with a high

intensity hallow cathode lamp(HI-HCl) according tothe recommendations of the manufacturers. Thesecharacteristics are tabulated in (Table 1).


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Table 1: The operational conditions of flame for determination of copper

Solid phase extractions were carried out by glassy

membrane disks, ENVI-18DISKTM

47mm diameter0.6 mm thickness containing octadecyl silica bonded

phase (30 m particles, 70 A pore size) obtained

from Supelco in conjunction with a standard Millipore47 mm filtration apparatus equipped with a vacuumpump. The pH measurements were carried out by anATC pH meter (EDT instruments, GP 353).

We show here that substoichiometric (i.e. under-oxidised) GO can be obtained by a modifiedStaudenmaier oxidation of graphite with potassiumchlorate (Schniepp et al, 2005).

In a concentrated sulphuricnitric acid mixture to

give a material with an empirical formula containingless oxygen than the fully oxidisedGO (C2.0O1.0Hx),

(Wood et al., 1983; Brodie Philos et al., 1859) for

example, C2.0O0.77H0.75. This material can then beexfoliated and functionalised in situ indichlorobenzene with octadecylamine (ODA) at mildtemperatures to give a black ODAGO nanosheet

dispersion. This dispersion can be purified by repeatedcentrifugation and redispersion. The overall yield ishigh, ca. 50%. See Scheme 1 for a schematic of thereaction processes and Supporting Information S1 fordetails (Shuai Wang et al., 2008).

Table 2: The effect of presence of ODAGO on extraction percent of copper (II)a

a Initial samples contained 10g of copper(II) in 100mL of water.b Values in parentheses are RSDS based on five individual replicate analyses.

Scheme 1: Schematic of the reaction preparation of purified and highly dispersible grapheme oxide nanosheets inorganic solvents

2.3. Sample extraction

Extraction were performed with glassy membranedisks, ENVI-18 DISKTM 47mm diameter 0.6 mm

thickness containing octadecyl silica bonded phase(30 m particles, 70 A pore size) from Supelco. Thedisks were used in conjunctions with a standard

Millipore 47mm filtration apparatus connected towater aspirator.46

1) Sample Treatment: The water samples werefiltered through 45m nylon filters. Sampling vessels

were polyethylene bottles soaked in 1 mol.L-1

HNO3overnight and rinsed twice with deionized water. The

analysis must be done within 2 days of samplecollection to limit the risk of interconversion ofcopper(II).Then, 5mL of methanol was added to a

90mL portion of each before analysis. The surface ofthe ENVI-18 DISKTM disks is not modified with

ODAGO and therefore could not retain Cu2+

ions


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properly. Instead, 10 mg of ODAGO was dissolvedin an appropriate volume of an organic solvent (5mL)miscible with water. The most suitable solvent underthe experimental conditions was acetone. The ODA

GO solution was added to aqueous solution of Cu2+

and the mixture was stirred gently.

2) Disk cleaning and conditioning: A disk wasplaced in the apparatus and was washed with 10mL ofmethanol to remove all contaminants arising from themanufacturing process and the environment. Then, the

disk was dried by passing air through it for severalminutes. To insure optimal extraction of the analytesof interest, the disk was again washed with 10mL ofmethanol, immediately followed by 10mL of water,

without letting the surface of the disk dry. This steppre-wets the disk surface prior to extraction. Improperperformance of this step causes slow flow rate andpoor analyte recoveries. It is important to avoid anyair contact with the surface of the disk before theaddition of the sample.

Scheme 2: Schematic structure of the solution-process able grapheme nanosheets

3) Sample addition: After completehomogenization, accurate volumes of the samplesolutions (100mL portions) were transferred to the topreservoir of the disk apparatus. At the same time, thesolution was drawn through the disk by applying amild vacuum. Application of vacuum was continueduntil the disk was completely dry (about 5 minute).4)Analyte elution: In order to elute the analyteselectively, exactly 5 mL of acidified solvents 0.1MHCl in methanol was passed through the disk andcollected into a 5.0 mL volumetric flask under theextraction funnel. It was found that ultra pure

alcoholic organic solvents were the best eluting agents.The concentration of copper (II) in the eluates werethen determined by FAAS using an externalcalibration graph.

2.4. Analysis of Sample paraffin-embedded tissues

from Liver loggerhead turtles

2.4.1. Specimens

Selected areas from fresh frozen tissues from Liver

loggerhead turtles specimens were sliced in three

pieces (numbered as 1, 2 and 3) of approximately10mm5mm2mm each. Sets of pieces of set 1(controls), were placed into a vacuum chamber at 50C overnight to dry (until a constant weight wasobtained), and the sets 2 and 3 were subjected to thestandard 10% buffered formalin fixation and paraffinembedding55 histological process using a tissueprocessor (Tissue-Tek VIP, Sakura Finetek USA Inc.,Torrance, CA). After the paraffin embedding process,tissues were subsequently excised from the blockswith a titanium knife and deparaffinized in xylene at55 C for 1 h in the tissue processor (the set 2), or with

hexane at 20 C for 1 week with frequent changes ofthe solvent in handling-based procedure (the set 3).Xylene was of a grade routinely used for the FFPEprocess and hexane was of Optima grade (FisherScientific). Upon deparaffinization, the tissue sampleswere dried in a vacuum chamber until constantweight

was obtained. Each dried sample (of the sets 13) wasdivided into three portions (510 mg each) to be

further analyzed as triplicates.


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Table 3: Effect of different eluting solvents on Percentage recovery of copper (II) adsorbed on the diska

aInitial samples contained 10 g of each copper in 100 mL water. b Values in parentheses are RSDs based on five individual replicate analysis.c Acidified solvents obtained by addition of 0.1M HCl.dAmmoniacal solvents obtained by addition of 0.1M NH3

Table 4: Percent recovery of copper from the modified membrane disk in the presence of 0.01 M of different counter anionsa

aInitial samples contained 10g of copper(II) in 100mL of water.

Table 5: Influence of the ODAGO amount on the recovery of Cu (II) ionsa

a Initial samples contained 10 g of each copper in 100 mL water. b Values in parentheses are RSDs based on five individual replicate analysis.

3. RESULTS AND DISCUSSION

3.1. Evaluation of the role of the ligand

Some preliminary experiments were performed forinvestigation of absence or presence of PAN on the

quantitative extraction of copper (II).It was concluded

that the membrane disk itself does not show anytendency for the retention of copper (II), butintroduction of 100mL portions of aqueous copper (II)

samples containing 10g of copper(II) and 10mg of

ODAGO leads to satisfactory its retention(Table 2).The latter case is most probably attributed to theexistence of a considerable interaction between copper(II) and the ODAGO. It should be mentioned thatformation of stable complexes between copper (II)

and ODAGO at pH=2 is probably due to an ion pair

formation mechanism. However, at pH higher than 2the retention and percentage recovery of copper (II)are negligible.


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Table 6: Separation of copper from binary mixturesa

a Initial samples contained 10g Cu2+ and different amounts of various ions in 100 mL water(0.1 M acetate ion).b Values in parentheses are RSDs based on five individual replicate analysis.

Table 7: Recovery of copper added to 1000mL of different water samples (containing 0.1Macetate at pH= 4.0-4.5)

a Values in parentheses are %RSDs based on five individual replicate analysisb Not detected

3.2. Choice of eluent

In order to select the most appropriate eluent for thequantitative stripping of the retained copper (II) on thedisks, 5mL of various non organic (each containing10% V.V

-1methanol) and different organic solvents

were tested. The results tabulated in Table2. As can be

seen, the best eluting solvents were found to be 5mLof methanol or ethanol, resulting in quantitativeelution of copper (II) from the disk. It should beemphasized that presence of methanol in any kind of

employed solvents helps to better the contact of eluentwith hydrophobic surface of the disk.

3.3. The effect of the pH

The pH of the sample solutions were adjusted todifferent values between 2-9 by addition of

hydrochloric acid or a suitable buffer such as sodiumacceate-acetic acid or sodium dihydrogen phosphate-disodium hydrogen phosphate, and then solutionspassed through the disks.


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Eventually, the metal ions were stripped by puremethanol or ethanol solutions followed by flameatomic absorption determination of the eluted copper(II).Then, percentage recovery at various pH valueswas determined (Fig .1). According to the results

shown in Fig.1 up to pH 4.0-4.5, complete recoveriesare obtained. However, at higher pH values,percentage recovery decreases. This is due to fact thatin an acidic solution the protonation of ODAGOoccurs and there is a weak tendency for retention

between Cu (II) and ODAGO , whereas at highervalues (pH>5), Cu(II) reacts with hydroxide ions to

produce Cu(OH)2. Therefore, sodium acceate-aceticacid buffer with pH=4.5 was used for thepreconcentration step. Other solvents used fordissolving ODAGO were methanol and ethanol. The

influences of these solvents on the recoveries as afunction of pH are compared and shown in Fig. 1.Mean while, other organic solvents were not testedbecause of their restricted solubility and formation oftwo phases with aqueous solutions and incompatibilitywith flame higher pH values (>7) were not testedbecause of the possibility of the hydrolysis ofoctadecyl silica in the disks.47 Cu(II) ions can be

retained quantitatively by the modified membranedisk through the pH range from 4.0 to 4.5 However, atlower pH (< 4.0), nitrogen atoms of the ODAGOcould be protonated and the stability of complex is

reduced.

3.4. Effect amount of counter anion

In order to investigate the effect of counter ion on therecovery Cu

2+ions by the modified disks, different

counter anions were tested Table 4, it is immediatelyobvious that the nature of the counter anion stronglyinfluences the retention of copper ions by the disk.The results revealed that the ODAGO behaves as aneutral ionophore in the pH range 4.0-4.5 (Moghimi,2006; Tehrani et al., 2005)so that the copper ions are

retained as ion pair complexes by the membrane disks.As seen, acetate ion is the most efficient counter anion

for the SPE of Cu (II) ions. The influence of theconcentration of sodium acetate ion on copper

recovery was investigated, and the results are shownin Table 4. As seen, the percent recovery of Cu

2+

increasedwith the acetate concentration until a reagentconcentration of about 0.1 M is reached, beyondwhich the recovery remained quantitative.

Moreover, acetate ion acts as a suitable bufferingagent, while it effectively contributes to the ions- pairformation; thus, in the SPE experiments, there was noneed for the addition of any buffer solution.

3.5. The influence of flow-rate

One of the most important parameters affecting solidphase extraction is the speed of the process. Hence,the effect of flow-rates on extraction efficiencies was

investigated. It was found that in the range of 10-100mL.min

-1, the retention of Cu (II) was not

considerably affected by the sample solutions flow-rates and leads to reproducible and satisfactory results(Fig. 2). Thus, the flow-rate was maintained at

89mL.min-1

throughout the experiment.

3.6. Quantity of the ODAGO

The optimum amount of ODAGO for thequantitative extraction of Cu (II) was also investigated

by adding various amounts of it to solution (between2-20 mg). The results are listed in Table 5. Theexperimental results revealed that the extraction of Cu(II) was quantitative using a sample solutioncontaining more than 10 mg ODAGO. Hence,subsequent extractions were performed with 15mg ofODAGO.

3.7. Disk efficiency

Undoubtedly, one of the major parameters affecting inthe SPE determinations is the efficiency of the used

membrane disks. However, to the best of ourknowledge this case has not been discussed elsewherein similar reports. Under the optimum experimentalconditions, it was found out that each ENV-18DISKTM disk could perform at least 14 replicateanalyses if organic eluting solvents are used. On theother hand, acidic, eluents practically decrease thenumber of time a disk could be used to 10replicates.These observations are represented in Fig. 3.

3.8. Analytical Performance

When solutions of 10g copper in 10, 50, 100, 500,1000, 2000, 2500 and 3000mL solutions under

optimal experimental conditions were passed throughthe disks, the Cu (II) was quantitatively retained in all

cases. Thus, the breakthrough volume for the methodmust be greater than 2500mL, providing aconcentration factor of >500. The limit of detection(LOD) of the method for the determination of Cu (II)was studied under the optimal experimental

conditions. The LOD based on 3 of the blank (5mLof methanol) is 3 ng per 1000mL.


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Table 8:The effect of the different Schiffs base molecular structures on their selectivity toward different metal traces by

using C18 octadecyl silica bonded phase sorbent

Fig. 1: Influence of sample pH and dissolving solvent of ODAGO on the percentage recovery of Cu (II)

The capacity of modified disks (5mg ODAGO)was determined by passing 50mL portions of samplesolutions containing 8mg of copper and 0.1M sodiumacceate-acetic acid buffer with pH 4.0-4.5, followedby the determination of the retained metal ions in the

eluting solution using AAS. The maximal capacity ofthe disk obtained from three replicate measurementswas 3894g of Cu2+ on the disk.

In order to investigate the selective separation and

determination of Cu2+ ions from its binary mixtureswith various metal ions, an aliquot of aqueoussolutions (50mL) containing 10g Cu2

+and mg

amounts of other cations was taken and the

recommended procedure was followed. The results aresummarized in Table 6. The results show that thecopper (II) ions in binary mixtures are retained almostcompletely by the modified disk, even in the presenceof up to about 100mg of various ions. Meanwhile,

retention of other cations by the disk is very low andthey can be separated effectively from the Cu

2+ion. It

is interesting to note that, in other experiments, wefound that in the presence of high enough

concentrations NH2OH.HCl as a suitable reducingagent (> 0.5M)48.no retention of the resulting singlecharge Cu+ ion can occur by the modified membranedisk.


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Fig. 2: The effect of the flow-rate on extraction percent of Cu (II)

Fig. 3: Influence of eluent (5mL of methanol) type on disk efficiency

3.9. Analysis of a real biological sample

To assess the applicability of the method to realsamples, it was applied to the extraction anddetermination of copper from different water samples.Tap water(Tehran, taken after 10 min operation of the

tap),rain water(Tehran, 26 January, 2013), Snow

water (Varamin , 16 February ,2013)and Seawater(taken from Caspian sea, near the Mahmoud-Abad shore) samples were analyzed(Table 7). As canbe seen from Table 4 the added copper ions can bequantitatively recovered from the water samples used.As is seen, the recovered copper ion reveals that the

results are quite reliable and are in satisfactoryagreement with those obtained by ICPAES.

Development of a methodology for thedetermination of Cu in FFPE tissue was performed ina number of steps to optimize the major factorsaffecting the precision of the analysis. (Tables 7)

4. CONCLUSION

Results presented in this work demonstrate well thetremendous possibilities offered by the solid phaseextraction of trace amounts of Cu (II) in watersamples using Octadecyl Silica membrane disks

modified by Functionalized Graphene with

octadecylamine (ODAGO) and its determination byFAAS. The method developed was simple, reliable,and precise for determining copper in water. Also, theproposed method was free of interference compared toconventional procedures to determine copper (Choi etal., 2003; Moghimi et al., 2009; Moghimi et al.,

2011).The method can be successfully applied to the

separation and determination of copper in binarymixtures.

Acknowledgements

The authour wish to thank the Chemistery Departmentof Varamin branch Islamic Azad University forfinancial support.


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Associate Professor Dr Ali Moghimi obtained his first degree from Analytical Chemistry Ph.D.,Faculty of Science, Science and Research branch, Islamic Azad University, Tehran, Iran science in

2005. Currently, Dr Moghimi serves head department of chemistry, Varamin (Pishva) Branch

Islamic Azad University. He has published numerous refereed articles in professional journals. Dr

Moghimi field of expertises are solid phase extraction, separation and chromatography. Dr Moghimi

also has conducted numerous consultancies and research works at national and international level.

He has published over 150 refereed articles in professional journals/proceedings and currently sits as

the Editorial Board Member for 11 International journals.

preconcentration of trace copper (ii) using octadecyl silica membrane disks modified functionalized...

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