ARTICLE

Activated carbon cloth filled pipette tip for solid phaseextraction of nickel(II), lead(II), cadmium(II), copper(II) andcobalt(II) as 1,3,4-thiadiazole-2,5-dithiol chelates forultra-trace detection by FAASMohamed A. Habilaa, Zeid A. ALOthmana, Erkan Yilmazb and Mustafa Soylakb

aChemistry Department, College of Science, King Saud University, Riyadh, Kingdom of Saudi Arabia;bFaculty of Sciences, Department of Chemistry, Erciyes University, Kayseri, Turkey

ABSTRACTA solid phase extraction method is established for preconcentra-tion of nickel, lead, cadmium, copper and cobalt using pipette tipsolid phase extraction. The presented process was dependent onchelation of analytes with 1,3,4-thiadiazole-2,5-dithiol, then allow-ing the solution to flow through an activated carbon cloth packedpipette tip. The adsorbed metal chelates on the surface of acti-vated carbon cloth were eluted by 5 mL of 3 M HNO3. Theconcentrations of nickel, lead, cadmium, copper and cobalt weredetected using a flame atomic absorption spectrometer (FAAS).The pipette tip solid phase extraction exhibit a preconcentrationfactor of 120. The limit of detection values were 2.7, 1.7, 1.3, 2.0and 2.9 µg L−1 for Ni(II), Pb(II), Cd(II), Cu(II) and Co(II), respectively.Validation of the method was checked by the analysis of TMDA-53.3 and TMDA-64.2 certified reference materials. The method wassuccessfully applied for water and fertiliser samples.

ARTICLE HISTORYReceived 18 November 2017Accepted 15 January 2018

KEYWORDS1,3,4-Thiadiazole-2,5-dithiol;pipette tip; solid phaseextraction; preconcentration;heavy metals; FAAS;environmental samples

1. Introduction

The extraction techniques of specific pollutant are based on the selective interactionbehaviour with the surrounding phases [1,2]. The extraction and separation havereceived more interest during the last decades because of the increase of pollutionpossibilities with a wide range of pollutants including heavy metals, pesticides and otherpersistent organic compounds [3–5]. From these pollutants, the heavy metals areclassified with the high hazard due to their non-biodegradable nature and their mobilityin the environmental components including soil, air, water and food [6–9]. The exposureto heavy metals such as lead, cadmium, copper and nickel may cause various healthproblems affecting the public health and retard the human overall development plans[10–12]. Therefore, following of the metals concentrations in the surrounding samples isthe way to ensure about the public health [13]. The available techniques for heavymetals detection include FAAS, ICP-MS, ICP-AES and UV-visible spectrophotometer [10–15]. However, in most of the analysis cases, a sample pretreatment procedure should be

CONTACT Mustafa Soylak soylak@erciyes.edu.tr Chemistry Department, Faculty of Sciences, Erciyes University,Kayseri, Turkey

INTERNATIONAL JOURNAL OF ENVIRONMENTAL ANALYTICAL CHEMISTRY, 2018VOL. 98, NO. 2, 171–181https://doi.org/10.1080/03067319.2018.1430794

© 2018 Informa UK Limited, trading as Taylor & Francis Group

applied to enrich the analysed pollutant as well as to solve the problem associated withmatrix by selective separation [13,14]. The most applicable sample pretreatments forseparation-preconcentration purposes [16–18] are solid phase extraction (SPE), copreci-pitation, membrane filtration and microextraction.

Among these techniques, the SPE is superior in accuracy, low detection limit, simpleoperation tools and high preconcentration factor [19]. The efficiency and selectivity ofthe solid phase extraction are significantly depending on the adsorbent nature andsurface properties. The sorbent materials may extend to include organic and inorganicadsorbents, carbon materials and nanocomposites [19–21]. Al-Rashdi et al. [22] haveused Dowex Marathon C as acid cation exchange resin for extraction and analysis ofsome metals in the dust samples from Saudi Arabia. Hossein et al. [23] applied ionicliquid-modified SiO2@Fe3O4 nanocomposite for solid phase extraction of zinc from milkand aqueous samples. Molaei et al. [24] have reported the grapheme combined withSiO2 and a pyrrole-thiophene (mGO/SiO2@coPPy-Th) for magnetic solid phase extraction(MSPE) of copper, lead, chromium, zinc and cadmium from aqueous samples.

Recently, the pipette tips have been used to enhance the solid phase extractionprocess. For example, Lee et al. [25] have analysed a tricyclic antidepressants fromhuman plasma by applying pipette tip SPE. The procedures were applied for extractionof amitriptyline, amoxapine, imipramine and trimipramine with LODs and LOQs for thefour drugs of 0.05–0.2 ng/0.1 mL and 0.2–0.5 ng/0.1 mL, respectively. Furthermore theanalysis of ketoconazole (KTZ) cis-enantiomers in urine was achieved by Andrade et al.[26] by applying a stereoselective HPLC/DAD procedure. The method was based on thepipette tip solid phase extraction using cigarette filters as selective adsorbent for KTZcis-enantiomers. Wang et al. [27] have combined the pipette tip solid-phase extractionwith high-performance liquid chromatography with diode array detection for analysis offlavonoids compound. de Oliveira et al. [28] have used HPLC-DAD for analysis offluoroquinolones in urine by pipette tip-solid phase extraction with imprinted polymersadsorbent. The method was used for detection of ciprofloxacin, enrofloxacino, marbo-floxacino and norfloxacin. Kahkha et al. [29] have applied the pipette-tip solid-phaseextraction with zirconium metal-organic framework for extraction of mercury. However,the application of the pipet tips solid phase extraction is still in its primary stage, andtheir application for heavy metal ions extraction is still limited.

1,3,4-Thiadiazole-2,5-dithiol is an organic ligand for metal ions [30,31]. It has beenused as chelating agent for some metal ions for their separation and preconcentrationfrom different environmental matrices [31–33].

This work is focused for applying the pipette tips solid phase extraction of nickel,lead, cadmium, copper and cobalt as 1,3,4-thiadiazole-2,5-dithiol chelates using acti-vated carbon cloth as adsorbent. The analytical parameters including pH, amount of1,3,4-thiadiazole-2,5-dithiol etc. were optimised.

2. Experimental

2.1. Chemicals and reagents

All chemical supplied in this work were in analytical grade purity. The heavy metalssolutions (1000 mg L−1) were prepared in this work from the metals nitrate salts

172 M. A. HABILA ET AL.

which were purchased from Sigma, St. Louis, USA. Activated carbon cloth (Code:Norm/AW1105, Norm company, Turkey) displayed a BET surface area and thickness of1000 m2 g−1 and 0.4 ± 0.1 mm, respectively. Working standard solutions wereobtained via serial dilution of stock standard solutions. 0.1% (w/V) 1,2,4 thiadiazole-2,5-dithiol (Sigma-Aldrich, St. Louis, MO, USA) solution was prepared using deionisedwater. The buffer solutions used at the presented solid phase extraction work wereprepared according to the literature [30–32].

2.2. Instruments

A flame atomic absorption spectrometer (FAAS) (Perkin-Elmer Model A 300) (Norwalk,CT, USA) was used for detection of preconcentrated analyte elements. Hollow cath-ode lamps of each analytes from Perkin-Elmer (Norwalk, CT, USA) and a 10-cm air-acetylene flame atomiser were used. The instrumental settings for analytes wererecommended in the manufacturer’s manual book.

A Nel pH-900 pH meter (Nel Company, Ankara, Turkey) with glass-electrode was usedfor pH measurements. Ultra-pure de-ionised water was prepared by reverse osmosisusing a Milli-Q Direct 16 system (Millipore Australia Pty Ltd, North Ryde, Australia). ALCPK 120 model centrifuge (Buckinghamshire, England) was used for centrifugationprocesses.

2.3. Pipette tip-solid phase extraction (PPT-SPE) procedure

A pipette tip was packed with 0.1 g of activated carbon cloth and washed withdistilled water and then, preconditioned with 2 mL of acetate buffer. The solutionsof mixed heavy metals including Ni(II), Pb(II), Cd(II), Cu(II) and Co(II) were adjustedto the desired pH with acetate buffer, then introduced to the chelation step byadding suitable amount of 1,3,4-thiadiazole-2,5-dithiol. The chelated metals werethen allowed to flow the pipette tip for solid phase extraction. Then, the pipettetip was washed with a 2 mL distilled water to remove the un-bounded species,and the adsorbed metals chelates were eluted with 5 mL of 3 M HNO3. The analyteelements were determined using a flame atomic absorption spectrometer.

2.4. Applications

Water samples such as tap water, wastewater, sea water, dam water and valley water aswell as the TMDA-53.3 and TMDA-64.2 reference materials were filtered through 0.45-µmmembrane filters. Then, the previously described procedures for PPT-SPE were applied.Fertiliser samples of 0.1 g were wet digested in a Teflon beaker with nitric acid (65% w/w) until obtaining clear solution which is completed to 10 mL and applied for PPT-SPEprocedure given above.

INTERNATIONAL JOURNAL OF ENVIRONMENTAL ANALYTICAL CHEMISTRY 173

3. Results and discussion

3.1. Optimisation stage

The preconcentration process developed in this work based on the chelation of nickel,lead, cadmium, copper and cobalt with 1,3,4-Thiadiazole-2,5-dithiol and then adsorptionof these metal chelates on activated carbon cloth. The adsorption of analyte chelatesonto activated carbon cloth (0.1 g) which is packed in a pipette tip of volume 10 mL wasoptimised regarding the pH of sample solution, amount of the 1,3,4-thiadiazole-2,5-dithiolş ligand sample volume etc.

The pH of the aqueous solutions [33–36] is a critical parameter for the metal chelationand adsorption of them on the adsorbent in solid phase extraction studies. Due to thispoint, the influences of the pH of the working media on the recoveries of analyteelements were investigated in the range from 2.0 to 7.5. The results are depicted inFigure 1. The pH of 7.0 is found the most suitable for all tested elements to achieve thequantitative recovery values (<95%).

In order to convert analyte metal ions to organometallic form by using differentchelating agents is one of the important steps on the quantitative recoveries of the tracemetal ions on the solid phase extraction works [35–38]. For the presented solid phaseextraction work, 1,3,4-thiadiazole-2,5-dithiol was selected as chelating agent for theanalyte metal ions and its amounts were tested in the range of 0–200 µL of 0.1% (w/V) 1,3,4-thiadiazole-2,5-dithiol of for the quantitative recoveries of analyte elements. Theresults are given in Figure 2. The quantitative recoveries were obtained in the range of20–50 µL of 0.1% (w/V) 1,3,4-thiadiazole-2,5-dithiol. 50 µL of 0.1% (w/V) 1,3,4-thiadiazole-2,5-dithiol was used for the further works.

The influences of repeated use of activated carbon cloth on the pipette tip on the recoveryvalues of analyte elements were investigated. Activated carbon cloth on the pipette tip couldbe used over 100 times without any loss of adsorption properties for analytes.

In order to reach to high preconcentration factor, the sample volume is one of theeffective factors [37–43]. The influences of the sample volume on the recoveries of theanalyte ions on the presented pipette tip solid phase extraction system were investi-gated in the range of 20–800 mL. The results are given in Figure 3. The quantitativerecoveries of nickel, lead, cadmium, copper and cobalt was obtaining in case of samplevolume up to 600 mL.

0

20

40

60

80

100

2 3 4 5 6 7 8

Rec

over

y, %

pH

Pb(II)

Cu(II)

Ni(II)

Cd(II)

Co(II)

Figure 1. Effect of the pH on the recovery of Ni(II), Pb(II), Cd(II), Cu(II) and Co(II) (N = 3).

174 M. A. HABILA ET AL.

The elution of the adsorbed 1,3,4-thiadiazole-2,5-dithiol chelates of nickel, lead,cadmium, copper and cobalt was studied using various eluents such as hydrochlo-ric acid, nitric acid and acetic acid with different concentration. Figure 4 presentsthe recovery of nickel, lead, cadmium, copper and cobalt in each case. Theachieved recoveries indicate that the 3 M HNO3 was suitable to elute all theadsorbed 1,3,4-thiadiazole-2,5-dithiol chelates of nickel, lead, cadmium, copperand cobalt. The quantity of is tested to control the s of nickel, lead, cadmium,copper and cobalt smallest final collected preconcentrated sample, which found tobe 5 mL.

The preconcentration factor was calculated as the ratio of the highest sample volumeto the eluent volume. The applications of the proposed pipette tip solid phase extraction(PPT-SPE) have resulted in reduction of sample volume from 600 mL before adsorptiononto activated carbon cloth to 5 mL after the elution process. This leads to a precon-centration factor of 120 which reveal the high extraction efficiency of the procedureunder study [44,45].

0

20

40

60

80

100

0 50 100 150 200

Rec

over

y, %

Volume of ligand, µL

Pb(II)

Cu(II)

Ni(II)

Co(II)

Cd(II)

Figure 2. Effect of the pre-chelation with 1,3,4-thiadiazole-2,5-dithiol on the recovery of Ni(II), Pb(II),Cd(II), Cu(II) and Co(II) (N = 3).

0

20

40

60

80

100

0 200 400 600 800

Rec

over

y, %

Sample volume, mL

Pb(II)Cu(II)Ni(II)Cd(II)Co(II)

Figure 3. Effect of sample volume pH on the recovery of Ni(II), Pb(II), Cd(II), Cu(II) and Co(II) (N = 3).

INTERNATIONAL JOURNAL OF ENVIRONMENTAL ANALYTICAL CHEMISTRY 175

3.2. Tolerance levels for the foreign ions

The presence of various cations or anions within the sample solutions is common forwater and food sample extracts [44–53]. These ions may alter the extraction process andreduce recovery of targeted analyses [54,55]. Therefore, the ability of the developedprocedure in this work which is based on formation 1,3,4-thiadiazole-2,5-dithiol chelatesof nickel, lead, cadmium, copper and cobalt to tolerate various matrix ions wereevaluated. Table 1 shows the recovery in case of applying foreign ions such as Na+,K+, Cl−, CO3

2−, Fe3+, Cr3+, F−, Ca2+ and SO42. The results indicate a high tolerance ability

of the developed PPT-SPE.

3.3. Analytical performance

The limit of detection (LOD) was evaluated from Equation (1) [17,18,20,44]

LOD ¼ 3 � STDPF

(1)

where STD is the standard deviation of seven blank readings, and PF is the preconcen-tration factor. The calculated values of limit of detection were 2.7, 1.7, 1.3, 2.0 and 2.9 µgL−1 for Ni(II), Pb(II), Cd(II), Cu(II) and Co(II), respectively. While the relative standarddeviations (RSDs) for analyte elements, evaluated from 11 replicates, were 4.4%, 1.2%,3.5%, 3.0% and 1.7% for Ni(II), Pb(II), Cd(II), Cu(II) and Co(II) respectively.

3.4. Applications

TMDA-53.3 and TMDA-64.2 was used as certified reference materials with known content ofheavy metals and applied for the developed PPT-SPE. The recoveries from these standard

Figure 4. Effect of the eluent type and concentration on the recovery of Ni(II), Pb(II), Cd(II), Cu(II) andCo(II) (N = 3).

176 M. A. HABILA ET AL.

Table1.

Toleranceof

thePPT-SPEto

common

foreignions

(N=3).

Coexistin

gion

Na+

K+/ Cl−

CO3−

2Fe

+3

Cr+3

F−Ca

+2

SO4−

2

Addedas

NaN

O3

KCl

Na 2CO

3Fe(NO3)3.9

H2O

K 2Cr

2O7

NaF

CaCl2

Na 2SO

4

Concentration(m

g/L)

25,000

1250

1000

1510

800

400

500

Recovery,%

Pb(II)

99±1

101±0

94±1

95±0

95±1

99±0

94±1

99±0

Cu(II)

95±1

100±0

98±0

95±0

96±1

101±0

97±0

98±0

Ni(II)

100±1

99±0

92±1

94±1

98±1

99±0

96±0

93±0

Co(II)

97±1

99±0

98±0

94±1

99±0

100±0

100±0

99±0

Cd(II)

97±1

94±1

99±0

96±0

98±1

95±0

95±0

95±0

INTERNATIONAL JOURNAL OF ENVIRONMENTAL ANALYTICAL CHEMISTRY 177

reference materials are recorded in Table 2 revealing a suitable agreement between therecovered values and the certified known values. Furthermore, the method for spikingknown concentrations of tested metals and evaluating the recoveries was operated formore optimisation of the developed PPT-SPE. The spiking was done in to wastewater andfood samples and the recovery was calculated and is presented in Table 3. The quantitativerecoveries were achieved in all tested elements in the range of 94–100%.

For application of the developed PPT-SPE, somewater and fertiliser sampleswere analysed.The detected concentrations of Ni(II), Pb(II), Cd(II), Cu(II) and Co(II) in the real samples are givenin Table 4.

4. Conclusions

The application of the pre-chelation concept before solid phase extraction process has led toan efficient extraction procedure which reached preconcentration factor of 200. The pre-

Table 2. Appling the PPT-SPE for analysis of TMDA-53.3 and TMDA-64.2 certified referencematerials (N=3).TMDA-53.3 TMDA-64.2

Certified value, µg L−1 Found, µg L−1 Recovery, % Certified value, µg L−1 Found, µg L−1 Recovery, %

Pb(II) 349 327 ± 10 94 286 260 ± 0 91Cu(II) 308 301 ± 1 98 270 262 ± 1 97Ni(II) 311 294 ± 10 95 260 265 ± 10 102Co(II) 252 245 ± 4 97 253 259 ± 5 102Cd(II) 118 119 ± 1 101 264 261 ± 3 99

Table 3. Spiking/recovery using the PPT-SPE from a tap water (N = 3).Analyte Prepared solution (µg L−1) Recovered solution (µg L−1) Recovery (%)

Pb(II) 0.0 0.0 –1.4 1.4 ± 0.1 1003.2 3.1 ± 0.1 97

Cu(II) 0 0 –0.1 0.09 ± 0.0 980.22 0.21 ± 0.1 95

Ni(II) 0 0.3 ± 0.1 –2.5 2.5 ± 0.1 1004.7 4.7 ± 0.1 1000 0 –1.7 1.6 ± 0.1 942.7 2.62 ± 0.02 99

Cd(II) 0 0 –1.5 1.5 ± 0.1 1002.5 2.5 ± 0.02 100

Table 4. Determination of analyte elements in water and fertiliser samples (N = 3).Water Samples (µg L−1)

Analyte Waste water Sea water Dam water Valley water Fertiliser samples (µg g−1)

Pb(II) 1.4 ± 0.3 1.5 ± 0.3 BDL BDL 1.0 ± 0.3Cu(II) 4.2 ± 0.02 1.5 ± 0.07 0.6 ± 0.03 0.6 ± 0.04 1.4 ± 0.1Ni(II) 17.1 ± 0.3 14.1 ± 1.4 1.3 ± 0.2 1.2 ± 0.0 7.9 ± 0.3Co(II) 1.9 ± 0.1 1.5 ± 0.0 0.5 ± 0.1 0.7 ± 0.1 1.2 ± 0.1Cd(II) 0.7 ± 0.06 0.4 ± 0.07 0.3 ± 0.02 0.4 ± 0.02 0.4 ± 0.01

BDL: below the detection limit.

178 M. A. HABILA ET AL.

chelation was achieved with 1,3,4-thiadiazole-2,5-dithiol ligand. The developed PPT-SPEprocedure reveals high efficiency for preconcentration of nickel, lead, cadmium, copper andcobalt. The procedure exhibit high ability to tolerate foreign ions includingNa+, K+, Cl−, CO3

2−,Fe3+, Cr3+, F−, Ca2+ and SO4

2−. The presented PPT-SPE was applied to analysis of nickel, lead,cadmium, copper and cobalt in natural water and fertiliser samples.

A comparison of the developed SPE method with the SPE methods reported inliterature for trace metals is shown in Table 5. The limit of detections, preconcentrationfactor and relative standard deviations of our method was generally better or compar-able than those reported studies [56–67].

Acknowledgment

The authors extend their sincere appreciation to the Deanship of Scientific Research at King SaudUniversity for its funding this Research Group-RGP-043.

Disclosure statement

No potential conflict of interest was reported by the authors.

Funding

This work was supported by the Deanship of Scientific Research at King Saud University [ResearchGroup- RGP-043].

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INTERNATIONAL JOURNAL OF ENVIRONMENTAL ANALYTICAL CHEMISTRY 179

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