Simultaneous coprecipitation of lead, cobalt, copper, cadmium, iron and nickel in food samples with zirconium(IV) hydroxide prior to their flame atomic absorption spectrometric determination

Food and Chemical Toxicology 47 (2009) 2302–2307

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Simultaneous coprecipitation of lead, cobalt, copper, cadmium, iron and nickel in food samples with zirconium(IV) hydroxide prior to their flame atomic absorption spectrometric determination Demirhan Citak a, Mustafa Tuzen a,*, Mustafa Soylak b a b

Gaziosmanpasßa University, Faculty of Science and Arts, Chemistry Department, 60250 Tokat, Turkey Erciyes University, Faculty of Science and Arts, Chemistry Department, 38039 Kayseri, Turkey

a r t i c l e

i n f o

Article history: Received 5 May 2009 Accepted 10 June 2009

Keywords: Heavy metals Zirconium(IV) hydroxide Preconcentration Coprecipitation Atomic absorption spectrometry

a b s t r a c t A simple and new coprecipitation procedure is developed for the determination of trace quantities of heavy metals (lead, cobalt, copper, cadmium, iron and nickel) in natural water and food samples. Analyte ions were coprecipitated by using zirconium(IV) hydroxide. The determination of metal levels was performed by flame atomic absorption spectrometry (FAAS). The influences of analytical parameters including pH, amount of zirconium(IV), sample volume, etc. were investigated on the recoveries of analyte ions. The effects of possible matrix ions were also examined. The recoveries of the analyte ions were in the range of 95–100%. Preconcentration factor was calculated as 25. The detection limits for the analyte ions based on 3 sigma (n = 21) were in the range of 0.27–2.50 lg L 1. Relative standard deviation was found to be lower than 8%. The validation of the presented coprecipitation procedure was performed by the analysis certified reference materials (GBW 07605 Tea and LGC 6010 Hard drinking water). The procedure was successfully applied to natural waters and food samples like coffee, fish, tobacco, black and green tea. Ó 2009 Elsevier Ltd. All rights reserved.

1. Introduction The presence of heavy metals in the environment is major concern because of their toxicity and threat to human life and environment (Blagojevic et al., 2008, 2009; Kazi et al., 2008; Karimi and Ghaedi, 2008; Barrento et al., 2009; Duran et al., 2009; Ekanem et al., 2009; Guillen et al., 2009). The accurate and precise determination of heavy metals in the food samples are important to obtain accurate results of them (Pyrzynska and Kilian, 2007; Gopalani et al., 2007; Ghaedi, 2007; Chirila et al., 2009; Gharehbaghi et al., 2009; Kazi et al., 2009). The atomic spectrometry techniques are extensively employed for the quantification of heavy metals. Flame atomic absorption spectrometry (FAAS) presents desirable characteristics, such as low costs, operational facilities, high analytical frequency and good selectivity among these techniques (Pereira and Arruda, 2003; Dolak et al., 2009; Jamshidi et al., 2009; Pérez-Quintanilla et al., 2009). However, the direct determination of trace metals by this technique is generally difficult because of matrix interference and low concentration of metals in samples (Baghban et al., 2009; Souza and Tarley, 2009; Ghaedi et al., 2008, 2009). Because of solving among other techniques two problems, separation–preconcentration techniques like solid phase extraction, * Corresponding author. Tel.: +90 356 2521616; fax: +90 356 2521585. E-mail address: [email protected] (M. Tuzen). 0278-6915/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.fct.2009.06.021

ion-exchange, cloud point extraction, membrane filtration, coprecipitation, etc. are used for trace metal ions before their determination (Gholivand et al., 2007; Rajesh and Manikandan, 2008; Bedoui et al., 2008; Madrakian and Ghazizadeh, 2008; Ihara et al., 2008; Faraji et al., 2009; Loonker and Sethia, 2009). The coprecipitation method is one of the most efficient way for the separation and concentrating the trace elements from sample matrix (Mizuike, 1983). It has several advantages, simple and fast, several analyte ions can be preconcentrated and separated from the matrix simultaneously. Several inorganic or organic coprecipitants can be used as efficient collectors of trace elements. Coprecipitation by hydroxide of various metal ions including cerium, scandium, magnesium, ytterbium, samarium, erbium, lanthanum, indium, dysprosium, and iron has been reported for the preconcentration–separation of trace elements from various media like natural water (Akagi and Horaguci, 1990; Hiraide et al., 1991; Elci and Saracoglu, 1998; Saracoglu et al., 2003; Atsumi et al., 2005; Minami et al., 2005). According to our literature survey, zirconium(IV) hydroxide is not used for the coprecipitation of multi-element ions, until now. In the present work, a coprecipitation system for the preconcentration of lead(II), cobalt(II), copper(II), cadmium(II), iron(III), nickel(II) ions by using zirconium (IV) hydroxide has been presented. The experimental conditions for coprecipitation of analyte ions including pH, zirconium(IV) concentration, sample volume, etc. were optimized.

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2. Experimental 2.1. Apparatus A Perkin–Elmer AAnalyst 700 (Norwalk, CT, USA) atomic absorption spectrometer with deuterium background corrector was used in this study. All measurements were carried out in an air/acetylene flame. The operating conditions adjusted in the spectrometer were carried out according to the Standard guidelines of the manufacturers. A 10 cm long slot-burner head, a lamp and an air/acetylene flame were used. A pH meter, Sartorius pp-15 Model glass-electrode was employed for measuring pH values in the aqueous phase. Nuve model NF 800 centrifuge was used to centrifuge of solutions. Milestone Ethos D closed vessel microwave system (maximum pressure 1450 psi, maximum temperature 300 °C) was used. Digestion conditions for microwave system for real samples were applied as 2 min for 250 W, 2 min for 0 W, 6 min for 250 W, 5 min for 400 W, 8 min for 550 W, ventilation: 8 min. 2.2. Reagents and solutions All chemicals used in this work, were of analytical reagent grade and were used without further purification. Deionized water (Milli-Q Millipore 18.2 MX cm 1 resistivity) was used for all dilutions. Laboratory glassware was kept overnight in a 10% v/v HNO3 solution and then rinsed with deionized double distilled water. Stock metal solutions, 1000 mg L 1 Sigma (St. Loius, MO, USA) were diluted daily for obtaining reference and working solutions. The standard solutions used for the calibration procedures were prepared before use by dilution of the stock solution with 1 mol L 1 HNO3. Stock solutions of diverse elements were prepared from the high purity compounds. 1000 mg L 1 solution of Zr(IV) was prepared freshly by dissolving zirconium(IV) chloride (E. Merck, Darmstadt, Germany) in 1.5 mL of concentrated hydrochloric acid and diluting to 50 mL with double distilled water. HCl and Sodium hydroxide was used for pH adjustment. The accuracy of the method was assessed by analyzing of GBW 07605 Tea and LGC 6010 Hard drinking water. 2.3. Test works for analytes The procedure was optimized with test works before coprecipitation of the analyte ions from real samples. For that purpose, 1 mL of 1000 mg L 1 zirconium(IV) solution was added to 25 mL of solution containing 5–20 lg of understudy analyte ions. Then the pH of the solution was adjusted to pH 2–10 by the addition of HCl or NaOH. After 10 min, the solution was centrifuged at 3500 rpm for 15 min. The supernatant was removed. The precipitate remained adhering to the tube was dissolved with 1 mL concentrated HNO3. Final volume was made up to 2 or 10 mL by deionized water. The concentration of the investigated analyte ions were determined by flame atomic absorption spectrometry.

Fig. 1. Effect of pH on coprecipitation of the analyte ions (N = 3).

trated HNO3.This is advantage for this study because to adjusting pH values 8.0 in natural waters is easy, and low quantity of reagent was required to maintain pH, which also reduced contamination risk. 3.2. Effects of zirconium(IV) amounts The influences of zirconium(IV) amounts on the coprecipitation of copper(II), cadmium(II), lead(II), iron(III), nickel(II) and cobalt(II) ions were also tested experimentally in the range of 0–3.0 mg. The results were shown in Fig. 2. Without any zirconium(IV), analyte ions were not quantitatively recovered except iron (III). The recoveries of metal ions investigated were in the range of 45–67% without zirconium(IV). After addition of zirconium(IV), the quantitative recoveries were obtained for analyte ions in the range of 1–2 mg. The optimum amount of zirconium(IV) was taken as 1 mg for further experiments.

2.4. Applications Triplicate 50 mL of LGC 6010 Hard drinking water were filtered through Millipore cellulose membrane filter (0.45 lm pore size). Optimum pH for proposed coprecipitation system was preferred to be 8.0. Then the procedure given Section 2.3 was applied. The levels of analyte ions in the analyzed ten samples were determined by flame atomic absorption spectrometry. GBW 07605 Tea (100 mg) certified reference material, fish (1.0 g), coffee (1.0 g), black tea (1.0 g), green tea (1.0 g) and tobacco (1.0 g) were digested with the mixture of 6 mL HNO3 (65%), 2 mL H2O2 (30%) in microwave digestion system and diluted to 50.0 mL with deionized water. A blank digest was carried out in the same way. Then the preconcentration procedure given above was applied to the final solutions.

3.3. Effect of sample volume The influences of the sample volume of aqueous solution on the recoveries of metal ions were also investigated in the sample volume range of 10–100 mL to obtain high preconcentration factor by using model solutions. The results are depicted in Fig. 3. The

3. Results and discussion To determine the optimal condition for maximum coprecipitation efficiencies for copper(II), cadmium(II), lead(II), iron(III), nickel(II) and cobalt(II) ions, some analytical parameters including pH, zirconium amount, sample volume, and interfering ions were examined. 3.1. Effect of pH For the quantitative coprecipitation efficiency of analyte ions, pH of the working media is a main factor. The effect of pH to the coprecipitation system was investigated in the range of 2–10. The results are shown in Fig. 1. pH values were adjusted with HCl or NaOH. The maximum recoveries of analytes were in the pH range 7–9. Optimum pH for proposed coprecipitation system was preferred 8.0. The precipitate was dissolved with 1 mL concen-

Fig. 2. Effect of zirconium amount on coprecipitation (N = 3).

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were obtained for interferic ions and their limits are given in Table 1. 3.5. Analytical performance

Fig. 3. Effects of sample volume on the recoveries of analytes (N = 3).

analyte ions were quantitatively (95%) recovered in the sample volume range of 10–50 mL. Above 50 mL of sample volume, the recoveries of all the investigated ions were not quantitative. The preconcentration factor is calculated by the ratio of the highest sample volume (50 mL) for each analytes and the lowest final volume (2 mL). The preconcentration factor for analytes was calculated as 25. 3.4. Effect of matrix ions As mentioned in the introduction, the one of the main problem in the atomic absorption spectrometric determination of the heavy metal ions is interference from the matrix. In our work, the influences of the some ions which are known as interferic ions in the FAAS determination were investigated. Quantitative recoveries

The limits of detection (LOD) of the coprecipitation method for the determination of investigated elements were studied under optimal experimental conditions by applying the procedure for blank solutions. The detection limits of the investigated elements based on three times the standard deviations of the blank (n = 21) were Co: 1.42 lg L 1, Pb: 2.50 lg L 1, Ni: 1.05 lg L 1, Cu: 1.55 lg L 1, Fe: 1.53 lg L 1 and Cd: 0.27 lg L 1. The calibration curves for analyte ions were drawn after setting various parameters of FAAS including wavelength, slit width, lamp current at an optimum level. The optimum concentration ranges and regression equations for analytes were given in Table 2. The statistical calculations are based on the average of triplicate readings for a standard solution of the analyte ions. The relative standard deviations for atomic absorption spectrometric measurements for analyte ions are between 3.9% and 7.2% in the model solutions. In order to validate the accuracy of the presented coprecipitation procedure for trace metal ions, different amounts of analyte ions were spiked in natural waters including a tap water from Tokat City, mineral water from Tokat City, Turkey and sea water from Blacksea, Turkey. The results were given in Table 3. Good agreement was obtained between the added and measured analyte contents. The recovery values calculated for the standard additions were in the range of 96–99%. These values were quantitative and it shows that the presented method can be applied for the preconcentration of analyte ions in real samples. 3.6. Application of the proposed method The developed coprecipitation method was applied to standard reference materials (GBW 07605 Tea, LGC 6010 Hard drinking

Table 1 Influences of some foreign ions on the recoveries of analytes (N = 3). Ion

Added as

Concentration (mg L

Na+ K+ Ca2+ Mg2+ Cl F NO3 SO24 PO34 Cr3+ Zn2+ Mn2+

NaCl KCl CaCl2 MgCl2 NaCl NaF KNO3 Na2SO4 Na3PO4 Cr(NO3)3 ZnSO4 MnSO4

20000 5000 5000 3000 30000 3000 5000 3000 1000 25 25 25

a

1

)

Recovery (%) Co

Pb

Ni

Cu

Fe

Cd

99 ± 3a 96 ± 2 97 ± 3 96 ± 2 98 ± 3 97 ± 3 95 ± 2 100 ± 3 99 ± 2 99 ± 3 100 ± 2 96 ± 2

95 ± 2 95 ± 3 95 ± 2 99 ± 3 96 ± 2 98 ± 3 97 ± 3 95 ± 3 95 ± 3 95 ± 2 97 ± 2 95 ± 3

95 ± 3 98 ± 2 99 ± 2 100 ± 1 95 ± 2 98 ± 3 97 ± 2 96 ± 2 98 ± 3 100 ± 2 98 ± 2 95 ± 3

95 ± 2 96 ± 2 95 ± 3 96 ± 3 96 ± 3 96 ± 3 100 ± 2 100 ± 2 95 ± 2 95 ± 2 95 ± 2 96 ± 3

96 ± 3 95 ± 3 96 ± 3 95 ± 2 95 ± 2 97 ± 2 99 ± 3 100 ± 2 97 ± 2 99 ± 2 98 ± 3 95 ± 2

95 ± 3 95 ± 2 95 ± 3 97 ± 3 95 ± 3 98 ± 2 96 ± 3 95 ± 3 95 ± 3 99 ± 2 95 ± 3 96 ± 2

Mean ± standard deviations.

Table 2 Statistical parameters of the calibration curves of the analytes. Analyte

Correlation coefficient

Linear range (mg L

Co Pb Ni Cu Fe Cd

0.9999 0.9999 0.9996 0.9999 0.9996 0.9995

0.25–5.0 0.5–10.0 0.25–5.0 0.25–5.0 0.25–5.0 0.02–2.0

1

)

Regression equation

R.S.D. (%)

A = 0.0383C + 0.0013 A = 0.0048C + 0.0005 A = 0.0219C + 0.00002 A = 0.02667C 0.0006 A = 0.0202C + 0.0036 A = 0.1405C + 0.0076

5.5 4.5 3.9 6.4 5.9 7.2

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D. Citak et al. / Food and Chemical Toxicology 47 (2009) 2302–2307 Table 3 Results for the % recovery of trace metal determination by standard addition method in real samples (Sample volume: 50 mL, final volume: 2 mL) (n = 4). Added (lg L

Element

1

)

Tap water

Mineral water

Found (lg L Co

0 5 10 0 5 10 0 5 10 0 5 10 0 10 20 0 5 10

Pb

Ni

Cu

Fe

Cd

1

)

BDL 4.9 ± 0.2a 9.9 ± 0.4 BDL 4.8 ± 0.2 9.8 ± 0.6 BDL 4.8 ± 0.3 9.7 ± 0.5 7.3 ± 02 12.1 ± 0.7 17.2 ± 0.5 36.9 ± 1.5 46.1 ± 1.9 56.2 ± 1.8 6.5 ± 0.2 11.3 ± 0.5 16.2 ± 0.6

Recovery (%)

Found(lg L

– 98 99 – 96 98 – 96 97 – 98 99 – 98 99 – 97 98

BDL 4.8 ± 0.2 9.7 ± 0.5 BDL 4.9 ± 0.2 9.9 ± 0.6 BDL 4.9 ± 0.5 9.6 ± 0.6 3.6 ± 0.1 8.5 ± 0.4 13.4 ± 0.8 24.5 ± 1.7 34.2 ± 1.8 43.8 ± 1.3 4.3 ± 0.1 9.1 ± 0.4 14.1 ± 0.6

Sea water

1

)

Recovery (%)

Found (lg L

– 96 97 – 98 99 – 98 96 – 99 99 – 99 98 – 98 99

9.5 ± 0.3 14.1 ± 0.7 19.2 ± 0.6 BDL 4.8 ± 0.2 9.7 ± 0.5 BDL 4.8 ± 0.4 9.5 ± 0.6 10.9 ± 0.5 15.6 ± 0.7 20.3 ± 0.9 16.2 ± 1.9 25.9 ± 0.9 35.5 ± 1.2 3.2 ± 0.1 8.2 ± 0.3 12.9 ± 0.5

1

)

Recovery (%) – 97 98 – 96 97 – 96 95 – 98 97 – 99 98 – 99 98

BDL: below detection limit. a Mean ± standard deviations.

Table 4 Validation of method using certified reference materials (n = 4). GBW 07605 Tea (lg g

Element

Co Pb Ni Cu Fe Cd

1

LGC 6010 Hard drinking water (lg L

)

1

)

Certified value

Our value

Certified value

Our value

0.18 4.4 4.6 17.3 264 0.057

0.20 ± 0.02a 4.3 ± 0.2 4.5 ± 0.3 16.5 ± 1.1 260 ± 15 0.060 ± 0.006

– 97 51 – 226 –

BDL 95 ± 3 50 ± 2 BDL 220 ± 10 BDL

BDL: below detection limit. a Mean ± standard deviations.

Table 5 The application of presented method in food samples for contents of analyte ions (n = 4). Fish (Sarda sarda) (lg g

Element

a

Co Pb Ni Cu Fe Cd

1

)

Coffee (lg g

1

)

BDL BDL BDL 2.70 ± 0.20 47.7 ± 2.5 BDL

0.95 ± 0.1 BDL BDL 2.45 ± 0.20 23.5 ± 1.2 BDL

Black tea (lg g

1

Green tea (lg g

)

BDL BDL BDL 4.63 ± 1.80 142 ± 8 BDL

1

)

BDL BDL BDL 4.92 ± 0.21 310 ± 16 BDL

Tobacco (lg g

1

)

BDL 1.70 ± 0.10 3.42 ± 0.15 7.45 ± 0.33 295 ± 13 0.95 ± 0.10

BDL: below detection limit. a Mean ± standard deviations.

Table 6 Comparison of the present system with other coprecipitation system by FAAS. Analytes 3+

2+

2+

2+

2+

2+

2+

3+

Fe , Pb , Ni , Cu , Mn , Co , Cd , Cr Fe3+, Pb2+, Cu2+, Mn2+, Co2+, Cr3+ Fe3+, Pb2+, Cr3+, Mn2+ Pb2+, Cu2+, Ni2+, Co2+, Cd2+, Mn2+ Cu2+, Fe3+, Pb2+, Cd2+, Co2+, Ni2+ Fe3+, Pb2+, Cu2+, Zn2+, Cr3+ Fe3+, Pb2+, Cu2+, Mn2+, Zn2+, Cd2+, Ni2+, Bi, Cr3+ Pb2+, Ni2+, Cu2+ Cd2+, Co2+, Fe3+

1

Co-precipitating agent

PF

pH

DL (lg L

Samarium hydroxide Erbium hydroxide Europium hydroxide Dysprosium(III) hydroxide Cerium(IV) hydroxide BPNBAT Cobalt-diethyldithiocarbamate Zirconium(IV) hydroxide

50 25 500 250 375 150 225 25

12.2 12.7 11–12 11 10.5 9 6 8

0.4–24.0 0.04–0.87 1.7–17.1 14.1–25.3 0.18–7.0 0.3–2.0 4–64 0.27–2.50

)

R.S.D. (%)

References

<10 <9 <10 <10 <9 <5 <7 <8

Saracoglu et al. (2003) Soylak et al. (2005) Soylak and Onal (2006) Peker et al. (2007) Divrikli and Elçi (2002) Bulut et al. (2008) Elçi et al. (1997) This work

PF: preconcentration factor; DL: detection limit; R.S.D.: relative standard deviation; BPNBAT: 3-benzyl-4-p-nitrobenzylidenamino-4,5-dihydro-1,2,4-triazole-5-on.

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water) for the determination of analyte ions. The results are reported in Table 4. The results based on the average of four replicates for analytes which show that the results are in good agreement with the certified values. The coprecipitation procedure was applied to the determination of copper(II), cadmium(II), lead(II), iron(III), nickel(II) and cobalt(II) ions in some food samples (fish, coffee, black tea, green tea, tobacco). The results were summarized in Table 5. The relative standard deviation values were lower than 8%. The results obtained for trace elements in analyzed food samples were acceptable to human consumption at nutritional and toxic levels. 4. Conclusions Coprecipitation with zirconium(IV) hydroxide offers a useful multi-element preconcentration technique in natural waters and food samples like fish, coffee, black tea, green tea and tobacco. The procedure has been successfully applied for the determination of trace quantity of understudy analytes with acceptable accuracy and precision. The coprecipitated analyte ions can be sensitively determined by atomic absorption spectrometry without any influence of zirconium(IV) hydroxide. The system is very simple, fairly rapid, and low cost. A comparison of the proposed method with other coprecipitation methods is summarized in Table 6 in terms of some optimization parameters. The proposed precipitation method is superior for having lower RSD, working pH near to neutral and lower detection limits when compared to other methods. Conflict of interest statement The authors declare that there are no conflicts of interest. Acknowledgement The authors are grateful for the financial support of the Unit of the Scientific Research Projects of Gaziosmanpasa University and the Unit of the Scientific Research Projects of Erciyes University. References Akagi, T., Horaguci, H., 1990. Simultaneous multielement determination of trace metals using 10 ml of seawater spectrometry with gallium coprecipitation and microsampling technique. Analytical Chemistry 62, 81–85. Atsumi, K., Minami, T., Ueda, J., 2005. Determination of cadmium in spring water by graphite-furnace atomic absorption spectrometry after coprecipitation with ytterbium hydroxide. Analytical Sciences 21, 647–649. Baghban, N., Shabani, A.M.H., Dadfarnia, S., Jafari, A.A., 2009. Flame atomic absorption spectrometric determination of trace amounts of cobalt after cloud point extraction as 2-[(2-mercaptophenylimino)methyl]phenol complex. J. Braz. Chem. Soc. 20, 832–838. Barrento, S., Marques, A., Teixeira, B., Carvalho, M.L., Vaz-Pires, P., Nunes, M.E., 2009. Influence of season and sex on the contents of minerals and trace elements in brown crab (Cancer pagurus, Linnaeus, 1758). Journal of Agriculture and Food Chemistry 57, 3253–3260. Bedoui, K., Bekri-Abbes, I., Srasra, E., 2008. Removal of cadmium (II) from aqueous solution using pure smectite and Lewatite S 100: the effect of time and metal concentration. Desalination 223, 269–273. Blagojevic, N.Z., Vukasinovic, V.L., Djurovic, D.D., 2008. Migration and total concentration of heavy metals in soil samples from the Zeta Valleyi Montenegro. Research Journal of Chemistry and Environment 12, 76–81. Blagojevic, N., Damjanovic-Vratnica, B., Vukasinovic-Pesic, V., Durovic, D., 2009. Heavy metals content in leaves and extracts of wild-growing Salvia officinalis from Montenegro. Polish Journal of Environmental Studies 18, 167–173. Bulut, V.N., Duran, C., Gundogdu, A., Soylak, M., Yildirim, N., Elçi, L., 2008. A new approach to separation and pre-concentration of some trace metals with coprecipitation method using a triazole. Talanta 76, 469–474. Chirila, E., Canuta, M., Pavel, O., 2009. Cd and Pb determination in some Romanian south eastern region cereals. Ovidius University Annals of Chemistry 20, 142– 145. Divrikli, U., Elçi, L., 2002. Determination of some trace metals in water and sediment samples by flame atomic absorption spectrometry after coprecipitation with cerium (IV) hydroxide. Analytica Chimica Acta 452, 231–235.

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