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Ionic liquid-based modified cold-induced aggregation microextraction (M-CIAME) as a novel solvent extraction method for determination of gold in saline solutions
Minerals Engineering 23 (2010) 823–825
Contents lists available at ScienceDirect
Minerals Engineering journal homepage: www.elsevier.com/locate/mineng
Technical Note
Ionic liquid-based modified cold-induced aggregation microextraction (M-CIAME) as a novel solvent extraction method for determination of gold in saline solutions Shokouh Mahpishanian, Farzaneh Shemirani * School of Analytical Chemistry, University College of Science, University of Tehran, Tehran, Iran
a r t i c l e
i n f o
Article history: Received 7 November 2009 Accepted 24 May 2010 Available online 22 June 2010 Keywords: Solvent extraction Gold Environmental samples
a b s t r a c t Modified-cold-induced aggregation microextraction (M-CIAME) was used for determination of gold in saline solutions. It is robust against the much higher concentration of salt (up to 40%). In this method sodium hexafluorophosphate (NaPF6) was added to the sample solution containing Au-TMK complex and a very small amount of 1-hexyl-3-methylimidazolium tetrafluoroborate [Hmim][BF4]. Afterward the solution was cooled in an ice bath and a cloudy solution was formed. After centrifuging, the extractant phase was analyzed using a spectrophotometric detection method. Under the optimum conditions, the limit of detection (LOD) was 0.7 ng mL 1 and the relative standard deviation (RSD) was 1.65% for 50 ng mL 1 gold. The method was applied for the determination of trace amount of Au in mineral and seawater with satisfactory results. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction Gold belongs to the group of transition metals. Its products are extensively used in various areas such as the petrochemical industry, medicine, electronics and nuclear power industries (Fazli et al., 2009). Several analytical techniques, such as inductively coupled plasma optical emission spectrometry (ICP-OES) (Tavakoli et al., 2008), flame atomic absorption spectrometry (FAAS) (Basri Senturk et al., 2007), electrothermal atomic absorption spectrometry (ETAAS) (Konecna and Komarek, 2007), spectrophotometric detection (Hope et al., 2007) and neutron activation analysis (NAA) (Lupu et al., 2004) have been applied for the determination of gold in different samples but the concentration of gold is too low for the direct application of the abovementioned analytical techniques. For this purpose, several techniques such as solid phase extraction (Tuzen et al., 2008), cloud point extraction (Tavakoli et al., 2008) and dispersive liquid–liquid microextraction (Shamsipur and Ramezani, 2008) have been developed. However, in the presence of a high content of salt the performance of these methods decreases, significantly. Cold-induced aggregation microextraction (CIAME) was presented by authors (Baghdadi and Shemirani, 2008). In CIAME, by increasing the salt content, the solubility of [Hmim][PF6] increases and that of Triton X-114 decreases. Triton X-114 was not used in modified-CIAME, so
* Corresponding author. Tel.: +98 21 61112481; fax: +98 21 66405141. E-mail address: [email protected] (F. Shemirani). 0892-6875/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.mineng.2010.05.010
the extractant phase merely contains [Hmim][PF6] which has a high density, so it can easily settle a salt content of up to 40%. In this work M-CIAME was used for extraction and preconcentration of Au(III) by thiomichlersketone (TMK) as a complexing agent. Analysis was carried out using a spectrophotometric detection method. Different conditions were studied and optimized. 2. Experimental 2.1. Instrumentation A spectrometer (UV–vis, lambda 25) was purchased from Perkin Elmer (Waltham, MA, USA). A Universal 320R refrigerated centrifuge with swing out rotor (12-place, 5000 rpm, Cat. No. 1628A) and a Jeio Tech BW-05G water bath were obtained from Hettich (Kirchlengern, Germany). 2.2. Reagents All reagents used were of analytical grade. TMK, ethanol, [Hmim][BF4] and all salts used were obtained from Merck (Darmstadt, Germany). NaPF6 purchased from ACROS (Geel, Belgium). A solution of 4 10 4 mol L 1 TMK was prepared by dissolving an appropriate amount of this reagent in 1-propanol. The solution of [Hmim][BF4] 0.6 mg lL 1, was prepared in acetone. A solution of 120 mg mL 1 NaPF6 was prepared by dissolving appropriate amount of NaPF6 in doubly distilled water. Stock solutions of Au(III) and those used for the interference study (1000 ng mL 1)
824
S. Mahpishanian, F. Shemirani / Minerals Engineering 23 (2010) 823–825
Fig. 1. Effect of NaPF6 and [Hmim][BF4] on the absorbance of the complex. Conditions: gold 50 ng mL ([Hmim][BF4] 50 lL for study of NaPF6 and NaPF6 1.2 mL for study of [Hmim][BF4]).
Table 1 Determination of Au (lg L
a
1
) in water samples.
Sample
Added Au3+ (lg L 1)
Found Au3+ (lg L 1)a
Recovery (%)
Mineral water
– 50 100
– 51.33 ± 0.23 99.12 ± 0.87
– 102.7 99.1
Sea water
– 50 100
– 49.08 ± 0.37 97.40 ± 0.76
– 98.2 97.4
Mean ± SD, n = 5.
were prepared by dissolving appropriate amounts of their respective salts in doubly distilled water. 2.3. Modified-CIAME procedure Ten milliliters of the sample containing Au(III), TMK (4.8 10 mol L 1) and [Hmim][BF4] (50 lL) at pH 4, was transferred to a conical-bottom glass centrifuge tube and was kept in a bath at 50 °C for 10 min. Then 1.0 mL NaPF6 was added to solution and was placed in an ice bath for 10 min. Then, the mixture was centrifuged for 5 min at 5000 rpm. The bulk aqueous phase was removed by a pipette. Afterwards, the IL-phase was dissolved in 350 lL of ethanol solution (85%) and the absorbance of the complex was measured at 545 nm. 3. Results and discussion 3.1. Effect of pH and TMK concentration The effect of pH on the complex formation of Au(III) was studied in a range of 2.0–7.5. The results reveal that the absorbance is relatively constant in a pH range of 3–5. Therefore, pH 4 was chosen. The effect of the TMK on the absorbance was studied in a range of 0.8 10 6–7.2 10 6 mol L 1. From the data collected a concentration of 4.8 10 6 mol L 1 was selected. 3.2. Effect of NaPF6 and [Hmim][BF4] In M-CIAME, NaPF6 was added to the sample solutions as an ionpairing agent. Furthermore a hydrophilic IL such as [Hmim][BF4]
1
, TMK 4.8 10
4
mol L
1
, pH 4, diluting agent 350 lL and
instead of [Hmim][PF6] was used, which was dissolved easily without the need for Triton X-114. The effect of NaPF6 was investigated in the range of 0.4–1.6 mL. According to the result (Fig. 1), 1.2 mL NaPF6 was chosen for the subsequent experiments. The effect of [Hmim][BF4] was studied in the range of 40– 130 lL (0.6 mg lL 1) in the presence of 1.2 mL NaPF6 (Fig. 1). Thus 80 lL [Hmim][BF4] was chosen. 3.3. Effect of salt concentration NaNO3 was chosen to study the salt effect. It was observed that phase separation occurred successfully up to 40% NaNO3. Consequently, it has been shown that M-CIAME is a powerful sample preparation technique for salinity solutions. 3.4. Effect of centrifuge conditions The effect of centrifugation rate, centrifugation time and centrifugation temperature on the absorbance were studied. The results showed that for the optimum conditions, 5000 rpm, 5 min and the temperature in the range of 0–25 °C were the optimum points. 3.5. Selectivity of the method Effects of common coexisting ions on the recovery of gold were studied. About 10000-fold excess Na+, K+, Ca2+, Mg2+, Cl , Br , SO24 , 100-fold excess Al3+, Fe2+, Co2+, Zn2+ and 10-fold excess Ni2+, Pb2+, Cr3+, Mn2+, Cd2+ did not interfere with the determination of gold. Interference of Pd2+ was eliminated in the presence of acetylacetone. 3.6. Figures of merit Under the optimum experimental conditions, the calibration curve was linear in a range of 1.8–160 lg L 1 with a correlation coefficient of 0.999. The calibration function was A(absorbance) = 0.0108C (lg L 1) + 0.094. The limit of detection (LOD = 0.7 ng mL 1) was calculated as the ratio of three times the standard deviation of the blank signals and the slope of the calibration curve after preconcentration. Enhancement factor (EF = 28) was obtained from the slope ratio of calibration curve after and before preconcentration. The precision (RSD), examined by five
S. Mahpishanian, F. Shemirani / Minerals Engineering 23 (2010) 823–825
replicate measurements of 50 lg L be 1.65%.
1
of Au solutions, was found to
3.7. Analysis of environmental samples In order to validate the accuracy and precision of the method, water samples and related spiked samples were analyzed by the modified-CIAME (Table 1).
4. Conclusion Modified-cold-induced aggregation microextraction (M-CIAME) was used as a sample preparation technique for the determination of gold in saline solutions. M-CIAME is simple and robust against a very high content of salt (up to 40%). Therefore, modified-CIAME is a powerful sample preparation technique for saline solutions and salt products.
Acknowledgment The authors extend their appreciation to University of Tehran for providing financial support to this research.
825
References Baghdadi, M., Shemirani, F., 2008. Cold-induced aggregation microextraction: a novel sample preparation technique based on ionic liquids. Analytica Chimica Acta 613 (1), 56–63. Basri Senturk, H., Gundogdua, A., Numan Bulut, V., Duran, C., Soylak, M., Elci, L., Tufekci, M., 2007. Separation and enrichment of gold(III) from environmental samples prior to its flame atomic absorption spectrometric determination. Journal of Hazardous Materials 149 (2), 317–323. Fazli, Y., Hassan, J., Karbasi, M.H., Sarkouhi, M., 2009. A simple spectrophotometric method for determination of gold(III) in aqueous samples. Minerals Engineering 22 (2), 210–212. Hope, G.A., Buckley, F.M., Munce, C.G., Woods, R., 2007. Gold enhanced spectroelectrochemical investigation of 2-mercaptobenzothiazole, isopropyl xanthate and butylethoxycarbonylthiourea adsorption on minerals. Mineral Engineering 20 (10), 964–969. Konecna, M., Komarek, J., 2007. Utilization of electrodeposition for electrothermal atomic absorption spectrometry determination of gold. Spectrochimica Acta Part B 62 (3), 283–287. Lupu, R., Nat, A., Ene, A., 2004. Determination of gold in Romanian auriferous alluvial sands and rocks by 14 MeV neutron activation analysis. Nuclear Instruments and Methods in Physico Research B 217 (1), 123–135. Shamsipur, M., Ramezani, M., 2008. Selective determination of ultra trace amounts of gold by graphite furnace atomic absorption spectrometry after dispersive liquid–liquid microextraction. Talanta 75 (1), 294–300. Tavakoli, L., Yamini, Y., Ebrahimzadeh, H., Nezhadali, A., Shariati, S., Nourmohammadian, F., 2008. Development of cloud point extraction for simultaneous extraction and determination of gold and palladium using ICPOES. Journal of Hazardous Materials 152 (2), 737–743. Tuzen, M., Saygi, K.O., Soylak, M., 2008. Novel solid phase extraction procedure for gold(III) on Dowex M 4195 prior to its flame atomic absorption spectrometric determination. Journal of Hazardous Materials 156 (1–3), 591–595.
Contents lists available at ScienceDirect
Minerals Engineering journal homepage: www.elsevier.com/locate/mineng
Technical Note
Ionic liquid-based modified cold-induced aggregation microextraction (M-CIAME) as a novel solvent extraction method for determination of gold in saline solutions Shokouh Mahpishanian, Farzaneh Shemirani * School of Analytical Chemistry, University College of Science, University of Tehran, Tehran, Iran
a r t i c l e
i n f o
Article history: Received 7 November 2009 Accepted 24 May 2010 Available online 22 June 2010 Keywords: Solvent extraction Gold Environmental samples
a b s t r a c t Modified-cold-induced aggregation microextraction (M-CIAME) was used for determination of gold in saline solutions. It is robust against the much higher concentration of salt (up to 40%). In this method sodium hexafluorophosphate (NaPF6) was added to the sample solution containing Au-TMK complex and a very small amount of 1-hexyl-3-methylimidazolium tetrafluoroborate [Hmim][BF4]. Afterward the solution was cooled in an ice bath and a cloudy solution was formed. After centrifuging, the extractant phase was analyzed using a spectrophotometric detection method. Under the optimum conditions, the limit of detection (LOD) was 0.7 ng mL 1 and the relative standard deviation (RSD) was 1.65% for 50 ng mL 1 gold. The method was applied for the determination of trace amount of Au in mineral and seawater with satisfactory results. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction Gold belongs to the group of transition metals. Its products are extensively used in various areas such as the petrochemical industry, medicine, electronics and nuclear power industries (Fazli et al., 2009). Several analytical techniques, such as inductively coupled plasma optical emission spectrometry (ICP-OES) (Tavakoli et al., 2008), flame atomic absorption spectrometry (FAAS) (Basri Senturk et al., 2007), electrothermal atomic absorption spectrometry (ETAAS) (Konecna and Komarek, 2007), spectrophotometric detection (Hope et al., 2007) and neutron activation analysis (NAA) (Lupu et al., 2004) have been applied for the determination of gold in different samples but the concentration of gold is too low for the direct application of the abovementioned analytical techniques. For this purpose, several techniques such as solid phase extraction (Tuzen et al., 2008), cloud point extraction (Tavakoli et al., 2008) and dispersive liquid–liquid microextraction (Shamsipur and Ramezani, 2008) have been developed. However, in the presence of a high content of salt the performance of these methods decreases, significantly. Cold-induced aggregation microextraction (CIAME) was presented by authors (Baghdadi and Shemirani, 2008). In CIAME, by increasing the salt content, the solubility of [Hmim][PF6] increases and that of Triton X-114 decreases. Triton X-114 was not used in modified-CIAME, so
* Corresponding author. Tel.: +98 21 61112481; fax: +98 21 66405141. E-mail address: [email protected] (F. Shemirani). 0892-6875/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.mineng.2010.05.010
the extractant phase merely contains [Hmim][PF6] which has a high density, so it can easily settle a salt content of up to 40%. In this work M-CIAME was used for extraction and preconcentration of Au(III) by thiomichlersketone (TMK) as a complexing agent. Analysis was carried out using a spectrophotometric detection method. Different conditions were studied and optimized. 2. Experimental 2.1. Instrumentation A spectrometer (UV–vis, lambda 25) was purchased from Perkin Elmer (Waltham, MA, USA). A Universal 320R refrigerated centrifuge with swing out rotor (12-place, 5000 rpm, Cat. No. 1628A) and a Jeio Tech BW-05G water bath were obtained from Hettich (Kirchlengern, Germany). 2.2. Reagents All reagents used were of analytical grade. TMK, ethanol, [Hmim][BF4] and all salts used were obtained from Merck (Darmstadt, Germany). NaPF6 purchased from ACROS (Geel, Belgium). A solution of 4 10 4 mol L 1 TMK was prepared by dissolving an appropriate amount of this reagent in 1-propanol. The solution of [Hmim][BF4] 0.6 mg lL 1, was prepared in acetone. A solution of 120 mg mL 1 NaPF6 was prepared by dissolving appropriate amount of NaPF6 in doubly distilled water. Stock solutions of Au(III) and those used for the interference study (1000 ng mL 1)
824
S. Mahpishanian, F. Shemirani / Minerals Engineering 23 (2010) 823–825
Fig. 1. Effect of NaPF6 and [Hmim][BF4] on the absorbance of the complex. Conditions: gold 50 ng mL ([Hmim][BF4] 50 lL for study of NaPF6 and NaPF6 1.2 mL for study of [Hmim][BF4]).
Table 1 Determination of Au (lg L
a
1
) in water samples.
Sample
Added Au3+ (lg L 1)
Found Au3+ (lg L 1)a
Recovery (%)
Mineral water
– 50 100
– 51.33 ± 0.23 99.12 ± 0.87
– 102.7 99.1
Sea water
– 50 100
– 49.08 ± 0.37 97.40 ± 0.76
– 98.2 97.4
Mean ± SD, n = 5.
were prepared by dissolving appropriate amounts of their respective salts in doubly distilled water. 2.3. Modified-CIAME procedure Ten milliliters of the sample containing Au(III), TMK (4.8 10 mol L 1) and [Hmim][BF4] (50 lL) at pH 4, was transferred to a conical-bottom glass centrifuge tube and was kept in a bath at 50 °C for 10 min. Then 1.0 mL NaPF6 was added to solution and was placed in an ice bath for 10 min. Then, the mixture was centrifuged for 5 min at 5000 rpm. The bulk aqueous phase was removed by a pipette. Afterwards, the IL-phase was dissolved in 350 lL of ethanol solution (85%) and the absorbance of the complex was measured at 545 nm. 3. Results and discussion 3.1. Effect of pH and TMK concentration The effect of pH on the complex formation of Au(III) was studied in a range of 2.0–7.5. The results reveal that the absorbance is relatively constant in a pH range of 3–5. Therefore, pH 4 was chosen. The effect of the TMK on the absorbance was studied in a range of 0.8 10 6–7.2 10 6 mol L 1. From the data collected a concentration of 4.8 10 6 mol L 1 was selected. 3.2. Effect of NaPF6 and [Hmim][BF4] In M-CIAME, NaPF6 was added to the sample solutions as an ionpairing agent. Furthermore a hydrophilic IL such as [Hmim][BF4]
1
, TMK 4.8 10
4
mol L
1
, pH 4, diluting agent 350 lL and
instead of [Hmim][PF6] was used, which was dissolved easily without the need for Triton X-114. The effect of NaPF6 was investigated in the range of 0.4–1.6 mL. According to the result (Fig. 1), 1.2 mL NaPF6 was chosen for the subsequent experiments. The effect of [Hmim][BF4] was studied in the range of 40– 130 lL (0.6 mg lL 1) in the presence of 1.2 mL NaPF6 (Fig. 1). Thus 80 lL [Hmim][BF4] was chosen. 3.3. Effect of salt concentration NaNO3 was chosen to study the salt effect. It was observed that phase separation occurred successfully up to 40% NaNO3. Consequently, it has been shown that M-CIAME is a powerful sample preparation technique for salinity solutions. 3.4. Effect of centrifuge conditions The effect of centrifugation rate, centrifugation time and centrifugation temperature on the absorbance were studied. The results showed that for the optimum conditions, 5000 rpm, 5 min and the temperature in the range of 0–25 °C were the optimum points. 3.5. Selectivity of the method Effects of common coexisting ions on the recovery of gold were studied. About 10000-fold excess Na+, K+, Ca2+, Mg2+, Cl , Br , SO24 , 100-fold excess Al3+, Fe2+, Co2+, Zn2+ and 10-fold excess Ni2+, Pb2+, Cr3+, Mn2+, Cd2+ did not interfere with the determination of gold. Interference of Pd2+ was eliminated in the presence of acetylacetone. 3.6. Figures of merit Under the optimum experimental conditions, the calibration curve was linear in a range of 1.8–160 lg L 1 with a correlation coefficient of 0.999. The calibration function was A(absorbance) = 0.0108C (lg L 1) + 0.094. The limit of detection (LOD = 0.7 ng mL 1) was calculated as the ratio of three times the standard deviation of the blank signals and the slope of the calibration curve after preconcentration. Enhancement factor (EF = 28) was obtained from the slope ratio of calibration curve after and before preconcentration. The precision (RSD), examined by five
S. Mahpishanian, F. Shemirani / Minerals Engineering 23 (2010) 823–825
replicate measurements of 50 lg L be 1.65%.
1
of Au solutions, was found to
3.7. Analysis of environmental samples In order to validate the accuracy and precision of the method, water samples and related spiked samples were analyzed by the modified-CIAME (Table 1).
4. Conclusion Modified-cold-induced aggregation microextraction (M-CIAME) was used as a sample preparation technique for the determination of gold in saline solutions. M-CIAME is simple and robust against a very high content of salt (up to 40%). Therefore, modified-CIAME is a powerful sample preparation technique for saline solutions and salt products.
Acknowledgment The authors extend their appreciation to University of Tehran for providing financial support to this research.
825
References Baghdadi, M., Shemirani, F., 2008. Cold-induced aggregation microextraction: a novel sample preparation technique based on ionic liquids. Analytica Chimica Acta 613 (1), 56–63. Basri Senturk, H., Gundogdua, A., Numan Bulut, V., Duran, C., Soylak, M., Elci, L., Tufekci, M., 2007. Separation and enrichment of gold(III) from environmental samples prior to its flame atomic absorption spectrometric determination. Journal of Hazardous Materials 149 (2), 317–323. Fazli, Y., Hassan, J., Karbasi, M.H., Sarkouhi, M., 2009. A simple spectrophotometric method for determination of gold(III) in aqueous samples. Minerals Engineering 22 (2), 210–212. Hope, G.A., Buckley, F.M., Munce, C.G., Woods, R., 2007. Gold enhanced spectroelectrochemical investigation of 2-mercaptobenzothiazole, isopropyl xanthate and butylethoxycarbonylthiourea adsorption on minerals. Mineral Engineering 20 (10), 964–969. Konecna, M., Komarek, J., 2007. Utilization of electrodeposition for electrothermal atomic absorption spectrometry determination of gold. Spectrochimica Acta Part B 62 (3), 283–287. Lupu, R., Nat, A., Ene, A., 2004. Determination of gold in Romanian auriferous alluvial sands and rocks by 14 MeV neutron activation analysis. Nuclear Instruments and Methods in Physico Research B 217 (1), 123–135. Shamsipur, M., Ramezani, M., 2008. Selective determination of ultra trace amounts of gold by graphite furnace atomic absorption spectrometry after dispersive liquid–liquid microextraction. Talanta 75 (1), 294–300. Tavakoli, L., Yamini, Y., Ebrahimzadeh, H., Nezhadali, A., Shariati, S., Nourmohammadian, F., 2008. Development of cloud point extraction for simultaneous extraction and determination of gold and palladium using ICPOES. Journal of Hazardous Materials 152 (2), 737–743. Tuzen, M., Saygi, K.O., Soylak, M., 2008. Novel solid phase extraction procedure for gold(III) on Dowex M 4195 prior to its flame atomic absorption spectrometric determination. Journal of Hazardous Materials 156 (1–3), 591–595.