Simultaneous Determination of Iron and Cobalt Using Spectrophotometry after Catanionic Mixed Micellar Cloud Point Extraction Procedure

Introduction

Iron and Cobalt are the most important metals in biological systems, as they are the constituent elements in haemoglobinand vitamin B₁₂ (Cyanocobalamin). The deficiency of these analytes might lead to deadly diseases like anaemiawhile the high levels of iron might causediseases like thalassemia.Excess of cobalt may result in cardiomyopathy or vasodilation in human beings.It is therefore important to determine thelevels of iron and cobaltaccurately.

Direct determination of these metals inwateris a complex process, because of their very lowconcentrations and the high interferences from other components in the solution. Hence, reducing the matrix effects is an important task prior to their determination. The cloud point extraction is an environmentally favourable technique which follows green chemistry principlesfor extraction. When the surfactants are heated they separate into two different phases at a particular temperature called cloud point temperature, the surfactant abundant phase and the water phase. Solutes/ metal ions can be removed into the surfactantphase. Incloud point extraction procedure,the two important factors for selection of surfactants is that the cloud point temperature should be close to room temperature and the other is extraction efficiency. The extraction of compounds is due to the hydrophobic and electrostatic interactions with the micelles. Maximum extraction efficiency is achieved by using two surfactants.

The method has been used for the extraction of metal complexes with ligands like APDC (ammonium pyrrolidinedithiocarbamate) [1– 4],8-HQ (8-hydroxyquinoline) [5, 6], 2-GB (2-guanidino benzimidazole) [7], TAN (1-(2-thiazolylazo)-2-naphthol) [8, 9 ],  PMBP (1-phenyl-3-methyl-4-benzoyl-5-pyrazolone) [10], PHBI (2-phenyl-1H-benzo[d] Imidazole) [11], MPMP (2-[(2-mercaptophenylimino)methyl]phenol) [3], Me-BTABr (2-[2-(6-methyl-benzothiazolylazo)]-4-bromophenol) [12], MPKO (methyl-2-pyridylketone oxime) [13], anthralin (1, 8-dihydroxyanthrone) [14] and ACDA (2-amino-cyclopentene-1-dithiocarboxylic acid) [15].The addition of salts also influences the cloud pointwhere the temperature decreases by salting out effect [16– 18].The retrieval of iron and cobalt in different matrices by cloud point extraction was reported in literature using expensive instruments likeatomic absorption spectrometry with graphite furnace (GFAAS) [12, 19], inductively-coupled plasma with OES(ICP-OES) [5, 6].

In this paper we report thespectrophotometric determination of Fe³⁺ and Co²⁺ metal ions simultaneously in the presence of thiocyanate ligand using catanionic mixed micelles of CTAB and SDS. The surfactantphase of catanionic mixed micellesformed from CTAB and SDS have both positive and negative entities of the surfactants [20], which resulted in a strong synergistic effect(indicated by a negative interaction parameter between the two surfactants(b) [21, 22] thereby increasing theefficiency of the extraction process.The factors affecting theextraction were optimised to get maximum efficiency and the developed system was used for the calculation of Fe³⁺ and Co²⁺ in different real samples of water.

Materials and Methods

Instrumentation

A Shimadzu spectrophoto meter was used for measuring absorbance. A systronics digital pH meter 335 was used for all pH measurements.

Reagents and Solutions

Analyticalgrade reagents were used.Sigma-Aldrich make Cetyltrimethylammonium bromide, CTAB and(Sodium dodecyl sulfate, SDS) were used. Aqueous solutions of 10% (w/v)CTABand 10% (w/v) SDS were made. Standard solutions of Fe³⁺ and Co²⁺ were made from ammonium ferric sulphate and cobaltous chloride respectively which are taken as stock solutions. An aqueous solution of the ligand, sodiumthiocyante (NaSCN) obtained from Lobachemie, India. 5 mol L^–1solution of NaSCN was made.

Experimental Procedure

In a graduated testtube, 0.15 mL of concentrated hydrochloric acid and standards of corresponding concentrations of analytes were added followed by 1.1 mL of 5mol dm^–3NaSCN, 1.1mL of 10% (w/v) CTAB and 50 µL of 10% (w/v) SDSand made up to 10 mL with Milli-Q water. The mixture was then heated to 50 °C for 15 minutes. After heating, two phases were observed. Phase separation was obtained completely after reducing the temperature of the system during a period of one hour. In this method surfactant rich phase was observed at the top and bulk aqueous phase was observed at bottom. The non-surfactant phase wasdecanted. Methanol was used to dissolve the surfactantphase containing the metal ions and absorbance was recorded at wavelengths of maximum absorbance (502 nm for Fe³⁺–SCN^– complex and 618 nm for Co²⁺–SCN^– complex).

Results and Discussion

To get maximum efficiency of the method, each reagent concentration was changed and keeping all other reagents constant and optimizing each reagent at a time.

Variation of % (v/v) of HCl

Three types of mineral acids (H₂SO₄, HNO₃ and HCl) were chosen for the initial study of the system. The recoveries of the analytes show that hydrochloric acid is the best acid for the extraction of these metal complexes simultaneously. The effect of HCl concentrationwas varied from  0 % (v/v) to 10 % (v/v). The extraction increases up to 1.5 % (v/v) of HCl and thereafter decreases. Figure 1 shows that the percentage concentration of HClfor the simultaneous extraction of Fe³⁺ and Co²⁺is 1.5 % (v/v).

 

Figure 1: Plot of recovery versus percentage concentration of HCl. Conditions: 0.55 mol L–1 of SCN–, 1.1 % CTAB (w/v), 0.05 % SDS (w/v), 50 °C of equilibration temperature, 15 minutes of equilibration time. Click here to View figure

Variation of the amount of SCN^–

The concentration of the monodentate ligand, SCN^– selected for complex formation with analytes Fe³⁺ and Co²⁺ was varied in the range (0.1 to 0.6) mol L^–1. The recoveriesincrease up to 0.55 mol L^–1concentration of SCN^–and then decrease for both the metals. Therefore, 0.55 mol L^–1 of SCN^–was used for the rest of the study(Fig.2).

Figure 2: Variation of amount of SCN–. Conditions: 1.5 % (v/v) of HCl, 1.1 % CTAB(w/v), 0.05 % SDS(w/v), 50 °C of equilibration temperature,15 minutes of equilibration time. Click here to View figure

Variation of % (w/v) of CTAB

Percentage of CTABwas changed from (0.1 to 1.2) % (w/v) and recovery of Fe³⁺ and Co²⁺was studied. The metal retrieval increases up to 1.1 % (w/v) of CTAB and then decreases (Figure 3).  1.1 % (w/v)CTAB was fixed for the rest of the study.

Figure 3: Plot of recovery versus% (w/v)CTAB. Conditions: 1.5 % (v/v) of HCl,0.55 mol L–1ofSCN–, 0.05 % (w/v) of SDS, 50 °C of equilibration temperature, 15 minutes of equilibration time. Click here to View figure

Optimization of % (w/v) of SDS

SDS concentration was varied from (0 – 0.1) % (w/v) to get maximum recovery. The extraction of analytes increases till 0.05 % (w/v) of SDS anddecreases thereafter (figure 4). Therefore, 0.05 %SDS concentration was used for maximum extraction of Fe³⁺ and Co²⁺.

Figure 4: Variation of % (w/v)of SDS. Conditions: HCl = 1.5 % (v/v) ,SCN– = 0.55 molL–1, CTAB = 1.1% (w/v) , equilibration temperature=50 °C, incubation time = 15 minutes. Click here to View figure

The metal extraction mechanism in for the mixed micellar system of CTAB and SDS can be explained by the following mechanism. The monodentate ligand, SCN^–and anionic surfactant, SDS, form a negative metal complex which is then form ion-pair complex with protons from strong acids or positive surfactant CTAB.

Optimization of incubation time and equilibration temperature

It is always advisable to have shortest incubation time and temperature close to room temperature along with maximum recovery of the method.In the present study the equilibration temperature was varied from 25 to 100 °C and equilibration time was changed from5 to 60 minutes. The optimum temperature was observed to be 50 °C and optimum time was found to be15 minutesrespectively.

Analytical figures of the method

The analytical parameters of the developed method were determined. The observed linearity ranges of Fe³⁺ and Co²⁺from the calibration graphs were found to be 0.139 – 0.838 µg mL^–1 and 5.89 – 35.4 µg mL^–1, respectively. Theequations obtained were A = 0.532446[Fe³⁺] + 0.004214 and A = 0.013357[Co²⁺] + 0.013000 with correlation coefficients of 0.9990 and 0.9934 for Fe³⁺ and Co²⁺. Thedetection limits for Fe³⁺ and Co²⁺ were as low as 1.54 ng mL^–1 and6.18 ng mL^–1, respectively. The preconcentration factor and phase volume ratio of the method are 40 and 0.025, respectively (Table 1).

Table 1: Analytical parameters for the two metals.

Parameter	Fe3+	Co2+
lmax (nm)	502	618
Linear range (mg mL–1)	0.13 – 0.84	2.9 – 35.4
Correlation coefficient (R2)	0.9990	0.9934
LOD (ng mL–1)	1.54	6.18
Preconcentration factor	40	40
Phase volume ratio	0.025	0.025
Extraction efficiency (%)	98.26	100.76

A comparison of the results obtained from the developed method with methods reported in literature for the retrieval of Fe³⁺ and Co²⁺ is given in Table 2.

Table 2: List of the details of the present method and previous methods

Analytes	Ligand	Surfactants	LOD	Technique	Matrix	References
Fe, Co and Ni	APDC	TX-114	19, 5 and 11 µg L-1 for Fe, Co and Ni.	FIA-FAAS	Waste, river, tap and sea water.	[9]
Fe	Ferron	TX-114	1.7 µg L-1	FI-FAAS	Water and milk	[42]
Co	PAN	TX-114	0.6 µg L-1	Spectrophotometry	Water samples	[14]
Co	Without	PONPE 7.5	10 ng L-1	ETAAS	Drinking water samples	[37]
Co, Ni	ACDA	TX-114	7.5 and 10 µg L-1 for Co and Ni	Spectrophotometry	Natural and waste water samples	[33]
Fe, Co	SCN–	CTAB and SDS	1.54 and 6.18 ng mL-1 for Fe and Co	UV-vis Spectrophotometry	Tap and sea water samples	Method developed in this paper.

Validation of the Method and Analysis of Real Samples

The developed cloud point extraction method usingCTAB and SDS mixed micellar system was employed for the simultaneous determination of Fe³⁺ and Co²⁺indifferentwater samples. 92 – 102 %spike recoveries were found (Table 3).

Table 3: Recovery values of Fe³⁺ and Co²⁺ in water samples along with spike recoveries.

Samples	Spiked (µg mL-1)		Detected (µg mL-1)		Recovery (%)
	Fe3+	Co2+	Fe3+	Co2+	Fe3+	Co2+
	–	–	0.0906±0.0023	1.733±0.06	–	–
Tap water	0.419	11.79	0.519±0.02	13.84±0.297	102.24±4.89	102.69±2.07
	0.698	23.57	0.783±0.04	25.62±1.09	99.2±5.65	101.34±4.36
	–	–	ND	ND	–	–
Sea water	0.419	11.79	0.403±0.02	11.27±0.36	96.18±5.18	95.59±3.05
	0.698	23.57	0.646±0.03	21.69±1.02	92.55±4.65	92.02±4.31
ND:Not Detected

Conclusion

A new cloud point extraction method based on catanionic mixed micelles of CTAB and SDS for thepreconcentration of Fe³⁺ and Co²⁺ and their determinationsimultaneously using spectrophotometry in different water samples in the presence of thiocyanate as ligand was developed. This new method is much simple and accurate and for the determination of Fe³⁺ and Co²⁺ at ng mL^–1 level.

Conflict of Interest

Contributing authors have no conflict of interest regarding the publication of this research work

Funding Resourse

there is no funding resourses.

References

1. Giokas, D. L.; Paleologos, E. K.; Tzouwara-Karayanni, S. M.;&Karayannis, M. I.J. Anal. At. Spectrom.2001, 16, 521–526
   CrossRef
2. Paleologos, E. K.; Giokas, D. L.; Tzouwara-Karayanni, S. M.; &Karayannis, M. I.Anal. Chim.Acta. 2002, 458, 241–248
   CrossRef
3. George, L. D.; Clésia, C. N.; Ana, R. A. N.; Marco, A. Z. A.;& Joaquim, A. N. Microchem J.2006, 82, 189–195
4. Dimosthenis, L. G.; Evangelos, K. P.; & Miltiades, I. K.Anal. Bioanal. Chem. 2002,373, 237–243
5. Francisco, L. F. S.; Wladiana, O. M.; & Gisele, S. L. Anal. 2015, 7, 9844–9849
6. Lingling, Z.; Shuxian, Z.; Keming, F.; Zhaosheng, Q.; &Jianrong, C. J. Hazard. Mater. 2012, 239-240, 206 – 212
7. Dallali, N.; Zahedi, M. M.; & Yamini, Y. Sci Iran. 2007 14, 291–296
8. Ghulam, A. K.; Tasneem, G. K.; Jameel, A. B.; Sirajuddin., Hassan, I. A.; Abdul, Q. S.; Hafeez, R. S.; Nida, F. K.; & Sham, K. W. J. Aoac Int.2010, 93, 1589–1594
9. Sidnei, G. S.; Pedro, V. O.; Fábio, R. P. R. J Brazil Chem Soc. 2010, 21, 234-239
10. Pei, L.; Hongbo, S.; Zhimei, S. J. Colloid Interface Sci. 2006, 304, 486–490
    CrossRef
11. Ghaedi, M.; Shokrollahi, A.; Niknam, K.; Soylak, M. Sep Sci Technol. 2009, 44, 773–786
    CrossRef
12. Valfredo, A. L.; Robson, S. F.; & Bruno, O. M. Sep. Purif. Technol.2007, 54, 349–354
13. Ghaedi, M.; Shokrollahi, A.; Ahmadi, F.; Rajabi, H. R.; Soylak, M.J. Hazard. Mater. 2008, 150, 533–540
    CrossRef
14. Assadollah, B.; Saeed, B.; & Mina, R. Microchem J. 2012, 100, 66–71.
    CrossRef
15. Safavi, A.; Abdollahi, H.; Hormozi, N. M. R.; Kamali, R. Spectrochimi Acta A. 2004,60, 2897–2901
    CrossRef
16. Tayyebeh, M.; Abbas, A.; Afrouz, M. Talanta, 2007, 71, 610–614
    CrossRef
17. Alaa, S. A.; Mohammed, A. K. Talanta, Y. M. RSC Adv.2015, 5, 52095–52100
    CrossRef
18. Wael, I. M.; Al-Ahmad, Z. A.; Mohamed, M. H. Anal. Methods. 2013, 5, 5234–5240
19. Raúl, A. G.; José, A. G.; Roberto, O.; Luis, D. M.; Soledad, C. Talanta. 2008, 76, 669–673
20. Sylvain, P.; Michael, G. J Colloid Interface Sci. 2009, 337, 472–484
    CrossRef
21. Sara, B. L.; Xiang, W.; Mohammad, R. I.; Emily, J. D.;Douglas, S. E. Phys. Chem.Chem. Phys. 2009, 11, 9315–9325
22. Shakerian, F.; Dadfarnia, S.; Haji Shabani, A. M.JIran Chem Soc.2009,6, 594–601
    CrossRef

---

This work is licensed under a Creative Commons Attribution 4.0 International License.