Cloud point extraction, preconcentration and spectrophotometric determination of trace amount of manganese(II) in water and food samples

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 131 (2014) 138–144

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Cloud point extraction, preconcentration and spectrophotometric determination of trace amount of manganese(II) in water and food samples Ayman A. Gouda ⇑ Chemistry Department, Faculty of Science, Zagazig University, Zagazig 44519, Egypt Faculty of Public Health and Informatics, Umm AL-Qura University, Makkah, Saudi Arabia

h i g h l i g h t s

g r a p h i c a l a b s t r a c t

 A new CPE procedure for the

0.5

0.4

Absorbance

preconcentration and determination of Mn(II) ion.  The influence of analytical parameters were optimized.  The detection and quantification limits were 0.80 and 2.67 ng mL1, respectively.  The method was applied in water and food samples.

0.3

0.2

0.1

0 0

25

50

75

100

125

150

175

200

225

-1

Quinalizarin concentration (µmol L )

a r t i c l e

i n f o

Article history: Received 8 March 2014 Received in revised form 9 April 2014 Accepted 17 April 2014 Available online 26 April 2014 Keywords: Cloud point extraction Manganese(II) determination Spectrophotometry Quinalizarin Water samples Food samples

a b s t r a c t A new cloud point extraction (CPE) process using the nonionic surfactant Triton X-114 to extract manganese(II) from aqueous solution was investigated. The method is based on the complexation reaction of manganese(II) with 1,2,5,8-tetrahydroxyanthracene-9,10-dione (quinalizarin) in the presence of borate buffer at pH 8.5 and micelle-mediated extraction of the complex. The enriched analyte in the surfactant-rich phase was determined by spectrophotometry at 528 nm. The optimal extraction and reaction conditions (e.g. pH, reagent and surfactant concentrations, temperature and centrifugation times) were evaluated and optimized. Under the optimized experimental conditions, the analytical characteristics of the method (e.g., limit of detection (LOD), linear range, preconcentration and improvement factors) were obtained. The proposed CPE method showed linear calibration within the range 5.0–200 ng mL1 of manganese(II) and the limit of detection of the method was 0.8 ng mL1 with an preconcentration factor of 50 when 25 mL of sample solution was preconcentrated to 0.5 mL. The relative standard deviation (RSD) and relative error were found to be 1.35% and 1.42%, respectively (CMn(II) = 150 ng mL1, n = 6) for pure standard solutions. The interference effect of some cations and anions was also studied. In the presence of foreign ions, no significant interference was observed. The method was applied to the determination of manganese(II) in water and food samples with a recovery for the spiked samples in the range of 95.87–102.5%. Ó 2014 Elsevier B.V. All rights reserved.

Introduction ⇑ Address: Chemistry Department, Faculty of Science, Zagazig University, Zagazig 44519, Egypt. Tel.: +20 552420204; fax: +20 552308213. E-mail address: [email protected] http://dx.doi.org/10.1016/j.saa.2014.04.075 1386-1425/Ó 2014 Elsevier B.V. All rights reserved.

Manganese; Mn(II) is an essential trace element that can be found in several food items, such as tea, grains, rice, soya beans,

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eggs, nuts and cereals. This metal is essential for humans and other species of the animal kingdom. Some organisms, such as diatoms, mollusks and sponges, can accumulate manganese. Manganese is necessary for the proper function of several enzymes and is an essential micro-nutrient for the function of the brain, nervous system and normal bone growth. It optimizes enzyme and membrane transport functions [1,2]. Similar to other essential metals, both excess and deficiency of manganese in the body can cause serious impairment of vital physiological and biochemical processes, excessive intake can cause lesions, headache, psychotic behavior, drowsiness and other related symptoms and/or diseases [3,4]. Manganese is usually present at trace levels in various environmental samples. Therefore, very sensitive techniques are necessary for monitoring of manganese in water and food samples such as spectrophotometry. But the direct determination of Mn(II) at very low concentrations is often difficult because of insufficient sensitivity of this technique as well as the matrix interferences occurring in real samples. For this reason, a preliminary separation and preconcentration step is often required. Many different techniques have been applied to the measurement of manganese, including electrochemical analysis which is one of the most sensitive analytical techniques, hence it has been frequently applied to trace-metal analysis [5–8]. Manganese speciation in human milk was conducted using size exclusion chromatography and strong anion exchange chromatography with ICP-MS detection [9]. Capillary electrophoresis-ICP-MS has very recently been applied to Mn speciation in liver extract [10]. Svendsen and Lund studied speciation of Cu, Fe and Mn in beer using ion exchange separation and size-exclusion chromatography in combination with electrothermal atomic absorption spectrometry [11].

Speciation analysis of Mn(II) in tea leaves and infusions with the aid of flame-AAS technique was successfully performed by Ozdemir and Güçer for total and soxhlet extractable organic-bound manganese fractions [12]. Manganese determination at trace levels in real samples is frequently difficult because of low concentration of the metal and matrix interferences. In this manner, the determination generally is associated to preliminary step for enrichment and elimination of interfering species. Several enrichment procedures have been developed for the determination of Mn(II), involving different analytical techniques such as coprecipitation [13–18], liquid– liquid [19,20], solid-phase extraction (SPE) [21–35]. Many cloud-point extraction (CPE) methods for Mn(II) determination have been developed involving different kinds of analytical techniques, and several chelating agents [36–50] have been used to determine and preconcentrate traces of Mn(II) from various samples. The proposed method was compared to a variety of other separation/preconcentration methods for determination of manganese reported recently in the literature. The distinct characteristics are summarized in Table 1. The use of micellar systems such as CPE for separation and preconcentration has attracted considerable attention in the last few years mainly because it is in agreement with the ‘‘green chemistry’’ principles. Green chemistry can be defined as those procedures for decreasing or eliminating the use or generation of toxic substances for human health and for the environment [51]. CPE is a green method for the following reasons: (a) it uses as an extractor media diluted solutions of the surfactants that are inexpensive, resulting in the economy of reagents and generation of few laboratory residues; and (b) surfactants are not toxic, not volatile, and not

Table 1 Comparison of the proposed method with reported separation/preconcentration CPE methods for manganese. Reagent

Surfactant

Sample volume (mL)

SRP diluting agent

Detection system

LODa (ng mL1)

EFb/PFc

Sample

Ref.

Magneson I

Triton X-114

25

FAAS

2.9

19

Water and food

[36]

PAR Br-TAO PMBP PMBP

OP-7 Triton X-114 Triton X-100 Triton X-100

100 2.8 10 10

FAAS FAAS GFAAS FAAS

5 0.5 0.02 1.45

20 14 31 20

Natural water Food Water Water

[37] [38] [39] [40]

PMBP TAR

– Triton X-114

10 70

GFAAS FAAS

0.02 0.6

31 84

Triton X-114

50

FAAS

0.28

57.6

Water Saline effluents of a petroleum refinery Water

[41] [42]

TAN 8-quinolinol

Triton X-114

100

1.0 mL of 0.1 mol L1 HNO3 in ethanol Distilled water Sulfuric acid 200 lL (0.1 mol L1 HNO3) 500 lL methanol in 0.1 mol L1 HNO3 – 500 lL methanol 1.0% (v/v) HNO3 in 200 lL methanol in 0.1 mol L1 HNO3 200 lL methanol in 0.1 mol L1 HNO3

FAAS

33

96

Water

[44]

Me-BTABr PAN

Triton X-114 Triton X-114

3.0 50

FAAS FAAS

0.7 0.39

17 49.1

Food Milk and water

[45] [46]

8-Hydroxyquinoline

Triton X-100

10

FAAS

1.9

10–20

Tea and water

[47]

TTA Dithizon

Triton X-114 Triton X-114

– –

–

ICP-OES ICP-OES

0.1–2.2 0.22

42–97 9

[48] [49]

Br-PADAP

Triton X-114

50

0.4 mL HNO3 (1:1 v/v)

ICP-OES

0.83

25

Quinalizarin

Triton X-114

25

500 lL methanol

S

0.80

103/50

Water Petroleum industry produced water Saline oil-refinery saline effluent and vegetable leaves Water and food

400 lL methanol in 0.1 mol L1 HNO3 1.0 mL methanol in 0.1 mol L1 HNO3

[43]

[50]

Present work 0

SRP: surfactant rich phase, Magneson I: p-nitrophenylazoresorcinol, PAR: 4-(2-pyridylazo)resorcinol, PAN: 1-(2-pyridylazo)-2-naphthol, Br-TAO: 4-(5 -bromo-20 -thiazolylazo)orcinol, PMBP: 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone, TAR: 2-(20 -thiazolylazo)-resorcinol, TAN: 1-(2-thiazolylazo)-2-naphthol, TTA: 1-(2-thenoyl)-3,3,3-trifluoraceton reagent, Me-BTABr: 2-[20 -(6-methyl-benzothiazolylazo)]-4-bromophenol, Br-PADAP: 2-(bromo-2-pyridylazo)-5-diethyl-amino-phenol, FAAS: flame atomic absorption spectroscopy, GFAAS: graphite furnace atomic absorption spectroscopy, ICP OES: inductively coupled plasma optical emission spectrometry, S: spectrophotometry. a Limit of detection. b Enrichment factor. c Preconcentration factor.

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easily flammable, unlike organic solvents used in liquid–liquid extraction [52–54]. CPE consist of three simple steps: (1) solubilization of the analytes in the micellar aggregates; (2) clouding; (3) phase separation for analysis. When a surfactant solution is heated over a critical temperature, the solution easily separates into two distinct phases: one contains a surfactant at a concentration below, or equal to, a critical micelle concentration; the other is a surfactant-rich phase. The hydrophobic compounds initially present in the solution and bound to the micelles are extracted to the surfactant-rich phase. This phenomenon is observed, in particular, for polyoxyethylene surfactants and can be attributed to the two ethylene oxide segments in the micelle that repel each other at low temperature when they are hydrated and attract each other when the temperature increases owing to the dehydration. Quinalizarin (1,2,5,8-tetrahydroxyanthraquinone) is a hydroxyl anthraquinone reagent which has been used as a colorimetric reagent for determination of some metal ions [55–60]. It exhibits an acid-base indicator behavior—orange in acidic form (neutral), blue in mild base (deprotonation of one hydroxyl group occurs) and purple in strong base (deprotonation of two hydroxyl groups occur). In the present work, 1,2,5,8-tetrahydroxyanthracene-9,10dione (quinalizarin) was used for the cloud point extraction (CPE) preconcentration of Mn(II) after the formation of a complex and spectrophotometric determination using Triton X-114. The factors influencing the efficiency of CPE extraction and spectrophotometric determination were systematically studied. The proposed CPE method was simple, selective and sensitive for the accurate determination of Mn(II) in water and food samples without interferences. Thus, the proposed method was successfully applied to the determination of trace amount of Mn(II) in water and food samples with satisfactory results. Experimental Apparatus All absorption spectra were made using Varian UV–Vis spectrophotometer (Cary 100 Conc., Australia) equipped with a 5.0 mm quartz cell was used for absorbance measurements. This spectrophotometer has a wavelength accuracy of ±0.2 nm with a scanning speed of 200 nm min1 and a bandwidth of 2.0 nm in the wavelength range of 200–900 nm. Hanna pH-meter instrument equipped with a combined glass-calomel electrode (Portogal) (HI: 9321) was used for checking the pH of prepared buffer solutions. A centrifuge with 25 mL calibrated centrifuge tubes (Isolab, Germany) were used to accelerate the phase separation process. A thermostated water bath with good temperature control was used for the CPE experiments. Reagents and solutions All chemicals used in this work, were of analytical reagent grade and were used without further purification. Bidistilled water was used to prepare all solutions. Laboratory glassware was kept in dilute nitric acid at least overnight and subsequently washed with bidistilled water and dried in a dust-free environment. Manganese(II) stock solution containing 500 lg mL1 was prepared by Mn(NO3)24H2O (Merck, Darmstadt, Germany) in a 1.0% nitric acid solution. Working manganese standard solution 200 lg mL1 was prepared on a daily basis by dilution from the stock standard. The non-ionic surfactant polyethylene glycol tertoctylphenyl ether (Triton X-114) (Sigma–Aldrich, USA) was used without further purification. Aqueous 0.2% (v/v) solution of Triton

X-114 was prepared by dissolving 0.2 mL of Triton X-114 in 100 mL of bidistilled water in 100 mL volumetric flask with stirring. A solution of 1.0  103 mol L1 quinalizarin (Friedrich Bayer & Co.) was prepared by dissolving appropriate amounts of this reagent in absolute ethanol (Merck). Acetate (3.6–6.0), borate (7.0–8.5) and ammonia (8.5–10) buffers were used to adjust the pH of solutions of manganese [61]. The solutions of various cations and anions used for the interference study were obtained from the respective high purity inorganic salts (Aldrich) by proper dilution in bidistilled water. Procedure An aliquot of manganese(II) standard solution was transferred to a 25 mL centrifuge tube, 1.0 mL of the 1.0  103 mol L1 quinalizarin solution and 3.0 mL of borate buffer solution (pH 8.5) were added. This was followed by the addition of 1.0 mL of (0.2% v/v) surfactant Triton X-114 solution. The solution was diluted to the mark (25 mL) with bidistilled water. This system was heated in a water bath at 50 °C for 10 min. Since the surfactant density is 1.37 g mL1, the surfactant rich phase typically settles through the aqueous phase. To separate the phases, the mixture was centrifuged for 5.0 min at 5000 rpm. After cooling in an ice-bath for 5.0 min, the surfactant-rich phase became a viscous phase, which could then be separated by inverting the tubes to discard the aqueous phase. The surfactant-rich phase of this procedure was dissolved and diluted to 0.5 mL with methanol and transferred into a 0.5 mL quartz cell. The preconcentration factor was 25/0.5 = 50 for standard solutions during calibration. The absorbance of the solution was measured at 528 nm. The blank solution was submitted to the same procedure with Mn(II). Procedure for real samples Analysis of water samples Prior to the preconcentration procedure, tap water, river water, sea water and mineral water samples were filtered through a 0.45 lm pore size membrane filter to remove suspended particulate matter and then were stored at 6 °C in the dark. To a 25 mL water sample, 1.0  103 mol L1 quinalizarin, 3.0 mL of borate buffer solution (pH 8.5) and 1.0 mL of a solution containing Triton X-114 (0.2% v/v) were added. After phase separation, the surfactant-rich phase was completed to 500 lL by methanol. The final solution was determined by spectrophotometry. Analysis of food samples The food samples (tomato paste, white bread, spinach, lettuce and cabbage) were purchased in supermarkets at Egypt. First, spinach, lettuce and cabbage samples were cleaned with tap water and double distilled water. Then, these samples, tomato paste and bread samples were dried at 110 °C. Each of the dried varieties of samples were ground to reduce particle size and then thoroughly mixed to ensure homogeneity samples individually. Masses of 500 mg of tomato paste, white bread, spinach, lettuce and cabbage were transferred into separate 250 mL beakers and 5.0 mL of a solution of nitric acid 1:1 (v/v) was added to moisten the samples thoroughly. This was followed by adding 10 mL of concentrated nitric acid and heating on a hot plate (150 °C) for 4.0 h. After cooling to room temperature, 5.0 mL of concentrated perchloric acid was added drop wise. The beaker was heated gently until completion of sample decomposition resulting in a clear solution. This was left to cool down and then was transferred into a 100 mL volumetric flask by rinsing the interior of the beaker with small portions of 0.1 M nitric acid and the solution was filled to the mark with bidistilled water. The samples were analyzed immediately after preparation by spectrophotometry.

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O

OH

Results and discussion To check the specificity of quinalizarin for Mn(II) complexation in water and food samples, the experiments were performed on standard solution of Mn(II) and water and food samples spiked with Mn(II). Fig. 1 shows the absorption spectra of a standard solution of Mn(II) complex with quinalizarin which extracted by CPE at pH = 8.5 and has a maximum absorbance at 528 nm in surfactant-rich phase and the complex formed without CPE was measured at 528 nm against a reagent blank. The Mn(II) might react with quinalizarin [58] and form the ML2 chelate as shown in Fig. 2.

OH O

O

OH

Mn

Optimization of the experimental conditions

OH Effect of pH Cloud point extraction of manganese was performed in different pH buffer solutions. The separation of metal ions by the CPE method involves prior formation of a complex with sufficiently hydrophobic character to be extracted into the small volume of surfactant-rich phase, thus obtaining the desired preconcentration. Extraction yield depends on the pH at which complex formation is carried out. Fig. 3 shows the effect of pH on the absorbance of manganese complex. It can be seen that the absorbance increases with an increase in pH up to 8.5. Hence the optimum pH value of 8.5 was chosen. In addition, the influence of the buffer amount was assessed, while the other experimental variables, except buffer solution amount, remained constant. The results have shown that if 3.0 mL or larger volume of buffer solution was added in 25 mL solution, no obvious variation took place in the absorbance. Therefore it was concluded that addition of 3.0 mL of buffer solution throughout the course of experiment would serve the purpose.

O OH

OH

O

Mn-quinalizarin complex Fig. 2. The formed Mn(II)–quinalizarin complex.

0.5

0.4

Absorbance

Effect of quinalizarin concentration Twenty-five milliliters of a solution containing 3.75 lg of Mn(II), 0.2% Triton X-114 and at a medium buffer of pH 8.5 containing various amounts of quinalizarin were subjected to the cloud point preconcentration process. The effect of quinalizarin concentration on the extraction and determination of Mn(II) complex was investigated in the range 2.0  104–2.0  103 mol L1. The absorbance as a function of the concentration of the complexing agent is shown in Fig. 4. The absorbance increased up to a quinalizarin concentration of 1.0  103 mol L1 for Mn(II) and

O

0.3

0.2

0.1

0 3

4

5

6

7

8

9

10

11

pH Fig. 3. Effect of pH of borate buffer on the absorbance after CPE. Conditions: Mn(II), 150 ng mL1; quinalizarin, (1.0  103 mol L1) and Triton X-114, 0.2% (w/v). Other experimental conditions are described under procedure.

reached near 100% quantitative extraction efficiency. A concentration of 1.0  103 M was chosen as the optimum concentration for the determination of Mn(II).

Fig. 1. Absorption spectra of manganese(II)-quinalizarin complex without CPE (———) and with CPE (-..-..-). Conditions: quinalizarin, (1.0  103 mol L1); Triton X-114, 0.2% (w/v) and pH 8.5.

Effect of nonionic surfactant (Triton X-114) concentration A successful CPE would be one which maximizes the extraction efficiency through minimizing the phase volume ratio, thus maximizing its concentrating factor. Three non-ionic surfactant (Triton X-114 Triton X-100 and Tween-80) were tested, and the experimental results show that the Triton X-114 was the best one of the three tested surfactants for the extraction of Mn(II)–quinalizarin complex. The variation in absorbance of manganese within the Triton X-114 concentration range of 0.01–0.5% v/v was examined. The

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incubation time was studied in the range of 5.0–20 min. An incubation time of 10 min was sufficient for the separation process. A centrifuge time period of 5.0 min was selected as optimum, as complete separation occurred within this time and no appreciable improvements were observed for longer periods.

0.5

Absorbance

0.4

0.3

0.2

0.1

0 0

25

50

75

100

125

150

175

200

225

-1

Quinalizarin concentration ( mol L ) Fig. 4. Effect of quinalizarin concentration on the absorbance after CPE. Conditions: Mn(II), 150 ng mL1; Triton X-114, 0.2% (w/v) and pH 8.5. Other experimental conditions are described under procedure.

absorbance of the complex was increased by increasing the Triton X-114 concentration up to 0.2% (v/v). So a concentration 0.2% (v/ v) was chosen as the optimum surfactant concentration in order to achieve factor and the highest possible absorbance. The results are shown in Fig. 5. Effects of equilibration temperature and time To achieve easy phase separation and efficient preconcentration, it is imperative to optimize the equilibration temperature and incubation time. It was desirable to employ the shortest equilibration time and the lowest possible equilibration temperature, as a compromise between completion of extraction and efficient separation of phases. The influence of the equilibration temperature was investigated by varying the temperature from 30 to 70 °C. The results demonstrate that in the temperature range of 40–60 °C, the extraction efficiency for the Mn(II)–quinalizarin complex was constant. Therefore, an equilibration temperature of 50 °C was chosen for further experiments. Higher temperatures lead to the decomposition of quinalizarin and the reduction of extraction yield. The dependence of extraction efficiency upon

Effects of diluent High viscosity of the surfactant-rich phase is drastically decreased using diluting agents. For the spectrophotometric method, the addition of a diluent into the surfactant-rich phase is often needed to obtain a homogeneous solution with compatible viscosity. Methanol, ethanol, acetone, N,N-dimethylformamide, and acetonitrile were tested as diluent solvents. Surfactant-rich phase was found to be freely soluble in methanol. Therefore, methanol was chosen in order to have appropriate amount of sample for transferring and measurement of the absorbance of the sample and also a suitable preconcentration factor. Hence the surfactant-rich phase was completed to 500 lL by methanol. Therefore, a preconcentration factor of 50 was archived using the proposed method. Interference studies In view of the high selectivity provided by spectrophotometry at the characteristic absorption wavelength of 528 nm, the only interference may be attributed to the preconcentration step. In order to perform this study, interfering ions in different concentrations were added to a solution containing 150 ng mL1 Mn(II) solution and were applied the proposed method. The tolerance limits were determined for a maximum error of ±5.0% and the results are given in Table 2. These results demonstrate that the common coexisting ions did not have significant effect on the extraction and determination of Mn(II). Quinalizarin method was observed to be fairly selective for Mn(II) ions at pH 8.5. Since commonly present ions in water and food samples did not affect significantly the recovery of Mn(II), the method can therefore be applied to determination of Mn(II) in water and food samples. Analytical characteristics The calibration graphs were obtained by preconcentrating 25 mL of standard solutions containing known amounts of the analyte in the presence of Quinalizarin and Triton X-114 in a medium buffered at pH 8.5 for CPE of Mn(II), and under the experimental

Table 2 Effect of interferent ions on preconcentration and recoveries of 200 ng mL1 manganese (n = 3).

0.5

Absorbance

0.4

0.3

0.2

0.1

0 0

0.1

0.2

0.3

0.4

0.5

0.6

Triton X-114 (% v/v) Fig. 5. Effect of Triton X-114 concentration on the absorbance after CPE. Conditions: Mn(II), 150 ng mL1; quinalizarin (1.0  103 mol L1) and pH 8.5. Other experimental conditions are described under procedure.

a

Ions

Added as

Maximum amount tolerable (mg L1)

Recovery (%) ± SDa

K+ Na+ Al3+ Cr3+ Fe3+ Ca2+ Mg2+ Zn2+ Pb2+ Co2+ Ni2+ Cd2+ Cu2+ NO 3 SO2 4  Cl F

KCl NaCl Al(NO3)3 Cr(NO3)3 FeCl3 CaCl2 MgCl2 ZnSO4 Pb(NO3)2 Co(NO3)2 NiSO4 Cd(NO3)2 CuSO4 KNO3 Na2SO4 NaCl NaF

5.0 12 1.0 1.0 1.0 2.0 1.0 1.0 1.0 1.0 1.0 1.0 0.5 5.0 5.0 5.0 5.0

97.0 ± 2.0 98.0 ± 2.0 96.0 ± 2.0 97.0 ± 2.0 95.0 ± 3.0 96.0 ± 4.0 97.0 ± 2.0 98.0 ± 2.0 96.0 ± 3.0 95.0 ± 2.0 96.0 ± 2.0 98.0 ± 3.0 97.0 ± 3.0 98.0 ± 2.0 97.0 ± 3.0 96.0 ± 2.0 95.0 ± 2.0

Mean ± standard deviation.

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conditions specified in the procedure. Linear relationships between the absorbance measured and the concentration of the metal in solution were obtained. Table 3 summarizes the analytical characteristics such as regression equation, linear range, and limits of detection and quantification, reproducibility and preconcentration and enhancement factors. The limit of detection, defined as CL = 3 SB/m (where CL, SB and m are limit of detection, standard deviation of the blank, and slope of the calibration graph, respectively) was 0.8 ng mL1. Because the amount of Mn(II) in 25 mL of sample solution is measured after preconcentration by CPE in a final volume of 0.5 mL (0.1 mL surfactant-rich phase + 0.4 mL methanol), the standard solutions are preconcentrated by a factor of 50. The enhancement factor calculated as the ratio of the slope of the calibration graph obtained after preconcentration procedure with CPE to the slope of calibration graph without CPE was also approximately 103. The relative standard deviation (RSD) and relative error for six replicate measurements of 150 ng mL1 of Mn(II) were found to be 1.35% and 1.42%, respectively. Analytical characteristics of the proposed method are shown in Table 3.

Table 4 Determination of manganese in water and food samples using the proposed method (n = 3). Samples Water samples Tap water

River water

Sea water

Mineral water

Food samples Tomato paste

White bread Spinach

Determination of manganese in water samples

Lettuce

In order to test the reliability of the proposed methodology, it was applied to the determination of manganese in tap water, river water, sea water and mineral water. For this purpose, 25 mL of each of the samples were preconcentrated with 1.0  103 mol L1 quinalizarin and 0.2% (v/v) Triton X-114 following the proposed method. The results are shown in Table 4. For calibration purposes, the working standard solutions were subjected to the same preconcentration procedure as used for the analyte solutions. In addition, the recovery experiments of different amounts of manganese were carried out, and the results are also shown in Table 4. The results indicated that the recoveries were reasonable for trace analysis, in a range of 95.87–99.42% and confirm the validity of the proposed method.

Table 3 Optimum conditions and analytical characteristics of the proposed method with and without CPE. Parameters

With CPE

Without CPE

Concentration of quinalizarin Concentration of surfactant pH Volume of borate buffer (mL) Equilibrium temperature (°C) Equilibrium time (min) Centrifugation rate (rpm) Centrifugation time (min) Diluent (mL) k max (nm) Calibration range (ng mL1) Molar absorptivity (L mol1 cm1) Sandell sensitivity (ng cm2) Regression equation (n = 6)a Slope Intercept Correlation coefficient (r) Limit of detection (ng mL1) Limit of quantification, (ng mL1) Reproducibility (RSD, %) (n = 6)

1.0  103 M 0.2% v/v 8.5 3.0 50 10 5000 5.0 0.5 528 5.0–200 2.101  106

1.0  103 M – 8.5 3.0 mL – – – – – 528 500–10,000 1.6189  104

0.0026

3.39

0.0031 0.0143 0.9998 0.80 2.67 1.35 (150 ng mL1) 50 103

0.00003 0.0053 0.9990 130 433 2.60 (8000 ng mL1) – –

Preconcentration factorb Enrichment factor a

a b

1

(ng mL – 50 100 – 50 100 – 50 100 – 50 100

(lg g1) 0 10 20 0 10 0 10 0 10 0 10

Found ± SD (ng mL1)

Recoverya (%)

1.74 ± 0.10 50.0 ± 0.80 100.0 ± 1.30 2.16 ± 0.16 51.0 ± 1.10 99.50 ± 1.40 7.80 ± 0.20 56.0 ± 0.90 107.0 ± 1.50 2.35 ± 0.10 50.5 ± 1.0 98.0 ± 1.20

– 96.90 98.43 – 98.0 97.55 – 97.20 99.42 – 96.70 95.87

NDb 9.82 ± 0.25 19.20 ± 0.60 3.20 ± 0.36 13.0 ± 0.90 24.60 ± 1.10 35.0 ± 1.40 20.0 ± 1.0 30.60 ± 1.40 37.80 ± 1.20 49.0 ± 1.50

– 98.20 96.0 – 98.50 – 101.10 – 102.0 – 102.5

)

Average of three determinations with 95% confidence level. Not detected.

Determination of manganese in food samples The proposed method was applied to the determination of manganese in food samples (tomato paste, white bread, spinach, lettuce and cabbage) collected from supermarkets and street markets in Zagazig, Egypt. These samples were subjected to digestion, preconcentration and manganese determination using the proposed procedure. The results are shown in Table 4. The percentage recovery (R) was calculated by using the equation:

R ¼ f100ðC m  C 0 Þ=mg: where Cm is a value of metal in a spiked sample, C0 is a value of metal in a sample and m is the amount of metal spiked. The obtained recoveries were reasonable for trace manganese analysis in food matrices, in a range of 96–102.5%. The results confirmed that the procedure is not affected by substances present in the material analyzed. The levels of manganese found in foods indicate that they are suitable for human consumption. Conclusion The proposed cloud point extraction was successfully applied for preconcentration and determination of trace amount of manganese(II) in water and food samples by detection using spectrophotometry. This study allowed the development of a new, rapid, easy to use, safe environmentally friendly and inexpensive methodology. Triton X-114 is of relatively low-cost and low toxicity. Quinalizarin is a very stable, and fairly selective complexing reagent. The proposed method showed good precision, accuracy and sensitivity for the determination of trace manganese metal in various water and food samples. References

1

A = a + bC, where C is the concentration of manganese(II) in ng mL . Preconcentration factor is defined as the ratio of the initial solution volume to the volume of surfactant rich phase. b

Cabbage

Added

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