Monitoring Of Copper Content In Some Food Samples Using

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Monitoring Of Copper Content In Some Food Samples Using

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Sys Rev Pharm 2021;12(2):219-230
A multifaceted review journal in the field of pharmacy

Monitoring Of Copper Content In Some Food Samples Using Micro Extraction Combined With Spectrophotometric Technique

Zianab Tariq1, Shaimaa Adnan*2

Department of Chemistry, College of Sciences ,University of Al-Qadisiyah ,Dewanyia,Iraq Department of chemistry, College of Education,University of Al-Qadisiyah, Dewanyia, Iraq2
Corresponding Author: [email protected]

A n organic reagent namely 2-(2-bromophenyl)imino)methyl)-4- (5,6-

dimethylpyridin-2-yl)diazenyl)phenol (R) was synthesized" ,characterized" and

used for the determination" of copper" after preconcentration using "Dispersive

liquid- liquid microextraction(DLLME) .In this precocentration method ,ethanol

and acetone were used as extraction and disperser solvents respectively and" the




yl)diazenyl)phenol" was used as a chelating agent for the extraction of" Cu(II),Uv-

Vis spectrophotometry was applied for the quantitation of the analyte after

preconcentration. The effect of various parameters on the extraction was

investigated,such as disperser and extraction solvent type and volume,,pH and

concentration of chelating agent.At optimum condition,the enrichment factors of

(105) was obtained ,the calibration graph was linear in the range (10-100) μg L-1

Cu +2" with detection limit of" (2.79) μg L-1 and "relative standard deviation"

(RSD) for seven "replicate measurements" of 20 μg L-1 of Cu +2 was (1.75)%."The

method was applied to the determination of" Cu +2 in some Bee honey samples.

Keywords: azo dyes, pyridine, shiff base, chelate complexes
Shaimaa Adnan Department of chemistry, College of Education ,University of Al-Qadisiyah, Dewanyia, Iraq2 *Corresponding author: Shaimaa Adnan email-address: [email protected]


Copper is widely distributed in nature and is

nutritionally essential metal, it plays an important role in

carbohydrate and lipid metabolism but it be comes toxic

to human if a large amount is accumulated in the tissue,

the main sources of this metal intake are drinking water

and food (1-5 ) . the quantification of copper in food is

very important considering the toxicity of this metal

therfore the monitoring of copper in food samples even at

ultra trace level is very essential , but such analyses are

difficult because such samples contain low concentration

of copper . several preconcentration procedures to

determine copper have been devised involving separation

techniques such as cloud point extraction (6 ), solid

phas extraction ( 7) , coprecipitation ( 8 ) , and dispersive

Liquid – Liquid microextraction ( 9 ) Dispersive liquid-

liquid microextraction (DLLME) is an extraction

technique developed within the last decade, which

involves the dispersion of fine droplets of extraction

solvent in an aqueous sample. Partitioning of analytes

into the extraction phase is instantaneous due to the very

high collective surface area of the droplets. This leads to

very high enrichment factors and very low solvent

consumption , relative to other solid or liquid phase

extraction methods(10).

Different conventional spectrophotometric techniques

have been already combined with DLLME for trace-

metals analysis (11-16), Among them, UV-Vis has been,

by far, the most widely used due to its simplicity,

availability versatility, speed, precision ,accuracy, and

cost-effectiveness. This technique is normally used in

analytical chemistry for quantitative determination of

different analytes such as transition metal ions, biological

macromolecules and highly conjugated organic

compounds ,

In the present" work, a new azo –schiff base reagent,

namely 2-(2-bromophenyl)imino)methyl)-4- (5,6-



synthesized ,characterized, and" exploited as a laboratory-made complexing agent to investigate the Dispersive liquid-liquid microextraction methodology for preconcentration of ultra trace amounts of copper ion using ethanol (extractant solvent) and acetone (disperser solvent) "and their determination by UV- Vis spectrophotometry. . The developed method was applied for the determination of " ultra trace amounts of copper(II) in bee honey samples

experimental Apparatus
(FTIR)Spectra(4000-400cm-1)in KBr disk were recorded on SHIMADZU FTIR-8400S fourier. transform. melting point were measured using Stuart, UK. Elemntal Analysis 3764,carlo erba Europ. 1HNMR were recorded on fourier transformation bruker spectrometer, operating at (400MHz) with (DMSO-ds) measurments were made at Department of chemistry, kashan university, Iran . For pH determinations, a Philip PW model 9421pHmeter with a combined glass electrode was used"

Reagents and Solutions

All the chemicals used were of analytical reagent grade,

and used without further purification. Distilled and

deionized water was used for diluting the samples and




5,6dimethylpyridine, salicylaldehyde , 2-bromoaniline

and ethanol were purchased from (GCC, England). Stock

solutions of Cu(II) ion (1000 mg L-1) were prepared by

dissolving (2.686g)CuCl2.2H2O (Merck) in deionized

water, respectively. Working standard solutions of metal

ion were freshly prepared by appropriate dilution of the

stock standard solution.. A acetate buffer solution (0.1

mol L–1) was prepared from acetic acid and sodium

acetate at different pH..



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Monitoring Of Copper Content In Some Food Samples Using Micro Extraction Combined

With Spectrophotometric Technique

" The reaction mixture was stirred for another 2 hours at





(0-5")oC " in ice-bath. After completion of "reaction ,the



reaction mixture was added to the ice cold water" ( 150

dimethylpyridin-2-yl)diazenyl)phenol (R)

ml) " with stirring .The crude product was" "separated by

Synthesis of 5-((5,6-dimethylpyridin-2-yl)diazenyl)2-hydroxybenzaldehyde (1)17-19

filtration , washed with distilled water and dried .The solids obtained recrystallized with ethanol to" get brown

dissolved 2-Amino-4,6-dimethylpyridine (0.01mol) in

crystals colored .The purity of the azo dye ligand (1) was

50 ml distilled water and 4 ml hydrochloric acid . The

determined by thin layer chromatography "(TLC) . " The

solution was diazotized with (0.75 gm, 0.01 mol in 25 ml

yield of the reaction was 88%" .

distilled water) sodium nitrate (NaNO2)was cooled and added drop – wise to solution of 2-Amino-4,6-

Synthsis of 2-(((2-bromophenyl)imino)methyl)-4((5,6-dimethylpyridin-2-yl)diazenyl)phenol 20-21 (R)

dimethylpyridine. " The resulting reaction mixture was

A mixture of ( 0.01mol) of 2-bromobenzaldehyde and

stirred of" 20 minutes ,formed a clear yellow

(0.01mol) (1) was refluxed for 3h in 20 mL of ethanol and

solution .In the resulting diazonium chloride

Add drops of acetic acid .The reaction mixture was cooled

solution,drop-wise, with cooled condition and stirring continuously at(0-5)oC,was added to solution of

and kept for24 hs.The crystals found was filtered, dried and recrystallized from ethanol to give compound (R) .

salicylaldehyde (0.01 mol) dissolved in 100 ml ethanol .

Fig. 1: Synthetic path of reagent (2-(2-bromophenyl)imino)methyl)-4- (5,6-dimethylpyridin-2-yl)diazenyl)phenol (R)"

Dispersive liquid-liquid microextraction procedure: The pH of a 10 ml of sample solution containing Cu+2 in
the rang (50-100) ng/ml was adjusted to (pH 6) with 1.0 mol/ L acetate buffer and 1ml of reagent R (1.0 10-4mol L-1)was placed in 10 ml glass test tube with conical bottom . then (400) μL of aceton(as disperser solvent) containing (100) μL ethanol (as extraction solvent) was injected rapidly in to the sample solution by using a (1mL) syringe.. A cloudy solution (water,acetone and ethanol) was formed in the test tube , in this step Cu+2 complex was extracted into very fine droplets of ethanol in few seconds, The mixture was then centrifuged for 5 min at 5000 rpm,after this process the dispersed fine droplets of ethanol were sedimented at the bottom of the test tube , then the sediment was diluted by 0.5 ml of methanol and the concentration of Cu (II) ion was determined spectrophotometry at λ max (590) nm.
Preparation of Bee honey samples : (22)

The honey samples were heated in a water bath at 40oC for 2 h. After cooling, aliquots containing 1 g of each sample were weighed directly into PTFE flasks, to which 0.5 mL of HNO3 and 0.5 mL of H2O2 were added and the mixture allowed to stand for12 h. Subsequently, the flasks were closed with screw caps and heated to 100oC for 3 h. After cooling to room temperature, the flasks were opened, the resulting solution transferred to graduated polypropylene vials and the volume brought to 25 mL by adding 0.5 M HCl. The aliquots of the final solution were extracted and analyzed for copper content according to the prescribed general procedure for DLLME
Infrared spectra The synthesized ligand and its complexes were characterized by FT-IR , compound (1) show absorption at (1724) cm-1 for (C=O), (2707) cm-1 for (CH)aldehyde,( 1450) cm-1 (-N=N-),(3309) cm-1 (OH) for phenol,and show band at (3008) for (C-H)aromatic ,and


Systematic Reviews in Pharmacy

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Monitoring Of Copper Content In Some Food Samples Using Micro Extraction Combined
With Spectrophotometric Technique band for (C-H) aliphatic at (2823)cm-1, (1535) cm-1 for (C=N)pyridine , 1627 cm-1 for (C=C) aromatic .

Fig (2) FT-IR spectra of compound (1)
The synthesized ligand (2) were characterized by FT-IR show absorption at (1650) cm-1 for new(C=N),( 1488) cm-1 (-N=N-),(3394) cm-1 (OH) for phenol,and show band

at (3062) for (C-H)aromatic ,and band for (C-H) aliphatic at (2923)cm-1 .

Fig ( 3) FT-IR spectra of ligand , compound (R)
1H NMR Spectra The1H-NMR(DMSO) spectrum data of compound (1) show δ:6.8-8.9( m , 5H , Ar-H ),1.7 (s ,6H, -CH3 ) ,9.3 ( s , 1H,OH ). , 11.6 (S,1H, C-H) Ald .


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Monitoring Of Copper Content In Some Food Samples Using Micro Extraction Combined With Spectrophotometric Technique
Fig ( 4 )1H NMR Spectra For compound (1) The1H-NMR(DMSO) spectrum data of compound (2) show δ:6.9-8.9( m , 9H , Ar-H ),1.8 (s ,6H, -CH3 ) ,6.02 ( s , 1H,CH-N ) .
Fig ( 5) 1H NMR Spectra For compound (R) 13C- NMR Spectra The13C-NMR(DMSO) spectrum data of compound (1) show δ:191(C12) , 153 (C9) ,152(C1) , 149(C5) , 141(C6) 134(C4) ,29(C13,C14) , 133-122(C aromatic)

Fig ( 6) 13C NMR Spectra For compound (1)
The13C-NMR(DMSO) spectrum data of compound (2) show δ:135(C13) , 151 (C9) ,150(C1) , 149(C5) , 147(C6) , 135(C4) ,25(C13,C14) , 112-132(C aromatic) .


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Monitoring Of Copper Content In Some Food Samples Using Micro Extraction Combined With Spectrophotometric Technique

Fig ( 7) 13C NMR Spectra compound (R)
Absorption spectra The absorption spectra of [(R) 2Cu] complex was recorded against a reagent blank prepared under the identical conditions. The spectra of Cu(II) complex show

the absorption maxima of 590 nm with molar absorpitivities of 0.11× 104 L mol-1cm-1. Whilst, the ligand (R) gave the absorption maxima of 484 nm as depicted in Figure 8 .

Fig. 8: Absorption spectra (a) Reagent = 1 x 10-3 M (b) [(R) 2Cu complex, Cu(II) =60 ng mL-1, [R] =0.3 mL of 1x 103M, Buffer pH = 6

The Reagent (R) reacts with Cu(II) ion at pH 6 forming a deep green complex, and the absorbance reached its maximum within 5 min and remained stable, for at least 24 h. The stoichiometry of [(R) 2Cu] complex was studied, under the established experimental conditions, by Job’s and mole ratio methods. The

obtained results indicated that the composition of complexes was (1: 2) with stability constant of 1.9x1010 L2M-1 In addition this complexes was characterized on the
basis of spectroscopic techniques and the suggested
related chemical structur is shown in Figure 9


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Monitoring Of Copper Content In Some Food Samples Using Micro Extraction Combined With Spectrophotometric Technique

Fig. 9: The probable chemical structure of the complex
Optimization of DLLME Procedure The effect of different experimental variables which impact the DLLME procedure for Cu+2 complex such as type of the extraction and disperser solvents, pH and the concentration of reagent, amount, were investigated using one variable-at-a-time (OVAT) strategy in searching of the optimum conditions, to maximize recovery percentage and other analytical figures of merit such as sensitivity and detection limit of Cu+2 complex in the selected matrices. Each experiment of the following variable was conducted followed the general DLLME procedure

Effect of type of the extraction and disperser solvents:
When we selected the extraction solvent some properties must be considered.The extraction solvent should a higher density than water,low solubility in water and an extraction capability of the interested compound.To study this effect four different solvents such as methanol,ethanol,chloroform and carbon tetra chloride were tested and according to the absorbance signals at (590) nm ,the most suitable solvent was ethanol ( Fig10 ) .. In the DLLME, disperser solvent should be miscible with both extraction solvent and. water Therefore ethanol, acetone, acetonitrile and methanol were tested as disperser solvent. Under the same conditions, and according to the absorbance signals at (590) nm ,the most suitable solvent was acetone.( Fig11)


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Monitoring Of Copper Content In Some Food Samples Using Micro Extraction Combined With Spectrophotometric Technique
Fig. 10 :Effect of type of the extraction solvent on the formation of Cu (II) complex by DLLME [Conditions: 40 ng mL-1 Cu(II) , 0.3 mL of 1x 10-3M (R)

Fig. 11 :Effect of type of the disperser solvent on the formation of Cu (II) complex by DLLME [Conditions: 40 ng mL-1 Cu(II) , 0.3 mL of 1x 10-3M (R)

Effect of pH
The solution pH plays an important role in the formation of metal complex with the chelating agent and their subsequent extraction by DLLME methodology. Thus, the effect of pH was studied in the range of 2 to 8 using different pH acetate buffer solutions. The results are depicted in Figure 4. As can be seen from Fig.4 that the

absorbance first increased with increasing pH and reached a maximum at pH 6.0. Thereafter, the absorbance gradually decreased because of partial dissociation of the complexes at higher pH, which may result in incomplete extraction of complexes. Therefore, pH 6.0 was selected as the optimum pH' for complete formation of for Cu(II) complex .


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Monitoring Of Copper Content In Some Food Samples Using Micro Extraction Combined With Spectrophotometric Technique

Fig. 12: Effect of pH on the formation of Cu (II) complex by DLLME [Conditions: 50 ng mL-1 Cu(II) , 0.3 mL of 1x 10-3M (R)

Effect of (2-(2-bromophenyl)imino)methyl)-4- (5,6-


) (R)


The effect of the (2-(2-bromophenyl)imino)methyl)-4-

(5,6-dimethylpyridin-2-yl)diazenyl)phenol concentration

was investigated by measuring the absorbance signal

according to the general DLLME procedure of solution

containing 50 ng mL−1 Cu(II) and varying volume from

0.1 to 0.5 mL of 1 x 10-3 mol L-1 from this reagent. the

analytical responses increase rapidly as the volume of reagent increases and reach maximum up to 0.3 mL and decrease thereafter with further increase in the chelating agent indicating that any excessive amount of chelating reagent was not necessary (Fig.13.). Consequently, 0.3 mL of 1 x 10-3 mol L-1 of 2-(2-bromophenyl)imino)methyl)-4(5,6-dimethylpyridin-2-yl)diazenyl)phenol ) was chosen as optimum for Cu(II) ion .

Fig. 13 Effect of concentration of reagent (R) on the DLLME of Cu(II) [Conditions: 50 ng mL-1 Cu (II), X mL of 1x 103M reagent , pH =6 ]

Calibration graphs
Under the optimized conditions established by DLLME procedure, a series of standard Cu(II) solutions ranging from 10-100 ng mL-1 respectively, was taken and subjected to the general DLLME in order to test the

linearity of the method.. The statistical evaluation for the calibration graphs has shown that a strong correlation between signal and Cu(II) concentration may exist(r = 0.9999). The statistical analytical results for the calibration data for Cu(II) is summarized in Table 1 .

Table 1 Method validation of the determination Cu
y = 0.0459+ 0.0065 x
0.9999 0.00605 10-100 2.79 9.30 153x10-3 0.11× 104

Regression equation
Correlation coefficient(r) Std. dev. of regression line (sy/x ) Concentration range ( ng mL-1) Limit of Detection ( ng mL-1) Limit of Quantitation ( ng mL-1) Sandell's sensitivity (μg cm-2) Molar absorptivity (
Composition of complex (M: L)*


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Monitoring Of Copper Content In Some Food Samples Using Micro Extraction Combined

With Spectrophotometric Technique

1.75 % 98.01 105

RSD% (n=7) Recovery% Enrichment factor(EF)**

** EF is calculated as the ratio of slope of calibration curves obtained with and without DLLME

"The proposed method has achieved enriching factor of
105 fold and this is what was allowed to get on the detection limit of 2.79 ng mL-1 for Cu(II) in aqueous solution. It can be concluded that the prepared ligand in this work beside DLLME -Spectrophotometry gave

satisfactory analytical figures of merit for Cu(II) which were much better than with those obtained by some previous studies (Table 2). But, they were in harmony with most studies that used analytical methods in combination with DLLME

Table 2:Comparison of the proposed of DLLME Method with reported methods in chemical literatures for the determination of Cu (II) ion .

preconcentration technique SI-DLLMG-FAAS DLLME-Fo-LADS

LOD µg / L 0.04 0.34
3 3 5 0.7 0.1 0.5 0.132

Linear μg / L (2-70)


(50-2000) (10-4000) (20-90) 0.5-500 -


water water+ human urine water water water environmental Rice and millet water and food drinking water + serum
Bee honey

23 24
25 26 27 28 29 30 31
This work

Recovery Test
Since the certificate reference materials (CRM's) for the determination of the copper in samples are not available, accuracy in term of recovery percent was studied by spiking of 20, 30, 40 Cu(II) to appropriate
Table 3 Accuracy of the proposed method.

amount of honey sample solution and the same steps were followed by general DLLME procedure, The results were tabulated in Table 3 “

Erel (%)
-2.0 -2.7 -1.25

Recovery (%)
98 97.3 98.75

amount metal ion amount metal

found(ng.mL- 1)

ion taken (ng.mL-








Interference Study
The effect of most diverse ions expected in the honey matrices on the determination of 50 ng /mL−Cu (II) solutions were studied following the general DLLME procedure. It is agreed that an extraneous ion deemed to interfere seriously when it gives a relative error percent of more than ± 5%. The results indicated that some of

metal ions like, Ca (II), Na (I), K (I), Mg(II),Co(II) , Ni( II)and Zn(II) have no appreciable effect on the copper ion responses, while the other metal ions such as Mn (II), and Cd(II) have exceeded the allowable limits of interferences for Cu(II) as shown in Table 4

Table 4. Effect of divers ions on the absorption signal of Cu(II) (50 ng mL−1, Abs= spectrophotometry

(0.364) by DLLME-

Erel ( %)



Interferent / Interfering



-0.55 0.27 0.81 1.35

-0.002 0.001 0.003 0.005

0.362 0.365 0.367 0.369

1000 1000 1000 1000

Na + K+ Ca+2 Mg+2


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With Spectrophotometric Technique

0.54 4.2 5.2
6.9 1.08

0.002 0.016 0.02 0.027 0.004

0.366 0.38 0.384
0.391 0.368

1000 500 500 500 1000

CO (II) Ni (II) Mn(II)
Cd (II) Zn (II)

A mixture of 0.01M oxalic acid, tartaric acid and sodium fluoride used to control the interferences of Cd(II) and.Mn(II) without any appreciable masking of Cu Ion
Applications Study According to the considerable analytical features that have been achieved in this method, such as,high recoveries, low detection limit and interference-free,the

method was employed for the detection, of copper ions in bee honey samples after the digestion procedures that described in experimental work and measured in triplicate. At the same time, the sample solutions were also determined by flame atomic absorption spectrometric method (FAAS).The results are presented in Tables 5.

Table5: Results of the estimation of Cu (II) ion in different Bee honey samples.

CONCLUSION In this piece of work, a new DLLME coupled with traditional spectrophotometric method using synthesized ligand was established for the determination of Cu(II) in Bee honey samples. The separation of copper ion was easily conducted in single extraction by DLLME using homemade organic reagents for the first time. The

determination of copper in food and water samples using amino acid as the complexing agent J . Food compos Anal . 23 , 95.” 4. S . J . Wang , H . Zheng , B . X . Ye ,2008. Simultaneous Determination of Cd (II), Cu (II), Pb (II) and Zn (II) in Human Plasma by Potentiometric Stripping Analysis J . chin . chem . Soc , 55 , 1080 ,.

Bee honey samples

Concentration of Cu (µg.g-1) "

Proposed method


Iraqi 1

0.096 ±0.0031

Iraqi 2


Iraqi 3

0.099± 0.0045

Turkish 1

0.078± 0.0016

Turkish 2


Turkish 3


Iranian 1


Iranian 2

0.071± 0.0038

Iranian 3

0.080± 0.0091

established method gave the distinct features which were represented by acceptable analytical figures of merit and high reliability compared with other sophisticated techniques (Table 2).

REFERNCES 1. M . J. Ahmed , I .Jahan and S . Banoo, 2002. A simple
spectrophotometric method for the determination of copper in industrial, environmental, biological and soil samples using 2,5-dimercapto-1,3,4thiadiazole. Anal . Sci ., 18 , 805 2. M . I . Toral , P. Richter , C . Rodriquez , 1997. Simultaneous determination of copper and iron by second derivative spectrophotometry using mixtures of ligands Talanta 45 , 147. 3. P . Liang , J . Yang , 2010. Cloud point extraction preconcentration and spectrophotometric










5. D . Citak , M . Tuzen ,2010 A novel preconcentration

procedure using cloud point extraction for

determination of lead, cobalt and copper in water

and food samples using flame atomic absorption

spectrometry Food chem . Toxi Col , 48 , 1399 .

6. N . Baghban , A . Mohammad ltaji, S , Dalfarnig and

A ., Ali Jafari, 2012 . "Cloud Point Extraction of Trace

Amounts of Copper and Its Determination by Flow

Injection Flame Atomic Absorption Spectrometry" . ,

croat chem Acta 85 , 1 ,. (cca1803-3). .

7. Y . Guoi "H . Zhao . Y . Han , X . Liu , S . Guan ,

Q .Zhay , X, 2017

. Simultaneous

spectrophotometric determination of trace copper,

nickel, and cobalt ions in water samples using solid

phase extraction coupled with partial least squares

approaches " Bian spectro chem. Acta A Mol Bio

mol spectrosc , 173 ,


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ExtractionDeterminationDllmeFood SamplesCopper Content