A highly sensitive spectrophotometric method for ... - Semantic Scholar

3 downloads 0 Views 95KB Size Report
copper in tap water, polluted water, human hair and alloys. ... medium to liberate iodine, which bleaches violet color of azure B and the absorbance is measured.
Journal of Scientific & Industrial Research Vol. 66, January 2007, pp. 28-31

A highly sensitive spectrophotometric method for the determination of trace copper using azure B as a chromogenic reagent Mendalin Mathew and B Narayana* Department of Studies and Research in Chemistry, Mangalore University, Mangalagangothri 574 199 Received 19 September 2005; revised 21 August 2006; accepted 08 November 2006 A simple, rapid and sensitive spectrophotometric method has been developed for the determination of trace amounts of copper in tap water, polluted water, human hair and alloys. The proposed method is based on the reaction of copper with potassium iodide in acidic medium to liberate iodine, which bleaches violet color of azure B and the absorbance is measured at 644nm. This decrease in absorbance is directly proportional to copper concentration. Beer’s Law was obeyed in the range 2.0-12.0µg/ml of copper. Molar absorptivity and Sandell’s sensitivity of the method were found to be 1.760 x 105 l /mol/cm and 3.61 x 10-4µg/cm2 respectively. The developed method has been successfully applied to the determination of copper in tap water, polluted water, human hair and alloys. Keywords: Azure B, Copper determination, Spectrophotometry

Introduction There are a number of gravimetric and complexometric reagent for the determination of copper; difficulty arises when sample containing trace amounts of copper needs to be analyzed. In such cases, spectrophotometric method may readily be adopted using selective and sensitive reagents. Several organic reagents proposed for spectrophotometric determination of copper(II) include 4-(2-thiazolylazo)resocinol1, 2,4–Dihydroxybenzophenone benzoic hydrazone (DHBPBH)2, 2–tetrazolylazo–5–diethylaminophenol3, dimethyl4 glyoxime , 4,5–dibromo-o-nitro-phenylflurone5, 6 cuprizone , 2–(1,3,4-triazolylazo)-5-diethylamino benzoic acid7, neocuproine8, oxime-thiosemicarbazones9, diamine–dioxime derivative10, variamine blue11, 4-vanillideneamino –3-methyl–5-mercapto– 1,2,4–triazole12, diacetylmonoxime benzoylhydrazone13, benzyl–α-monoxime isonicotinoyl hydrazone14, 2,5–dihydroxyacetophenonebenzoichydrazone15, 5(4-dimethylaminobenzylidene) rhodamine16, chromazurine S17 and copper-thymol blue-hydrogen peroxide system18. Azure B (C15H16ClN3S), a green crystalline powder, is redox reagent (Fig. 1), which can be used as a chromogenic reagent for spectrophotometric determination. It is ___________________ *Author for correspondence Fax: 0091-824-2287367 E-mail: [email protected]

harmful if swallowed and is skin, eye and respiratory irritant. Toxicology is not fully investigated. In the present investigation, azure B has been used as a selective, rapid and sensitive spectrophotometric reagent for the determination of copper. Materials and Methods Reagents and Instruments

A Secoman Anthelie NUA022 UV-visible spectrophometer with 1 cm quartz cell and a WTW 330 pH meter were used. All reagents were of analytical grade and double distilled water was used. Standard stock solution (1000 µg/ml) of copper was prepared by dissolving CuSO4.5H2O (3.92 g) in water (1000 ml) and standardized by the bicyclohexanone oxalyldihydrazone method19. Potassium iodide (2 %), 2 M HCl and 1 M sodium acetate solutions were used. Solution of azure B (0.1%) in methanol - water was used. Procedure to Determine Copper

An aliquot of the solution containing copper (2-12 µg/ml) was transferred into a series of calibrated flasks (10 ml each). 1 ml of 2% KI2 solution followed by 1 ml of 2M HCl was added to it. Mixture was gently shaken until the appearance of yellow color, indicating liberation of iodine. Azure B (0.1%, 0.5 ml) was added to the solution, and reaction mixture was shaken for 2 min and then diluted to 10 ml in a standard flask with distilled water.

MATHEW & NARAYANA: NEW METHOD FOR DETERMINATION OF TRACE COPPER USING AZURE B

29

Fig. 1 Scheme for the determination of copper using azure B

Fig. 2 Absorption spectrum of colored azure B

Fig. 4 Calibration plot for the determination of copper (II) using standard VAMMT method

Absorbance of resulting solution was measured at 644 nm (Fig. 2) against a reagent blank. A blank was prepared by replacing copper solution with distilled water. Absorbance corresponding to the bleached color, which in turn corresponds to the copper concentration, was obtained by subtracting the absorbance of blank solution from that of the test solution. Amount of copper present in the volume taken was computed from the calibration graph (Figs 3 and 4). Determination of Copper in Natural Water and Polluted Water

Fig. 3 Calibration plot for the determination of copper (II) using azure B as a reagent

An aliquot (≤ 4 ml) of water, spiked with a known amount of Cu (II), was treated with 0.5 ml each of 1 M NaOH and 0.2 M EDTA. The solution was mixed and centrifuged to remove any formed precipitate. Centrifugate was transferred to a 10 ml calibrated flask and Cu was determined (Table 1).

J SCI IND RES VOL 66 JANUARY 2007

30

Table 1 Determination of copper in various samples using azure B as reagent Sample

Nazareth et al12 method

Proposed method

Natural water

Polluted water

Human haird (0.5g)

Copper added µg/ml

Copper found µg/mla

Recovery %

Copper found µg/mla

Recovery %

F-testb

t-testc

4.0 6.0 10.0 4.0 6.0 10.0 4.0 6.0 10.0

4.02±0.01 5.99±0.02 9.99±0.01 4.10±0.02 6.04±0.03 10.05±0.03 4.01±0.03 6.05±0.02 10.04±0.02

100.5 99.8 99.9 102.5 100.6 100.5 100.2 100.8 100.4

4.04±0.02 6.03±0.03 10.02±0.02 4.09±0.03 6.08±0.03 10.02±0.03 4.02±0.02 6.02±0.02 10.03±0.03

101.0 100.5 100.2 102.2 101.2 100.2 100.5 100.3 100.3

4.0 2.25 4.0 2.25 1.00 1.0 2.25 1.0 2.25

2.0 1.57 2.99 0.620 1.14 1.58 0.620 2.37 0.62

a

mean ± standard deviation (n=5); bTabulated F- value for (4,4) degrees of freedom at 95% probability level is 6.39; cTabulated t- value for 8 degrees of freedom at 95% probability level is 2.776; dTested and shown to be free from copper Table 2 Determination of copper (II) in alloys using azure B as a reagent

Table 3 Determination of copper (II) in copper sulfate solution using azure B as a reagent

Copper found Copper found* Relative error (VAMMT) % (Azure B) % %

Copper taken Copper founda Standard Recovery Student’s µg/ml µg/ml deviation % t-valueb

Alloys German silver Bronze Brass Aluminium bronze Gun metal

71.28 80.87 67.43 77.32 85.03

71.22 80.56 67.72 77.23 84.97

-0.084 -0.383 0.430 -0.116 -0.070

*Average of five determinations Determination of Copper in Human Hair

A known amount of human hair (0.5 g) sample was digested with a 10 ml mixture of HCl and HNO3 (3:2 v/v) for 10 min. The solution was spiked with a known amount of copper (II), cooled and neutralized with dilute ammonia and analyzed (Table 1). Determination of Copper in Alloys

Samples (1.0-1.5 g) of copper based alloys were dissolved in conc. HNO3 (if tin is present aqua-regia is used) and the oxide of nitrogen expelled with the use of conc. H2SO4 until evolution of the brown fumes ceased. Residue was extracted with distilled water and made up to 100 ml standard flask. Suitable aliquots (≤ 4 ml) of the solution were pipetted out in 10 ml calibrated flask and copper content was determined directly (Table 2). Results and Discussion Absorption Spectra

The reaction of copper with potassium iodide in acidic medium liberate iodine, which bleaches violet color of azure B to colorless leucoform of azure B (Fig. 1) and the absorbance of the reaction system was measured at 644 nm.

2.55 5.10 10.20

2.56 5.08 10.18

0.01 .03 0.02

100.39 99.61 99.80

2.23 1.49 2.23

a

Average of five determinations; bTabulated student’s t- value for four degree of freedom at 95% probability level is 2.78 Effect of Iodide Concentration and Acidity

Effect of iodide concentration acidity on colour development was studied with Cu (14 µg/ml). The oxidation of iodide to iodine by Cu was effective at pH 1.0-1.5, which could be maintained by adding 1 ml of 2 M HCl in the final volume of 10 ml. The liberation of iodine from KI2 in an acidic medium was quantitative. Appearance of yellow color indicated the liberation of iodine. However, concentration of HCl (1.0-1.2 ml) should be maintained. It was found that 1 ml of each of 2% KI2 and 2 M HCl were sufficient for the liberation of iodine from iodide by copper. Analytical Data

Adherence to Beer’s law was studied by measuring absorbance of solutions varying Cu concentration. Beer’s law was obeyed in the range of 2-12 µg/ml copper. Molar absorptivity and Sandell’s sensitivity for Cu (10 µg/ml) were found to be 1.760x105 l/mol/cm and 3.61x10-4 µg/cm2 respectively. The determination of Cu (II) from copper sulphate solution (Table 3) shows that accurate and consistently reproducible results are obtainable with relative error (≤ 0. 4 %) and standard deviation (≤ 0.4 µg/ml).

MATHEW & NARAYANA: NEW METHOD FOR DETERMINATION OF TRACE COPPER USING AZURE B

Effect of Diverse Ion

Effect of some ions that often accompany copper was studied by adding different amounts to copper solutions. An error (± 2%) in absorbance was considered tolerable. Tolerance limits of various foreign ions is as follows (µg/ml): Al(III), Pt(IV), 10 each; In(III), 25; Ni(II), Co(II), V(IV), Ti(IV), Mo(VI), U(VI), 50 ml each; Hg(II), Cd(II), Zn(II), 75 each; Mg(II), Ba(II), Fe(III), borate, 100 each; acetate, chloride, 150 each; and bromide, phosphate, 200 each. Some reductants such as nitrite, sulfite (100 µg/ml each) were found to interfere. However, some of these ions could be masked by the addition of an appropriate amount of EDTA solution. Fe3+ was masked using sodium fluoride.

3

4

5

6

7

Applications

Developed method was successfully applied to the quantitative determination of traces of Cu in tap water, polluted water, human hair and alloys. Analysis of the above alloy samples compared favorably with reported method12. Various synthetic mixtures of Cu with Mo, Ba, Mg and U metal ions were prepared and the amount of Cu in the mixture was determined by proposed method. Precision of proposed method was evaluated by a replicate analysis of samples containing Cu in different concentrations. Conclusions The reagent provides a simple, rapid, sensitive and accurate method for the spectrophotometric determination of copper. The reagents have an advantage of high sensitivity, selectivity and low absorbance of the reagent blank. The method needs neither heating for the complete color development nor extraction into any organic phase. Most of the common metal ions, which are associated with copper either in mineral or in alloys, do not interfere in its determination and hence the method can be used for the analysis of alloys, minerals and artificial mixtures for their copper content. Acknowledgement Authors thank the Microtron Centre of Mangalore University for technical help.

8

9

10

11

12

13

14

15

16

17

References 1 Zheng L, Wang S Z & Xu D, Spectrophotometric determination of microamounts of lead in copper alloy with 4-(2- thiazolylazo)Resorcinol, Yejin Fenxi, 18 (1998) 58-59. 2 Reddy V K, Thippaiah J, Rao C K, Reddy P R & Reddy T S, 2,4 – Dihydroxybenzophenone benzoic hydrazone for

18

19

31

Spectrophotometric determination of Cu(II) and Fe(III) in soil and cement, J Indian Chem Soc, 76 (1999) 275-276. Lin C P, Liang H D, Ge C & Pan F Y, Spectrophotometric determination of copper with 2- tetrazolylazo –5diethylaminophenol, Guangpu Shiyanshi, 17 (2000) 564-567. Muralikrishna U & Sivaramakrishna A, Simultaneous spectrophotometric determination of copper (II) and nickel (II) using dimethylglyoxime as a reagent, Asian J Chem, 13 (2001) 289-293. Shen L, Spectrophotometric determination of trace of copper in aluminium alloys with 4,5-dibromo-o- nitrophenylflurone, Tejin Fenxi, 22 (2002) 43-44. Rumori P & Cerda V, Reversed flow injection and sandwich sequential injection method for the spectrophotometric determination of copper (II) with cuprizone, Anal Chim Acta, 486 (2003) 227-235. Ge C H, Liang H D & Pan F Y, Study on spectrophotometric determination of copper (II) with 2 –(1,3,4- triazolylazo)-5diethylamino benzoic acid, Guangpu Shiyanshi, 20 (2003) 402-405. Ercage E Ercag A & Apak R, Spectrophotometric determination of the soil fumigant; dazomet with copper (II)neocuprione reagent, Anal Chim Acta, 505 (2004) 95-100. Reddy K H & Prasad N B L, Spectriophometric determination of copper (II) in edible oils and seeds using novel oximethiosemicarbazones, Indian J Chem, 43A (2004) 111-114. Thipyapong K & Suksai C, Spectrophotometric determination of copper (II) using diamine-dioxime derivative, Bull Korean Chem Soc, 24 (2003)1767-1770. Narayana B, Mathew M, Sreekumar N V & Vipin K, A facile spectrophotometric method for the determination of copper (II) using variamine blue as a chromogenic reagent, J Indian Chem Soc, 80 (2003) 937-938. Nazareth R A, Narayana B & Sreekumar N V, Spectrophotometric determination of copper using 4vanillideneamino – 3- methyl – 5- mercapto – 1,2,4 – triazole (VAMMT), Indian J Chem, 40A (2001) 1016. Chandrasekhar K B, Reddy K H & Reddy T S, Simultaneous second derivative Spectrophotometric determination of nickel (II) and copper (II) in alloys using diacetylmonoxime benzoylhydrazone (DMBH), J Indian Chem Soc, 80 (2003) 930-933. Sekar K B C & Reddy K H, Benzil- alpha- monoxime isonicotinoyl hydrazone (BMH) as a chromogenic reagent for spectrophotometric determination of copper (II) Res J Chem Environ, 8 (2004) 12-14. Kudapali Y S & Suresh T, Spectrophotometric determination of copper (II) with 2,4 – Dihydroxybenzophenone benzoic hydrazone, Orient J Chem, 20 (2004) 313-316. Ojeka E O & Iyun j F, 5(4-Dimethylaminobenzylidene) rhodamine as a reagent for the spectrophotometric determination of copper and manganese, Glob J Pure Appl Sci, 10 (2004) 577-583. Tang C, Spectrophotometric determination of copper in Ginseng, Guangdong Weiliang Yuansu Kexue, 10 (2003) 42-44. Bao D G & Bai Y, Catalytic spectrophotometric determination of trace copper in copper- thymol bluehydrogen peroxide system, Fenxi Huaxue, 33 (2005) 144. Vogel A I, Text Book of Quantitative Chemical Analysis’, 5th edn (ELBS, Longman, London) 1989.