Micellanized spectrophotometric method for the determination of beryllium using haematoxylin

Spectrochimica Acta Part A 67 (2007) 1333–1338

Micellanized spectrophotometric method for the determination of beryllium using haematoxylin B.P. Dayananda, H.D. Revanasiddappa ∗ , T.N. Kiran Kumar Department of Chemistry, University of Mysore, Manasagangothri, Mysore 570006, India Received 5 July 2006; accepted 11 October 2006

Abstract A simple and sensitized spectrophotometric method for the determination of trace amounts of beryllium has been described. The method is based on the formation of a ternary complex by the reaction of beryllium with haematoxylin in the presence of micellar medium (cationic surfactant, cetyltrimethylammonium bromide). The ternary complex of beryllium has a maximum absorbance at 592 nm and showed an excellent sensitivity (molar absorption coefficient of 7.07 × 104 L mol−1 cm−1 and the Sandell’s sensitivity being 1.27 × 10−4 ␮g cm−2 ) and reproducibility (withinday precision: R.S.D. ≤ 0.36%, n = 5, between-day precision: R.S.D. ≤ 0.65%, n = 5). Linearity was achieved over the range 0.01–0.1 ␮g mL−1 of beryllium with a correlation coefficient of 0.9999. The effect of foreign substances on the determination has been examined. The proposed procedure has been applied to the determination of beryllium in water samples. © 2006 Elsevier B.V. All rights reserved. Keywords: Beryllium; Spectrophotometric method; Haematoxylin; Micelle; Surfactant; Cetyltrimethylammonium bromide

1. Introduction The contents of beryllium in the earth’s crust [1], in soil [2] and in coal [3] are about 2–6, 1.2–2.1 and 2.5 ␮g g−1 , respectively. By way of rain, beryllium and its compounds in the earth’s crust, in soil, or in gaseous vapor and fly ash [4,5] discharged from coal-burning industries may dissolved in water [6] enter the sources of water and present in the sediments [7]. Since beryllium improves the characteristics of metals, producing greater tensile strength, electrical conductivity and resistance to corrosion, pure beryllium and its metal alloys (such as Cu, Al, Mg, Ni) have been widely used for electrical equipment, electronic instrumentation, structural components for aircraft, missiles, satellites and nuclear reactors [8,9]. Beryllium and its compounds are highly toxic and may cause lung disease (berylliosis) [8,9], eye and mucous membrane irritation, fatigue and weight loss, and is probably a human carcinogen [10,11]. Hence, beryllium is classified by USEPA in Group B2 [11]. Generally, atomic absorption spectrometry (AAS) [12,13], inductively coupled plasma atomic emission spectrometry (ICP-AES) [14], inductively coupled plasma optical emission

∗

Corresponding author. Tel.: +91 821 2419669. E-mail address: [email protected] (H.D. Revanasiddappa).

1386-1425/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2006.10.020

spectrometry (ICP-OES) [15], PVC-based membrane sensors [16,17], particle induced gamma-ray emission and nuclear reaction analysis (PIGE-NRA) [18], spectrofluorimetry [19,20] are the common and recent techniques used in the determination of trace level Be. Many of these methods present difficulties in speciation analysis in addition to being highly expensive techniques. Spectrophotometry, however, continues to enjoy a wide popularity because of its rapidity, accuracy, precision and cost-effectiveness. Marczenko [21] has reviewed the reported spectrophotometric methods for the determination of beryllium till 1986. There are many methods that use color reaction systems in spectrophotometry using the reagents: Chrome Azurol S [21,22], 8-hydroxyquinaldine [23], Eriochrome Cyanine R [24,25], Methylthymol Blue [26], Eriochrome Brilliant Violet B [27], Chromal Blue G [28], Molybdenum Blue [29], Calcichrome [30], 1-(2-thiazolylazo)-2-naphthol [31], Thorin I [32], N-phenyl-2-furohydroxamic acid [33], etc. Recently, spectrophotometric determination of beryllium using Xylenol Orange [34] and Chrome Azurol S using cetyltrimethylammonium bromide [35] have been reported. Some of these methods are not satisfactory, showing poor convenience, low sensitivity and low reproducibility. These limitations have prompted the authors to develop a simple and reproducible analytical method. In the present investigation, a simple and sensitive spectrophotometric method for the determination of beryllium has

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been developed, which is based on the reaction of beryllium with haematoxylin and the sensitizing effect of a cationic surfactant, cetyltrimethylammonium bromide (CTA) on the absorbance of the binary complex.

blank. Unknown concentrations are determined from a calibration graph established from known concentrations of beryllium.

2. Experimental

Tap and ground water samples were filtered through a filter paper with a pore size of 0.45 ␮m (Millipore), preserved in nitric acid (1 mL of concentrated nitric acid per liter) in a polyethylene bottle that had been carefully cleaned with nitric acid. In order to eliminate the chlorine in tap water the samples were treated for 5 min with 5 g of activated charcoal and filtered before being transferred into a polyethylene bottle. Beryllium in water samples was analyzed according to general procedure described in Section 2.4, after separating it by cation-exchange column (in nitric acid–methanol medium) [37], to avoid the possible interference (matrix effect) of ions commonly associated with water samples.

2.1. Instrumentation Analytic Jena AG model Specord-50 spectrophotometer with 1.0 cm matched quartz cuvettes was used for all absorbance measurements. The pH measurements were made with an Elico model IL-610 digital pH meter. 2.2. Reagents All chemicals used were of analytical reagent grade and doubly distilled water was used throughout. Be(II) solution (1000 ␮g mL−1 ) was prepared by dissolving 1.965 g of BeSO4 ·4H2 O (Merck) in 0.2 M hydrochloric acid and standardized by phosphate method [36]. The working standard solution was freshly prepared every day by dilution with the acid (0.2 M HCl). Haematoxylin (Sigma–Aldrich) solution (0.01%) was prepared by dissolving 25 mg of haematoxylin in 250 mL of ethanol. Cetyltrimethylammonium bromide (Sigma–Aldrich) solution (0.1 M) was prepared by dissolving 9.112 g of CTA in 250 mL of water by warming. A 10% aqueous solution of hexamine (pH 9.0) was prepared and used. Hexamine buffer of pH 8.6 was prepared by adjusting the pH of 10% aqueous hexamine solution with dilute hydrochloric acid. Solutions of diverse ions: solutions of metal ions were prepared by dissolving the respective salts in water or in dilute acids. The solutions were standardized by conventional methods wherever necessary. Solutions of anions were prepared by dissolving the corresponding sodium or potassium salts in water. 2.3. Procedure for determination of beryllium as binary complex Aliquots of standard solution containing 0.25–2.5 ␮g of Be(II) were transferred into a series of 10 mL calibrated flasks. A volume of 1 mL of haematoxylin (0.01%) was added followed by the addition of 3 mL of buffer (pH 9.0). The contents were diluted to the mark with water and the absorbance was measured after 1 h of mixing, at 555 nm against a reagent blank. Unknown concentration of beryllium was determined by reference to the calibration graph. 2.4. Procedure for determination of beryllium as ternary complex Aliquots of standard solution containing 0.1–1.0 ␮g of Be(II) were transferred into a series of 10 mL calibrated flasks. Volumes of 1 mL each of haematoxylin (0.01%) and CTA (0.05 M) were added followed by the addition of 3 mL of buffer (pH 8.6). The contents were diluted to the mark with water and the absorbance was measured after 1 h of mixing, at 592 nm against a reagent

2.5. Pretreatment and analysis of water samples

3. Results and discussion Beryllium forms a binary complex with haematoxylin at pH 9.0. An attempt was made to increase the sensitivity of the method in presence of micelle. The sensitivity was significantly improved by the addition of CTA at pH 8.6. In comparison, the molar absorption coefficient of beryllium–haematoxylin in the presence of a micelle was nearly three times greater than in its absence. 3.1. Choice of surfactant The effect of cetyltrimethylammonium bromide, zephiramine (cationic) and Triton X-100 (non-ionic) surfactants on the absorbance of beryllium–haematoxylin binary complex was studied at optimum experimental conditions ([Be] = 7.77 × 10−6 M). A maximum enhancement in the absorbance of the complex was occurred in presence of CTA (cationic). Therefore, CTA was selected as a micellar medium in the proposed procedure. 3.2. Absorption spectra The absorption spectra of beryllium–haematoxylin binary complex at pH 9.0 and beryllium–haematoxylin in presence of CTA (ternary complex) at pH 8.6 are shown in Fig. 1. Beryllium–haematoxylin binary complex and its blank have maximum absorption at 555 (curve B) and 478 (curve A) nm, respectively. The addition of CTA to the ligand at pH 8.6 is accompanied by hypsochromic shift (maximum absorption at 440 nm) with hypochromic effect (curve C). Moreover, bathochromic shift of the complex (maximum absorption at 592 nm) was observed with hyperchromic effect (curve D). 3.3. Optimization of experimental conditions The experimental conditions were optimized by studying the influence of following parameters with 7.77 × 10−6 M Be(II) in a final volume of 10 mL.

B.P. Dayananda et al. / Spectrochimica Acta Part A 67 (2007) 1333–1338

Fig. 1. Absorption spectra of haematoxylin complexes in aqueous and micellar media. [Be] = 7.77 × 10−6 M; [haematoxylin] = 2.81 × 10−5 M; [CTA] = 5 × 10−3 M. (A) Haematoxylin vs. buffer at pH 9.0; (B) Be(II) + haematoxylin vs. haematoxylin at pH 9.0; (C) haematoxylin + CTA vs. CTA + buffer at pH 8.6; (D) Be(II) + haematoxylin + CTA vs. haematoxylin + CTA at pH 8.6.

3.3.1. Effect of pH The effect of pH on the formation of beryllium–haematoxylin complex in aqueous and micellar media was examined (Fig. 2), at the respective maximum absorption wavelengths. It was found that the maximum absorbance of beryllium–haematoxylin binary complex was obtained when the solution was buffered in the pH range 8.8–9.2. Therefore, a buffer solution of pH 9.0 was used in the procedure. The absorbance of beryllium–haematoxylin ternary complex (in presence of CTA) was found to be constant and maximum in the pH range 8.4–8.8. Hence, an optimum pH of 8.6 was maintained for the determination of beryllium in micellar medium. 3.3.2. Effect of reagent concentration The effect of haematoxylin concentration on the formation of beryllium–haematoxylin complex in aqueous and micellar media was investigated (Fig. 3) at the optimum pH values. The maximum absorbance was observed in the range 2.11 × 10−5 to 3.51 × 10−5 M haematoxylin in both the media. Therefore, 1 mL of 0.01% haematoxilin was used in the proposed procedures to attain a final reagent concentration of 2.81 × 10−5 M.

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Fig. 3. Effect of haematoxylin concentration (2.81 × 10−4 M) on the absorbance of: (a) beryllium–haematoxylin and (b) beryllium–haematoxylin in presence of CTA; [Be] = 7.77 × 10−6 M.

Fig. 4. Effect of CTA concentration (0.05 M) on the absorbance of beryllium–haematoxylin; [Be] = 7.77 × 10−6 M.

mum pH of 8.6. The maximum sensitizing action of CTA was achieved in 5 × 10−3 M media of CTA in a final volume of 10 mL (1 mL of 0.05 M CTA in 10 mL). A lower concentration was accompanied by a decrease in the absorbance values. 3.3.4. Effect of time The absorbance of beryllium–haematoxylin binary and ternary complexes increased gradually for 1 h and remained constant for 1 h for binary complex and 2 h for ternary complex. Therefore, a standing time of 1 h was adopted in both procedures.

3.3.3. Effect of CTA concentration The effect of CTA concentration on the absorbance of beryllium–haematoxylin ternary complex was studied (Fig. 4) by keeping a fixed final concentration of beryllium (7.77 × 10−6 M) and haematoxylin (2.81 × 10−5 M) at the opti-

3.4. Stoichiometry of the complexes

Fig. 2. Effect of pH on the absorbance of: (a) beryllium–haematoxylin and (b) beryllium–haematoxylin in presence of CTA. Condittions as in Fig. 1.

Fig. 5. Composition of beryllium–haematoxylin complex by the continuous variation method.

The composition of beryllium–haematoxylin binary complex in the absence of micelle was determined by Job’s method of continuous variation (Fig. 5) and by the molar ratio method

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inary separation of beryllium is necessary in the real sample analysis. 3.6. Analytical characteristics

Fig. 6. Composition of beryllium–haematoxylin complex by the mole ratio method.

(Fig. 6). The maximum absorbance was produced at a molar ratio of 1:3 (metal:ligand). Attempt to determine the composition of the ternary complex was not made because more than 480-fold molar excess of CTA was required for complete complex formation.

Calibration graphs were linear (r = 0.9999) over the concentration range 0.025–0.25 and 0.01–0.1 ␮g mL−1 of Be(II) for the beryllium–haematoxylin and beryllium–haematoxylin in presence of CTA, respectively. The value of molar absorption coefficient as determined by the least-squares method for 10 results was 2.54 × 104 L mol−1 cm−1 for beryllium–haematoxylin. The corresponding value in the presence of micelle was 7.07 × 104 L mol−1 cm−1 . Sandell’s sensitivities were found to be 3.55 × 10−4 (binary complex) and 1.27 × 10−4 (ternary complex) ␮g cm−2 . The detection limit (DL = 3.3σ/S) and quantitation limit (QL = 10σ/S) (where ‘σ’ is the standard deviation of the blank, n = 10 and ‘S’ is the slope of the calibration curve) of beryllium determination were 0.074 and 0.226 ␮g mL−1 in aqueous and 0.0029 and 0.0009 ␮g mL−1 in micellar media, respectively.

3.5. Effect of interfering substances The influence of various foreign substances on the determination of Be(II) was examined individually in micellar medium. The results are summarized in Table 1. The interference study indicated that the haematoxylin procedure is not selective for the determination of beryllium. Therefore, prelim-

Table 1 Effect of interfering substances Substance added

Molar ratio (substance/Be)

Absorbance at 592 nm ([Be] = 0.05 ␮g mL−1 )

Interference (%)

None Zn(II) Mn(II) Co(II) Cu(II) Pb(II) Ni(II) Cd(II) Ca(II) Ba(II) Mg(II) Al(III) La(III) Fe(III) In(III) Ga(III) As(III) Zr(IV) V(V) EDTA Fluoride Phosphate Acetate Oxalate Tartrate Cyanide Thiocyanate

– 10 10 10 100 10 10 10 100 100 100 10 100 100 10 10 10 100 100 100 100 10 100 10 100 10 100

0.392 0.159 0.181 0.152 0.380 0.221 0.434 0.418 0.401 0.396 0.254 0.465 0.293 0.325 0.451 0.458 0.357 Precipitated Precipitated 0.327 0.325 0.145 0.378 0.197 0.298 0.294 0.365

– −59.4 −53.8 −61.2 −3.1 −43.6 +10.7 +6.6 +2.3 +1.0 −35.2 +18.6 −25.3 −17.1 +15.1 +16.8 −8.9 – – −16.6 −17.1 −63.0 −3.6 −49.7 −24.0 −25.0 −6.9

3.6.1. Within-day and between-day precision studies To ascertain the ruggedness of the method, five replicate determinations at different concentration levels of beryllium in presence of micelle were carried out. The within-day R.S.D. values were ≤0.36%. The between-day R.S.D. for different concentrations of beryllium obtained from the determinations carried out over a period of 5 days were found to be ≤0.65%. The results indicate that the proposed method has an advantage of excellent reproducibility both within-day and between-day precision (Table 2). 3.7. Analytical application in water samples Although the proposed procedure utilizing haematoxylin in micellar medium was not selective, it was applied successfully for the determination of beryllium in water samples as described in Section 2.5. The water samples tested negative for beryllium. Different amounts of beryllium(II) was spiked to the samples and analyzed for beryllium(II) by the proposed and Chrome Azurol S in presence of CTA [21] methods. Table 3 shows the results obtained for all the water samples. These results confirm the validity of the proposed method.

Table 2 Within-day and between-day precision studies on the determination of beryllium in micellar medium Beryllium taken (␮g)

0.25 0.50 0.75 a

Within-day

Between-day

Beryllium found (␮g)

R.S.D. (%)

Beryllium founda (␮g)

R.S.D. (%)

0.249 ± 0.0009 0.499 ± 0.0006 0.748 ± 0.0004

0.36 0.12 0.05

0.248 ± 0.0016 0.497 ± 0.0009 0.747 ± 0.0007

0.65 0.18 0.09

Average value of five determinations carried out over 5 days.

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Table 3 Determination of beryllium in water samples Sample

Be(II) added (␮g)

Proposed method

Reference method [21]

Be(II) founda (␮g)

R.S.D. (%)

Recovery (%)

Be(II) founda (␮g)

R.S.D. (%)

Recovery (%)

F-testb

t-Testc

Tap water

0.3 0.5

0.297 ± 0.006 0.496 ± 0.005

2.0 1.0

99.0 99.2

0.295 ± 0.007 0.495 ± 0.006

2.4 1.2

98.3 99.0

1.4 1.4

0.5 0.3

Ground water

0.4 0.6

0.392 ± 0.007 0.593 ± 0.006

1.8 1.0

98.0 98.8

0.394 ± 0.008 0.592 ± 0.006

2.0 1.0

98.5 98.7

1.3 1.0

0.4 0.3

a b c

Mean ± standard deviation (n = 5). Tabulated F-value for (4, 4) degrees of freedom at P(0.95) is 6.39. Tabulated t-value for 8 degrees of freedom at P(0.95) is 2.306.

Table 4 Comparison of molar absorption coefficient of the present work with some other methods Reagent

Reference

λmax (nm)

Molar absorption coefficient (L mol−1 cm−1 )

Haematoxylin + cetyltrimethylammonium bromide Chrome Azurol S + cetyltrimethylammonium bromide 8-Hydroxyquinaldine Eriochrome Cyanine R + hexadecylpyridinium chloride Eriochrome Brilliant Violet B Chromal Blue G Molybdenum Blue Calcichrome 1-(2-Thiazolylazo)-2-naphthol + Triton X-100 Thorin I N-phenyl-2-furohydroxamic acid

This work 21 23 25 27 28 29 30 31 32 33

592 615 380 530 560 610 780 625 555 523 420

7.07 × 104 9.45 × 104 3.5 × 103 5.36 × 104 5.95 × 104 3.1 × 104 9.46 × 103 9.7 × 103 2.25 × 104 1.36 × 104 2.7 × 104

4. Conclusion A simple, sensitive and reproducible spectrophotometric determination of beryllium was established by using haematoxylin in presence of a cationic surfactant, cetyltrimethylammonium bromide. The proposed method, owing to no need for solvent extraction, could be applied to assay of beryllium in different water samples. The proposed method has the advantage of excellent reproducibility both within-day and between-day precision (Table 2). The sensitivity in terms of molar absorption coefficient of the developed method is found to be superior or almost equally good to many of the other spectrophotometric methods reported for beryllium (Table 4). Acknowledgements One of the authors (B.P. Dayananda) gratefully acknowledges the University Grants Commission, New Delhi and Department of Collegiate Education, Government of Karnataka for awarding a Teacher Fellowship to carryout this work. References [1] I. Nukatsuka, K. Sakai, R. Kudo, K. Ohzeki, Analyst 120 (1995) 2819. [2] E. Merian (Ed.), Metals and Their Compounds in the Environment: Occurrence, Analysis and Biological Relevance, VCH Publishers, New York, 1991, p. 775. [3] B.J. Alloway, D.C. Ayres (Eds.), Chemical Principles of Environmental Pollution, second ed., Blackie Academic and Professional, London, 1997, p. 49.

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