Spectrophotometric determination of nickel(ii) with 2-hydroxy-3-methoxybenzaldehyde

Indian Journal of Chemistry Vol. 46A, October 2007, pp. 1625-1629 Spectrophotometric determination of nickel(ii) with 2-hydroxy-3-methoxybenzaldehyde thiosemicarbazone A Praveen Kumar, P Raveendra Reddy* & V Krishna Reddy Department of Chemistry, Sri Krishnadevaraya University, Anantapur 515 003 (AP), India Email: raveendrareddy_sku@yahoo.com Received 7 March 2007, revised 31 August 2007 2-Hydroxy-3-methoxy benzaldehyde thiosemicarbazone has been synthesized, characterized and its analytical application investigated. It reacts with nickel(ii) in aqueous solution at ph 4.0-8.0 and at room temperature to form a yellow coloured ML (1:1) complex with absorption maximum at 410 nm and molar absorptivity 2.05 10 4 l mol -1 cm -1. Beer s law is obeyed in the range of 0.058-2.347 µg ml -1 of Ni(II). A method for the determination of nickel(ii) by second order derivative spectrophotometry has also been proposed. Interference of various diverse ions has been studied. The proposed methods have been successfully applied to determination of nickel in aluminium-based steels, drinking water, plant samples and in vegetable oil. IPC Code: Int. Cl. 8 G01N21/25 Nickel is one of the important alloying elements for steel and cast iron, while Urease, a nickel enzyme, is an essential micronutrient. Nickel is biologically important, being an essential trace element in human diet. Nickel bound to ribonucleic acid, has a special affinity for bone and skin and plays an important role in pigmentation. It has been reported that normal human plasma contains 0.012-0.085 ppm of nickel(ii). Several thiosemicarbazones have been employed as chromogenic agents for the spectrophotometric determination of nickel 1-6. Some of them are less sensitive 1,2, some are less selective 3,4 while others involve extraction into carcinogenic organic solvents 5,6. In the present note, a simple, selective and sensitive spectrophotometric method was developed for the determination of nickel(ii) in aluminum based steels, drinking water, plant samples and in vegetable oils using 2-hydroxy-3-methoxy benzaldehyde thiosemicarbazone (HMBATSC). UV-160A) fitted with 1 cm quartz cells and Phillips digital ph meter (model L1 613) respectively. Preparation and characterization of 2-hydroxy-3-methoxy benzaldehyde thiosemicarbazone (HMBATSC) The reagent (HMBATSC) was prepared by literature method. 2-Hydroxy-3-methoxy benzaldehyde (I) (11.25 g) and thiosemicarbazide (II) (4.55 g) were dissolved in sufficient volume of methanol and the mixture was refluxed for 60 min. The contents were allowed to cool and the product was separated by filtration. The crude sample obtained (C 9 H 11 O 2 SN 3 yield 80%) was recrystallised twice from hot methanol. Pure light yellowish green crystals of 2-hydroxy-3-methoxy benzaldehyde thiosemicarbazone (HMBATSC) (III) (m.pt. 220-222 C) were obtained (Scheme 1). A 0.01 M solution of HMBATSC in dimethyl formamide (DMF) was employed in the present studies. The infrared spectrum of the compound was recorded using Perkin-Elmer 137 IR spectrometer in KBr. The peaks observed at 3458 cm -1 and 3342 cm -1 may be assigned to symmetric and asymmetric -N-H stretching frequency of primary amino group. The peak observed at 3164 cm -1 may be assigned to OH stretching frequency of phenolic group due to intramolecular hydrogen bonding. The peak observed at 3028 cm -1 may be assigned to Ar-H stretching Experimental The absorbance and ph measurements were made on a Shimadzu UV-visible spectrophotometer (model

1626 INDIAN J CHEM, SEC A, OCTOBER 2007 frequency of aromatic proton, and that observed at 1595 cm -1 to C=N stretching frequency of azomethine. The peaks observed in the range 1530-1361 cm -1 were characteristic of aromatic ring stretching frequency. A strong peak observed at 1056 cm -1 may be assigned to C = S stretching frequency. The 1 H-NMR spectrum of the compound was recorded with DRX 300 NMR spectrometer in DMF solvent. The peak observed at δ value 8.2 (1H) was characteristic of phenolic OH group. The peak found at δ value 7.88 (3H) may be due to aromatic protons, while that observed at δ value 4.0 (3H) due to methyl group attached to hetero atom (oxygen atom). The peak observed at δ value 6.8 (2H) may be due to -NH 2 protons attached to thionyl group (C = S), and the peak observed at δ value 9.0 is due to aldehydic proton. The peak at δ value 11.4 may be due to NH proton (azomethine). NiSO 4.7H 2 O (0.2808 g) was dissolved in doubly distilled water containing a few drops of conc. H 2 SO 4 in a 100 ml standard flask to get a 1 10-2 M solution, which was standardized gravimetrically using dimethyl glyoxime 7. The working solutions were prepared daily by diluting the stock solution to an appropriate volume. All other chemicals used were of analytical grade. The buffer solutions were prepared by mixing 1 M hydrochloric acid and 1 M sodium acetate (ph 1.0-3.0) and 0.2 M acetic acid and 0.2 M sodium acetate (ph 3.5-7.0). The ph s of these solutions was checked with a ph meter. Determination of nickel(ii) In different sets of 10 ml volumetric flasks, each containing 5 ml of buffer solution (ph 6.0) and 1 ml of HMBATSC (8 10-3 M), varying volumes of 1 10-4 M nickel(ii) solution were added and made up to the mark with doubly distilled water. The absorbance was measured at 410 nm against the reagent blank, and the calibration plot was prepared. For the above solutions, second order derivative spectra were recorded with a scan speed of fast (nearly 2400 nm min -1 ), slit width of 1 nm with 9 degrees of freedom, in the wavelength range of 390-540 nm. The derivative peak height was measured by the peak-zero method at 415 nm and 448 nm. The peak height was plotted against the amount of nickel(ii) to obtain the calibration plot. The calibration graph follows the straight-line equation, y= mc + b; where c is the concentration of the solution, y is measured absorbance or peak height and m and b are constants. By substituting the corresponding experimental data substituted in the above equation, the calibration equations were calculated as A = 0.3045c + 0.0048 for zero order data and A 415 = 0.7400c + 0.0120 and A 448 = 0.4901c + 0.0380 for second derivative data, which give the best straight lines. Nickel(II) gives yellow coloured complex with 2-hydroxy-3-methoxy benzaldehyde thiosemicarbazone (HMBATSC) as shown in Scheme 2. The absorption spectra of HMBATSC and its nickel(ii) complex [Ni- HMBATSC] were recorded in the wavelength range 350-600 nm at ph 6.0 against the buffer solution and reagent blank respectively. The spectra show that nickel(ii) complex has two absorption maxima at 365 nm and 410 nm. At 365 nm, the reagent shows considerable absorbance. At 410 nm, the complex shows large absorbance while the reagent blank shows negligible absorbance. Hence, analytical studies were made at 410 nm. The effect of ph on the colour formation was studied to arrive at the optimum ph. Plot between ph and absorbance shows that maximum colour was obtained in the ph range of 5.5-6.5. Therefore, the ph 6.0 was chosen for further studies. The optimum concentration of the reagent required for the maximum colour formation was studied by measuring the absorbance at 410 nm. The results indicate that a 20-fold molar excess of the reagent is essential to get maximum absorbance. The reaction between Ni(II) and HMBATSC was instantaneous at room temperature and the absorbance of the complex remained constant for more than 72 h. The composition of the complex was determined using Job s method and confirmed by molar ratio method. The results indicate a 1:1 stoichiometry between the metal ion and the reagent under the experimental conditions. The stability constant of the complex calculated from Job s method was found to be 1.93 10 6.

NOTES 1627 The plot between absorbance and the amount of Ni(II) under optimal conditions was established and the straight line obeys the equation A = 0.3045C + 0.0048. Further, Beer s law was obeyed in the range of 0.058-2.347 µg ml -1. The molar absorptivity and Sandell s sensitivity were found to be 2.05 10 4 lit mol -1 cm -1 and 0.0287 µg cm -2 respectively. The standard deviation for ten determinations of 1.174µg ml -1 of nickel is ± 0.0047. The regression analysis of the linear curve gave the angular coefficient (m) and correlation coefficient (γ) are as 0.3045 and 0.9997 respectively. Effect of foreign ions The effect of various anions and cations on the determination of Ni(II) under optimal conditions was studied and presented in Table 1. From the interference studies, it was clear that all the anions studied did not interfere even when present in more than 200-fold excess. Majority of cations did not interfere when present in more than 50-fold Table 1 Tolerance limits of foreign ions [Amount of Ni(II) =1.173 µg ml -1 ] Foreign ion Tolerance Foreign Tolerance limit ion limit (µg ml -1 ) (µg ml -1 ) Ascorbic acid 1760 Th(IV) 450 Tartrate 1410 K(I) 390 Bromate 1280 Ti(IV) 340 Thiosulphate 1120 Li(I) 280 Sulphate 960 Mg(II) 250 Citrate 900 Pb(II) 240 Phosphate 950 Al(III) 135 Oxalate 880 Zn(II) 130 Bromide 800 V(V) 12,102 a Thiourea 750 Zr(IV) 100 Iodide 640 Co(II) 12,100 a Nitrate 620 Fe(II) 10,100 b Acetate 600 Ce(IV) 85 Formate 440 Mn(II) 78 Chloride 355 Cr(III) 60 Fluoride 210 Pt(IV) 60 Te(IV) 640 Mo(VI) 52 Cd(II) 560 Ru(III) 51 W(VI) 520 Cu(II) 45 Na(I) 460 a Masked in the presence of 1760 µg of ascorbic acid b Masked in the presence of 1410 µg of tartrate excess. Cu(II) was tolerated up to 40-fold excess. Fe(II), V(V) and Co(II) interfered when present in more than 10-fold excess. However, Fe(II), in presence of 1410 µg of tartrate and V(V) and Co(II), in presence of 1760 µg of ascorbic acid, were tolerated up to 100-fold excess. Derivative method A sensitive second order derivative spectrophotometric method was developed for the determination of nickel(ii). For the second derivative spectra (Fig. 1), the derivative amplitudes at 415 nm (valley) and at 448 nm (peak) were proportional to the concentration of Ni(II). The derivative amplitudes were measured for different concentrations of Ni(II) and plotted against the amount of Ni(II). The plots were linear and obeyed Beer s law in the range 0.029-3.030 µg ml -1 at 415 nm and 0.029-3.285 µg ml -1 at 448 nm. In the second order derivative method, the tolerance limit of Fe(II) increased from 10 fold (direct method) to 20 fold (second derivative method). The angular coefficient (m) of the linier plot was found to be 0.7400 and 0.4901 at 415 nm and 448 nm respectively. The correlation coefficients (γ) are calculated as 0.9993 and 0.9995 at 415 nm and 448 nm respectively. Application to real samples The proposed method was employed for the determination of nickel(ii) in drinking water and in aluminium based alloys. Fig 1 Second derivative spectra of Ni(II) HMBATSC versus reagent blank. [Ni (II) (µg ml -1 ) = (1) 0.2347; (2) 0.4694; (3) 0.7041; (4) 0.9388].

1628 INDIAN J CHEM, SEC A, OCTOBER 2007 The water samples were collected from different parts of Anantapur district (Andhra Pradesh, India). The water samples (1 liter) were collected in clean 2 liter beakers and slowly evaporated to about 25 ml. Then, 5 ml of H 2 O 2 was added and evaporated to dryness. It was then dissolved in 20 ml of water and filtered to remove insoluble substance. The filtrate was collected in 100 ml volumetric flask quantitatively and diluted to the mark with distilled water. Two untreated water samples collected from different places around Anantapur town (Andhra Pradesh, India) have been analyzed after treating the water sample using the procedure as described above. About 0.4 g alloy sample (BAS-20, BAS-85) was treated with 15 ml of 1:1 HCl. To this, 3 ml of HNO 3 was added and the contents boiled until dissolution was complete. Then, 10 ml of water and 40 ml of 4N Table 2 Determination of nickel in drinking water Water sample Amount of nickel (µg ml -1 ) Recovery (%) Added Found a 1 1.1 1.2 2.2 96 0.8 2.0 105 1.0 2.2 104 2 1.0 0.5 1.4 94 a Average of five determinations ammonium hydroxide solution were added and filtered through a Whatman filter paper (No. 41). The filtrate was collected into 25 ml volumetric flask and made up to the mark with distilled water. Known aliquots of the above alloy sample solutions were taken in a 10 ml flask containing 5 ml of buffer solution (ph 6.0), 1410 µg ml -1 of tartrate (to mask Fe(II)) and 1 ml of the HMBATSC solution (8 10-3 M).The contents were made up to the mark with distilled water. The contents, if necessary, were filtered and the absorbance of the resulting solution was measured at 410 nm against the reagent blank. The amount of nickel(ii) present in the sample solution was determined from the predetermined calibration plot. The results are presented in Tables 2 and 3. Second order derivative method Ni(II) was determined in alloy steels, plant leaves and vegetable (groundnut) oil samples by second derivative spectroscopic method. The plant leaves were supplied by Andra Pradesh Agricultural research institute (APARI), Hyderabad (A.P.) India. Steel sample (0.1-0.5 g) was dissolved completely in minimum amount of aqua regia by slow heating on a sand bath and then heated till the evolution of oxides of nitrogen fumes ceased. After cooling, 5-10 ml of 1:1 of H 2 O: H 2 SO 4 mixture was added and evaporated to dryness. Sulphuric acid treatment was Table 3 Determination of nickel (II) in aluminum based alloys and alloy steel samples Sample Cert. Comp. (%) Amount of nickel(ii) (%) Relative error Present Found a (%) Aluminium based alloys BAS-20 Cu 4.10; Ni 1.93; Fe b 0.43; Mn 0.19; Si 0.29; Mg 1.61; Rest Al BAS-85 Cu 0.90; Ni 0.91; Fe b 1.15; Mn 0.02; Si 2.04; Mg 0.18; Zn 0.01; Rest Al Alloy steel samples Copper-nickel alloy Alloy NTPC Ball bearing material BCS 364 Gun metal Monel a Averages of five determinations b 1410 µg ml -1 of tartrate to mask Fe(II) Cu 67; Fe 0.83; Mn 0.08; Si 0.29; Ni 31.20 Fe 65; Cr 15; Cu 4.5; Mn 2; Ni 10.00 Cu 80.00; Sn 9.35; Pb 9.25; Ni 0.28; Sb 0.18; Zn 0.13; As 0.065; P 0.056; Al 0.002; Si 0.003. Zn 1.37; Sn 9.22; Cu 87.95; Pb 1.13; Fe 0.01; P 0.07; Ni 0.24 Ni 63.01; C 0.15; S 0.002; Mn 0.07; Si 0.05; Fe 2.50; Cu 31.0 1.93 1.90-1.5 0.91 0.92 1.1 31.20 31.42 +0.70 10.00 9.92-0.80 0.280 0. 275-1.78 0.240 63.10 0.244 +1.66 63.25 +0.24

NOTES 1629 Table 4 Determination of nickel (II) in plant leaves and vegetable oil Sample Ni(II) (%) Relative AAS Present error method 8 method a Pisum sativum (Hulls) 2.060 ± 0.003 2.065 ± 0.004 Mangifera indica leaves 2.150 ± 0.004 2.154 ± 0.002 Eucalyptus leaves 1.038 ± 0.002 1.033 ± 0.005 Azadirachta indica leaves 1.481 ± 0.005 1.486 ±0.003 Hydrogenated Ground nut oil 0.56 0.57 +1.78 a Average of five determinations carried out three times to remove all the nitric acid. The residue was dissolved in 20 ml of distilled water, filtered and the filtrate was made up to 100 ml in a calibrated volumetric flask with distilled water. The sample solution was appropriately diluted to obtain the concentration in the required range. Freshly collected plant samples were cleaned and dried for one hour in open air protecting from mineral contamination. The dried samples were finely powdered in a mortar. The powdered material was brought into solution by dry ashing method. Hydrogenated edible groundnut oil (100 g) was dried in a hot air oven at 100 o C and subsequently dissolved in 20 ml mixture of 1:2:5 of H 2 SO 4 :H 3 PO 4 : HNO 3. The contents were heated until sulphurous acid fumes were evolved and the volume was reduced to about 5 ml. A small quantity of distilled water was added and filtered through an acid washed Whatman 41 filter paper into a 100 ml volumetric flask and made up to the mark with distilled water. To known aliquots of the above samples taken in 10 ml volumetric flasks, 5 ml of buffer solution of (ph 6.0) and 1 ml of HMBATSC (8 10-3 M) were added and the contents were made up to the mark with distilled water. The second derivative spectra were recorded and the amplitude of the derivative curves at 448 nm was measured. The amount of nickel present in the samples was calculated from the derivative amplitude with the help of predetermined calibration plot. The results are presented in Table 4. The analytical characteristics of the zero order, second order derivative methods in the present investigations for Ni(II) show that the derivative method is more sensitive than the zero order method. References 1 Ferreira S L C, Santos B F, de Andrade J B & Spinola Costa A C, Microchim Acta, 122 (1996) 109. 2 Malik A K, Kaul K N, Lark B S, Faube W & Rao A L J, Turk J Chem, 25 (2001) 99. 3 Kumar A & Jain M, Chem Anal, 39 (1992) 73. 4 Bansal A K & Nagar M, J Indian Chem Soc, 83 (2006) 731. 5 Boladani S N, Tewari M, Agarawal A & Sekhan K C, Fr J Anal Chem, 349 (6) (1994) 478. 6 Odashima T, Kohata K, Yogi K & Ishii H, Bunseki Kagaku, 44(2) (1995) 135. 7 Vogel A I, A Textbook of Quantitative Inorganic Analysis, 5 th Edn. (Longman ) 1989, p 327. 8 Folin M, Contiero E & Calliari J, Anal Chim, 81 (1991) 39.