IBN AL- HAITHAM J. FOR PURE & APPL. S CI. VOL. 24 (1) 2011 A new Spectrophotometric Method For The Determination of La (III) With 3-Hydroxy -4-(2-hydroxy- Phenyl azo) Naphthalene -1- Sulfonic Acid Received in : 27 June 2010 Accepte d in : 9 November 2010 S. A. Darweesh , A. S. Hammodi , R. M. Mahmmod Departme nt of Chemistry, College of Education Ibn -AL- Haitham, Unive rsity of Baghdad Abstract A simple, rapid and sensitive sp ectrop hotometric method has been p rop osed for the determination of La (III) using 3-hy droxy -4-(2-hy droxy -p henyl azo) naphthalene -1- sulfonic acid as a chromogenic reagent. This method is based on the formation of a red-pink colored comp lex, up on the reaction of La(III) with the reagent in an alkaline medium (p H= 9.50), having a maximum absorbance at 459 nm. Beer's law is valid in the concentration range 0.5- 12 µg.ml -1 with a Sandell's sensitivity value of 0.0188 µg.cm -2 and molar absorp tivity of 7376.12 L.mol -1 .cm -1 . The st oichiometric comp osition of the chelate is 1:3. The effect of the p resence of different cations as interferants in the determination of La(III) under the given op timum conditions were invest igated. Key words :Spectrophotme tric , Dete rmination of La (I II) ,3-Hydroxy -4- (2-hydroxy-Phenyl azo) Naphthale ne -1- Sulfonic Acid Introduction A basic characterist ic of the lanthanide group is the chemical similarity of individual members. Consequently , data on the total lanthanide content often suffer in p ractical p roblems, p articulary when all the lanthanides behave similary , such as the p roduction of alloy st eel or when the ratio of the individual members is constant as in geochemistry .[1] Lanthanum and its comp ounds are used in high technology app lications, such as sup erconductors, sup ermagnets, nuclear chemist ry , laser, alloy and also as anticoagulants[2]. Various methods such as isotop ic dilution mass sp ectrometry (ID-M S)[3], instrumental neutron activation analysis (INAA)[4], inductively coupled p lasma mass sp ectrometry (ICD- M S)[5], and inductively coupled p lasma atomic emission sp ectrometry (ICPAES)[6,7] are available for the determination of La . These methods require costly equip ments or a reactor facilities for (INAA); most of the laboratories are not equip p ed with these instruments, interest. Az o dy es are a very imp ortant class of organic comp ounds receiving att ention in the scientific literature. Recently , azo metal chelates have drawn the att ention of some research due to their excellence in sensitivity and st ability as op tical recording medium[8,9]. M oreover, the complexes of some azo dy es with metal ions, such as Co(II), Ni(II), Zn(II) and Pd(II) have been recently invest igated as recording materials for DVD-R (Digital Versatile Disc-Recordable)[10] . 3-Hy droxy -4-(2-hy droxy p henyl azo) naphthalene -1- Sulphonic acid (M .wt 366.33 gm/mole), (also called solochrome violet (Rs), see Schem 1) is an azo dy e, used as metal IBN AL- HAITHAM J. FOR PURE & APPL. S CI. VOL. 24 (1) 2011 indicator in the chelatometric determination of Al (III) in natural water[11,12]. In addition, Rs is a reactive azo dy e belonging to the largest class of dy es commonly emp loyed in textile industry [13]. No information is available about the sp ectrop hotometric determination of La(III) with Rs reagent. In this p resent work, an att emp t to adopt the reagent Rs as a chromogenic agent for a sp ectrop hotometric determination of La(III) was done and the op timum reaction conditions for excellent metal ion sensitivities are evaluated. S chem 1 : The molecular structure of Sol ochrome violet (RS ) Experimental A Cintra 5 GBS Scientific equip ment UV – Visible sp ectrop hotometer , with 1 cm quartz cells and a Philip s model PW-9421 p H-meter was used for the absorbance and p H measurements resp ectively.Infrared measurements were carried out on a Shimadzu-IR Prest ege -ZI Fourier transform infrared. Reagents A stock (100 µg .ml -1 ) solution of La(III) was p repared by dissolving 0.0117 gm of La2O3 p urity ( 99.5% ) (fluka) in 20 ml 5M HNO3 and then diluted to 100 ml with distilled water Rs- Reagent p urity (99.5%) (BDH) 2.72×10 -3 M solution was p repared by dissolving 0.0996 gm in a 100ml distilled water by using a volumetric flask. Buffer solution (p H=10.0) was p repared by mixing 3.21 gm NH4Cl with 2.24 gm KCl then 22.7 ml of NH4OH was added and diluted to 100 ml with distilled water in volumetric flask[14], the p H being adjust ed with a few drop s of 0.5M NaOH or 0.5 M HCl. Procedure for preparation of synthetic sample Different water samples (Tap and river) were collected from various sites. The water samples were filtered through aWathman filter p aper No 41. To 20 ml of each sample 0.0117 gm of La2O3 was added followed by addition of 20 ml of 5M HNO3 and the mixture was heated with continous st irred until comp lete dissolution. The volume was then made to 100 ml with sample water . Test solutions were then p repared by subsequent dilution with the same water samp le. IBN AL- HAITHAM J. FOR PURE & APPL. S CI. VOL. 24 (1) 2011 General Procedure To various volumes of 7.198×10 -4 M (100 µg. ml -1 ) lanthanum (III) solution, 0.5ml of 2.72×10 -3 M reagent and 0.5ml of buffer solution (p H=9.5) were added, then the resultant solutions were diluted to the 10ml with dist illed water. The absorbance were measured at 459 nm against the reagent blank solution. Re sults and Discussion The ligand 3-hy droxy -4- (2-hy droxy p henyl azo) naphthalene -1-sulfonic acid reacts with La(III) to form a st able red-pink comp lex sp ecies, which is highly soluble in water. The absorp tion sp ectrum of the La(III)- reagent complex in aqueous solution was st udied over the wavelength range 190-800 nm. The comp lex exhibited an absorp tion maximum at 459 nm against reagent blank (Fig.1). Effect of pH The effect of p H on the development up on the reaction between La(III) and reagent was st udied at 459 nm. The p H being adjust ed with a few drop s of 0.5M HCl and 0.5M NaOH. A p lot of absorbance against p H (Fig.2) ,showed that the absorbance was increased gradually as the p H increased and a maximum absorbance was obtained at the p H 9.50. The absorbance then decreased at p H value above 9.5, Hence a p H of 9.50 was used in all the subsequent exp erimental work. Effect of reagent concentration Various volumes ( 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1 and 1.2 ml ) of reagent solution were added to 6µg.ml -1 of La(III) solution, 0.5 ml of 2.72 × 10 -3 M was found to be enough to develop the color to its fully intensity and a large excess of reagent solution has deleterious effect on t he absorbance (Fig.3). Effect of reaction time The reaction is instantaneous, and the La(III)- reagent comp lex att ained maximum and constant absorbance immediately after addition of the reagent and diluting the solution to the final volume. The color obtained remained st rictly unaltered for at least 2 hours. S toichiometry of the complex The stoichiometry of the comp lex has been st udied by the mole ratio method . A series of solutions were p repared by transferring 1 ml aliquots of La(111) solution (3.24x10 -4 ) M , then increasing amount of reagent solution ranging from ( 1.62x10 -4 m mole-1.45x10 -3 m mole ) were added. To each solution 0.5 ml of buffer solution was added and the p H was adjust ed to 9.50 with a few drop s of 0.5 M HCl and for 0.5 M NaOH and the resulted solutions were diluted up to the 10 ml with distilled water . The absorbances were measured at 459 nm against the reagent blank solution. The obtained results are given in table (1) and fig (4) which shows that the ratio of La : Rs in the comp lex is 1:3, therefore a st ructure of the comp lex could be prop osed as shown in scheme (2). IBN AL- HAITHAM J. FOR PURE & APPL. S CI. VOL. 24 (1) 2011 S cheme (2) : The propose d structure of the [ La(III) – (Rs)3 ] -3 complex. The IR sp ectra of the ligand and comp lex (Fig 5, a and b) show sharp bands at 3417 and 1620 cm -1 , which can be att ributed to the - OH and –N=N group s resp ectively. The band at 1620 cm -1 disapp eared and a new band at 1404 cm -1 app eared while the band which corresp oned to – OH group brodened, these indicate that the coordination in the formed charge transfer complex occur through the azo group and one of the hydroxy l group [15]. Cal ibration graph (Analytical data) Under the op timum exp erimental conditions of the p rop osed method, a linear calibration graph was given and obtained between absorbance and concentration in the range given in (Fig. 6). The correlation coefficient, intercep t and slop e were calculated using least – square method .The mean Sandell , s sensitivity and the app arent molar absorp tivity values together with the limits of detection (D.L) and quantification (Q.L)[16] comp iled in table(2), are indicative of the high sensitivity of the prop osed method. Method Validation The accuracy of the method was evaluated by p erforming five replicate analyses on La(III) st andard solutions at three different amounts of La(III) within the working range and calculating the p ercentage error. The p recision was determined by calculating the relative st andard deviations for five determinations at each level. (Table 3). IBN AL- HAITHAM J. FOR PURE & APPL. S CI. VOL. 24 (1) 2011 Effect of foreign i ons The effects of over 10 ions on the determination of 7 µg.ml -1 of La (III) were st udied and the results are summarized in (Table 5).As can be seen, a large number of ions have no significant effect on the determination of La(III). On the other hand the most serious interferences were from Ce(III), Ho(III) and Pr(II) ions, so that p rior sep aration would be essential. Application to real sample s To evaluate the analytical app licability and to check the accuracy of the p rop osed method, the method was app lied to t he determination of La(III) in tap and river water sp iked with La(III) (i.e sy nthelic samples) and the obtained result is summarized in (Table 6). Conclusions The p resent st udy described the use of solochrom violet (Rs) reagent for the development of selective , sensitive and accurate sp ectrop hotometric methods for the determination of La (111) with (Rs) reagent, the accep table –linearity and accuracy of the results indicated that the method can be app lied for routine analysis of La(111) in real samples . Re ferences 1. Henderson,P.(1984). Rare Earth Geochemistry , Elsevier, Amst erdam.p213-219. 2. Vijayan,S.; M elnky ,A.J.; Singh,R.D.and Nut tall,K;(1989), Recovery of Lanthanides and Yttrium from red mud by selective leaching . M in. Eng. 41,p 13-17. 3.Ft hirlwall, F. (1982), A triple – Filament method for rapid and p recise analy sis of rare – earth elements by isotop e dilution Chem. Geol. 35:155-166. 4. Jackobs,J.W.; Koritev,R.L.; Balchard,D.D. and Haskin.L.A. (1977), J. Radioanal. Inter ference from uranium in neutron activation analy sis or rare – earths in silicate rocks. Chem. 40: 93-99 . 5.Date, A.R.and Gary,A.L. (1985), Determination of As, La, Bi and Hg in water samples by flow – injection inductively coupled p lasma mass sp ectrometry with an- situ nebulizer , hy dride generator .Spectrochim, Acta part B 40 :115. 6.Crock, J.G.and lichte,F.E. (1982), Determination of rare earth elements in geological materials by inductively coupled argon p lasma / atomic emission sp ectrometry . Anal. Chem.. 54 :1329-1332. 7. Djingova,R.and Ivanova,J. (2002),Determination of rare earth elements in soils and sediments by inductively coupled p lasma atomic emission sp ectrometry after cation – exchang sep aration. Talanta 57(5): 821-829. 8.Wang,S.; Shen,S. and Xu,H. (2000) Sy nthesis sp ectroscop ic and thermal prop erties of a series of azo metal chelate dy es Pigments 44:195 . 9.Chapman, D.D.; Goswami, R. and Kovacs,C.A. (1995), Invest igation of op tical nonlinearities of azo nickel chelate comp ound by the z–scan technique. European Patent Ap p lication EP 0649884. 10.Park,H.; Kim,E.R.; Kim,D.J. and Lee,H. (2002), Op tical p rop erties of nickel(11) – azo comp lexes thin films for p otential app lication as high – recordable op tical recording media Bull. Chem. Soc. Jap an 75, p2067 . 11.Britt ain,H.C. (1979), Ap p lication of 8- hydroxy l quinoline –S- Sulfonic acid in the sp ectrop hotometric determination of some lanthanides Anal. Chim. Acta, 106: 401. 12.Wang,X.; Lei,J.; Gan,S.; Bi. N. and wei,Z.(2001), Determination of the sp eciation of aluminum (111) in natural waters by adsorp tion stripp ing Voltammetry and complexation with A 111 . solochrome violet RS Analytica Chimica Acta, Number 1:499. IBN AL- HAITHAM J. FOR PURE & APPL. S CI. VOL. 24 (1) 2011 13.M rowetz,M . and Selli,E. (2005), Enhanced photocataly tic formation of hydroxy l radicals on fluorinated TiO2. Phy s. Chem .Chem. Phy s; 7:1100. 14.Basavaiah,K. and Shakunthala,V. (2004), charan Ion- p air comp lexometric determination of cyp roheptadine hydrochloride using bromophenol-blue. J of Science Asia 30: 163-170. 15- Silverstein, Robert M .; Bassler Clay ton G. and M orrill, Terence C.(1981) ,Sp ectrometric Identification of Organic comp ounds .4th Edition. John Wiley &Sons, USA.p 318-322. 16- Siddap p a,K.;M allikkarjun,M .;Reddy ,P.T .andTambe.M .(2008),Determination of La (III) by sp ectrohp otometric analysis Ecl.Quim, Saopaulo,33(4):41-46. 17-Fernandez L. and Olsina,R. (1990),Sensitive sp ectrop hotometric determination of Lanthanum with 2 – (3,5-dichloro-2-py rid(azo) -5-dimethy laminop henol). Analytical Sciences:Vol 6 (3): 112-121. 18- Guo Z ien F.; Jiao M ai, Liang,P. and X. Bu. Lu.(1999), Study on the sp ectrop hotometricDetermination of rare earths with a new chromogenic reagent . dibromo – p –M ethy l- chlorosulfonazo- Chinese chemical lett ers 10 (10):851-854 . 19- Govinda ,P.; M ohan Reddy ,K.P.; Krishna Reddy ,V. and Raveendra Reddy .P.(2008), 2- Hy droxy – 1-naphthaldehyde-P-hy droxy benzoic hydrazone as a Sp ectrop hotometric reagent for t he determination of lanthanum(111) . Indion.J. Of chemistry . 47A :1381-1383. 20- Yadvendra,K. and Shrivast ar.P.(1997), Solvent extraction sp ectrop hotometric and Indvctively coupled p lasma atomic emission sp ectroscop ic determination of Lanthanum(111) with Crown hy droxomic acid. Tolanta, 45(2):397-404 . 21- Kokare ,B.N.; Han,S.H. and Amuse.M .A.(2009),Solvent extraction of lanthanum(111) by N – n- octy laniline from Salicy late media.Desalination and water treatment.12:79 – 86 Table (1) : Mole ratio method results Conc. of reagent CL:CM Absorbance 1.62 x 10 -5 0.5 0.025 3.24 x 10 -5 1.0 0.070 4.90 x 10 -5 1.5 0.140 6.50 x 10 -5 2.0 0.180 8.09 x 10 -5 2.5 0.240 9.72 x 10 -5 3.0 0.290 1.14 x 10 -4 3.5 0.295 1.30 x 10 -4 4.0 0.291 1.45 x 10 -4 4.5 0.273 IBN AL- HAITHAM J. FOR PURE & APPL. S CI. VOL. 24 (1) 2011 Table (2): Se lected analytical paramete rs obtained with optimization experiments. Parameter Proposed method Linear dynamic rang e (µg.ml -1 ) 0.5-12 Intercept 0.0116 Slope 0.0531 Correlation coeffici ent (r) 0.9979 Molar absorptivity(L.mol -1 .cm -1 ) 7376.12 Sandell Sensitivity (µg.cm -2 ) 0.0188 Detection limit * (µg.ml -1 ) 0.475 Quantitation limit ** (µg.ml -1 ) 1.440 3.3 x S.D of blank * D.L = ---------------------------- Slop of calibration curve 10 x S.D of blank ** Q.L = -------------------------------- Slop of calibration curve Table (3): Evaluati on of accuracy and precisi on of the propose d method. Amount of La(III) (µg.ml -1 ) (Error %) * (R.S.D%) * Taken Found (mean) 5.0 5.04 0.80 2.11 7.0 6.91 1.28 1.41 10.0 10.38 3.80 3.10 * for five determinations Table (4): show the p rop osed method has accep table linearity ranges when it comp ared with other method. Table(4):Comparison of propose d method with other reported spectrophotome tric methods. Reagents Beer , s law limit µg. ml -1 Ref. 2-(3,5-dichloro-2-p y ridy(azo)-5- dimethy l amino phenol) 0.6-40 17 Dibromo-p -methy l – chlorosulfon-azo 1.0 – 15 18 2-Hy droxy -1-naphthaldihyde–p - hy droxy benzoic hydrazone 0.22 – 8.33 19 Crown hy droxamic acid 1.2 – 20 20 N-n – octy l aniline 0.45 – 18 21 3- hy droxy l-4- (2- hy droxy l-p henyl azo) naphthalene -1- sulfonic acid 0.5 – 12 This work IBN AL- HAITHAM J. FOR PURE & APPL. S CI. VOL. 24 (1) 2011 Table (5): Determination of 7 µg.ml -1 of La(III) in the presence of foreign i ons Foreign ions Amount added (µg.ml - 1 ) Amount found (µg. ml - 1 ) Error % Cu +2 0.50 1.20 7.08 7.11 + 1.14 + 1.57 Cd +2 0.50 2.90 7.14 7.09 + 2.0 - 1.28 Ni +2 0.50 2.50 7.15 7.02 + 2.14 + 0.28 Co +2 1.50 3.00 6.91 7.11 - 1.28 +1. 57 Al +3 0.75 1.00 7.09 7.05 + 1.28 + 0.71 Cr +3 0.75 1.00 7.06 7.10 + 0.85 + 1.42 Mn +2 0.70 1.25 7.09 7.11 + 1.28 + 1.57 Zn +2 0.70 1.25 7.11 7.15 + 1.57 + 2.14 Ho +3 0.70 1.50 7.30 7.52 + 4.28 + 7.42 Ce +3 0.70 1.50 7.20 7.39 + 2.85 + 5.57 Pr +3 0.70 1.50 7.22 7.15 + 3.14 + 2.14 Table (6): Determination of La(III) added to a water samples µg.ml -1 . Samp le Sp iked M easured Recovery % Tap water 4 6 8 3.80 6.10 8.80 98.0 100.5 102.5 River water 4 6 8 4.30 6.40 8.70 103.0 102.0 101.8 IBN AL- HAITHAM J. FOR PURE & APPL. S CI. VOL. 24 (1) 2011 Fig.(1):Absor ption S pectra of a: 6 µg.ml -1 (La(III)) b: 6 µg.ml -1 La(III) ( 4.31x10 -5 M),1.36×10 -4 M ( Reagent)at pH=9.50 c: blank 1.36 ×10 -4 M (Reagent) at pH=9.50 against disti lled water. 0 0.1 0.2 0.3 0.4 7 8 9 10 11 12 pH A b s o rb a n c e Fig.(2):Effect of pH on the absorbance of 6 µg.ml -1 La(III), 1.36 ×10 -4 M (Reagent) at 459 nm. IBN AL- HAITHAM J. FOR PURE & APPL. S CI. VOL. 24 (1) 2011 0 0.1 0.2 0.3 0.4 0 0.2 0.4 0.6 0.8 1 1.2 Reagent Volume (ml) A b s o rb a n c e Fig.(3):Effect of reagent volume on the absorbance of 6 µg.ml -1 Lanthanum (III) sol uti on. Fig.(4): Mole ratio plot of Lanthanum (III) determination by the propose d method. IBN AL- HAITHAM J. FOR PURE & APPL. S CI. VOL. 24 (1) 2011 Wavenumb er 1/Cm Fig.(5-a): IR S pctrum of the reagent Wavenumb er 1/Cm Fig.(5-b):IR S pectrum of the La(III) – reagent complex IBN AL- HAITHAM J. FOR PURE & APPL. S CI. VOL. 24 (1) 2011 Fig. (6) : Calibration graph 2011) 1( 24المجلد مجلة ابن الھیثم للعلوم الصرفة والتطبیقیة كسي هیدرو -3باستخدام كاشف ) 111(طریقة طیفیة جدیدة لتقدیر الالنثانوم حامض السلفونیك -1-نفثالین )یل ازو فن هیدرروكسي -2( -4- 2010حزیران 27:استلم البحث في 2010تشرین الثاني 9:البحث في قبل رؤى مؤید محمود ،ازهار صادق حمودي ، سمر احمد درویش جامعة بغداد ، ابن الهیثم –كلیة التربیة ،قسم الكیمیاء الخالصة – 2(-4-هیدروكســي -3باســتعمال ) 111(طریقــة طیفیــة بســیطة وســریعة وحساسـة لتقــدیر الالنثــانوم تاقترحـ د بلـون احمـر ارجــواني حـامض السـلفونیك كاشـف لـوني تعتمــد الطریقـة علـى تكـوین معقـ -1-نفثـالین ) هیدروكسـي فنیـل ازو p = 9.5 مـع الكاشــف فـي وســط قاعـدي La )111(تفاعــل لنتیجـة H الــذي اظهـر اعظــم امتصـاص عنــد طـول مــوجي مل . مایكروغرام ) 12- 0,5(لقد اظهرت الطریقة انطباق قانون بیر لمدى من التراكیز یتراوح بین . نانومیتر 459مقداره 7376.12عامل االمتصاص المولي یساوي وكان م، ­²سم .مایكروغرام 0.0188وكانت قیمة حساسیة ساندل تساوي ¹ˉ تقـدیر فـيلقـد تمـت دراسـة تـاثیر وجـود متـداخالت مختلفـة ).كاشف : فلز ( 1:3لمعقد المتكون بنسبة ا ¹־سم. ¹־مول.لتر )111 (La بتطبیق الطریقة تحت الظروف المثلى. فنیل ازو هیدروكسي ، (La) تعیین المطیافیة ،:الكلمات المفتاحیة