A%a(yst, October, 1980, Vol. 105, j!@. 965-973 965 Pyr i d i n e- 2 - aceta I d e h yd e Sa I icy I oy I h yd razo ne as an Analytical Reagent and its Application to the Determination of Vanadium M. Garcia-Vargas, M. Gallego * and M. de la Guardiat Department of Analytical Chemistry, Faculty of Sciences, University of Seville, Seville, Spain The synthesis, characteristics and analytical applications of pyridine-2- acetaldehyde salicyloylhydrazone (PASH) are described. The reagent reacts with vanadium(V) to produce a yellow 1 : 1 complex (A,,, =415 nm, E = 1.87 x lo4 1 mol -I cm-I in chloroform). The yellow complex, extracted into chloroform, has been used for the spectrophotometric determination of vanadium in a steel, a lead - vanadium concentrate and a phosphoric acid sample.A procedure based on the standard additions method has been applied satisfactorily to the determination of trace amounts of vanadium a t the parts per billion level (parts per lo9). Keywords: Pyridine-2-acetaldehyde salicyloylhydvazone reagent; vanadium determination; standard additions method; spectropkotometvy The uses of aroy1hydrazones1-l2 as analytical reagents have been described in an earlier paper.13 Aroylhydrazones behave as bidentate,s9Q tridentatel0*l1J3 or tetradentate12 ligands, forming coloured chelates with transition metal ions. In moderately acidic media or alkaline solution the hydrogen atom of the -CONH- group can split off and neutral metal chelates are formed.10~11J3 In this paper, the synthesis, properties and analytical applications of pyridine-2-acetal- dehyde salicyloylhydrazone (PASH) are reported.An extraction - spectrophotometric method for the determination of trace amounts of vanadium has been investigated and the effects of interferences have been widely studied. In order to avoid some interferences, masking and cation-exchange procedures have been used. The determination of small amounts of vanadium in different materials is described. The standard additions method has been used to determine vanadium a t the sub-parts per million level. PASH Experimental Apparatus A Pye Unicam SP8000 spectrophotometer was used for recording spectra in the ultraviolet and visible regions of the spectrum. A Perkin-Elmer - Coleman 55 (digital) and a Beckmann DU spectrophotometer were used for absorbance measurements at fixed wavelengths in the visible and ultraviolet regions of the spectrum, respectively; 1-cm silica or glass cells were used.A Philips PW 9408 pH meter, with glass - calomel electrodes, was used for pH measurements. * Present address: Faculty of Sciences, University of Cordoba, Cordoba, Spain. t Present address: Faculty of Sciences, University of Valencia, Valencia, Spain. A Pye Unicam SPlOOO infrared spectrophotometer was also used.966 GARCIA-VARGAS et al. : PYRIDINE-2-ACETALI)EHYDE Analyst, vd. 105 Reagents All solutions were prepared with analytical-reagent grade chemicals using distilled water. Synthesis of PASH. A 1.05-ml volume of pyridine-2-acetaldehyde was added to 2 g of salicyloylhydrazide dissolved in 20 ml of hot absolute ethanol.TWO drops of concentrated hydrochloric acid were added and the mixture was heated in a water-bath. The yellow crystals were filtered off and recrystallised twice from ethanol. The product (yield about 64%) had a melting-point of 230-234 "C, and elemental analysis gave C 65.85%, H 5.15% and N 16.70°/0; the calculated values for C,,H,,O,N, are: C 65.87y0, H 5.13% and N 16.460/,. A 0.05y0 mi V solution was prepared by dissolving 0.05 g of the reagent in 3 ml of hrN-dimeth:glformamide and diluting to 100 ml with chloroform. This solution was prepared by dissolving vanadium(V) oxide in 1 M sodium hydroxide solution, standardising it gravimetric- ally using ~upferr0n.l~ Dowlex 50-X8 resin, hydrogen form. Slurry 5.0 g of cation-exchange resin, 20-50 mesh, with distilled water and pour into a column 30 cm long and 2 cm in diameter with glass sinter bed support and a tap a t the bottom.Procedure for the Determination of Vanadium(V) To 10-50 ml of sample solution in a separating funnel containing up to 100 pg of vanadium(V), add 2 ml of 0.5 M potassium chloride solution and 1.5 ml of 1 M hydrochloric acid and extract the mixture with one 10-ml volume of PASH reagent solution. Shake the funnel vigorously for 2 min, allow the phases to separate and transfer the lower (organic) layer into a 10-ml flask containing anhydrous sodium sulphate. Measure the absorbance of the yellow chloroform extracts after 45 min a t 425 nm against distilled water or at 415 nm against a reagent blank, prepared in a similar way but without the vanadium.The calibration graph was prepared by using standard solutions of vanadium(V) treated in the same way. Pyridine-2-acetaldehyde salicyloylhydrazone reagent solution. This solution was stable for several days. Vanadium( V ) standard solution, 5.295 g 1-1 of vanadium( V ) . Working standards were prepared from this solution as necessary. Results and Discussion Properties of Pyridine-2-acetaldehyde Salicyloylhydrazone The bands were assigned to the stretching vibrations of the N-H bond (3290 cni-l), the =C-H bond (3050 cm-l), the C=O bond (1640 cm-l), the C=N bond (1550 cm-I) and the N-N bond (920 and 875 cm-l). The solubility in other solvents, such as water, methanol, ethanol, chloroform and benzene, is about 1 g 1-1 or less. A reagent solution in ethanol or chloroform of 5 x M concentration shows two absorption maxima at 298 and 311 or a t 300 and 323 nm, with molar absorptivities of 2.6 x lo4 and 2.56 x lo4 or 1.94 x lo4 and 1.92 x lo4 1 mol-l cm-l, respectively.M) shows bathochromic shifts a t pH less than 4 or greater than 6. Hydrolysis of PASH to pyridine-2- acetaldehyde and salicyloylhydrazide occurs slowly in aqueous solution. The percentage of decomposed reagent at pH 2.6,4.4,7.0 and 9.0 after 1 h was 33.3,13.5,0 and O%, respectively. The method used by Phillips and Merrit16 was used for the determination of the ionisation constants. The first pK may be caused by protonation of the pyridine nitrogen atom and the second by deprotonation of the hydroxyl group. Oxidising and reducing substances in moderate concentration do not alter the absorption spectra of PASH.PASH appears to be a bidentate or tridentate ligand with a convenient steric arrangement of its donor groups and contains a conjugated system of x electrons connected with the donor system. The reaction of the reagent in aqueous ethanolic solution a t different pH values with 40 cations was investigated. It forms soluble, coloured complexes with lead(II), iron(III), The infrared spectrum of PASH in potassium bromide dics was obtained. PASH has a solubility in NN-dimethylformamide of 35.7 g 1-l. The change in pH on the spectra of aqueous solutions of the reagent (3.14 x The average pK values were found to be 4.0 and 6.0. The chelates of PASH are generally uncharged.October, 1980 SALICYLOYLHYDRAZONE AS A REAGENT FOR VANADIUM 967 chromium(III), bismuth(III), cerium(IV), zirconium(1V) and vanadium(V).With uranium(V1) a soluble yellow complex that precipitates after several minutes is formed (Table I). TABLE I CHARACTERISTICS OF PASH REACTIONS WITH METAL IONS IN ACETATE BUFFER Colour of complex Metal ion in solution Amsx./nm Fe(II1) . . . . Yellow - brown 350 Pb(I1) . . . . Yellow - green 360 Cr(II1) . . . . Yellow - green 358 Bi(II1) , . . . Yellow 378 Ce(1V) . . . . Yellow 358 V(V) . . . . Yellow 386 U(V1) . . . . Yellow 360 Zr(1V) . . . . Yellow 355 PD* 4.78 4.20 4.20 4.78 3.54 3.81 4.92 4.49 * pD = -log (minimum detectable mass of metal ion, g/volume, ml). Study of Vanadium - PASH System Formation of vanadium complex in aqueous ethanolic solution produces a yellow complex.Absorption spectra of the complex are shown in Fig. 1(A). complex remains stable for a t least 12 h at pH 4.7 (acetate buffer). The addition of a 0.05;/, m/V solution of PASH in ethanol to a solution of vanadium(V) ions The 350 400 450 Wavelengthinrn Fig. 1. Absorption spectra of vanadium complexes with PASH. A, Vanadium(V) complex in aqueous ethanolic medium a t pH 4.7 (C, = 2.3 pg ml-l); B, vanadium(1V) complex in aqueous ethanolic medium a t pH 4.7 (C, = 2.3 pg ml-l); and C, vanadium(V) com- plex extracted into chloroform a t pH 1.3 (C, = 1.4 pg ml-I); D and E, reagent blanks of A and C, respectively. The influence of pH on absorbance is shown in Fig. 2(A), a t 386 nm after a 30-min reaction time. The yellow complex is formed immediately in aqueous media (at the optimum pH range) but most of the metallic chelates are insoluble and this causes numerous interferences.It is concluded that in aqueous media the vanadium(V) - PASH complex is not of great analytical interest. Stoicheiometry of the complex and oxidation state of vanadium method and was found to be 1:l [Fig. 3(A)]. under analogous conditions, was also 1:l [Fig. 3(B)]. The optimum pH range is 3.5-6.0. The stoicheiometry of the vanadium(V) complex was evaluated by the continuous variation The metal to ligand ratio for vanadium(IV),968 GARCIA-VARGAS et d. : PYRIDISE-%ACETALDEHYDE Analyst, VOl. 105 0 1 2 3 4 5 6 7 8 PH Fig. 2. Influence of pH on the formation crf vanadium(V) - PASH complex: A, in aqueous ethanolic solution a t 386 nm (C, = 1.2 pg ml-l); and B, extracted into chloroform a t 415 nm (C, == 1.4 pg ml-l). From the experimental evidence it was concluded that the reagent forms the yellow complex with vanadium(V).The presence of ascorbic acid in the vanaccliurn(V) solution, before the PASH reagent was added, changed the absorption peak from 386 to1 380 nm. When vanad- ium(1V) was used the presence of ascorbic acid did not alter the absorption peak at 380 nm [Fig. 1(A) and (B)]. 0.8 1 0.7 0.6 0.5 -? p 0.4 n a 0.3 0.2 0.1 OI m I t I / I l l , I , 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 [VI [ V l + [PASHI Fig. 3. Stoicheiometry of vanadium complexes, in aqueous media a t pH 4.7 (continuous variation method) : A, vanadium(V) - PASH complex: and B, vanadium(1V) - PASH complex. Extraction of the complex of vanadium(V), the yellow complex is formed immediately in the organic phase.When a solution of PASH in an organic solvent is shaken with an aqueous acidic solution WhenOctober, 1980 SALICYLOYLHYDRAZONE AS A REAGENT FOR VANADIUM 969 chlorobenzene is used the resulting complex is stable; the interferences of foreign ions are high. Of the other solvents tried, chloroform proved to be the best as the complex shows a major bathochromic shift. The absorption spectrum of the vanadium(V) - PASH complex in chloroform is shown in Fig. 1(C). It is stable for at least 10 h after a 35-min reaction time and presents one band in the visible region, at 415 nm. A bathochromic shift is produced in the absorption spectra of the complex, from 386 nm (aqueous media) to 415 nm (organic media).The reported absorb- ances were measured at 415 and 425 nm. The latter wavelength was used as the reagent itself does not absorb at this wavelength. The maximum constant absorbances were obtained in the pH range 0.9-2.8 [Fig. 2(B)]. An aliquot of 10-50 ml of solution containing 14 pg of vanadium(V) was extracted with 10 ml of a solution of 0.01-0.05~0 m/V PASH in chloroform. The extraction was quantitative with 0.03% m/V of the reagent solution and remained constant with increasing concentration. Therefore, 10 ml of 0.0576 m/V reagent solution was adopted as the concentration of solution containing the complexing ligand to be used. The shaking time was varied from 0.25 to 5 min, while the other variables were kept constant. A shaking time of between 1 and 2.5 min did not produce any change in absorbance if the volume ratio Vorg.:Vas.was between 1 : l and 1: 2.5. On the other hand, shaking for 2 min was necessary for the complete extraction of vanadium(V) if the volume ratio Vorg.:Vaa. was 1 : 5. Spectrophotometric Determination of Vanadium(V) with PASH Based on the experimental work, a method is proposed for the determination of trace amounts of vanadium involving the formation of the yellow complex with PASH and its extraction into chloroform. Beer’s law is obeyed between 0.5 and 2 pg ml-l of vanad- ium(V) in the organic phase at 415 nm. The optimum concentration range, evaluated by Ringbom’s method, is 1-1.75 pg ml-l of vanadium. The yellow complex gave a molar absorptivity of E = 1.87 x lo4 1 mol-l cm-l at 415 nm [in the chloroform phase (10 ml)].The Sandell sensitivity of the method is 0.003 pg cm-2 of vanadium. The precision was estimated for 10-50-ml aliquots of 10 pg of vanadium(V) solu- tion, and the relative error of the method is 0.44%. The method is more sensitive for vanadium than many existing methods, and it has been compared, advantageously, with other methods previously reported that use related ligands (Table 11). TABLE I1 CHARACTERISTICS OF VANADIUM - HYDRAZONE COMPLEXES Molar Metal t o Optimum absorptivity/ ligand Compound acidity h,,,,/nm 1 mol-1 cm-1 ratio Reference Hydrazinium hydrazinecarbodithioate pH 4-6 460 1100 1 : 2 16 Anthranilic acid isopropylidenehydrazide . . . . 0.2-1.0 N H,SO, 525 5 100 1 : 2 17 Nicotinic acid hydrazide . ... pH 1.8-2.2 420 750 1 : 1 18 Pyridine-2-acetaldehyde - salicyloylhydrazone . . .. . . pH 0.9-2.8 415 18700 1 : 1 Effect of Foreign Ions For the determination of 10 pg of vanadium by this method, the foreign ions can be tolerated at the levels given in Tables I11 and IV. The limiting value of the concentration of foreign ions was taken as that value which caused an error of not more than 2.5% in the absorbance. Cations were added in the form of chlorides, nitrates or acetates to a maximum of 10000 pg ml-1; anions were added in the form of sodium or potassium salts. Several foreign ions, at high concentrations, produce a general decrease in the absorbance of the vanadium - PASH chelate in a wide range of concentrations. This effect is summarised in Table V. From the data in this table it may be assumed that vanadium can be determined, without great error, in the presence of these ionic concentrations, but with a lower sensitivity.In these instances, standards and samples must be matched for the foreign ion Concentration.970 GARCIA-VARGAS et al. : PYRIDINE-2-ACETALDEHYDE Analyst, Val. 105 TABLE I11 TOLERANCE LIMITS OF EXTRACTIVE DETERMINATION OF VANADIUM(V) Results obtained using a 10-1.18 sample of vanadium, Ion added La(III), Cd(II), Pb(II), As(V), Ba(II), Sr(II), ammonium, alkali metals, C1-, Br-, C104-, C104-, NO,-, BO,-, SOa2-, COs2-,* PO,,-, BO,,-, benzoate, acetate, cltrate . , .. .. . . .. .. .. .. .. Mg(II), Ca(II), SiOSa- . * .. .. .. .. .. .. . * Mn(II), Be(II), tartrate .. .. .. .. phthalate, dimethylglyoxime (DMG) .. .. .. .. .. . * Zr(IV), In(III), S,O,e- * . .. .. .. .. .. * . .. Th(IV), EDTA .. . . .. .. .. .. .. .. .. U(VI), oxalate .. .. * . * . .. .. .. .. .. H,O% .. .. .. .. Al(III), Cr(III), Se(IV), Ag(Ij; Hg(I), Zn(II), Tl(I): A s ( I ~ ~ ) , CO,;-, B,0,2 -, F-, Sn(IV), Hg(II),'Co(II); Fe(IIii, Ti(IV), CNL, Fe(CN),3 -. . .. .. .. * Heating gently before extracting. Amount tolerated/ pg ml-1 10000 5 000 2 500 1000 750 500 250 200 100 TABLE IV ELIMINATION OF INTERFERENCES BY ADDITION OF MASKING AGENTS Amount tolerated/pg ml-1 7 r-----. -___ Without With masking Foreign ion masking agent agent Masking agent Mo(V1) . . . . 50 250 Tartrate, 1000 p g ml- . . . . 10 100 Tartrate, 10100 pg ml-1 . . .. 2 100* H,O,, 200 pg ml-1 w (VI) Fe(I1) Sn(I1) . . .. 25 100* HNO,, 1 ml Ce(1V) .. . . 2 10 PO4$-, 500 p,g ml-1 Pd(I1) . . . . 1 25 DMG,? 10 mg Sb(II1) . . . . 1 10 Tartrate, 2500 p g ml-1 I - . . . . . . 50 100* HNO,, 'J ml * Heating before extracting. t DMG = dimethylglyoxime. The tolerance limits for the extractive determination of 10 pg of vanadium for copper(II), nickel(I1) and bismuth(II1) are low, 1, 2 and 2 pg ml-l, respectively. To remove these metal ions, when present, a cation-exchange column was used.19120 The fodlowing solutions were percolated through 5 g of cation-exchange resin: 10 mg of nickel(] 1) in 10 ml of 1 M hydro- chloric acid; 5 mg of copper(I1) in 10 In1 of 1 M hydrochloric acid; LO mg of nickel(I1) in 10 ml of 1 M nitric acid; 5 mg of copper(I1) in 10 ml of 1 M nitric acid; 10 mg of bismuth(II1) in 10 ml of 1 M nitric acid.In addition each of these solutions contained 10 pg of vanadium(V) and 2 drops of a 3% rn/V solution of hydrogen peroxide. The vanadium(V) was eluted using 20 ml of 1 M hydrochloric acid [when copper(I1) and nickel(I1) were present] or 1 M nitric acid [when copper(II), nickel(I1) and bismuth(II1) were present:. The flow-rate was kept a t 3 ml min-l. The eluate was neutralised with concentrated sodium hydroxide solution and then the extractive - spectrophotometric method was applied as described above. The recovery of vanadium was 92.6-105.7%. The precision was estimated for 10 pg of vanadium in 10 ml of 1 M hydrochloric acid or 1 M nitric acid, and the relative error of the method was less than 3%. If necessary this cation-exchange procedure may be applied to other foreign ions; for example, 10mg of cobalt(I1) can be separated from 10 pg of vanadium by applying this procedure to 10 ml of a solution in 1 M hydrochloric acid.Applications materials. The method has been applied satisfactorily to the determination of vanadium in differentOctober, 1980 EFFECT OF SALICYLOYLHYDRAZOKE AS A REAGENT FOR VANADIUM TABLE V SOME FOREIGN IONS AT HIGH CONCENTRATIONS ON THE ABSORPTION OF VANADIUM - PASH CHELATE Absorbance of a 10-pg sample of vanadium is 0.367. Concentration/ Vanadium recovery*/ Ion added pg ml-1 Absorbance pg ml-1 97 1 Zn(I1) , . . . 5 000 7 500 Cr(II1) . . . . 5 000 7 500 10000 . . 5 000 7 500 10000 W I ) ' ' . . 2 500 5 000 Al(II1) . . . * 2 500 5 000 7 600 10000 As(I1) . . . .2 500 5 000 7 500 A m ' . 0.470 0.465 0.210 0.216 0.212 0.268 0.275 0.268 0.250 0.253 0.295 0.269 0.293 0.297 0.344 0.335 0.342 1.28 1.27 0.57 0.59 0.58 0.73 0.75 0.73 0.68 0.69 0.80 0.73 0.80 0.81 0.94 0.92 0.93 * Results are the means of three determinations. Determination of vanadium in a mineral, a steel and a phosphoric acid sample Results of the analysis of vanadium in mineral and steel samples from the Bureau of Analysed Samples Ltd. support the precision and reliability of this method. Lead - vanadium concentrates and high-speed steel were dissolved in a mixture of concentrated nitric and perchloric acids (2 + 1 VjV) and aqua regia, respectively. Triplicate results were obtained in both instances. Lead - vanadium concentrates (BAS No. 70aG) had the following certificate composition: lead 65.4 and vanadium(V) oxide 3.20y0.The vanadium content found was 3.18 & 0.030/0 (for V,O,). High-speed steel (BAS No. 64b) had the following certificate composition: carbon 0.9, vanadium 1.99, chromium 4.55, molybdenum 4.95 and tungsten 7.05%. The vanadium content found was 1.96 f 0.02y0. A phosphoric acid sample, used in the detergent industry, has also been analysed for vanadium. The average composition of the phosphoric acid analysed was phosphorus(V) oxide 38, sulphuric acid 3.5, calcium oxide 0.15, silica 1, magnesium oxide 0.7, aluminium oxide 0.3, fluoride 2, iron 0.190,; m/V, and vanadium and chromium 204 and 215 pg ml-l, respectively. The vanadium found by the spectrophotometric determination was 207 & 2 pg ml-l (the mean result of four determinations).Determination of vanadium by the standard additions method The majority of the methods for the determination of parts per million and sub-parts per million amounts of vanadium require pre-concentration of vanadium by c~precipitation,~~-*~ ion e x c h a x ~ g e ~ ~ ~ ~ ~ - ~ ~ or liquid - liquid extra~tion.*~-~4 The PASH method may also be applied to the determination of vanadium at parts per billion levels (parts per lo9), which decreases the lower limit of the vanadium determination through the taking of a larger volume of the aqueous phase in relation to the chloroform phase and applying the standard additions method.l3 The method consists in adding several increasing known amounts of vanadium(V) (0, 1.25, 2.5 and 3.75 pg) to four aliquots of sample solution.The extraction procedure described above is then applied and the absorbances are measured a t 425 nm. The absorbances are plotted against the concentrations of the four vanadium-containing solutions of each sample. The straight line is extrapolated back to the concentration axis and the negative intercept gives the concentration of the sample solution.972 GARCIA-VARGAS et al. : PYRIDINE-2-ACETALDEHYDE Analyst, VoL. 105 All parameters in the regression equation were calculated by the principle of least squares and all regression curves were practically linear, the correlation coefficients being equal to or higher than 0.995. This method was applied to the phosphoric acid sample mentioned above. The sample solution was first diluted 1000 times and then aliquots of 5, 10 or 20 ml were taken.The results obtained are shown in Table VI. The vanadium content was found to be 4.12 3 0.13 pg (sample A, 20-ml aliquots of the dilute sample), 2.05 & 0.06 pg (sample B, 10-ml aliquots of the dilute sample) and 1.07 & 0.04 pg (sample C, 5-ml aliquots of the dilute sample). TABLE VI REGRESSION ANALYSIS OF CURVES BASED ON STANDARD ADDITIONS METHOD FOR DETERMINATION OF VANADIUM Equation of regression Correlation Sample* Aliquot taken/ml curve coefficient A . . .. 20 y = 0.0296% & 0.1221 0.998 B .. . . 10 y = 0 . 0 3 0 4 ~ & 0.0624 0.998 D . . .. 50 y = 0.0367% & 0.0887 0.999 E . . .. 50 y = 0.0354% & 0.0466 0.998 c .. .. 5 y = 0.0295% f 0.0316 0.996 * A, B and C correspond to the phosphoric acid sample mentioned in text (dilute 1000 times, previously).D and E correspond to vanadium-containing solutions in 0.1 M potassium chloride (50 and 25 pg 1-1, respectively). In order to study the accuracy of the standard additions method, two vanadium-containing solutions were made, containing 50 and 25 pg of vanadium(V) in 1000 1111 of 0.1 M potassium chloride solution. The method was applied to 50-ml aliquots of both samples as described above. The results obtained are shown in Table VI, samples D and E. The vanadium recovery was 96.7% for 50 pg 1-1 of vanadium(V) and 105.2% for 25 pg 1-1 of vanadium(V). Conclusion Other methods are available for the determination of trace amounts of vanadium using hydrazones (Table 11), but none of them is completely satisfactory.This paper describes a study of the optimum conditions for a selective and sensitive spectrophotometric method for the determination of vanadium. The method is relatively free from interferences because most of the metallic chelates of PASH are not extracted into chloroforin and the absorption peaks of these chelates are in the ultraviolet region. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. References Katiyar, S. S., and Tandon, S. N., Talanta, 1964, 11, 892. Vasilikiotis, G. S., and Tossidis, J . A,, Microchem. J., 1969, 14, 380. Uno, T., and Taniguchi, H., Bunseki Kagaku, 1971, 20, 997. Odashima, T., and Ishii, H., Nippon Kagaku Kaishi; 1973, 729. Vasilikiotis, G. S., Micvochem. 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