INTRODUCTION:

The potential application of hydrazone derivatives for the spectrophotometric determination of metal ions had reviewed by singh et al¹. Few hydrazone reagents^2-4 were used for the spectrophotometric determination of Molybdenum (VI). In the light of good analytical characteristics of hydrazones, herein we report zero and first order derivative spectrophotometric determination of Molybdenum (VI) in aqueous medium.

EXPERIMENTAL:

Spectrophotometric measurements were made in an shimadzu 160 A microcomputer based UV –Visible spectrophotometer equipped with 1.0 cm quartz cells, an ELICO LI- 120 digital P^H meter was used for P^H adjustments. All reagents used were of AR grade unless otherwise stated. All solutions were prepared with distilled water. The standard Mo(VI) solution (0.01M) was prepared by dissolving 1.236 gm of Ammonium Molybdate ((NH₄)₆Mo₇ O₂₄,4H₂O) AR (SD Fine Chem Ltd Rasayan) in a few ml of doubly distilled Water and made upto the mark in a 100 ml standard flask.

The stock solution was standardized by complexometric titration with EDTA. The working solutions were prepared by diluting the stock solution to an appropriate volume.

The reagent Diacetyl Monoxime Isonicotinoylhydrazone(DMIH) was prepared by simple condensation of Diacetyl Monoxime and Isonicotinic hydrazide in 1:1 mole ratio and its structure is given in fig 1.

Fig1. Structure of Diacetyl Monoxime Isonicotinoylhydrazone(DMIH)

The reagent solution (0.01 M) was prepared by dissolving 0.22 grams of DMIH in 100 ml of dimethyl Formamide. The reagent is stable for 48 hours. Buffer solutions were prepared by mixing 1 M hydrochloric acid – 0.2 M sodium dihydrogen phosphate.

Reaction with metal ions: The reactions of some important metal ions were tested at different P^H values. The samples were prepared in 10 ml volumetric flasks by adding 3 ml of buffer (P^H 1.0 – 11.0), 0.5 ml of metal ion (1X 10 ^-3 M) and 0.5 ml of DMIH (1 X 10 ^-2 M) solutions. The solution mixture was diluted up to the mark with distilled water. The absorbance was measured in 300 – 600 nm range against reagent blank .The results are summarised in Table -1

Recommended Procedure:

Determination of Mo(VI) (Zero order spectrophotometry) : An aliquot of the solution containing 0.48 -5.76 µg /ml of Mo(VI), 3 ml of buffer solution of P^H 5.0 and 0.5 ml of 0.01 M DMIH reagent were taken in a 10 ml volumetric flask and the solution was diluted up to the mark with distilled water .The absorbance of the solution was recorded at 346 nm in a 1.0 cm cell against reagent blank prepared in the same way but without Mo(VI) metal solution .The measured absorbance was used to compute the amount of Mo (VI) from the calibration plot

Determination of Mo (VI) by first order derivative spectrophotometry: The first order derivative spectrum was recorded for the above solution of Mo (VI)– DMIH with a scan speed having degrees of freedom 9 in a wave length range 300 - 600 nm. The derivative spectrum was measured by peak height (h) method at 402 nm. The peak height (h) at 402 nm is proportional to the concentration of Mo (VI) Therefore the peak heights were measured at this wave length for the construction of calibration plots.

RESULTS AND DISCUSSION:

Diacetyl Monoxime Isonicotinoylhydrazone(DMIH) reagent can be easily prepared like any other Schiff base reagent. This new chromogenic reagent DMIH was not used for spectrophotometic determination of Mo(VI) so far.

The reactions of some important metal ions with DMIH are summarized in table 1. The colour reactions are mainly due to the complex formation of DMIH with divalent, trivalent,tetravalent and hexavalent metal ions like Hg(II), Ru(III), Au(III), Th (IV), Mo(VI) and U(VI) in acidic buffer medium to give intense coloured complexes .

Table -1: Analytical Characteristics of Diacetyl Monoxime Isonicotinoyl hydrazone(DMIH)

Sl No	Metal Ion	P^H	λ _max ( nm)	Molor absorptivity ( L.mol ^-1 cm ^-1) X10 ⁴
1	Ru (III)	4.5	346	1.4
2	Hg (II)	5.5	351	2.23
3	U(VI)	3.25	364	1.63
4	Th(IV)	5.0	352	2.265
5	Au(III)	4.5	361	1.5
6	Mo(VI)	5	346	1.93

Determination of Mo (VI) using DMIH: Mo(VI) reacts with DMIH in acidic medium to give greenish yellow coloured water soluble complex. The colour reaction between Mo(VI) and DMIH are instantaneous even at room temperature in the P^H range 1.0 -7.0 .The absorbance of the greenish yellow coloured complex remains constant for more than 2 hours. The maximum colour intensity is observed at P^H5.0.

A 5 fold molar excess of reagent is adequate for full colour development. The order of addition of buffer solution, metal ion and reagent has no adverse effect on the absorbance. The complex formation reaction between Mo (VI) and DMIH has been studied in detail based on the composition of the complex as determined by using Job’s and molar ratio methods. Some of the important physico-Chemical and analytic characteristics of Mo (VI) and DMIH are summarized in table -2

Table-2: Some of Physico- Chemical and analytical characteristics of Mo (VI) –DMIH Complex

Characteristics	Results
λ _max ( nm)	346
PH Range(Optimum)	1.0-7.0
Mole of reagent required per mole of metal ion for full colour development	5 folds
Molar absorptivity ( L.mol ^-1 cm ^-1)	1.93 X10⁴
Sandell’s sensitivity( µg/ Cm²⁾	0.00259067
Beer’s law validity range (µg / ml)	0.48- 5.76
Optimum concentration range (µg / ml)	0.96- 4.8
Composition of complex ( M:L) obtained in job’s and mole ratio method	1:1
Stability Constant of the complex	4. 731X10 ⁶
Standard deviation for 10 determination	0.0005
Relative standard deviation	0.08

Derivative spectrophotometry is an important useful technique as it decreases the interference i.e increase the tolerance limit value of the foreign ions. Therefore it may be useful for the determination of metal ions having overlapped spectra. The recommended procedure has been used for the determination of Mo(VI)

The zero order and first order derivative spectra of Mo (VI) complex of DMIH are given in Fig 2 and 3 respectively.

Fig 2. Zero order absorption spectra of (a) reagent DMIH 1X10 -2 M vs water blank at PH 5.0 (b) Mo (VI) - DMIH complex vs reagent blank at PH =5.0 ,Mo(VI) =1X10 -3 M; DMIH=1X10-2 M

Table 3: Tolerance limit of Foreign Ions in the determination of 2.5 µg / ml Ru(III)

Ion Added	Tolerance Limit(µg / ml)		Ion Added	Tolerance Limit(µg / ml)
Ion Added	Zero Order	First Derivative	Ion Added	Zero Order	First Derivative
Urea	60.6	60.6	Bi⁺³	208.98	208.98
Sulphate	48	48	Ba⁺²	206	206
Phosphate	47.5	47.5	Zn⁺²	65.4	65.4
Nitrate	62	62	Zr⁺⁴	91.2	91.2
Acetate	59	59	U⁺⁶	357	357
Oxalate	67	67	W⁺⁶	183.8	183.8
Thio Urea	76	76	Al⁺³	26.98	26.98
Tartarate	141	141	Ag +	108	108
Ascorbic Acid	88	88	Ca⁺²	60	60
Fluoride	28.5	28.5	Ni⁺²	58.7	58.7
Iodide	63.5	63.5	Pd⁺²	106.4	106.4
Bromide	40	40	V⁺⁵	50.9	50.9
Chloride	53.25	53.25	Sr⁺²	87.6	87.6
Mn ⁺²	82.35	82.35	Sb⁺³	121.8	121.8
Sn⁺²	118.7	118.7

Table 4: Estimation of Molybdenum(VI) (µg / ml) in synthetic alloy samples

Sample (µg / ml)	Amount of Mo(VI) (µg / ml)
Nickel Based high Temperature Alloy	Composition Certified	Composition found *	Relative Error (%)
i) Udimet – 500(a)	4.800	4.851	+1.06
ii) Udimet – 700(b)	5.200	5.195	-0.10

* Average of best three determinations among five determinations

a) Cr=18 ; CO =18.5; Al =2.9;Mo=4.8;C=0.08;B=0.006;Zr =0.05;Ti=2.9

b) Cr=1.5 ; CO =18.0; Al =4.3;Mo=5.20;C=0.08;B=0.003;Ti=3.5

Effect of diverse ions : The effect of various diverse ions in the determination of Mo(VI) was studied to find out the tolerance limit of foreign ions in the present method. The tolerance limit of foreign ions was taken as the amount of foreign ion required to cause an error of ± 2% in the absorbance or amplitude. The results are given in table - 3. The data obtained in the derivative method is also incorporated.

Fig.3. First order Derivative Spectrum of Mo(VI) –DMIH Complex Vs Reagent Blank at

P^H 5.0, Mo(VI) =1X10^-3 M, DMIH = 1X 10^-2 M

Applications: The proposed method was applied for determination of Mo (VI) in various synthetic samples of alloy.

Analysis of synthetic alloy sample: Into a series of 10 ml volumetric flasks, each containing 5 ml of buffer P^H 5.0 solution, a known aliquots of the sample solution and 1ml of the reagent (1X 10^-2 M) solution, 0.5 ml of Fluoride (1 X 10^-1 M) (to mask iron) and 0.5 ml of (1 X 10^-1 M) Ascorbate (to mask Titanium) solutions are added and made up to the mark with distilled water. The absorbance of these solutions is measured at 346 nm. From the measured absorbance, the amount of Mo(VI) is computed by referring to pre constructed calibration plot at 346 nm. The obtained results are given in the table-4.

CONCLUSIONS:

The present method using DMIH as a spectrophotometric reagent for the determination of Molybdenum (VI) in aqueous medium is sensitive and simple. The determination of Mo(VI) using DMIH is not a laborious and there is no need of heating the components or extraction. Further the reagent is easy to synthesize using available chemicals .Moreover the present method is simple, rapid,reasonably sensitive and selective for the determination of Molybdenum (VI)

ACKNOWLEDGEMENT:

The authors are thankful to the Jawaharlal Nehru Technological University, Anantapur for providing research facilities to carry out the present work.

REFERENCES:

1. Singh R.B., Jain.p and Singh. R.P, Talanta 29.77( 1982)

2. Pramanic .J,Ghosh .J.P,Mazumdar. M and Das. H.S J.Indian Chem. Soc. 58.235 (1981)

3. Chaudhry S.P and Shome S.C J.Indian Chem.Soc. 68. 430 (1991)

4. Kawatkar S.G. and Manoli.P.S, Acta cien. Indica, 24 C, 109 (1998)

Received on 11.10.2010 Modified on 25.10.2010

Asian J. Research Chem. 4(2): February 2011; Page 282-284