CHAPTER 4 NEW REAGENTS FOR THE...

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CHAPTER 4

NEW REAGENTS FOR THE SPECTROPHOTOMETRIC

DETERMINATION OF VANADIUM IN ALLOYS, SYNTHETIC AND

PHARMACEUTICAL SAMPLES

4.1 INTRODUCTION

4.2 ANALYTICAL CHEMISTRY

4.3 APPARATUS

4.4 REAGENTS AND SOLUTIONS

4.5 PROCEDURES

4.6 RESULTS AND DISCUSSION

4.7 APPLICATIONS

4.8 CONCLUSIONS

4.9 REFERENCES

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4.1 INTRODUCTION

Vanadium is an essential trace element to man and animals. It was first

discovered by del Rio in 1801 [1-3]. Unfortunately, a French chemist incorrectly

declared Del Rio's new element as only impure chromium and Del Rio thought

himself to be mistaken and accepted the French chemist's statement. The element was

rediscovered in 1830 by Sefstrom, who named the element in honor of the

Scandinavian Goddess Vanadis because of its beautiful multicolored compounds. It

was isolated in nearly pure form by Roscoe in 1867. Vanadium of 99.3 to 99.8 %

purity was not produced until 1922.

Vanadium has abundance in the earth’s crust of about 0.02 %. Vanadium is

found in about 65 different minerals among which carnotite, roscoelite, vanadinite

and patronite are the important sources of the metal [4]. Vanadium is also found in

phosphate rock and certain iron ores, and is present in some crude oils in the form of

organic complexes. It is also found in small percentages in meteorites. High-purity

ductile vanadium can be obtained by the reduction of vanadium trichloride with

magnesium or with magnesium-sodium mixtures. Much of the vanadium being

produced are now made by calcium reduction of V2O5 in a pressure vessel, an

adaptation of a process developed by McKechnie and Seybair. Natural vanadium is a

mixture of two isotopes, 50V (0.24 %) and 51V (99.76 %). 50V is slightly radioactive,

having a half-life of > 3.9×1017 years. Nine other unstable isotopes are recognized.

Pure vanadium is a bright white metal and is soft and ductile. It has good corrosion

resistance to alkalies, sulfuric and hydrochloric acid and salt water, but the metal

oxidizes readily above 660 0C. The metal has good structural strength and a low

fission neutron cross section, making it useful in nuclear applications. Vanadium is

used in producing rust resistant spring, and high speed tool steels. It is an important

carbide stabilizer in making steels. About 80 % of the vanadium now produced is

used as ferrovanadium or as a steel additive. Vanadium foil is used as a bonding agent

in cladding titanium to steel. Vanadium pentoxide is used in ceramics and as a

catalyst. It is also used in producing a superconductive magnet with a field of 175,000

gauss. Vanadium and its compounds are toxic and should be handled with care.

Ductile vanadium is commercially available and commercial vanadium metal of about

95 % purity.

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Major sources for the emission of vanadium in the environment include

combustion of fuel oils, dyeing, ceramics, ink, catalyst and steel manufacturing.

Vanadium in trace amounts represents an essential element for normal cell growth,

but it can be toxic when present in higher concentrations. It plays an important role in

physiological systems including normalization of sugar levels and participation in

various enzyme systems as an inhibitor and cofactor of the oxidation of amines [5].

In spite of being a nutritional element, vanadium is not accumulated by the biota. The

only organisms known to bio-accumulate it to any significant degree are some

mushrooms, tunicates and sea squirts. The occurrence of vanadium in sea squirts is

supposed to be one of the main sources of this metal in crude oil and oil shales.

In biology, vanadium ion is an essential component of some enzymes,

particularly the vanadium nitrogenase used by some nitrogen fixing microorganisms.

Vanadium is essential to sea squirts in vanadium chromagen proteins. The

concentration of vanadium in their blood is more than 100 times higher than the

concentration of vanadium in the seawater around them. Rats and chickens are also

known to require vanadium in very small amounts and deficiencies result in reduced

growth and impaired reproduction. Administration of oxovanadium compounds have

been shown to alleviate diabetes mellitus symptoms in certain animal models and

humans. Much like the chromium effect on sugar metabolism, the mechanism of this

effect is unknown.

Vanadium poisoning is an industrial hazard [6]. Environmental scientists have

declared vanadium as a potentially dangerous chemical pollutant that can play havoc

with the productivity of plants, crops and the entire agricultural system. High amounts

of vanadium are said to be present in fossil fuels such as crude petroleum, fuel oils,

coals and lignite. Burning of these fuels release vanadium into the air that then settle

on the soil. Vanadium compounds act chiefly as an irritant to the eyes and respiratory

tract. Exposure may cause conjunctivitis, rhinitis and reversible irritation of the

respiratory tract. More severe cases may cause bronchitis, bronchospasms and asthma

like disease. It may cause polycythemia, red blood cell destruction and anemia,

albuminuria and hematuria, gastrointestinal disorders, nervous complaints and severe

cough [7]. Recently, vanadium has been noticed as the index element in urban

environmental pollution, especially air pollution [8]. Laboratory and epidemiological

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evidences suggest that vanadium may also play a beneficial role in the prevention of

heart disease [9]. Shamberger has pointed out that human heart disease death rate is

lower in countries where more vanadium occurs in the environment [10]. The

National Institute for Occupational Safety and Health (NIOSH) has recommended that

35 mgm-3 of vanadium be considered immediately dangerous to life and health. This

is the exposure level of a chemical that is likely to cause permanent health problems

or death.

The determination of vanadium provides significant information regarding its

biological effects and the extent of air pollution. Soldi et al. reported that this element

was a useful marker for the potential release of toxic metals from fossil fuels,

especially oils, as it is always present in these materials [11]. Thus, highly and

selective methods are still required for trace vanadium determination in different

kinds of samples.

4.2 ANALYTICAL CHEMISTRY

Several methods have been reported in the literature for the analysis of

vanadium. Various analytical techniques based on fluorescence spectroscopy [12],

atomic absorption spectroscopy [13], inductively coupled plasma-atomic absorption

spectroscopy [14], capillary electrophoresis [15], stripping voltametry [16], neutron

activation analysis [17], high-performance liquid chromatography [18] and ion

exchange separation method [19] are used for its determination.

A survey of literature revealed that a large number of reagents are suitable for

the spectrophotometric determination of vanadium. Telep and Boltz reported

hydrogen peroxide as a reagent for the spectrophotometric determination of vanadium

[20]. The method was based on the reaction of vanadium(V) with H2O2 in acid

medium to form a reddish-brown colored complex. The complex showed maximum

absorption at 290 nm. Beer's law was valid over the concentration range 0-125 ppm of

vanadium. Eeckhout and Weynants reported diphenylbenzidine as a reagent for the

determination of vanadium [21]. The yellow color resulted from the reaction between

dilute solution of V(V) and diphenylbenzidine was the basis for the

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spectrophotometric method for the determination of vanadium. Beer's law was valid

over the concentration range 1-��-1 of vanadium.

Motojima reported oxine as a reagent for the spectrophotometric

determination of vanadium [22]. This method was based on the extraction of

vanadium-oxine complex with chloroform and the complex exhibited an absorption

maximum at 550 nm. Baggett and Huyck reported spectrochemical determination of

vanadium in alkali brines [23]. In this method samples were adjusted to a pH value of

5.0, treated with 8-quinolino1 and quinolates extracted with chloroform. The

chloroform extract was concentrated by evaporation to a known volume and placed on

a graphite electrode previously coated with 20% sodium hydroxide and dried in an

oven with a carbon dioxide atmosphere. Excitation was carried out by a 2300 volt

alternating current arc with photographic recording of the spectra and molybdenum

was used as the internal standard.

Jones and Watkinson described a spectrophotometric method for the

determination of vanadium in plant materials [24]. With minor modifications it was

used to determine vanadium in soils. Priyadarshini and Tandon reported N-benzoyl-

N-phenylhydroxylamine as a reagent for the spectrophotometric determination of

vanadium [25]. Ariel and Manka reported a spectrophotometric method for the

determination of chromium(VI) and vanadium(V) [26]. The presence of iron(III) was

developed by exploiting the color changes which resulted from the oxidation of

o-dianisidine in strong acid medium.

Shibata described a solvent extraction and spectrophotometric determination

of vanadium with 1-(2-pyridylazo)-2-naphthol [27]. Janauer et al. reported a sensitive

and precise spectrophotometric method for the determination of microgram quantities

of vanadium in hydrochloric acid-methanol medium [28]. The photometric reagent

was the azo dyestuff solochrome black-RN, which formed a violet colored complex

with vanadium, which showed maximum extinction at 560 nm. Beer's law obeyed

within the concentration range from 0 to 25 �g of vanadium per 10 ml of test solution.

Sailendra Nath and Poddar described spectrophotometric determination of vanadium

with o-hydroxyacetophenone oxime as a reagent [29,30]. Reagents like

p-methoxybenzothiohydroxamic acid [31], 2-(2-thiazolylazo)-5-(diethylamino)phenol

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[32] and morin [33] were also used as reagents for the spectrophotometric

determination of vanadium. Gagliardi and Ilmaier described a sensitive method for the

spectrophotometric determination of vanadium with 4-(2-pyridylazo)resorcinol(PAR)

[34]. The method was applicable to the analysis of alloys.

Goyal and Tandon described the comparative studies of the reaction of 7-

arylazo-8-hydroxyquinoline-5-sulphonic acid (Azoxine S) dye with vanadium, which

showed that 2:1 yellow, water-soluble complex formed over the pH range 2.5–6.0 and

the phenyl derivative was the most suitable for spectrophotometric determination of

0.2–1.4 ppm of vanadium [35]. The color formed instantaneously and was stable for

about 8 hours. The molar abso�� max =400 was 1.15×104� ��

equilibrium constant for complex formation was of the order of 102. These dyes were

used as indicators in the direct complexometric determination of vanadium(IV). The

interference of a number of anions and cations were reported. Tamotsu et al. reported

protocatechuic acid as a spectrophotometric reagent for the determination of

vanadium [36].

Tandon and Bhattacharya used N-aryl hydroxamic acid as a reagent for the

spectrophotometric determination determination of vanadium [37]. Wakamatsu and

Otomo described an extraction and spectrophotometric determination of

vanadium(IV) with Tiron [38]. The vanadium(IV)-Tiron chelate was extracted into a

mixed solvent mixture 1:4, isopentyl alcohol:chloroform in the presence of

1,3-diphenylguanidinium salt. Beer’s law was obeyed upto 36 ��vanadium per 10

mL of the solvent.

Chakraborti reported 3-hydroxy-1,3-diphenyltriazene and its substituted

derivatives as spectrophotometric reagents for vanadium(V) [39]. Izquierdo and

Lacort described 5,7-dichloro-2-methyl-8-hydroxy-quinoline as a reagent for the

vanadium determination by spectrophotometry [40]. Satyanarayana and Mishra

reported 1,2,3-phenyloxyamidine as a reagent for solvent extraction and

spectrophotometric determination of vanadium(V) [41]. The course of investigations

on the development of organic analytical reagents were able to introduce a type of

functional group for metal ions. 1,2,3-Phenyloxyamidine possessed several useful

properties as an analytical reagent. It was stable and can be readily prepared from

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common laboratory chemicals. The reagent has great potentialities for the

colorimetric and gravimetric determination of metal ions. Studies carried out in these

laboratories showed that this was an excellent reagent for the spectrophotometric

determination of vanadium(V) by solvent extraction and for the gravimetric

determination of copper and nickel with the functional group.

Naoichi et al. described a spectrophotometric determination of vanadium(V)

with N-benzoyl-N-phenylhydroxylamine [42]. Vojkovic et al. reported the application

of 1-phenyl-2-methyl-3-hydroxy-4-pyridone (HX) for the spectrophotometric

determination of vanadium(V) by extraction into chloroform [43]. The method was

based on the extraction condition and three types of complexes were formed. At pH

1.0-2.2, an orange colored complex of the composition with a maximum absorption at

497 nm was formed. However, at 0.75-1.25 M hydrogen ion concentration and in the

presence of the excess of chloride ions a blue colored complex of the composition

VO2Cl(HX)2 with a maximum absorption at 625 nm was found. In the presence of an

excess perchlorate ions and at 0.3-0.4 M hydrogen ion concentration a blue colored

complex of composition VO2ClO4(HX)3 with a maximum absorption at 605 nm was

established. The latter complex was not recommended for the determination as an

excess of perchlorate influenced the absorption. Procedures for the determination at

497 or 625 nm were very fast and simple. The complexes were also isolated in

crystalline form and identified by elemental analysis and infrared spectroscopy. The

molar absorptivity at 497 nm was 4100 Lmol-1cm-1 and at 625 nm 5600 Lmol-1cm-1.

Uchida et al. reported a spectrophotometric determination of vanadium(V)

with 2-nitroso-5-dimethylaminophenol [44]. Nardillo and Catoggio described a

spectrophotometric determination of vanadium with 3-methyl catechol in alloy steels

[45]. Reagents like 1-(4-tolyl)-2-methyl-3-hydroxy-4-pyridone [46], 4-(4,5-dimethyl-

2-thiazolylazo)-2-methylresorcinol [47] and N-methylaminothioformyl-N'-

phenylhydroxylamine [48] were used for the spectrophotometric determination of

vanadium.

Akama et al. described a spectrophotometric determination of vanadium(V)

using 4-benzoyl-3-methyl-1-phenyl-5-pyrazolone [49]. Bag et al. reported

spectrophotometric method for the determination of vanadium with

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2:2′-diaminodiphenyldisulphide in strong acidic solution [50]. Vanadium(V) formed a

1:1 cornflower blue colored complex with 2:2′-diaminodiphenyldisulphide in 18 N

sulfuric acid solution which passed onto 1:2 complex with large amount of reagent.

The absorption maxima of the complexes were 590 nm and 700 nm respectively. The

Beer’s law was obeyed in the concentration range 8-36 ppm. The percent relative

error was 2.72. The composition of the complexes were determined by the modified

jobs and molar ratio method. The calculated dissociation constants were 1.6×10–2 and

5×10–9 at 25 °C. The molar extinction coefficient was 1100, while the Sandell’s

sensitivity was 0.046 μgcm-2.

Reddy and Reddy reported extraction and spectrophotometric determination of

vanadium [51]. In this method vanadium(V) formed a 1:1 yellow colored complex

with salicylaldehyde thiosemicarbazone in n-butanol. The yellow colored complex

was quantitatively extracted from acetic acid medium into n-butanol. Beers law was

obeyed in the range 0.5-6.5 ppm of the metal. Large number of foreign ions did not

interfere.

Montelongo et al. reported a spectrophotometric determination of

vanadium(V) with 4-(1��-1��-triazolyl-3�-azo)-2-methylresorcinol [52]. The

method was based on the reaction of vanadium with the reagent at pH 8.10

(Tris-HClO4 buffer solution), produced a pink-violet, 1:1 complex (λmax=525 nm,

ε=2.55×104 Lmol–1cm–1) in a 50% methanol-water medium, which was the basis for

the spectrophotometric determination of 0.1 to 1.51 ppm of vanadium. The method

was applied for the determination of the vanadium content in low alloy steels.

Salinas and Arrabal described a method for the extract and spectrophotometric

determination of vanadium(V) [53]. The violet colored complex formed with

isophthaldihydroxamic acid was extracted into trioctylmethylammonium chloride in

ethylacetate (λmax=380 nm, ε=7.50×103 Lmol–1cm–1; λmax=510 nm, ε=5.51×103

Lmol–1 cm–1) and the range of the determination was 14-80 μg.

Escriche et al. reported a spectrophotometric method for the determination of

vanadium [54]. The method was based on the oxidation of pyrogallol red and

vanadium was determined by the decrease in absorbance of its characteristic band at

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490 nm and at pH 4. The decrease in absorbance was proportional to the

concentration of vanadium(V) over the range 0–1.83 ppm. The limit of detection of

vanadium was found to be 0.05 ppm. In the presence of potassium bromate the

determination was possible in the ppb levels. The method described the study of the

selectivity of the method with respect to possible interference from 20 species

contained in ferrous and non-ferrous alloys, which was classified according to their

possible mechanism of interference.

Abdullah et al. reported thiophene-2-hydrazide as a reagent for the

spectrophotometric determination of trace amount of vanadium in aqueous solution

[55]. The intense yellow, water-soluble, stable and binary complex formed in acidic

medium was used for the determination of 0.5–5 ppm of vanadium ion with a molar

absorptivity of 12.1×103 Lmol–1cm–1 at 410 nm. Moreover, the color formation was

very fast. Interferences due to foreign ions were examined.

El-Shahat et al. reported phenylfluorone as a reagent for the

spectrophotometric determination of vanadium [56]. The method was based on the

formation of a 1:1 complex of vanadium - phenylfluorone exhibited an absorption

maximum at 520 nm. The Beer's law was valid over the concentration range of 2-15

μg of vanadium in 10 mL at pH 4. The relative standard deviation was 2 % and the

molar absorptivity of the system was 2.1×104 Lmol-1cm-1.

Bhaskar and Surekha reported 2-acetylpyridine thiosemicarbazone as a reagent

for the spectrophotometric determination of vanadium [57]. Vanadium formed a

golden yellow complex at pH 3.5 with 2-acetylpyridine thiosemicarbazone in aqueous

medium. The complex exhibited maximum absorbance at 400 nm, with molar

absorptivity of 5.6×103 Lmol-1cm-1. The metal and ligand stoichiometric ratio was 1:1

and the Beer's law was valid over the concentration range 0-8 ppm of vanadium.

Svjetlana and Vladimir reported desferrioxamine-B as a reagent for the

determination of vanadium [58]. A naturally occurring trihydroxamic acid,

desferrioxamine-B, reacted with the vanadium(V) ion in strong acidic aqueous

94

solution and produced a stable 1:1 complex. This red-violet chelate used for the

spectrophotometric determination of trace amounts of vanadium(V). Molar

absorptivity of the system was 3.15×103 Lmol-1cm-1 and Beer's law was valid over the

vanadium concentration range 0.5-50 ppm.

Krasiejko and Marczenko presented a sensitive and highly selective method

for the spectrophotometric determination of microgram amounts of vanadium(V) [59].

First, vanadium was isolated by extraction with N-benzoyl-N-phenylhydroxylamine

(BPHA) in chloroform from 4 M hydrochloric acid medium. Then, chloroform was

evaporated and the residue mineralized with mixture of concentrated perchloric and

nitric acid. Finally, a color reaction of vanadium(V) separated with 2-(5-bromo-2-

pyridylazo)-5-diethylaminophenol (5-Br-PADAP) in an acetate buffer (pH 4.5). The

molar absorptivity of the method was 5.48×104 Lmol–1cm–1 at 585 nm. The proposed

method was applied for the determination of traces of vanadium in aluminium

samples. The results obtained showed a good precision and accuracy of the method.

Eshwar and Sharma used 1-(2'-thiazolylazo)-2-naphthol as reagent for the

extractive spectrophotometric determination of vanadium in high speed steel [60].

The sparingly soluble complex formed between vanadium(V) and 4-(2-thiazolylazo)

resorcinol was extracted with chloroform. The complex exhibited an absorption

maximum at 610 nm with molar absorptivity 1.50×104 Lmol-1cm-1. Beer's law was

valid over the concentration range 0.08-2.24 ��-1 of vanadium.

Marczenko and Lobinski described an extraction and spectrophotometric

determination of trace amounts of vanadium with 3,5-dinitrocatechol(DNC) and

brilliant green(BG) [61]. Beer's law was obeyed up to a vanadium concentration of

0.3� ��-1 and the molar absorptivity was 1.7×105 Lmole��cm�� at 630 nm. The

molar ratios of the components and the form of the vanadium(V) cation in the

extracted compound was determined and the formula [VO(OH)(DNC)2�2][BG+]2 was

proposed. Titanium, molybdenum, tungsten, EDTA and thiocyanate interfered

seriously. The proposed method has been applied to determination of traces of

vanadium (about 10�� %) in alums. Mandelohydroxamic acid [62], alizarine

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complexone and cetylpyridinium halides [63] were also reported as reagents for the

determination of vanadium in steels.

Kshatriya and Basant developed a selective and sensitive method for the

spectrophotometric determination of vanadium(V) in biological materials with

N-benzylpalmito hydroxamic acid (BPHA) [64]. Vanadium(V) was extracted with

BPHA into chloroform at 3-7 M HCl. The reagent reacted with vanadium to form a

reddish-violet complex with molar absorptivity of 3.79×103 Lmol-1cm-1 at 500 nm.

Beer's Law was obeyed in the concentraction range of 2-8 ppm vanadium.

Aman et al. reported an improved spectrophotometric determination of

vanadium using benzidine-phosphoric acid [65]. Vanadium reacted with benzidine in

acidic medium, which formed a pink colored complex showed maximum absorbance

at 520 nm. The method was successfully applied to the determination of vanadium in

thermal gas turbine deposits and fuel oil sludge.

Yang et al. reported diantipyryl-(3, 4-dioxymethenyl) phenylmethane as a

reagent for the determination of vanadium in herbal medicine [66]. Molar absorptivity

of the system was 3.21×105 Lmol-1cm-1 at 470 nm. Beer's law was obeyed in the range

of 0.2-�� !�" ��#��$�#��% &%�� $��$�

acids [67] were also reported as reagents for the determination of vanadium in

pharmaceutical and steel samples.

Biao and Rong reported chlorpromazine as a sensitive reagent for the

determination of vanadium [68]. Chlorpromazine reacted with vanadium(V) at room

temperature to form a bright red complex, which exhibited an absorption maximum at

520 nm. Beer's law was obeyed in the concentration range of 2-��

10 mL with molar absorptivity of 5.10×103 Lmol-1cm-1.

Costa et al. reported a simple and sensitive spectrophotometric method for the

determination of vanadium(IV) using 2-(5-bromo-2-pyridylazo)-5-

diethylaminophenol (Br-PADAP) [69]. The method was based on the oxidation of

vanadium(IV) to vanadium(V) by the addition of iron(III) cation, followed by a

complexation reaction of iron(II) with a spectrophotometric reagent (Br-PADAP).

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The iron(II) reacted with Br-PADAP which formed a stable complex with a large

molar absorptivity. The vanadium(IV) determination was possible, with a calibration

sensitivity of 0.549 �� for an analytical curve of 18.8 ngm1-1� ��,

molar absorptivity of 2.80×104 Lmol-1cm-1 and a detection limit of 5.5 ngm1-1. The

proposed method was applied for the vanadium(IV) determination in the presence of

several amounts of vanadium(V'��(�� % #�%� � ��#�� )*'�

�� +�� ),*'��(��$�%��

the accuracy obtained were satisfactory (R.S.D. < 2%). Reagents such as N-

phenylcinnamohydroxamic acid and azide [70], 2'-hydroxyacetophenone

benzoylhydrazone [71,72] were also reported for the spectrophotometric

determination of vanadium.

Ahmed and Banoo developed a sensitive, fairly selective direct

spectrophotometric method for the determination of trace amount of vanadium(V)

with 1,5-diphenylcarbohydrazide [73]. The reagent 1,5-diphenylcarbohydrazide

(DPCH) reacted in slightly acidic (0.0001–0.001 M H2SO4 or pH 4.0–5.5) 50%

acetone media with vanadium(V) to give a red–violet chelate which showed

maximum absorption at 531 nm. The average molar absorption coefficient and

Sandell’s sensitivity were found to be 4.23×104 Lmol��cm�� and 10 ngcm�� of

vanadium respectively. Linear calibration graph were obtained for 0.1–�� of

vanadium. The stoichiometric composition of the chelate was 1:3 (V:DPCH). The

reaction was instantaneous and absorbance remain stable for 48 h. The interference

�� $��%��%��$��#�!��%��%�&��%� �� of

vanadium. The method was successfully used in the determination of vanadium in

several standard reference materials (alloys and steels), environmental waters (potable

and polluted), biological samples (human blood and urine), soil samples, solution

containing both vanadium(V) and vanadium(IV) and complex synthetic mixtures. The

��%��$�%��$$ �$��)%-�.��).

Agnihotri et al. reported a highly sensitive and selective spectrophotometric

determination of vanadium(V) using 6-chloro-3-hydroxy-7-methyl-2-(2-thienyl)-4H-

chromen-4-one as a complexing agent in a weakly acidified (HCl, pH 0.84–1.09)

medium [74]. The greenish-yellow complex was quantitatively extracted into carbon

tetrachloride and showed maximum absorbance at 417–425 nm. The method obeys

97

/��0%� #�+� �� 1� �� of vanadium having molar absorptivity and Sandell’s

sensitivity of 8.26×104 Lmol-1cm-1��2��$�� of vanadium respectively. The

method applied to the determination of vanadium in steels, reverberatory flue dust and

water samples. 6-Chloro-3-hydroxy-2-[2'-(5'-methylfuryl)]-4H-chromen-4-one used

as a reagent for the determination of vanadium in various synthetic samples [75].

Vanadium reacted with 6-chloro-3-hydroxy-2-[2'-(5'-methylfuryl)]-4H-chromen-4-

one, which formed a dark yellow (1:1) colored species exhibited an absorption

maximum at 432 nm. Beer's law was valid over the concentration range 0.2-1.4

��-1 of vanadium. Molar absorptivity and Sandell's sensitivity of the system was

3.98×104 Lmol-1cm-1��$�-2 respectively. The reagents 5,7-dichlorooxine,

rhodamine-6G [76] and isothipendyl hydrochloride [77] were also used and reported

for the determination of vanadium in steels and minerals.

Mohamed and Fawy reported a catalytic spectrophotometric method for the

determination of vanadium in seawater samples [78]. The method was based on the

catalytic effect of vanadium on the bromate oxidative coupling reaction of metol with

2,3,4-trihydroxybenzoic acid (THBA). The optimum reaction conditions are 6.4×10-3

M of metol, 2.0×10-3 M of THBA and 0.16 M of bromate at 35º C and in the presence

of an activator-buffer solution of 1.0×10-2 M of tartarate (pH=3.10). The reagent

phenothiazine derivatives were also reported for the determination of vanadium in

steels, minerals, biological samples and soil samples [79].

Di et al. reported a spectrophotometric method for the determination of

vanadium(V) based on the formation of tungstovanadophosphate-3,3',5,5'-

tetramethylbenzidine-N-propanesulfonic (TMBPS) charge transfer complex [80]. The

spectrophotometric measurements were directly carried out at 450 nm and the

apparent molar absorptivity was 2.74×104 Lmol-1cm-1. The linear range of the

determination was 0.02-1.0 ��1. The sensitivity was enhanced with a flotation-

extraction preconcentration method and the apparent molar absorptivity was 3.10×105

Lmol-1cm-1.

Dian-Wen and Li-Xian reported arsenazo-M as a reagent for the determination

of vanadium in iron ores [81]. This method was based on decolorizing reaction of

arsenazo-M by vanadium(V) in H2SO4 medium. The decrease in color was directly

proportional to the amounts of vanadium. The maximum absorption was at 547 nm

98

and the molar absorption coefficient was 1.04×103 Lmol-1cm-1. Beer’s law was valid

over the concentration range 0-�� 3��-Hua et al. used

2-(5-carboxy-1,3,4-triazolylazo)-5-diethylamino benzoic acid [82] as a reagent for the

spectrophotometric determination of vanadium in an aluminium alloy sample.

Agnihotri et al. reported 2,4-dihydroxyacetetophenonebenzoylhydrazone

(DABH) and pyridine as reagents for the spectrophotometric determination of

vanadium in variety of synthetic samples [83]. The method was based on the

formation of light brown complex of vanadium with 2,4-dihydroxyacetophenone

benzoylhydrazone and pyridine. The molar absorptivity and relative standard

deviation of the method was 2.83×104 Lmol-1cm-1 and 0.19 % for vanadium

$��$�� -1 respectively. Beer's law was valid over the vanadium

concentration range 0-��-1. 2-(2-Quinolylazo)-5-diethylaminophenol was also

used as spectrophotometric reagent for the determination of vanadium in water and

biological samples [84].

Cherian and Narayana reported a simple and sensitive spectrophotometric

method for the determination of trace amounts of vanadium using thionin as a

chromogenic reagent [85]. The method was based on the reaction of vanadium(V)

with potassium iodide in acidic medium to liberate iodine. Bleaching of the violet

color of thionin by the liberation of iodine was the basis of the determination and was

measured at 600 nm. Beer's law was obeyed over the range of 0.2-�� -1 of

vanadium. The molar absorptivity, Sandell's sensitivity, detection limit and

quantitation limit of the method were found to be 2.298×104 Lmol-1cm-1, 0.520×10-2

��$�-2��-1 ��-1 respectively. The method was applied to the

analysis of vanadium in synthetic and alloy samples.

Kiran Kumar and Revanasiddappa reported variamine blue as a reagent for the

spectrophotometric determination of trace amounts of vanadium [86]. The method

was based on the oxidation of variamine blue to a violet colored species on reaction

with vanadium(V), having an absorption maximum at 570 nm. Beer’s law was obeyed

in the range of 0.1-2.0 ��-1. The molar absorptivity and Sandell’s sensitivity were

found to be 1.65×104 Lmol-1cm-1� ��$�-2 respectively. Optimum reaction

conditions were evaluated in order to delimit the linear range. The effect of interfering

99

ions on the determination was described. The proposed method was successfully

applied to the determination of vanadium in steel, pharmaceutical, environmental and

biological samples.

Mastoi et al. developed a spectrophotometric method for the determination of

vanadium with 2-pyrrolealdehyde phenylsemicarbazone (PPS) [87]. The linear

calibration curve was obtained with 2.5-20 ��-1 of vanadium. Copper(II),

cobalt(II), iron(II) and palladium(II) were also determined separately using PPS with

linear calibration curves within 2.5-12.5, 5-15, 2.5-15 and 1-��-1 at 362, 355,

355 and 365 nm, respectively. The vanadium in crude oil was determined with

relative standard deviation of 2.5-5.0%. The method has been applied for the analysis

of copper from copper wires, cobalt from pharmaceutical preparation and palladium

from palladium on barium sulphate with RSD within 2.6-4.5%.

Sao et al. reported a reagent system using rhodamine-B dye for the

determination of vanadium [88]. The method was based on the reaction of vanadium

with acidified potassium iodide to liberate iodine. Bleaching of the pink color of

rhodamine-B by the liberation of iodine was the basis of the determination and was

measured at 553 nm. Beer's law was obeyed over the concentration range of 2-�2��

of vanadium in final solution volume of 25 mL (0.08-0.64 ppm). The apparent molar

absorptivity and Sandell's sensitivity were found to be 1.3×105 Lmol-1cm-1 and 0.0009

��$�-2 respectively. The method was simple, sensitive and satisfactorily applied to

ppm level for the determination of vanadium in different environmental and

biological samples.

Qi-Li and De-Yun described a simple and highly sensitive spectrophotometric

method for the determination of vanadium(V) [89]. The method was based on

catalytic oxidation of 1,8-dihydroxynaphthalene-3,6-disulfonic acid and

phenylhydrazine with potassium chlorate. The molar absorptivity was 7.8×106 at the

wavelength of 506 nm, detection range was 0.2-5.0 ngmL-1. It was successfully

applied to the determination of trace amounts of vanadium in spring water, black

bean, corn, tea leaves, and rhodiola schalinensis A leaves.

100

Xianzhong and Yun developed a spectrophotometric determination of

vanadium in carbonaceous shales (stone coal ores) [90]. The method was based on the

reaction of vanadium(V) with the chromophore reagent 2-(5-bromo-2-pyridylazo)-5-

diethylaminophenol (5-Br-PADAP) in the presence of hydrogen peroxide. In a 0.072

M sulfuric acid medium, 5-Br-PADAP reacted with vanadium(V) to form a red-violet

complex with maximum absorption peak at 596 nm with an apparent molar absorption

coefficient of the complex of 8.45×104 Lmol��cm��. Beer's law was obeyed in the

range 0–�� %�# �� +�� $��#�� $��$��

0.9995. Interferences due to various non-target ions were also investigated and high

quantities of other common inorganic ions were tolerable. The method involved the

dissolution of the ore sample by Na2O2 fusion, followed by filtering of the alkali

solution after which Fe(III), Cu(II), Ni(II) and Co(II) etc. were effectively separated

from the solution by precipitation in a NaOH solution. Selectivity was increased with

the use of EDTA as a masking agent. The vanadium in ore sample was determined

with a relative deviation (RSD) between 0.20 and 0.76 %, and has been successfully

applied to the determination of vanadium-bearing stone coal ores. The results

indicated that the accuracy of 5-Br-PADAP spectrophotometry was comparable with

the ICP-AES method.

Kumar et al. developed a facile, sensitive, selective and rapid

spectrophotometric method for the determination of trace amounts of vanadium(V) in

various samples [91]. The method was based on the interactions of

3-methyl-2-benzothiazolinone hydrazone hydrochloride (MBTH) with N-(1-naphthyl)

ethylenediamine dihydrochloride (NEDA) in the presence of vanadium formed a blue

colored derivative or on oxidation of dopamine hydrochloride (DPH) by vanadium in

acidic medium and coupling with MBTH, yielded pink colored derivative. The blue

colored derivative having an absorbance maximum at 595 nm was stable for 9 days

and the pink colored derivative with maximum absorption 526 nm was stable for 5

days. Beer’s law was obeyed for vanadium in the concentration range 0.05–6.0 ��-

1 (blue color derivative) and 0.06–7.0 ��-1 (pink color derivative), respectively.

The optimum reaction conditions and other important analytical parameters were

established. Interference due to various non-target ions was also investigated. The

proposed methods were applied to the analysis of vanadium(V) in environmental,

biological, pharmaceutical and steel samples.

101

Kumar et al. described a simultaneous second-derivative spectrophotometric

determination of cobalt and vanadium using 2-hydroxy-3-methoxybenzaldehyde

thiosemicarbazone (HMBT) [92]. HMBT reacted with Co(II) and vanadium(V) at pH

6.0 formed green-colored complexes in aqueous dimethyl formamide. The second

derivative spectrum of Co(II) complex showed a zero amplitude at 434.5 nm and a

large amplitude at 409.5 nm, while the V(V) complex showed a sufficient amplitude

at 434.5 nm and a zero amplitude at 409.5 nm. The derivative amplitudes obeyed

Beer’s law at 409.5 and 434.5 nm for Co(II) and V(V) in the range 0.059–3.535 and

0.051–��4�� -1 respectively. This enabled the simultaneous determination of

Co(II) and V(V) without separation. Foreign ions did not interfere in the present

method. The method was applied to the simultaneous determination of Co(II) and

V(V) in synthetic mixtures and alloy steel samples. However, most of the reported

methods suffer from a number of limitations, such as interference by a large number

of ions, low sensitivity and need extraction into organic solvents. Therefore a simple

and reliable spectrophotometric method for the determination of vanadium is clearly

recognized.

The present work is to develop a simple spectrophotometric method for the

determination of vanadium using toluidine blue, safranine O and leuco xylene cyanol

FF. The developed method has been successfully applied to the analysis of the

vanadium in alloys, synthetic and pharmaceutical samples.

102

4.3 APPARATUS

A Secomam Anthelie NUA 022 UV-Visible spectrophotometer with 1 cm

quartz cell was used. A WTW pH 330 pH meter was used.

4.4 REAGENTS AND SOLUTIONS

All chemicals were of analytical reagent grade or chemically pure grade and

distilled water was used throughout the study. Vanadium stock solution

(1000 μgmL-1) was prepared by dissolving 0.2395 g of Na3VO4 in 100 mL of water

and standardized volumetrically [93]. The following reagents were prepared by

dissolving appropriate amounts of reagents in distilled water. Toluidine blue (0.05 %),

safranine O (0.1 %), leuco xylene cyanol FF (0.1 %) (0.1 g of xylene cyanol FF was

dissolved in 25 mL of water containing 30 mg of zinc dust and 2 mL of 1 M acetic

acid, stirred well and kept aside for 20 minutes. The resulting solution was then

diluted to 100 mL with water), hydrochloric acid (2 M), potassium iodide (2 %),

sodium acetate solution (1 M) and sulfuric acid (0.05 M).

4.5 PROCEDURES

4.5.1 Using Toluidine Blue as a Reagent

Aliquots of sample solution containing 0.4–8.0 μgmL-1 of vanadium solution

were transferred into a series of 10 mL calibrated flasks. A volume of 1 mL of 2 %

potassium iodide solution was added followed by 1 mL of 2 M hydrochloric acid and

the mixture was gently shaken until the appearance of yellow color, indicating the

liberation of iodine. A 0.5 mL of 0.05 % toluidine blue solution was then added to it

followed by the addition of 2 mL of 1 M sodium acetate solution and the reaction

mixture shaken for 2 minutes. The contents were diluted to 10 mL with distilled water

and mixed well. The absorbance of the resulting solutions were measured at 628 nm

against the corresponding reagent blank. A reagent blank was prepared by replacing

the analyte(vanadium) solution with distilled water. The absorbance corresponding to

the bleached color which in turn corresponds to the analyte(vanadium) concentration

was obtained by subtracting the absorbance of the blank solution from that of test

103

solution. The amount of the vanadium present in the volume taken was computed

from the calibration graph (Figure IVB1).

4.5.2 Using Safranine O as a Reagent

Aliquots of sample solution containing 0.5–12.4 μgmL-1 of vanadium were

transferred into a series of 10 mL calibrated flasks. A volume of 1 mL of 2 %

potassium iodide solution was added followed by 1 mL of 2 M hydrochloric acid and

the mixture was gently shaken until the appearance of yellow color, indicating the

liberation of iodine. A 0.5 mL of 0.1 % safranine O solution was then added to it

followed by the addition of 2 mL of 1 M sodium acetate solution and the reaction

mixture shaken for 2 minutes. The contents were diluted to 10 mL with distilled water

and mixed well. The absorbance of the resulting solutions were measured at 530 nm

against the corresponding reagent blank. A reagent blank was prepared by replacing

the analyte(vanadium) solution with distilled water. The absorbance corresponding to

the bleached color which in turn corresponds to the analyte(vanadium ) concentration

was obtained by subtracting the absorbance of the blank solution from that of test

solution. The amount of the vanadium present in the volume taken was computed


4.5.3 Using Leuco Xylene Cyanol FF as a Reagent (LXCFF)

Aliquots of sample solution containing 0.05–8.0 μgmL-1 of vanadium were

transferred into a series of 10 mL calibrated flasks. Then, volumes of 0.5 mL of the

0.05 M H2SO4 and 0.7 mL of the 0.1% LXCFF were added and the mixture was kept

on a water bath (≈90°C) for 15 minutes, after being cooled to room temperature

(27 ± 2°C), the contents were diluted to the mark with sodium acetate buffer of pH 4,

and mixed well. The absorbance of the xylene cyanol FF dye formed was then

measured at 614 nm against the reagent blank prepared in the same manner, without

vanadium. The amount of the vanadium present in the volume taken was computed


4.5.4 Determination of Vanadium(V) in Vanadium Steel and Synthetic Mixtures An accurately weighed amount of vanadium steel (~0.5 g) was treated with 15

mL of concentrated sulfuric acid and 1 mL of concentrated nitric acid and the solution

104

boiled gently to dissolve the sample. The oxides of nitrogen formed were expelled,

the solution was cooled and diluted to 50 mL with double distilled water. Chromium

was extracted with 5 mL of methyl isobutyl ketone [88]. A 0.01 M solution of

potassium permanganate was added dropwise until the solution appeared pink. The

solution was allowed to stand for 5 minutes, warmed and 0.05 M oxalic acid solution

added slowly with stirring until the pink color of the solution was discharged. The

solution was diluted to 100 mL with distilled water. Using the suitable aliquot of the

solution vanadium content was determined using the proposed procedure.

Synthetic mixtures were prepared by mixing exact concentration of different

metal ions keeping the composition of the synthetic mixture as constant and 1 mL of

this sample solution was used for the determination of vanadium(V) according to the

procedure described above. The results are listed in Table 4B1, 4B2, 4B3, 4C1, 4C2

and 4C3.

4.5.5 Determination of Vanadium(V) in Pharmaceutical Sample

A volume of 10 mL of neogadine elixir (Raptakos Brett & Co. Ltd. Mumbai,

India) sample was treated with 10 mL of concentrated HNO3 and the mixture was

then evaporated to dryness. The residue was leached with 5 mL of 0.5 M H2SO4. The

solution was diluted to a known volume with water after neutralizing with dilute

ammonia. An aliquot of the made up solution was analysed for vanadium according to

the general procedure for vanadium determination. The results are listed in Table

4D1.

4.6 RESULTS AND DISCUSSION

4.6.1 Absorption Spectra

4.6.1.1 Using toluidine blue as a reagent

This method involves the liberation of iodine by the reaction of vanadate with

potassium iodide in an acidic medium. The liberated iodine bleaches the blue color of

toluidine blue and absorbance of the solution is measured at 628 nm. This decrease in

absorbance is directly proportional to the vanadium concentration. The absorption

spectrum of colored species of toluidine blue is presented in Figure IVA1 and reaction

system is presented in Scheme IV.

105

4.6.1.2 Using safranine O as a reagentThis method involves the liberation of iodine by the reaction of vanadate with

potassium iodide in an acidic medium. The liberated iodine bleaches the pinkish red

color of safranine O and absorbance of the solution is measured at 530 nm. This

decrease in absorbance is directly proportional to the vanadium concentration. The

absorption spectrum of colored species of safranine O is presented in Figure IVA2

and reaction system is presented in Scheme IV.

4.6.1.3 Using leuco xylene cyanol FF as a reagent In this method vanadium quantitatively oxidize leuco xylene cyanol FF into

its blue colored xylene cyanol FF dye in a sulfuric acid medium ( pH 1.4-3.9 ) on a

boiling water bath (∼90°C for 15 minutes); the resulting colored dye shows a

maximum absorbance at 614 nm in an acetate buffer medium ( pH 4.0-4.5 ). The

reagent blank have negligible absorbance at this wavelength. The absorption spectra

of the colored species of LXCFF are presented in Figure IVA3 and reaction system is

presented in Scheme IV.

4.6.2 Effect of the Reagent Concentration and Acidity

4.6.2.1 Using toluidine blue and safranine O as reagents

The effect of iodide concentration and acidity on the reaction system is studied

with 2 μgmL-1 vanadium. The oxidation of iodide to iodine by vanadium is effective

in the pH range 1.0-1.5, which can be maintained by adding 1 mL of 2 M HCl in a

final volume of 10 mL. The liberation of iodine from potassium iodide in an acidic

medium is quantitative. It is found that 1 mL of 2 % KI and 1 mL of 2 M HCl are

sufficient for the liberation of iodine from iodide by vanadium. A 0.5 mL of each

0.05 % toluidine blue and 0.1% safranine O is used for subsequent decolorization.

Constant and maximum absorbance values are obtained in the pH range of

4±0.2. Hence the pH of the reaction system is maintained at 4±0.2 throughout the

study. This can be achieved by the addition of 2 mL of 1 M acetate buffer solution in

a total volume of 10 mL. The maximum absorbance is obtained instantaneously and

requires no heating under the reaction conditions. Under the optimum reaction

106

conditions, toluidine blue and safranine O reaction systems are found to be stable for

a period of 4 hours.

4.6.2.2 Using leuco xylene cyanol FF as a reagent

The oxidation of LXCFF by vanadium is studied. Of the various acids

(sulfuric acid, hydrochloric acid and phosphoric acid) studied, sulfuric acid is found to

be the best acid for the system. Constant absorbance readings are obtained in the 0.1-

1.5 mL range of 0.05 M sulfuric acid (or pH 1.4-3.9) at a temperature 90°C for 15

minutes. An increase of the pH above 3.9 markedly affected the stability and

sensitivity of the dye. Color development did not take place below pH 1.4. Hence a

volume of 0.5 mL of 0.05 M sulfuric acid (or maintained pH=2) in a total volume of

10 mL is used in all subsequent work.

The optimum concentration of LXCFF leading to maximum color stability is

found to be 0.7 mL of 0.1 % reagent per 10 mL of the reaction mixture. The

absorbance values are measured in the pH range of 3.5-4.0. This can be achieved by

adding 3 mL of acetate buffer of pH=4. Appreciable results are obtained when the

entire reaction mixture is diluted with the same acetate buffer solution of pH=4. A

change in the pH of the final reaction mixture is affected by the intensity of the

colored dye. The formed colored dye is stable for more than 24 hours.

4.6.3 Analytical Data

4.6.3.1 Using toluidine blue as a reagentThe adherence to Beer’s law is studied by measuring the absorbance values of

solutions varying vanadium concentration. A straight line graph is obtained by

plotting absorbance against concentration of vanadium. Beer’s law is obeyed in the

range of 0.4–8.0 μgmL–1 of vanadium (Figure IVB1). The molar absorptivity and

Sandell’s sensitivity of the system is found to be 2.141×104 Lmol-1cm-1 and 2.36×10-3

μgcm-2 respectively. Correlation coefficient (n=10) and slope of the calibration curve

are 0.995 and 0.141 respectively. The detection limit (DL=3.3σ/s) and quantitation

limit (QL=10σ/s) [where σ is the standard deviation of the reagent blank (n=5) and s is

the slope of the calibration curve] of vanadium determination are found to be 0.234

μgmL-1 and 0.709 μgmL-1 respectively.

107

4.6.3.2 Using safranine O as a reagentAdherence to Beer’s law is studied by measuring the absorbance values of



range of 0.5–12.4 μgmL-1 of vanadium (Figure IVB2). The molar absorptivity and

Sandell’s sensitivity of the system is found to be 3.06×104 Lmol-1cm-1, 1.66×10-3

μgcm-2 respectively. Correlation coefficient (n = 10) and slope of the calibration

curve are 0.997 and 0.144 respectively. The detection limit (DL=3.3σ/s) and

quantitation limit (QL=10σ/s) [where σ is the standard deviation of the reagent blank

(n=5) and s is the slope of the calibration- curve] for vanadium determination are

found to be 0.635 μgmL-1 and 1.920 μgmL-1 respectively.

4.6.3.3 Using leuco xylene cyanol FF as a reagent

Adherence to Beer’s law is studied by measuring the absorbance values of



range of 0.05–8.0 μgmL-1 of vanadium (Figure IVB3). The molar absorptivity and

Sandell’s sensitivity of the colored system is found to be 1.16×104 Lmol-1cm –1 and

4.38×10-3 ��$�-2 respectively. The detection limit (DL=3.3 σ/s) and quantitaion limit

(QL=10 σ/s) [where σ is the standard deviation of the reagent blank (n=5) and s is

the slope of the calibration- curve] for vanadium determination are found to be 0.027

μgmL-1 and 0.08 μgmL-1 respectively.

4.6.4 Effect of Divers IonsThe effect of various ions at microgram levels on the determination of

vanadium is examined. The tolerance limits of the interfering species are established

at those concentrations, which caused not more than ±2.0 % changes in the

absorbance value during the determination of a fixed amount of vanadium (2 μgmL-1).

The tolerance limits of the foreign ions are given in Table 4A1 and 4A2. In this

reaction system, various oxidants such as Cu2+, Cr6+, Fe3+, iodate and periodate

interfered. Interference of chromium can be removed by extracting with 5 mL methyl

isobutyl ketone [94]. Iron and copper can be masked with sodium fluoride and 2-

108

mercaptoethanol respectively. However, the tolerance level of other ions may be

increased by the addition of 1 mL of 1 % EDTA.

4.7 APPLICATIONS

The developed method is applied to the quantitative determination of

vanadium in alloys, synthetic and pharmaceutical samples, the results are summarized

in Table 4B1, 4B2, 4B3, 4C1, 4C2, 4C3 and 4D1 respectively. The precision of the

proposed method is evaluated by replicate analysis of samples containing vanadium at

five different concentrations.

4.8 CONCLUSIONS

1. The reagents provide simple method for the spectrophotometric determination of

vanadium.

2. The developed method does not involve any extraction step and hence the use of

organic solvents, which are generally toxic are avoided.

3. The developed method does not involve any stringent reaction conditions and

offers the advantages of high stability of the reaction system for toluidine blue

(more than 4 hours), safranne O (more than 5 hours) and leuco xylene cyanol FF

(more than 24 hours).

5. The developed method has been successfully applied to the analysis of the

vanadium in alloy samples, synthetic mixtures and pharmaceutical samples. A

comparison of the method reported is made with earlier methods and is given in

Table 4D2.

109

FIGURE IVA1 ABSORPTION SPECTRUM OF COLORED SPECIES OF TOLUIDINE BLUE

Wavelength (nm)

200 300 400 500 600 700 800 900

Abs

orba

nce

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

FIGURE IVA2

ABSORPTION SPECTRUM OF COLORED SPECIES OF SAFRANINE O

Wavelength (nm)

200 300 400 500 600 700 800

Abs

orba

nce

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

110

FIGURE IVA3ABSORPTION SPECTRA OF COLORED SPECIES OF LEUCO XYLENE

CYANOL FF Vs REAGENT BLANK (a) AND REAGENT BLANK Vs DISTILLED

WATER (b)

Wavelength (nm)

300 400 500 600 700 800 900

Abs

orba

nce

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

a

b

FIGURE IVB1

ADHERANCE TO BEER’S LAW FOR THE DETERMINATION OF VANADIUM

USING TOLUIDINE BLUE AS A REAGENT

C oncen tra tion o f vanad ium (µgm L -1)

0 2 4 6 8 10 12

Ab

sorb

an

ce

0 .0

0 .2

0 .4

0 .6

0 .8

1 .0

1 .2

111

FIGURE IVB2 ADHERANCE TO BEER’S LAW FOR THE DETERMINATION OF VANADIUM

USING SAFRANINE O AS A REAGENT

Concentration of vanadium (µgm L-1)

0 2 4 6 8 10 12 14 16

Abs

orba

nce

0 .0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

FIGURE IVB3

ADHERANCE TO BEER’S LAW FOR THE DETERMINATION OF VANADIUM

USING LEUCO XYLENE CYANOL FF AS A REAGENT

C oncentration of Vanadium (µgm L -1)

0 2 4 6 8 10 12 14

Abs

orba

nce

0 .0

0.5

1.0

1.5

2.0

2.5

112

SCHEME IV

2 VO43- + 12 H+ + 2 I - 2 VO2+ + I2 + 6 H2O

N

S+

CH3

NH2(CH3)2N

NH

S

CH3

NH2(CH3)2N

I2 , H+

Toluidine Blue(Colored) Toluidine Blue(Colorless)

N

N+

CH3

NH2NH2

CH3 NH

N

CH3

NH2NH2

CH3 I2 , H+

Safranine O(Colored) Safranine O(Colorless)

NH

CH3

CH3 CH3

NH

CH3

SO3H

SO3Na

H + V5+

NH

CH3

CH3 CH3

N

CH3

SO3H

SO3Na

+ V4+

Xylene Cyanol FF (Colorless) Xylene Cyanol FF (Colored)

113

TABLE 4A1 EFFECT OF DIVERSE IONS ON THE DETERMINATION OF VANADIUM

(2 μgmL-1) USING TOLUIDINE BLUE AND SAFRANINE O

Foreignions

Tolerancelimit

��-1

Foreignions

Tolerancelimit

��-1

Fe3+ *

Ni2+

Cu2+ *

Cd2+

Bi3+

Al3+

Ca2+

Ba2+

In3+

Gd3+

Ti4+

Mo6+

105001550075050010001000750500500250

Cr6+ *

Mg2+

F-

PO43-

Iodate*

CitrateOxalateNitrate

02250100750< 4

15001500500

* Masked with masking agent

TABLE 4A2

EFFECT OF DIVERSE IONS ON THE DETERMINATION OF VANADIUM

(2 μgmL-1) USING LEUCO XYLENE CYANOL FF

Foreignions

Tolerancelimit

��-1

Foreignions

Tolerancelimit

��-1

Fe3+*

Ni2+

Cu2+

Cd2+

Na+

K+

Sm3+

Eu3+

Mg2+

Zn2+

Mn2+

Al3+

Ca2+

Co2+

≤ 1500200650200015001000500100025007506502000500

La3+

Cr2O72-*

F-

In3+

PO43-

Ti4+

Mo6+

Gd3+

OxalateAcetate

TartaratecitrateSulfateIodate*

Nitrate

500≤ 1100150050

10002501000150010002020

1000≤ 1

1500

* Masked with masking agent

114

TABLE 4B1

DETERMINATION OF VANADIUM IN VANADIUM STEELS USING

TOLUIDINE BLUE AS A REAGENT

Sample Composition%

% of vanadium present

% of vanadium

founda

Relativeerror (%)

Recovery(%)

1 C,0.56; Si, 0.24; Mn, 0.91; Ni, 0.23; Cr, 1.03; Mo, 0.04; V, 0.12, Cu, 0.19, P,0.022, S, 0.018

0.120

0.119 ±

0.015 -0.83 99.20

2 C,0.17; Si, 0.13; Mn, 0.53; Ni, 0.20; Cr, 0.20; Mo, 0.85 ; V, 0.28; Cu, 0.10; P,0.015; S, 0.025

0.280

0.278 ±

0.02 -0.71 99.30

a. Mean ± standard deviation (n = 5)

Cu is masked using 2-mercaptoethanol.

TABLE 4B2

DETERMINATION OF VANADIUM IN VANADIUM STEELS USING

SAFRANINE O AS A REAGENT

Sample Composition%


% of vanadium

founda

Relativeerror (%)

Recovery(%)


0.120

0.118 ±

0.02 -0.83 99.20


0.280

0.279 ±

0.01 -0.36 99.30



115

TABLE 4B3

DETERMINATION OF VANADIUM IN VANADIUM STEELS USING LEUCO

XYLENE CYANOL FF AS A REAGENT

Sample Composition %


% of vanadium founda

Relativeerror (%)

Recovery(%)


0.120

0.122 ±

0.06 +1.66 101.66


0.280

0.274 ±

0.02 -2.14 97.85



TABLE 4C1

DETERMINATION OF VANADIUM IN SOME SYNTHETIC MIXTURES USING

TOLUIDINE BLUE AS A REAGENT

Sample Compositions of m�!� ��)��-1) *�� )*'�)��-1) Recovery Added Founda ±SD (% )

1 Zn2+ (25)+Cd2+ (25) 1.00 1.01±0.03 101.0

2 Zn2+ (25)+Cd2+ (25)+CrVI (5)+Mn2+ (20) 0.50 0.49±0.03 98.0

3. Zn2+ (25)+Cd2+ (25)+CrVI (5)+Mn2+ (20) 0.50 0.52±0.50 104.0

+Ca2+ (50)

a. Average of five analyses of each samples ± standard deviation (n = 5)

Chromium is masked using methyl isobutyl ketone.

116

TABLE 4C2 DETERMINATION OF VANADIUM IN SOME SYNTHETIC MIXTURES USING

SAFRANINE O AS A REAGENT

5��#�� 3��%��%� �� !� �� )��-1) *�� )*'� )��-1)Recovery Added Founda ±SD (% )

1 Zn2+ (25)+Cd2+ (25) 1.00 0.98±0.02 98.0

2 Zn2+ (25)+Cd2+ (25)+CrVI (5)+Mn2+ (20) 0.50 0.48±0.04 96.0

3. Zn2+ (25)+Cd2+ (25)+CrVI (5)+Mn2+ (20) 0.50 0.50±0.08 100.0

+Ca2+ (50)

a. Average of five analyses of each samples ± standard deviation (n = 5)


TABLE 4C3

DETERMINATION OF VANADIUM IN SOME SYNTHETIC MIXTURES USING

LEUCO XYLENE CYANOL FF AS A REAGENT

5��#�� 3��%��%� �� !� �� )��-1) *�� )*'� )��-1)Recovery

Added Founda ±SD (% )

1 Zn2+ (25)+Cd2+ (25) 1.00 1.02±0.03 102.0

2 Zn2+ (25)+Cd2+ (25)+CrVI (5)+Mn2+ (20) 0.50 0.48±0.06 96.0

3. Zn2+ (25)+Cd2+ (25)+CrVI (5)+Mn2+ (20) 0.50 0.47±0.12 94.0

+Ca2+ (50)

a. Average of five analyses of each samples ± standard deviation (n = 5),


117

TABLE 4D1DETERMINATION OF VANADIUM IN PHARMACEUTICAL SAMPLE USING

TOUIDINE BLUE, SAFRANINE O AND LEUCO XYLENE CYANOL FF AS

REAGENTS

Reagent Samples V V Recovery used Added found a (%)

��)��-1'��)��-1) ± SD Toluidine Blue b Neogadine Elixir® -- 1.82 ± 0.02 98.91

(10mL/100mL) 4.0 5.81 ± 0.04 99.75

6.0 7.78 ± 0.05 99.33

Safranine O b Neogadine Elixir® -- 1.80 ± 0.02 97.8

(10mL/100mL) 5.0 6.82 ± 0.06 99.7

10.0 11.77 ± 0.04 99.4

Leuco Xylene Cyanol FF b Neogadine Elixir® -- 1.81 ± 0.05 98.3

(10mL/100mL) 3.0 4.83 ± 0.03 99.8

6.0 7.74 ± 0.07 98.7


b. Raptakos Brett & Co. Ltd. Mumbai 400 030, India. [Each 10 mL contains iodised

peptone-0.64 mg, magnesium chloride-13.34 mg, manganese sulphate-2.66 mg,

sodium metavanadate-0.44 mg, zinc sulphate-21.42 mg, pyridoxine HCl-0.50 mg,

cyanocobalamin-0.33 mg, nicotinamide-6.66 mg, alcohol(95 %)-0.63 mL, total

alcohol 6 %(v/v)], vanadium taken-1.84 ��-1.

118

TABLE 4D2 COMPARISON OF THE METHOD REPORTED WITH EARLIER METHODS

ε = Molar absorptivity, ss = Sandell’s sensitivity

Reagent Method Beer’s law)��-1)

ε (Lmol-1cm-1)%%�)��$�-2)

λmax(nm)

Ref. No.

Arsenazo-M Spectrophotometry 0-�� ε = 1.04×103

-----547 81

DABH Spectrophotometry 0-1.5 ε = 2.83×104 ---- 83Thionin Spectrophotometry 0.2-10 ε = 2.298×104

ss = 0.520×10-2600 85

Variamine blue Spectrophotometry 0.1-2.0 ε = 1.65×104

ss = 3.0×10–3570 86

Rhodamine-B Spectrophotometry 0.08-0.64 ε = 1.3×105

ss = 9.0×10–4553 88

Proposed MethodToluidine blue

Safranine O

Leuco xylene cyanol FF

Spectrophotometry

Spectrophotometry

Spectrophotometry

0.4–8.0

0.5–12.4

0.05–8.0

ε = 2.141×104

ss = 2.36×10-3

ε = 3.06×104

ss = 1.66×10-3

ε = 1.16×104

ss = 4.38×10-3

628

530

614

119

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