INTRODUCTION:

Chromium is a chemical element which has the symbol Cr and atomic number 24, first element in Group. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odorless, tasteless, and malleable. The name of the element is derived from the Greek word "chrōma" meaning color, because many of its compounds are intensely colored. It was discovered by Louis Nicolas Vauquelin in the mineral crocoite (lead chromate) in 1797. Crocoite was used as a pigment, and after the discovery that the mineral chromite also contains chromium this latter mineral was used to produce pigments as well.

Chromium was regarded with great interest because of its high corrosion resistance and hardness. A major development was the discovery that steel could be made highly resistant to corrosion and discoloration by adding chromium to form stainless steel. This application, along with chrome plating (electroplating with chromium) are currently the highest-volume uses of the metal. Chromium and ferrochromium are produced from the single commercially viable ore, chromite, by silicothermic or aluminothermic reaction or by roasting and leaching processes.

Although trivalent chromium (Cr(III)) is required in trace amounts for sugar and lipid metabolism, few cases have been reported where its complete removal from the diet has caused chromium deficiency. It is toxic in larger amounts. Hexavalent chromium (Cr (VI)) is toxic and carcinogenic, so that abundant chromium. Literature reveals a number of methods^1-12 to determine iron spectrophotometrically.

EXPERMENTAL METHODS:

Schimedzu, PRI UV- visible – recording spectrophotometer, UV-240 and Elico digital pH meter L1-120 were used in the present investigation. Isonitriso p-isopropyl acetophenone Phenyl Hydrazone was prepared by refluxing equimolar amount of isonitriso p-isopropyl acetophenone¹³ with phenyl hydrazine for 4 hours. On cooling the reaction mixture, a yellow colored product separated out which was collected by filtration and washed with ethanol. The resulting HIPAPH was recrystalized using aqueous ethanol as the procedure recommended by Vogel¹⁴. All the reagents used are of analytical grade and all the solutions are prepared in double distilled water. 1.04g of chromium (VI) salt (K₂Cr₂O₇) potassium dichromate was dissolved in deionized double distilled water and the solution was made up to 1000mL. Buffer of different pH values were prepared by standard procedure. Hydrochloric acid – potassium chloride buffer (pH 2.0 to 4.0), acetic acid – Sodium acetate buffer (pH 4.0 to 7.0) and ammonium chloride and ammonium hydroxide buffer (pH 8.0 to 12.0) were prepared. 0.2% solution of HIPAPH prepared in DMF.

GENERAL PROCEDURE:

An aliquot of the solution containing 10 – 200 µg of chromium (VI) was taken. To this 3.0mL of acetic acid – Sodium acetate buffer and 1.0mL of 0.4% HIPAPH are added and the total volume was diluted to 10mL by deionized double distilled water and the mixture was transferred into a 50 ml separatory funnel. The reddish yellow colour complex Cr(VI)-HIPAPH formed was formed was extracted into 10mL of MIBK, after shaking vigorously for 3.0 minutes, the absorbance of Cr(II)-HIPAPH complex was measured at 443nm against the reagent blank.

RESULTS AND DISCUSSION:

Methyl isobutyl ketone (MIBK) is chosen as solvent, since it was found that the metal complex effectively extracted. The Cr (VI) complex was readily extractable into MIBK and no change was observed to the extent of extraction when the mixture was shaken from 1.5 to 5.0 minutes. Hence 3.0 minutes of shaking time was enough for the complete extraction of complex in to MIBK. The optimum pH for the extraction of metal ion into the organic phase increase as the pH increase from 4.0 to 7.0 and again decrease from7.0 to10.0. It was observed that a ten fold excess of reagent was sufficient to produce maximum intensity of colour. This is equal to 1.0mL of 0.4 % HIPAPH solution.

With the optimum conditions developed the calibration curve was constructed. It was observed that Beer’s law was obeyed for the constructed range of 0.5 to20.0 ppm of Cr (VI) shown in Figure-1. The exact concentration range was determined by constructing a Ringbom plot. Based on the slope of the Ringbom plot (1.7392) shown this ratio between the relative error in concentration and photometric error is 1.5601. For a photometric error of one percent AP=0.01. Hence, the relative error in concentration is 0.016501. Chromium (VI) can be determined accurately by these methods in the range of 1.0 to 18.0 ppm. Sandell´s sensitivity of the reaction obtained from Beer’s law is 2.67x10^-3µg/cm² and the molar obsorptivity of the complex is calculated as 2.78 x 10³lit.mol^-1.cm^-1. Aliquots containing 9.0 mg/mL of Cr (VI) gave a standard deviation of 0.9432x10^-3 and co-efficient of variation is 0.2087 percent.

The composition of Chromium (VI) complex was found to be 1:6 according to Job’s method. Molar ratio method and Asma`s method, the instability constant of the complex was found to be 1.5432 x10^-7by Edmonds and Birnbanm`s method.

Anions like fluoride, chloride and EDTA do not interfere when present up to 5,000µg. Acetate, tartaric and iodide do not have any effect in the determination when present up to 4500 µg. Sulphate, bromide, bicarbonate, and thiocyanate can be tolerated up to 2000µg. The interference due to Fe (III), Cu (II) and Co (II) can be eleminated by using 1.0 mL of 0.4percent citrate solution.

FIG.1: APPLICABILITY OF BEER`S LAW Cr- (HIPAPH)₆COMPLEX

The effect of diverse ion on the extraction and spectrophotometric determination of Cr (VI) were studied and the results are presented in Table-1. From the Tabe-1 cations like Ba(II), Sr(II) and U(VI) do not have any effect on the extracts of Cr- (HIPAPH)₆ complex, when present up to5000µg. Zinc (II) and Tin (II) do not interfere in the determination of Cr (VI), even when present up to 4,500 µg. Pb (II) and Mn (II) can be tolerated up to 4,000µg. Fe (III), Cu (II) and Co (II) interfere in the determination of Cr(VI) even when present in trace amounts.

Table – 1: Effect of Foreign lons on the Extraction of Hg (II) – HIPAPH complex

Foreign ion	Sources of the ion	Tolerance Limit (µg)
Ba (II)	BaCl₂ 2H₂O	5000
Sr (II)	Sr (NO₃)₂	5000
U (VI)	UO₂ (CH₃COO)₂ 2H₂O	5000
Zn (II)	ZnSO₄ 7H₂O	4500
Sn (II)	SnCl₂	4500
Pb (II)	PbCl₂	4000
Mn(II)	MnSO₄ H₂O	4000
Fe (III)^*	FeCl₃	3000
Cu (II)^*	CuCl₂	3000
Co (II)^*	CoCl₂ 6H₂O	3000
Fluoride	NaF	5000
Chloride	KCL	5000
Acetate	CH₃COONH₄	4500
Tartrate	COOK. CHOH. CHOH. COONa. 4H₂O	4500
Iodide	KI	4500
Sulphate	Na₂SO₄	2000
Bromide	KBr	2000
Bicarbonate	NaHCO₃	2000
Thiocyanate	NH₄SCN	2000

* Masked by using 1mL of 0.4% citrate

Concentration of the metal ion Cr (VI) – 18 µg/Ml,

Concentration of the reagent (HIPAPH) – 1.0mL of 0.4 %, pH: 6.0, λ_{max: 443.}

Application of the Developed Method:

The developed extractive-spectrophotometric method was applied for the determination of chromium (VI) in sewage waste and food samples.

Table – 2: Determination of Cr (VI) in Sewage Waste (10.0g sample)

S. No	Area of sewage waste	Metal ion found		Recovery % present method
S. No	Area of sewage waste	*Present method^(µg)**	AAS method (µg)	Recovery % present method
1	Steel plant area	19.8	19.9	99.5
2	HPCL area	14.7	14.9	98.6
3	Hindustan Zinc Ltd. Area	15.6	15.7	99.3

* Average value of three determinations

Reagent concentration: 1.0mL of 0.4 %, pH: 6.0, λ_max: 443

Table-3: Determination of Chromium (VI) in Leaves Samples

S. No.	Name of the Leave Sample	Chromium found		Recovery (%)
S. No.	Name of the Leave Sample	By thiocyanate method (mg)	*By present method^(mg)**	Recovery (%)
1	Goa Beans	0.15	0.16	94.0
2	Soya Leaves	11.9	11.8	99.1

* Average value of three determinations

Reagent concentration: 1.0mL of 0.4 %, pH : 6.0, λ_max: 443.

Determination of Chromium (VI) In Sewage Water:

The proposed method was applied for the determination of chromium (VI) in sewage water collected in different parts in Visakhapatnam city. 10.0g of the dried sample (sewage waste) was weighed and brought into solution by dry ash method. The results are shown in Table-2.

The results showed that the concentration of chromium (VI) is 19.8µg in sample-1, 14.7µg in sample-II and 15.6µg in sample-III. The results are compared with atomic absorption spectrophotometry and they are found to be in good agreement.

Analysis of Chromium (VI) in Goa Beans and Soya Leaves:

Determination of chromium (VI) content in leaves samples was carried out using for present method. 5g of dried leaves determinant was weighed and brought to the solution by dry ash method¹⁵. The results presented in Table –3 shows that the chromium content obtained by the present method was in good agreement with the standard thiocyanate method. The results indicate that chromium content in Soya leaves (11.9) is more when compared to the Goa Beans (0.15 mg).

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Received on 16.11.2010 Modified on 27.11.2010

Asian J. Research Chem. 4(2): February 2011; Page 313-315