INTRODUCTION:

The cursory look at the above literature survey reveals that Iron forms chelate complexes with many organic reagents which are bonded through N, O and / S atoms. Out of the reagents used for the extraction and spectrophotometric determination of Fe (III), many reagents suffer limitations as of, interference by other ions, lengthy and tedious procedure for reagent preparation, requirements of surfactants, the stability of complex with time, lack of appropriate solvent for extraction. Survey of innumerable applications of Iron leave a scope for as many reagents as can be applied for the extraction and spectrophotometric determination of Iron.

The present work describes a spectrophotometric method for quantitative estimation of Iron (III) with NSS.

MATERIALS AND METHODOLOGY:

Apparatus: Glassware used in the present investigations was all made up of Borosil. The burettes pipettes and standard flasks were calibrated in accordance with method described in vogel¹. An analytical balance of 0.001g sensitivity of Contech-120 (model CA-123) used for weighing the samples.

All measurements of absorption spectra² were made on one cm silica cells or 1 cm glass cells. The spectrophotometer used was Jasco (UV/VIS/NIR)Model-630.The calibration of the spectrophotometer was checked measuring absorption spectrum of 0.004% solution of potassium chromate in 0.05 M potassium hydroxide solution and also with 0.0058% solution of potassium permanganate in 1M sulphuric acid. The observed spectrum was in good agreement with the spectrum reported in the literature.

RESULTS AND DISCUSSION:

Absorbance Maxima:

The absorption spectrum of Fe (III) NSS complex in Ethyl acetate shows maximum absorbance at 429 nm. The absorbance due to the reagent at this wavelength was negligible. Hence, 429 nm was selected for the absorbance measurement³ in spectro-photometric determination of Fe (III) against blank.

pH study:

The extraction of Iron (III) with NSS was carried out over pH range of 1–7, 1 cm³ of aqueous solution of 100 ppm Iron (III) stock solution and 1 cm³ of 0.02% solution of the reagent⁴ were used. It reveals that 99% of metal is extracted into organic phase in the pH range between 5.2 to 5.6. It was found that complex does not form above pH 7. The analytical work for estimation of Iron (III) was carried out at pH 5.4. (Figure 1)

Figure 1

Solvent study:

Various solvents were tried to determine the maximum extraction of Iron (III). Ethyl acetate was found to be most suitable solvent⁵ as it showed the highest extraction. The extraction of Iron (III) was minimum in solvents Chloform and Carbon Tetra Chloride.

Equilibration Time:

The absorbance of Fe (III) – NSS Complex was checked by varying the time of equilibration from 30 seconds to 15 minutes. It was observed that equilibration time of 1 minute was found to be optimum for complete extraction of Iron (III).

Stability of complex with time:

For this study, 1cm³ of 100 ppm solution was extracted with reagent in Ethyl acetate and absorbance of complex in Ethyl acetate was measured at different intervals of time. The study of stability of complex with variation in time showed that the complex was stable up to 48 hours, after which absorbance decreased slowly.

Effect of reagent concentration:

The effect of variation in concentration of NSS in the range of 0.1 to 2.0 cm³ of 0.02% NSS on the extraction and the color development was tried. It was observed that 0.8 cm³ of 0.02% NSS was sufficient for complete extraction and color development⁶.

Effect of salting out agents on absorbance of Fe (III)-NSS complex:

Different sorting out agents such as sulphates, chlorides, carbonates and nitrates of Sodium, Potassium, Barium, Magnesium, Ammonium and Calcium were used in the extraction of Fe (III) (1cm³ of 100 ppm solution). It was observed that there was no effect on absorbance.

Calibration Curve:

Different amounts of Iron (III) form 1.0 – 8.0 µg / cm³ were extracted quantitatively under optimum experimental conditions and the Ethyl acetate extract was measured at 429 nm against reagent blank. The plot of absorbance against concentration of Iron (III) gave a straight line (Figure 2) indicating that Beer’s Law is obeyed in this range. The molar absorptivity calculated was found to be 1.41 * 10⁴ dm³ mol^-1 cm^-1 and the sensitivity of the method as defined by Sandal’s was 3.3 * 10^-2 µg / cm².

Figure 2

Nature of the extracted species:

The absorption spectrum of the Ethyl acetate extracts of the aqueous solution containing Fe (III): NSS in molar concentration ration 1: 1, 1: 2, 1: 3 and 1: 4 indicated that under the experimental conditions, the nature of absorption spectrum remains identical irrespective of the reagent concentration with no change in the value of wavelength maxima. However, the absorbance increases as the molar reagent concentration increases w.r.t the metal concentration. The composition of the extracted species was determined by Job’s Continuous Variation Method and verified by Mole Ratio Method⁷.

Job’s Continuous Variation Method:

A series of solutions were prepared by mixing 0.0 to 10.0 cm³ of 5.0 x 10^-4 M Fe (III) solution with 10.0 to 0.0 cm³ of 5.0 x 10^-4 M NSS solution, such that the volume of each mixture was 10.0 cm³ each solution was treated at optimum pH as per procedure and the absorbance was then measured against blank. The absorbance values were plotted against mole ratio of Fe (III) to NSS⁸. It shows sharp maxima at 0.5 Mole Fraction of Iron (III), indicating that the colored complex extracted into Ethyl acetate was formed by the reaction of Fe (III) and NSS in the ratio 1:1.(Figure:3)

Figure: 3

Mole Ratio Method:

A series of solutions containing 1 cm³ of 5.0 x 10^-4 Fe (III) increasing amounts of 5.0 x 10^-4 molar NSS were added. Each mixture was treated similarly and absorbance was measured using blank. The absorbance values were plotted against the mole ratio of NSS to Iron (III)⁹. It shows a sharp break corresponding to mole ratio 1:1 which supports the composition of Fe (III): NSS Complex.

Interference Study:

The effect of diverse ions on the Iron (III) determination was studies in presence of a definite amount of Foreign Ion. Various cations and anions were investigated in order to find the tolerance limit of these foreign ions in the extraction of Iron (III). The tolerance limit of the foreign ion was taken as the amount required causing an error of not more than +2% in the recovery of Iron (III).

Effect of masking agents:

The ions which interfere in the spectro-photometry determination of Iron (III) were masked by using appropriate masking agents. (Table: 1)

Table:1

Sr No	Interfering Ion	Masking Agent Added
1	Ag (I)	Potassium Iodide
2	Cd (II)	Potassium Iodide
3	Pb (II)	Sodium Thiosulphate
4	Mn (II)	Sodium Fluoride
5	Ce (IV)	Sodium Fluoride
6	Cr (II)	Ammonium Acetate
7	Citrate	Sodium Molybdate
8	Tartarate	Sodium Molybdate
9	EDTA	Boiling with Conc.HNO₃
10	CN^--	Boiling with Conc.HNO₃and formaldehyde
11	Zr (IV)	Sodium Fluoride
12	Ni (II)	Sodium Cynide
13	Pd (II)	Sodium Thiosulphate

Applications of method:

The present method was applied for the determination of amount of Iron (III) in various samples as alloys, milk samples, synthetic mixtures, beverages and industrial waste water. The results obtained were well in agreement with those of standard methods. (Table: 2)

Table:2 Determination of Iron (III) using NSS from Different Samples

Sr No	Sample	Amount of Fe (III)
Sr No	Sample	Standard Method	Present Method
Iron Alloys
1	Steel	35.0%	34.99%
2	Hematite	67.2%	66.12%
Synthetic Mixture
1	Fe(III) 5mg + Zn(II) 5mg	4.99mg	4.98mg
2	Fe (III) 5mg + Mg (II) 5mg	4.99mg	4.99mg
	Industrial Waste Water at Sarawali -Kalyan	4.9ppm	4.98ppm

REFERENCES:

1) Vogel A.I. Text Book of Quantitative Inorganic Analysis . Longman Green and Co. Ltd., London.1961.

2) Ross S.D. and Wilson D.W. Spectrovision 4,10 (1961).

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Received on 26.06.2014 Modified on 12.07.2014

Asian J. Research Chem. 7(8): August 2014; Page 695-697