Determination of Manganese in Tap Water by a New Extraction-photometric Method

Manganese is considered to be the 12th most abundant element in the biosphere. Its concentration in earth crust reaches as high as 0.098%. It is widely distributed in soil, water, sediment and biological materials. Manganese has accumulative properties. Due to this accumulating in the organism chronic manganese excess affects the central nervous system, with the symptoms resembling those of Parkinson's disease [1].


Introduction
Manganese is considered to be the 12 th most abundant element in the biosphere. Its concentration in earth crust reaches as high as 0.098%. It is widely distributed in soil, water, sediment and biological materials. Manganese has accumulative properties. Due to this accumulating in the organism chronic manganese excess affects the central nervous system, with the symptoms resembling those of Parkinson's disease [1].
In the literature there is data on the use of o-nitrobenzolazosalicylic acid for determination of nickel, zinc, ferrous, cobalt [6][7][8][9]. But no data about determination of manganese with o-nitrobenzolazosalicylic acid can be found in the literature.
The heteroligand complex of manganese(II) has been investigated with 1,10-phenantroline (Phen) from aromatic diamines and with o-nitrobenzolazosalicylic acid (oNBASA) from chromogenic organic reagents and the new rapid, simple and sensitive extraction-photometric method of manganese determination with these reagents have been worked out by us.

Experimental Instruments
Absorption measurements were collected on a SF-46 spectrophotometer or KFK-3 photoelectrocolourimeter using 1 cm cuvette. The pH-meter EV-74 is used for pH measurements.

Reagents
Stock solution of 1.52 × 10 -2 M manganese(II) was prepared from MnCl 2 •4H 2 O salt with qualification "p.f.a." (Pure for analysis) and quantity of manganese standardized gravimetrically [10]. Working solution of 4.5 × 10 -4 M manganese(II) was prepared by dilution of stock solution with distilled water. Solution of oNBASA with 5 × 10 -3 M concentration was prepared by dissolving the required amount in water, in which pH was arrived to 12 in advance. Solution of Phen with 1 × 10 -2 M concentration was prepared by dissolving the required amount of preparate which was the production in firm "Chemapol" in 50% ethanol (by volume). Universal or borate buffer solutions or 0.1 M CH3COOH and NaOH solutions were used for obtaining appropriate pH.

Procedure
Appropriate amount of solutions of Phen and oNBASA have been added to the definite amount of solution of manganese(II) in test-tube with stoppers or in separator funnel. Then total volume has been diluted to 10 ml by adding of buffer solution. The mixture has been shaked for 1 minute with adding of 5 ml solvent. Colored extract has been transferred to the cuvette when the phases separated and absorbance has been measured relative to the water. The analogical experiment has been carried out without manganese and absorbance of the extract of reagent has been measured also relative to the water.

Results and Discussion
Investigations show that the derivatives of salicylic acid form colored complexes with transition metals [6][7][8][9] and this can be used in developing an extraction-photometric method for the determination of these metals, also of manganese(II).
absorbance takes place at pH 10 ( Figure 1) and wavelength of 370 nm have been selected for the present work ( Figure 2).
The influence of the concentration of Phen and oNBASA was studied. The optimal concentration of Phen and oNBASA for formation of the complex was found to be 6 × 10 -4 M and 2.5 × 10 -4 M, respectively.
Excess amount of Phen and oNBASA does not affect the formation and extraction of the complex. Because, in the condition of complexing the carboxyl group of the chromogenic organic reagent is ionized and charged form is preferably in the aqueous phase. The heteroligand complex of Mn(II) with Phen and oNBASA was extracted with chloroform and dichloroethane . Optimal volume of aqueous and organic phase was found to be 25-50 and 5 ml, respectively. Mn-Phen-oNBASA complex is formed immediately after adding the reagents and extraction equilibrium is achieved by shaking up 1 minute.
The sequence of reagents to be added does not affect the complex formation and extraction. The intensity of color of the complex does not change depending on time and stable during the day.

Content of complex
The stoichiometric coefficients of the complexing were established. The molar ratio Mn: Phen: oNBASA was proved by the method of straight line and crossing the lines [11]. The results for the light absorption of the extracts at 370 nm showed that the complex was formed at a ratio Mn: Phen: oNBASA=1:2:2. By the method of Nazarenko [12] was established that the complexing form of manganese are the ions Mn +2 . The same amount of complex two times was extracted consistently and extraction percentage was found: 98.76%.

Effect of diverse ions
In order to assess the usefulness of the proposed method the influence of strange ions on the extraction-photometric determination of manganese was studied. The tolerance of the method of foreign

Determination of manganese(II) in tap water
Water sample was taken in the flask 2 l and was evaporated to dryness. Dry residue was dissolved in a buffer solution with pH 10 and by filtering was transferred to a 50 ml flask. Aliquot part was transferred to the separator funnel or test-tube. 2 ml buffer solution with appropriate pH, 0.6 ml Phen and 0.5 ml oNBASA was added. Then was diluted by the same buffer solution to 10 ml and was extracted with chloroform for 1 minute. Absorbance was measured in SF-46 in the cuvette of 1 cm when the phases separated. Amount of manganese was determined from the calibration graph. Amount of manganese have been determined in tap water by the proposed method: 0.018 ± 0.009 mkg/ml.

Conclusions
At the first time the heteroligand complex of manganese(II) has been investigated with 1,10-phenantroline (Phen) and o-nitrobenzolazosalicylic acid (oNBASA) from chromogenic organic reagents. The new rapid, simple and sensitive extraction-photometric method of manganese determination with these reagents have been worked out and applied to determination of manganese(II) in tap water by us.