FIELD OF INVENTION:
This invention relates to the quantitative estimation of manganese in water using modified formaldoxime method by UV-Visible Spectrophotometer. In this modified method, hazardous and poisonous potassium cyanide [KCN] is replaced by triethanolamine. The stability of formaldoxime reagent as well as that of manganese formaldehyde complex increased in the modified method.
BACKGROUND OF INVENTION;
This method was originally developed by E. B. Sandell wherein a considerable amount of highly toxic KCN was used as to reduce the interference produced by iron and copper is prevented by complexing with cynide in the presence of tartrate and removing the excess of cyanide with zinc, which forms a more stable cyanide complex than manganese but a less stable one than copper and iron.
In the original procedure of Sandell, 0.5 ml of 2(M) tartaric acid is added to 10-25 ml of sample solution (containing greater than 10 ppm manganese) followed by neutralization with ammonia and subsequent addition of 4mi 10% KCN. The solution is boiled for 1 minute, cooled and 5 ml 2 (M) tartaric acid is added. Further, 2 ml of 1% zinc solution and 5ml of 1% hydroxylamine sulphate is added to the solution. The entire content is transferred to another 100ml volumetric flask and diluted up to the mark. 50 ml of this solution is quantitatively transferred to another to 100ml volumetric flask followed by addition of 8ml formaldoxime reagent and 5ml of concentrated ammonia and diluted to 100ml. The absorbance of the final solution is measured against the reagent blank.
In Sandell's method, the formaldoxime reagent is prepared by dissolving 10g paraformaldehyde and 23.5 gm of hydroxylamine sulphate in100ml of water having stability of one week only.
There are numerous spectrophotometric methods for the determination of manganese. Among these methods, permanganate method In which oxidation of manganese to permanganate with potassium (or sodium) periodate' or ammonium persulphate (peroxydisulphate) 2 and a measurement of the charge-transfer band of permanganate at about 528 nm has been long used as a standard method for manganese determination3, 4.This method is less sensitive compared to other spectophotometric methods based on complex formation with chromogenic reagents that provides good sensitivity. However, it suffers serious interferences from any cations and anions in spite of having high detection limit of 0.05µ/ml4 ,5. Because of its distinctive and stable colour, permanganate ion is usually used in the determination of manganese whenever it furnishes the requisite sensitivity. Oxidation by persulphate has an advantage being faster, and the interference of chloride can be prevented by addition of mercuric sulphate. However, oxidation of manganese by persulphate is to be carried out carefully as excessive boiling and slow cooling during oxidation results in loss of permanganate colour.2 Further, persulphate method requires special reagents containing considerable amount of nitric and phosphoric acid. Manganese in higher states of oxidation reacts with various organic compounds viz. o-tolidine, tetramethyldiaminodiphenylmethane, 7 tetramethyldiaminotriphenylmethane and benzidine8 to give strongly coloured oxidation products. Many methods of spectrophotometric determination of manganese have been developed, most of them based on the reaction of this metal with chromogenic reagent.9-17 Apart from these methods, photometric determination of manganese using formaldoxime18-20 is considered to be a more sensitive method (0.005µ cm-2/ 0.001 absorbance, λmax= 45Dnm)21 wherein considerable amount of hazardous reagent potassium cyanide (KCN) is required as masking agent for Cu and Fe. Moreover, formaldoxime solution is stable for a week only. Determination of manganese in potable water is practiced even at grass root level and thus needs reagents that are safe.
KCN is a potent inhibitor of cellular respiration, acting on mitochondrial cytochrome c oxidase and hence blocking oxidative phospyorylation. This prevents the body from oxidizing food to produce useful energy. Lactic acidosis then occurs as a consequence of anaerobic metabolism. Initially, acute cyanide poising causes a red or ruddy complexion in the victim because the tissues are not able to use the oxygen in the blood; The effects of potassium and sodium cyanide are identical. The person may die within 45 minutes if not treated medically. During this period, convulsions may occur. Death occurs mainly by cardiac arrest.
Accordingly, use of poisons like KCN is to be avoided. Therefore, there is a need to modify this formaldoxime method, which would overcome the existing inadequacies in the determination of manganese. Thus, this reports a modified method for spectrophotometric determination of manganese in water using non-hazardous and stable formaldoxime reagents.
OBJECTS OF THE INVENTION
The object of the present invention is to estimate manganese quantitatively in drinking water having concentration of manganese in the range 0.05 to 5.0 ppm, Another object of the present invention is to provide a 24 hours stable manganese formaldoxine complex, (CH2NO) 3Mn.
Still another object of the present invention is to provide formaldoxime reagent which is stable for 12 months.
Yet another object of the present invention is to develop a quantitative method of determination of manganese which is practically free from any interference. Another object of the present Invention is to provide a quantitative method of determination of manganese without using toxic KCN.
Still another object of the present invention is to estimate manganese in drinking water using triethanolamine instead of KCN.
Still further object of the present invention is to employ the principle of determination of manganese in field condition by colour comparison method.
BRIEF DESCRIPTION OF THE INVENTION:
According to this invention, there is provided a process for the estimation of manganese in drinking water when the concentration of manganese is in the range of 0.05 to 5 ppm using formaldoxime.
DETAILED DESCRIPTION OF THE INVENTION
An analytic Jena Specord 40 -UV-Visible spectrophotometer with 1cm quartz cell was
used for the absorbance measurements and a Eutech Instruments pH 510, pH meter was
used.
All the chemicals used were of analytical grade or chemically pure grade and used as
received without further purification unless otherwise mentioned. Double distilled water
was used throughout the study. Standard manganese stock solution (l.0mgMn/ml) was
prepared by dissolving accurately weighed 1.0034 g manganese metal (Fluka, purity >
99%) by 10 ml redistilled HNO3 and diluted to l000ml with 1% v/v HCI.
Subsequent working standard solutions of manganese used for the preparation of
calibration curves were prepared by exact dilution.
A fonnaldoxime solution was prepared by mixing 10g hydroxylamine hydrochloride and
2Dg sodium acetate in a beaker followed by addition of 5ml of 35% formaldehyde and
80ml distilled water respectively. The contents were mixed thoroughly and warmed in a
water bath for 10 minutes and cooled at room temperature. To the mixture, 3ml
triethanolamine was added, mixed and filtered off by Whatman 42 filter paper. The
reagent so filtered was found to be stable for twelve months when stored in a stopper
bottle.
A 5% (W/V) ethylene diaminetetra-acetic acid disodium salt (Na2EDTA) solution was prepared fresh by dissolving requisite amount of the same in distilled water. A 10 %(W/V) solution of ammonium fluoride was prepared just prior to the experiment Triethanolamine was used as received.
In this method, bivalent manganese reacts with formaldoxime (formaldehyde oxime) in alkaline medium and forms a water soluble stable reddish brown complex (CH2NO2)Mn (ref.22) possessing the absorption maxima at 450nm[pH~9.3). In the proposed method the formaldoxime reagent is stabilized for twelve months using a stabilizing reagent. The interferences due to various ions are prevented by adding masking reagent. In order to assess the potential analytical applications of the proposed method, the influence of foreign ions on the determination of manganese was investigated. The precision of the method was checked by replicate determination of standard manganese solution. Utility of the method was evaluated by investigating the recovery of manganese from water samples by recommended procedure. Finally, the method was verified by comparing the results of manganese content of water samples by this method with the extensively used pursulphate method.
Preparation Calibration Curve
An aliquot of a sample solution containing overall of 0.05-5.0 ppm of manganese was transferred into a series of 50ml calibrated volumetric flasks. 1. ml triethanolamine and 2ml ammonia solutions were added and mixed thoroughly. To this, 1ml formaldoxime regent was added and mixed thoroughly. To this, 1ml formaldoxime reagent was added and allowed to stand for two minutes. This was followed by addition of 2ml Na2 EDTA and 1 ml ammonium fluoride solution. Volume of the contents was made upto 50ml with distilled water, mixed thoroughly and allowed to stand for 30 minutes and the absorbance was measured at 450 nm against the corresponding reagent blank. The absorbance values so obtained were plotted against particular manganese concentrations to construct the calibration curve (Figure 1). The absorption maxima of manganese formaldehyde complex are recorded in Figure 2.
Comparison of Proposed method with standard persulphate method:
In order to ascertain the precision of the method, water samples spiked with known amounts of manganese were analyzed by the proposed method. The results are summarized in table 1. Further, recovery of manganese from spiked water samples were carried out by adding known amounts of manganese in the already spiked water samples (Table 2). Determination of manganese in natural water sources were carried out by persulphate as well as proposed method, the results of which are summarized in Table 3,
Comparison with established method:
Manganese content of five numbers water samples were determined (in six replicates) by the proposed method and simultaneously by the standard persulphate method. The data so obtained were subjected to normality test by Kolmogorav -Smimov test and found to follow normal distribution (p>0.05). All the sets of results were compared statistically by calculating the t-value (Table 3). This indicates that there is no significant difference between the results obtained by the proposed procedure and the standard persulphate method for determination of manganese in water.
RESULTS
Analytical data
Beer's law was obeyed in the range of 0.05-5.0 ppm. The molar absorptivity and Sandell's sensitivity for the coloured system was found to be 3.45x 104 L mol-1 cm-1,5.40x 10-3 µg cm2 respectively. The detection limit (DL= 3.3s/S) and quantitation limit (QL= 10s/S) (where s is standard deviation of the reagent blank (n = 5) and S is the slope of the calibration curve, figure 1) for the manganese determination was found to be 0.028 µg ml-1 and 0,028 µmL and 0.086 µ mL-1 respectively (pgml-1 = ppm)
It has been observed form this study that the manganese formaldoxime compound obeys Beer's law up to 5.0 ppm manganese and the colour of the compound is stable up to 24 hours. This precision of the proposed method is presented in Table 1,
In order to establish the reliability and applicability of the proposed method, recovery experiments were performed using spiked water samples. The recoveries ranged from 99.2 to 100.8% (Table 2),
Effect of Interfering Ions
The effect of various ions on the determination of manganese was examined. The tolerance limits of interfering species were established at those concentrations that do not cause more than 2% error in absorbance values of manganese formaldoxime complex (Table 4).
Application
The proposed method was applied for the quantitative determination of manganese in water samples of different resources. The accuracy of the method was checked by similar way as shown in Table 3. The observed results show a good agreement between the two methods.
Conclusions
The proposed method is very simple, highly selective, sensitive and reproducible for the determination of manganese. The method also replaces the use of hazardous KCN and overcomes the problems associated with the previously reported spectrophotometer methods for the determination of manganese. The method is free from interferences of most foreign ions more than any method. The proposed method was used for the determination of manganese in water of different sources. Thus, the proposed method can be successfully applied to determination of manganese in water samples which can save the time of analysis.
Table 1: Precision of the proposed method
(Table Removed)
Table 2: Recovery of manganese from water samples
(Table Removed)
Table 3: determination of Manganese In water samples using the proposed procedure and comparison with persulphate method.
(Table Removed)
*Values are means of 6 determinations (Tabulated t-value for 10 degrees of freedom and at 5% level of significance = 2,228 & Tabulated F-value for 10 degrees of freedom and at 5% level of significance = 5.05); degrees of freedom = (6+6+2) = 10
Kolmogorov-Smimov test indicated normality of data (p>0.05). Paired t test and F-test were done. No significant difference (p>0.05) was observed, in either mean or variance, between the results through proposed method and persulphate method.
Table 4: Effect of foreign iOns on the determination of 1 .Oppm Mn in water samples.
(Table Removed)

WE CLAIM:
1 A method for the estimation of manganese in drinking water wherein the concentration of manganese is in the range of 0.05 to 5 ppm using formaldoxime.
2. The method as claimed in claimed 1, wherein formaldoxime forms a complex with manganese which remains stable for 12 months,
3. The method as claimed in claim 1, wherein the quantity of manganese is determined by colour comparison method.
4. The method as claimed in claim 1, wherein the said formaldoxime was prepared by mixing hydroxylamine hydrochloride and sodium acetate by the addition of formaldehyde and distilled water,
heating the mixture in a water bath,
adding the diaminetetra-acetic acid to the warm mixture.
Subjecting the mixture to the step of filtration.