1. INTRODUCTION:
Anothrones are known as carcinogenic compounds. Anthrone derivatives are found to have biological activity1-3. These compounds have an azomethine nitrogen atom and this is responsible for their reactivity with a number of transition metal ions which form colored complexes. Its derivatives such as anthralin and anthraquinone, their functions were studied with the inner mitochondrial membrane. Anthralin readily oxidizes to anthralin dimer and anthraquinone; these compounds have also been identified as skin metabolites4. Solubilities of some 9-anthrone derivatives and aminoanthraquinone derivatives in supercritical carbon dioxide were studied using a simple and reliable static method5-6. Anthranoid laxatives are the most commonly used purgatives in the therapy of acute and chronic constipation7-13. Further the metal complexes formed with these reagents are of great medicinal value in the treatment of diseases like colorectal cancer, psoriasis, chronic constipation, tumor related problems regarding.
In this article, the authors present fourth derivative spectrophotometric method for the simultaneous determination of cobalt, nickel and iron.
2. EXPERIMENTAL PROCEDURES:
i) Preparation of APH: The reagent anthrone phenylhydrazone was prepared by simple condensation of anthrone with phenyhydrazine by adopting the standard procedure. The structure of compound is given below,
NNHC6H5 Anthrone phenylhydrazone (APH)
The structure has been established based on IR, mass and NMR spectra. The m.p. of APH is 145-149 0C.
ii) Solutions preparation:
Buffer solutions are prepared using HCl, CH3COOH and NaOAC in acidic medium and NH4OH, NH4Cl in basic medium.
iii) Preparation of metal and reagent solutions:
The standard Co(II), Ni(II) and Fe(II) solutions were prepared using analytical reagent grade CoCl2.6H2O, NiCl2.6H2O and FeSO4. Appropriate quantity of APH is dissolved in DMF for making 0.01M reagent solution.
Procedure:
a. Preparation of standard derivative spectrum:
4 ml of basic buffer solution of pH 10, varying concentrations of each of the metal solutions of Co(II), Ni(II) and Fe(II), 6 ml of 10-3 M of APH are taken in a 25 ml volumetric flask, the contents are made up to the mark with double distilled water and the amplitudes of these solutions were measured between 350-750 nm against reagent blank.
Shimadzu 160A UV-visible spectrophotometer (Japan) equipped with 1 cm quartz cell was used in these investigations for making amplitude measurements. A pH meter ELICO L1-120(Hyderabad) is used to make pH measurements.
b. Preparation and analysis of samples:
Food samples or alloy samples were weighed accurately and digested with nitric acid and perchloric acid for determination of Co, Ni and Fe. The residue was dissolved with 10 ml double distilled water for determination. 3 ml of the digested sample solution, 4 ml of basic buffer solution of pH 10 and 6 ml of APH reagent were taken into a 25 ml volumetric flask. The derivative spectra of analytes in the sample were recorded using the same procedure. According to the concentrations and amplitudes of standard solutions, the contents of the sample can be calculated from derivative spectrum obtained from sample.
3. RESULTS AND DISCUSSION:
a. Derivative spectra of Co, Ni and Fe complexes
The zero order spectrum of a mixture containing cobalt, nickel and iron in presence of APH gives only one peak, no resolution takes place and hence simultaneous determination is not possible and is shown in fig-1. Hence we have made an attempt to use first, second and third order derivative spectra but, no fruitful results obtained. Finally we have made an attempt to use a 4th order derivative spectrum for possible simultaneous determination of the three metal ions and it is shown in figure-2. The 4th order derivative spectra are recorded in one case keeping Co(II) constant and varying both Ni(II) and Fe(II) concentration and is shown in figure-3. In the second case the Ni(II) concentration is kept constant and both Co(II)andFe(II) concentrations are varied shown in fig-4. In the third case the Fe(II) concentration is kept constant and both Ni(II) and Co(II) concentrations are varied shown in fig-5. Graphs are drawn between Co(II) concentration against peak amplitude, Ni(II) concentration against peak amplitude and Fe(II) concentration against peak amplitude. Linear graphs are obtained in all the three cases and shown in the figures-6, 7 and 8. Hence using the fourth order derivative spectrophotometric method, we can determine Co in presence of Ni and Fe and vice-versa.
Fig-1: Zero order spectrum of Co (II)+Ni(II)+Fe(II) in presence of APH
[Co (II)] = [Ni (II)] = [Fe (II)] 1x10-5M;
[APH] = 2.4x10-4 M, pH = 10;
Figure-2: 4th order derivative spectrum of Co(II)+Ni(II)+Fe(II) in presence of APH
[Co(II)] = [Ni(II)]=[Fe(II)]=1x10-5 M, [APH] =2.4x10-4 M, pH=10;
a) 0.5 ml of Co(II), Ni(II) and Fe(II) each
b) 1.0 ml of Co(II), Ni(II) and Fe(II) each
c) 1.5 ml of Co(II), Ni(II) and Fe(II) each
d) 2.0 ml of Co(II), Ni(II) and Fe(II) each
e) 2.5 ml of Co(II), Ni(II) and Fe(II) each
b. Influence of the variables:
APH is a kind of high sensitive carcinogenic reagent and it can form colored complexes with many transition metals in neutral and basic medium. The experiments are carried out in the pH range 7- 12. The results showed that the absorbances of three complexes were highest and the complexes are stable in the pH range 10-11. The effect of pH on the absorbances are shown in the figures-9, 10 and 11. Further Co(II), Ni(II) and Fe(II) do not form stable complexes in acidic medium. It may be due to the hydrolysis of the reagent or the complex itself. In highly alkaline medium (>pH11) slow turbidity develops which may be due to formation of hydroxides. Studies relating to the effect of time revealed that the complex is stable for a considerable amount of time.
Figure-3: 4th order derivative spectrum of Co(II)+Ni(II)+Fe(II) in presence of APH.
Cobalt concentration is kept constant by varying concentration of both Ni2+ and Fe2+
[Co(II)] = [Ni(II)] = [Fe(II)] = 1x10-5 M, [APH] =2.4x10-4 M, pH=10;
a) 0.5 ml of Co(II), 1.0 ml of Ni(II) and 1.0 ml of Fe(II)
b) 1.0 ml of Co(II), 1.5 ml of Ni(II) and 1.5 ml of Fe(II)
c) 1.5 ml of Co(II), 2.0 ml of Ni(II) and 2.0 ml of Fe(II)
d) 2.0 ml of Co(II), 2.5 ml of Ni(II) and 2.5 ml of Fe(II)
e) 2.5 ml of Co(II), 3.0 ml of Ni(II) and 3.0 ml of Fe(II)
Figure-4: 4th order derivative spectrum of Co(II)+Ni(II)+Fe(II) in presence of APH.
Nickel concentration is kept constant by varying concentration of both Co2+ and Fe2+
[Co(II)] = [Ni(II)] = [Fe(II)] = 1x10-5 M, [APH] =2.4x10-4 M, pH=10;
a) 1.0 ml of Co(II), 0.5 ml of Ni(II) and 1.0 ml of Fe(II)
b) 1.5 ml of Co(II), 1.0 ml of Ni(II) and 1.5 ml of Fe(II)
c) 2.0 ml of Co(II), 1.5 ml of Ni(II) and 2.0 ml of Fe(II)
d) 2.5 ml of Co(II), 2.0 ml of Ni(II) and 2.5 ml of Fe(II)
e) 3.0 ml of Co(II), 2.5 ml of Ni(II) and 3.0 ml of Fe(II)
Figure-5: 4th order derivative spectrum of Co(II)+Ni(II)+Fe(II) in presence of APH.
Iron concentration is kept constant by varying concentration of both Ni2+ and Co2+
[Co(II)] = [Ni(II)] = [Fe(II)] = 1x10-5 M, [APH] =2.4x10-4 M, pH=10;
a) 1.0 ml of Co(II), 1.0 ml of Ni(II) and 0.5 ml of Fe(II)
b) 1.5 ml of Co(II), 1.5 ml of Ni(II) and 1.0 ml of Fe(II)
c) 2.0 ml of Co(II), 2.0 ml of Ni(II) and 1.5 ml of Fe(II)
d) 2.5 ml of Co(II), 2.5 ml of Ni(II) and 2.0 ml of Fe(II)
e) 3.0 ml of Co(II), 3.0 ml of Ni(II) and 2.5 ml of Fe(II)
Figure-6: 4th order derivative amplitude vs concentration of Co(II)
pH=10, a=peak; b=valley; c=peak+valley;
Figure-7: 4th order derivative amplitude vs concentration of Ni (II)
pH=10, a=peak; b=valley; c=peak + valley;
Figure-8: 4th order derivative amplitude vs concentration of Fe (II)
pH=10, a=peak; b=valley; c=peak + valley;
Fig-9: Effect of pH on the absorbance of cobalt (II)-APH system
[Cobalt (II)]=3x10-5 M, [APH] =2x10-4 M
Fig-10: Effect of pH on the absorbance of nickel (II)-APH system
[Nickel (II)] =3x10-5 M, [APH] =2x10-4 M
Fig-11: Effect of pH on the absorbance of iron (II)-APH system
[Iron(II)] =3x10-5 M, [APH] =2x10-4 M
Fig-12: Effect of metal ion concentration on absorbance
λmax=373 nm, [Co (II)] =4x10-5 M, [APH]=2.4x10-4 M, pH=10
 |
Fig-13: Effect of metal ion concentration on absorbance
λmax=364 nm, [Ni (II)] =4x10-5 M, [APH] =2.4x10-4 M, pH=11;
Fig-14: Effect of metal ion concentration on absorbance
λmax=359 nm, [Fe (II)] =4x10-5 M, [APH]=2.4x10-4 M, pH=10;
Table-1: Tolerance limit of foreign ions
Tolerance limit of foreign ions in the determination of 0.841μg/ml of Co(II), 1.35 μg/ml of Ni (II) and 0.15 μg/ml of Fe(II)
pH = 10 λmax = 364 nm
|
Foreign ion
|
Tolerance limit (μg/ml) |
Foreign ion
|
Tolerance
|
|
Thiourea |
94 |
Mn(IV) |
1.54 |
|
Tartrate |
319 |
U(VI) |
86.21 |
|
Sulfate |
755 |
Ru(III) |
11.20 |
|
Phosphate |
163 |
Se(IV) |
112 |
|
Fluoride |
17 |
Pb(II) |
2.54 |
|
Chloride |
44.21 |
Cd(II) |
3.84 |
|
Iodide |
63.8 |
Zr(IV) |
3.73 |
|
Nitrate |
112.23 |
Ti(IV) |
127.68 |
|
Oxalate |
16.57 |
Sn(II) |
2.27 |
|
EDTA |
316.4 |
Mg(II) |
1.55 |
|
Thiosulfate |
55.23 |
Zn(II) |
1.74 |
|
Bromide |
440 |
W(VI) |
735.4 |
|
Citrate |
841 |
Pd(II) |
0.35 |
|
Acetate
|
144.3 |
Hg(II) |
11.19 |
|
Cu(II) |
2.45 |
||
|
Mo(VI) |
65.25 |
The effect of metal ion concentrations (4x10-5 M) on absorbances is studied by keeping the reagent concentration constant (2.4x10-4 M). The absorbance values are measured at 373, 364 and 359 nm for cobalt, nickel and iron respectively against suitable blank solution containing no metal ion. Linear plots are obtained in all the three cases when graphs are plotted between the metal ion concentration and absorbance and are presented in the figures-12, 13 and 14. The determination limits were 0.201-1.807, 0.411-4.811 and 0.0207-0.202 µg/ml for cobalt, nickel and iron respectively. The stoichiometry of these three metal ions with APH was studied by Job`s method of continuous variation and also the mole ratio method. Both the methods indicated the formation of a 1:1.4, 1:2 and 1:1 complex for cobalt, nickel and iron respectively. By knowing this stoichiometry a 35 fold concentration of APH is taken to react with the three metal ions. The stability constants of Co(II), Ni(II) and Fe(II)-APH complexes were calculated from Job`s method. They are found as 1.530x105, 2.486x104 and 1.049x104 for Co(II), Ni(II) and Fe(II) respectively. The effect of interfering species of 23 metal ions commonly found in food samples is investigated. The most interfering ions tested did not interfere in the determination and shown in table-1.
4. APPLICATION:
The present method is applied for the determination of three metal ions simultaneously in sesame, laver, soyabean powder and alloy samples The repeatability and precision of the method were satisfied with RSD in the range of 0.0863-0.0888% for five determinations. Therefore, the three metal ions can be directly determined after digestion without any pretreatment by the proposed method. Accuracy of the proposed method was validated using a certified reference material of tea and grape leaves (GBW07605 and GBW08501, Chinese Standard material center) (AAS and APARI, Hyderabad). The values determined by the proposed method and the determined values (n=5) of the certified reference material were within the given guarantee values and shown in the table-2.
5. CONCLUSION: In this article, a multi-component analysis with 4th order derivative spectrophotometry has been developed. The proposed method has been successfully applied for the simultaneous determination of Co, Ni and Fe in certified reference materials and food samples after digestion without further pretreatment. Compared with the traditional spectrophotometry, the proposed method provides good results for three analytes in terms of accuracy and precision and allows 44 determinations per hour for the digested food samples, and the results proved to be satisfactory and meet the criterion of food analysis.