Optimized and validated spectrophotometric methods have been proposed for the determination of iron and cobalt individually and simultaneously. 2-hydroxy-1-naphthaldehyde-p-hydroxybenzoichydrazone (HNAHBH) reacts with iron(II) and cobalt(II) to form reddish-brown and yellow-coloured [Fe(II)-HNAHBH] and [Co(II)-HNAHBH] complexes, respectively. The maximum absorbance of these complexes was found at 405 nm and 425 nm, respectively. For [Fe(II)-HNAHBH], Beer’s law is obeyed over the concentration range of 0.055–1.373
Iron and cobalt salts are widely used in industrial materials [
A good number of reviews have been made on the use of large number of chromogenic reagents for the spectrophotometric determination of iron and cobalt. Some of the recently proposed spectrophotometric methods for the determination of iron [
0.01 M iron(II) and cobalt(II) solutions were prepared by dissolving appropriate amounts of ferrous ammonium sulphate (Sd. Fine) in 2 M sulphuric acid and cobaltous nitrate (Qualigens) in 100 mL distilled water. The stock solutions were diluted appropriately as required. Other metal ion solutions were prepared from their nitrates or chlorides in distilled water. 1% solution of cetyltrimethylammonium bromide (CTAB), a cationic surfactant in distilled water is used. Buffer solutions of pH 1–10 are prepared using appropriate mixtures of 1 M HCl–1 M CH3COONa (pH 1–3.0), 0.2 M CH3COOH, 0.2 M CH3COONa (pH 3.5–7.0), and 1 M NH4OH and 1 M NH4Cl (pH 7.5–10.0). HNAHBH was prepared by mixing equal amounts of 2-hydroxy-1-naphthaldehyde in methanol and p-hydroxybenzoichydrazide in hot aqueous ethanol in equal amounts and refluxing for three hours on water bath. A reddish brown coloured solid was obtained on cooling. The product was filtered and dried. It was recrystallized from aqueous ethanol in the presence of norit. The product showed melting point 272–274°C.
The structure of the synthesized HNAHBH was determined from infrared and NMR spectral analysis.
The soil sample (5.0 g) was weighed into a 250 mL Teflon high-pressure microwave acid digestion bomb and 50 mL aquaregia were added. The bomb was sealed tightly and then positioned in the carousel of a microwave oven. The system was operated at full power for 30 minutes. The digested material was evaporated to incipient dryness. Then, 50 mL of 5% hydrochloric acid was added and heated close to boiling to leach the residue. After cooling, the residue was filtered and washed two times with a small volume of 5% hydrochloric acid. The filtrates were quantitatively collected in a 250 mL volumetric flask and diluted to the mark with distilled water.
A 0.1–0.5 g of the alloy sample was dissolved in a mixture of 2 mL HCl and 10 mL HNO3. The resulting solution was evaporated to a small volume. To this, 5 mL of 1 : 1 H2O and H2SO4 mixture was added and evaporated to dryness. The residue was dissolved in 15 mL of distilled water and filtered through Whatman filter paper no. 40. The filtrate was collected in a 100 mL volumetric flask and made upto the mark with distilled water. The solution was further diluted as required.
A wet ash method was employed in the preparation of the sample solution. 0.5 g of the sample was dissolved in a 1 : 1 mixture of nitric acid and perchloric acid. The solution was evaporated to dryness, and the residue was ashed at 300°C. The ash was dissolved in 2 mL of 1 M sulphuric acid and made up to the volume in a 25 mL standard flask with distilled water.
Blood and urine samples of the normal adult and patient (male) were collected from Government General Hospital, Kurnool, India. 50 mL of sample was taken into 100 mL Kjeldal flask. 5 mL concentrated HNO3 was added and gently heated. When the initial brief reaction was over, the solution was removed and cooled. 1 mL con. H2SO4 and 1 mL of 70% HClO4 were added. The solution was again heated to dense white fumes, repeating HNO3 addition. The heating was continued for 30 minutes and then cooled. The contents were filtered and neutralized with dil. NH4OH in the presence of 1-2 mL of 0.01% tartrate solution. The solution was transferred into a 10 mL volumetric flask and diluted to the volume with distilled water.
Different water samples were collected from different parts of Anantapur district, A. P, India and filtered using Whatman filter paper.
A known quantity of the sample was taken in a beaker and dissolved in minimum volume of alcohol. Then added 3 mL of 0.01 M nitric acid and evaporated to dryness. The dried mass was again dissolved in alcohol. This was filtered through Whatman filter paper, and the filtrate was diluted to 100 mL with distilled water. The lower concentrations were prepared by the appropriate dilution of the stock solution.
A Perkin Elmer (LAMBDA25) spectrophotometer controlled by a computer and equipped with a 1 cm path length quartz cell was used for UV-Vis spectra acquisition. Spectra were acquired between 350–600 nm (1 nm resolution). ELICO model LI-120 pH-meter furnished with a combined glass electrode was used to measure pH of buffer solutions.
Iron(II) and cobalt(II) react with HNAHBH forming reddish brown and yellow coloured complexes. The colour of the complexes was stable for more than two days.
The absorption spectrum of [Fe(II)-HNAHBH] shows maximum absorbance at 405 nm. The preliminary investigations indicate that the absorbance of the complex is maximum and stable in pH range of 4.5–5.5. Hence pH 5.0 was chosen for further studies. A considerable increase in the colour intensity in the presence of 0.1% CTAB was observed. Studies on reagent (HNAHBH) concentration effect revealed that a maximum of 15-fold excess reagent is required to get maximum and stable absorbance for the complex. From the absorption spectra of [Fe(II)-HNAHBH] the molar absorptivity, coefficient
Numerous cations and anions were added individually to the experimental solution containing 0.558
Tolerance limits of foreign ions, Amount of Fe(II) taken = 0.558
Foreign ion | Tolerance limit ( | Foreign ion | Tolerance limit ( | Foreign ion | Tolerance limit ( |
---|---|---|---|---|---|
Sulphate | 1440 | Na(I) | 1565 | La(III) | 18 |
Iodide | 1303 | Mg(II) | 1460 | Ag(I) | 15 |
Phosphate | 1424 | Ca(II) | 1440 | Hg(II) | 16 |
Thiosulphate | 1424 | K(I) | 1300 | U(VI) | 6,60a |
Tartrate | 1414 | Ba(II) | 1260 | Mn(II) | 4,55a |
Thiourea | 1140 | Pd(II) | 63 | Th(IV) | 3,50a |
Bromide | 1138 | Cd(II) | 45 | In(III) | 4,60a |
Nitrate | 930 | Bi(III) | 42 | Sn(II) | <1,50a |
Carbonate | 900 | W(VI) | 37 | Co(II) | <1,55a |
Thiocyanate | 870 | Hf(IV) | 36 | Ni(II) | <1,60b |
Chloride | 531 | Ce(IV) | 28 | Zn(II) | <1,80b |
Fluoride | 285 | Cr(VI) | 27 | Al(III) | <1,45a |
EDTA | 124 | Mo(VI) | 22 | Cu(II) | <1,50a |
Citrate | 115 | Zr(IV) | 19 | ||
Oxalate | 95 | Sr(II) | 18 |
In the presence of
The applicability of the developed direct method was evaluated by applying the method for the analysis of some surface soil and alloy steel samples for their iron content. Different aliquots of sample solutions containing suitable amounts of iron were treated with known and required volume of HNAHBH at pH 5.0 and 0.1% CTAB and diluted to 10 mL with distilled water. The absorbance of the resultant solutions was measured at 405 nm, and the amount of iron present was computed from the predetermined calibration plot. The results were compared with the certified values and presented in Tables
Determination of iron in surface soil.
Sample | Source of the sample | Amount of iron (mg Kg−1) ± SD* |
---|---|---|
S1 | Groundnut cultivation soil | 40.98 ± 0.45 |
S2 | Cotton cultivation soil, | 27.48 ± 0.36 |
S3 | Sweet lemon cultivation soil, | 44.88 ± 0.24 |
S4 | Paddycultivation soil | 20.86 ± 0.37 |
*Average of five determinations.
Determination of iron in alloy steels.
Alloy steel composition (%) | Amount of iron (%) | ||
Certified value | Present | Relative error (%) | |
4.13 | 0.17 | ||
(34.26 Zn, 0.38 Si, 1.2 Cd, 48.57 Sb, 0.95 S, and 0.32 F) | 34.26 | 0.01 | |
(9.29 Al, 1.04 Ca, 9.53 Fe) | 9.53 | 0.08 |
*Average of five determinations.
Different amounts of Fe(II) (0.027–1.375
First-order derivative spectra of [Fe(II)-HNAHBH]. Amount of Fe(II)
Second-order derivative spectra of [Fe(II)-HNAHBH]. Amount of Fe(II)
Third-order derivative spectra of [Fe(II)-HNAHBH]. Amount of Fe(II)
The derivative amplitudes measured at the analytical wavelengths as mentioned above for different derivative spectra were plotted against the amount of Fe(II). The calibration plots are linear in the range 0.027–1.375
The influence of some of the cations, which showed serious interference in zero order method, on the derivative amplitudes was studied by the reported methods and the results obtained are shown in Table
Tolerance limits of some cations in derivative methods.
Foreign ion | Tolerance limit (in folds) | |||
Direct method | First derivative | Second derivative | Third derivative | |
Ag(I) | 14 | 18 | 35 | 22 |
Hg(II) | 11 | 20 | 40 | 30 |
U(VI) | 11 | 12 | 25 | 18 |
Mn(II) | 7 | 20 | 16 | 20 |
Th(IV) | 5 | 10 | 16 | 20 |
In(III) | 7 | 28 | 48 | 34 |
Au(III) | 4 | 35 | 55 | 28 |
Sn(II) | <1 | 8 | 15 | 22 |
Co(II) | <1 | interfere | 7 | 15 |
Ni(II) | <1 | interfere | 5 | 10 |
Cu(II) | <1 | 5 | 12 | 10 |
Analytical characteristics of [Fe(II)-HNAHBH].
Parameter | Direct method | First derivative | Second derivative | Third derivative | ||
---|---|---|---|---|---|---|
405 nm | 427 nm | 421 nm | 435 nm | 415 nm | 426 nm | |
Beer’s law range ( | 0.055–1.373 | 0.027–1.376 | 0.027–1.376 | 0.027–1.376 | 0.027–1.376 | 0.027–1.376 |
Molar absorptivity, (L mol−1 cm−1) | — | — | — | |||
Sandell’s sensitivity, ( | 0.0012 | — | — | — | ||
Angular coefficient (m) | 0.974 | 0.072 | 0.006 | 0.093 | 0.002 | 0.085 |
Y-intercept (b) | 0.0047 | −0.0045 | ||||
Correlation coefficient | 0.9997 | 0.9999 | 0.9999 | 0.9999 | 0.9999 | 0.9999 |
RSD (%) | 2.19 | 0.85 | 0.76 | 0.89 | 1.31 | 1 |
Detection limit ( | 0.065 | 0.1 | 0.022 | 0.0268 | 0.036 | 0.304 |
Determination limit, ( | 0.197 | 0.3 | 0.068 | 0.8 | 0.11 | 0.914 |
Composition (M : L) | 2 : 3 | — | — | — | ||
Stability constant | — | — | — |
Known aliquots of the prepared food and biological sample solutions were treated with suitable volumes of HNAHBH, buffer solution, and CTAB surfactant and diluted to the volume in 10 mL volumetric flasks. The first-order derivative spectra were recorded, and the derivative amplitudes were measured at analytical wave lengths. The amounts of Fe(II) in the samples were computed from predetermined calibration plots and presented in Table
Determination of iron in food and biological samples.
Samples | Amount of iron( | |||||
Found | Recovered | |||||
present | AAS | Added | present | AAS | % recovery | |
Wheat | 5 | 97.6 | ||||
Rice | 5 | 102 | ||||
Tomato | 5 | 104 | ||||
Orange | 5 | 96 | ||||
Banana | 5 | 98.3 | ||||
Prostate gland | 6.5 | 103 | ||||
Benign (enlarged prostate gland | 6.5 | 95.12 |
[Co(II)-HNAHBH] complex shows maximum absorbance at 425 nm. Maximum and stable absorbance of the complex is achieved in the pH range of 5.0–7.0. Hence pH 6.0 was chosen for further studies. A marginal increase in the absorbance was observed in presence of 0.15% of CTAB. 10-folds excess of HNAHBH is sufficient to get maximum absorbance. Molar absorptivity of the complex was calculated as
The effect of various anions and cations normally associated with Co(II) on the absorbance of the experimental solution was studied. The tolerance limits of the tested foreign ions, which bring about a change in the absorbance by ±2% were calculated and presented in Table
Tolerance limits of foreign ions, amount of Co(II) taken = 1.767
Foreign ion | Tolerance limit ( | Foreign ion | Tole limit ( | Foreign ion | Toler limit ( |
---|---|---|---|---|---|
Tartrate | 1707 | Na(I) | 1666 | Au(III) | 20 |
Phosphate | 1425 | Mg(II) | 1530 | Sr(II) | 18 |
Sulphate | 1440 | Ca(II) | 1426 | Mo(VI) | 15 |
Oxalate | 1320 | K(I) | 1200 | Tl(IV) | 13 |
Bromide | 1198 | Ba(II) | 1162 | Pd(II) | 11,100c |
Thiourea | 1140 | Hf(IV) | 72 | Th(IV) | 6,60a |
Thiosulphate | 1120 | Se(IV) | 64 | U(VI) | 5,60a |
Nitrate | 930 | Cd(II) | 56 | Mn(II) | 5,50a |
Chloride | 525 | W(VI) | 55 | Cu(II) | 2,50a |
Carbonate | 300 | Zr(IV) | 46 | Ni(II) | <1,80b |
Fluoride | 285 | Pb(II) | 42 | Zn(II) | <1 |
EDTA | 144 | Hg(II) | 40 | Sn(II) | <1 |
Citrate | 115 | Cr(VI) | 26 | In(III) | <1,60a |
Bi(III) | 21 | Ga(III) | <1,50a | ||
Ru(III) | 21 | V(V) | <1,50b |
In the presence of
Among anions, except EDTA and citrate, all other tested ions were tolerable in more than 200-fold excess. EDTA and citrate were tolerable in 144- and 150-fold excess, respectively. Of the tested cations, some of them did not interfere even when present in more than 500 fold excess, many cations were tolerable between 10–80-folds. Cations which interfere seriously are masked with suitable anions.
Suitable aliquots of the soil, blood, and urine sample solutions were taken and analyzed for cobalt content by the proposed method, and the results are presented in Tables
Determination of cobalt in surface soil samples.
Sample and source | Cobalt ( | ||
Present method* | Reference method | ||
S1 | Agricultural land | ||
S2 | Agricultural land (black soil, Tadipatri.) | ||
S3 | Riverbed soil (Tungabhadra river, Kurnool) | ||
S4 | Industrial soil (electroplating industry, Anantapur) |
*Average of four determinations.
Analysis of blood and urine samples for cobalt content.
Sample source | Sample | Cobalt ( | |
Present | AAS | ||
Normal adult (male) | Blood | ||
Urine | |||
Anemia patient (female) | Blood | ||
Urine | |||
Paralysis patient | Blood | ||
Urine | |||
Pulmonary patient | Blood | ||
Urine |
Variable amounts (0.059–4.712
Second-order derivative spectra of [Co(II)-HNAHBH]. Amount of Co(II)
Third-order derivative spectra of [Co(II)-HNAHBH]. Amount of Co(II)
The derivative amplitudes measured for different concentrations of Co(II) at appropriate wavelengths for 2nd and 3rd order derivative spectra were plotted against the amount of Co(II) which gave linear plots in the specified concentration regions. All the parameters like detection limit, correlation coefficient, and relative standard deviation values are presented in Table
The selectivity of the derivative methods was evaluated by studying the effect of metal ions closely associated with cobalt on its derivative amplitudes under experimental conditions. The results are presented in Table
Tolerance limit of foreign ions (
Diverse ion | Zero order | Second derivative | Third derivative |
---|---|---|---|
Th(IV) | 6 | 55 | 35 |
U(VI) | 5 | 40 | 45 |
Mn(II) | 5 | 60 | 20 |
Cu(II) | 2 | 80 | 45 |
Ni(II) | <1 | 30 | 50 |
Zn(II) | <1 | 45 | 20 |
Sn(II) | <1 | 25 | 18 |
In(III) | <1 | 15 | 28 |
Ga(III) | <1 | 20 | 35 |
V(V) | <1 | 15 | 20 |
Analytical characteristics of [Co(II)-HNAHBH].
Parameter | Direct method | Second derivative | Third derivative | ||
---|---|---|---|---|---|
425 nm | 431 nm | 443 nm | 437 nm | 449 nm | |
Beer’s law range ( | 0.118–3.534 | 0.059–4.712 | 0.059–4.712 | 0.059–1.380 | 0.056–1.380 |
Molar absorptivity, (L mol−1 cm−1) | — | — | — | — | |
Sandell’s sensitivity, | 0.003 | — | — | — | — |
Angular coefficient (m) | 0.375 | 0.0003 | 0.093 | 0.0002 | 0.009 |
Y-intercept (b) | 0.0197 | ||||
Correlation coefficient | 0.9999 | 0.999 | 0.9999 | 0.9999 | 0.9999 |
RSD (%) | 1.37 | 1.84 | 4.3 | 1.15 | 7.6 |
Detection limit ( | 0.04 | 0.06 | 0.13 | 0.04 | 0.21 |
Determination limit, ( | 0.124 | 0.18 | 0.39 | 0.114 | 0.65 |
Composition (M : L) | 2 : 3 | — | — | — | |
Stability constant | — | — | — |
Suitable aliquots of water and pharmaceutical samples were taken and analysed for cobalt by second-order derivative method. The results obtained in the analysis of water samples by the proposed method are presented in Table
Determination of cobalt in environmental water samples.
Sample | cobalt ( | |||
---|---|---|---|---|
Added | Found | Recovery (%) | RSD (%) | |
Tap water (municipality water supply, Anantapur) | 0.0 | 0.32 | — | 2.5 |
1.5 | 1.80 | 98.90 | 1.8 | |
3.0 | 3.35 | 100.90 | 3.0 | |
4.5 | 4.83 | 100.20 | 2.2 | |
River water (Penna, Tadipatri.) | 0.0 | 1.52 | — | 3.0 |
1.5 | 3.00 | 99.34 | 1.6 | |
3.0 | 4.55 | 100.66 | 2.8 | |
4.5 | 5.95 | 98.84 | 4.0 | |
Drain water (vanaspati industry, Tadipatri. | 0.0 | 3.60 | — | 1.7 |
1.5 | 5.31 | 104.12 | 3.2 | |
3.0 | 6.48 | 98.18 | 2.5 | |
4.5 | 8.07 | 99.63 | 3.6 |
Determination of cobalt in pharmaceutical tablets.
Sample (mg/tablet) | Amount of cobalt ( | ||
Reported | Found* | Relative error (%) | |
Neurobion forte | 7.45 | 7.4 | −0.67 |
Basiton forte | 7.42 | 7.24 | −2.42 |
*Average of four determinations.
Iron and cobalt occur together in many real samples like alloy steels, biological fluids, and environmental samples. In most cases, the characterizations of these samples include the determination of their metal ion content. The need for the determination of iron and cobalt in environmental and biochemical materials has increased after reports on different roles of these metals in human health and diseases. We are now reporting a simple, sensitive, and selective second-order derivative spectrophotometric method for the simultaneous determination of Fe(II) and Co(II) using HNAHBH without the need to solve the simultaneous equations.
The 2nd order derivative spectra recorded for [Fe(II)-HNAHBH] and [Co(II)-HNAHBH] at pH 5.5 showed sufficiently large derivative amplitude for cobalt at 426 nm while the Fe(II) species exhibit zero amplitude (Figure
Second-order derivative spectra of (a) [Fe(II)-HNAHBH] and (b) [Co(II)-NAHBH]. Amount of Fe(II) (
Aliquots of solutions containing 0.055–1.650
Linear regression analysis of the determination of Fe(II) and Co(II) in mixture by second derivative spectrophotometry.
Metal ion determined | Wave length (nm) | Other metal present ( | Slope | Intercept | Correlation coefficient | |
Fe(II) | Co(II) | |||||
Fe(II) | 436 | 0.9994 | ||||
0.589 | 0.9995 | |||||
Co(II) | 426 | 0.9999 | ||||
0.33 | 0.9998 |
Fe(II) and Co(II) were mixed in different proportions and then treated with required amount of HNAHBH in the presence of buffer solution (pH 5.5) and 0.15% of CTAB and diluted to the volume in 10 mL volumetric flasks. The second-order derivative spectra for these solutions were recorded (350–600 nm) and the derivative amplitudes were measured at 436 nm and 426 nm. The amounts of Fe(II) and Co(II) in the mixtures taken were calculated from the measured derivative amplitudes using the respective predetermined calibration plots. The results obtained along with the recovery percentage and relative errors are presented in Table
Simultaneous second-order derivative spectrophotometric determination of Fe(II) and Co(II).
Amount taken ( | Amount found* ( | Relative error (%) | |||
Fe(II) | Co(II) | Fe(II) | Co(II) | Fe(II) | Co(II) |
0.06 | 0.59 | 0.053 (96.3) | 0.572 (98.8) | −3.6 | −2.8 |
0.12 | 0.59 | 0.120 (103.4) | 0.592 (100.5) | 3.44 | 0.5 |
0.23 | 0.59 | 0.230 (99.1) | 0.586 (99.4) | −0.86 | −0.5 |
0.33 | 0.59 | 0.334 (101.2) | 0.572 (98.8) | 1.21 | −2.8 |
0.44 | 0.59 | 0.441 (100.2) | 0.590 (100.1) | 0.22 | 0.2 |
0.55 | 0.59 | 0.542 (98.5) | 0.586 (99.3) | −1.45 | −0.5 |
0.33 | 0.59 | 0.328 (99.3) | 1.120 (94.9) | −0.60 | −0.7 |
0.33 | 1.18 | 0.326 (89.6) | 2.280 (96.6) | −1.21 | −5.0 |
0.33 | 2.36 | 0.324 (98.1) | 3.600 (101.7) | −1.81 | −3.3 |
0.33 | 3.54 | 0.336 (101.8) | 4.670 (98.9) | 1.81 | 1.6 |
0.33 | 4.72 | 0.332 (100.6) | 4.670 (98.9) | 0.60 | −1.0 |
The developed second-order derivative spectrophotometric method was employed for the simultaneous determination of iron and cobalt in some alloy samples. Appropriate volumes of the alloy samples were treated with required amount of HNAHBH at pH 5.5 in the presence of 0.15% CTAB and diluted to 10 mL in standard flasks. The second-derivative curves for the resultant solutions were recorded, and the derivative amplitudes were measured at 426 nm and 436 nm. The amounts of iron and cobalt in the samples were evaluated with the help of predetermined calibration plots and presented in Table
Determination of iron and cobalt in alloy samples.
Sample (composition) | Amount (%) | Relative error (%) | ||||
Certified | Found ( | |||||
Fe(II) | Co(II) | Fe(II) | Co(II) | Fe(II) | Co(II) | |
Elgiloy-M | 15 | 40 | 1.33 | 1.52 | ||
Rim alloy | 68 | 12 | 1.88 | 0.66 | ||
Sofcomag 25 | 75 | 25 | 1.48 | 3.92 | ||
Sofcomag 49 | 51 | 49 | 2.18 | 0.36 |
A comparison of the analytical results of the proposed methods was made with those of some of the recently reported spectrophotometric methods and presented in Table
Comparision of the results with already reported methods.
Metal ion | Reagent | pH/medium | Aqueous/extraction | Beer’s law | Interference | Reference | ||
---|---|---|---|---|---|---|---|---|
Fe(II) | Thiocyanate-phenanthroline | 520 | — | Aqueous | 0–24 | 1.87 | — | [ |
Fe(II) | 2-[2-(3,5-Dibromopyridyl-azo]-5-dimethyl amino-benzoic acid | 615 | 2.0–7.0 | Extraction | 0–5.5 | 9.36 | Tl(I), Zn(II), Cr(III), W(VI), Co(II), Cu(II), Ni(II), and Pd(II) | [ |
Fe(II) | 1,10-Phenanthroline and picrate | 510 | 2.0–9.0 | Extraction | 0.1–3.6 | 13 | EDTA, CN- | [ |
Fe(II) | 4-(2-Pyridylazo)resorcinol | 505 | 6.0–7.5 | Extraction | 0–2.0 | 6 | Ni(II), Co(II), Pb(II), and EDTA | [ |
Fe(II) | 1,10-Phenanthroline-tetraphenylborate | 515 | 4.25 | Aqueous | 2.24–37.29 | 1.2 | — | [ |
Fe(II) | 1,3-Diphenyl-4-carboethoxy pyrazole-5-one | 525 | 3.5–4.0 | Aqueous | 0.5–10 | 1.156 | Cu(II), Co(II), Zn(II), Mo(VI), EDTA | [ |
Fe(II) | Dyformyl hydrazine | 470 | 7.3–9.3 | Aqueous | 0.25–13 | 0.3258 | — | [ |
Fe(II) | 4,7-Diphenyl-1,10-phenanthroline and tetraphenylborate | 534 | — | Extraction | 0–20.0 | 2 | — | [ |
Fe(II) | Thiocyanate-acetone | 480 | HClO4 | Aqueous | — | 2.1 | Cu(II), | [ |
Fe(II) | 2-Hydroxy-1-naphthaldehyde-p-hydroxybenzoic hydrazone | 405 | 5 | Aqueous | 0.05–1.37 | 5.6 | Sn(II), Co(II) Ni(II) Zn(II) Al(III) Cu(II) | Present method |
Co(II) | Sodium isoamyl xanthate | 400 | 4.5–9.0 | Aqueous | 3.0–35 | 1.92 | [ | |
Co(II) | 2-Pyridine carboxalde hydeisonicotinyl-hydrazine | 346 | 9 | Aqueous | 0.01–2.7 | 7.1 | Au(III), Ag(I), Pt(III) | [ |
Co(II) | 2-Hydroxy-1-naphthalidene salicyloyl hydrazone | 430 | 8.0–9.0 | Extraction | 0–10 | 0.16 | [ | |
Co(II) | Pyridine-2-acetaldehyde salicyloyl hydrazone | 415 | 1.0–6.0 | Extraction | 0.5–7.0 | 1.04 | — | [ |
Co(II) | Bis-4-phenyl-3-thiosemicarbazone | 400 | 4 | — | 0.6–6.0 | 2.2 | — | [ |
Co(II) | 2-Hydroxy-l-naphthalidene-salicyloylhydrazone | 430 | 8.0–9.0 | Extraction | 0–10 | 1.6 × 103 | — | [ |
Co(II) | 2-(2-Quinolynylazo)-5-dimethylamino aniline | 625 | 5.5 | Extraction | 0.01–0.6 | 4.3 | Many cations and anions | [ |
Co(II) | 2-Hydroxy-3-methoxy benzaldehyde thiosemicarbazone | 390 | 6 | Aqueous | 0.06–2.35 | 2.74 | — | [ |
Co(II) | 2-Hydroxy-1-naphthaldehyde-p-hydroxybenzoic hydrazone | 425 | 5 | Aqueous | 0.12–3.54 | 2.3 | Ni(II), Zn(II), Sn(II), In(III), and Ga(IIII) | Present method |