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Metal Ions Separation Via Paper Chromatography: Enhanced Methods Using Eluting Solutions

Arijit Das , Digvijoya Sarmaa, Paresh Debnath, Bijaya Paul
World Journal of Chemical Education. 2023, 11(4), 134-140. DOI: 10.12691/wjce-11-4-2
Received September 28, 2023; Revised October 31, 2023; Accepted November 07, 2023

Abstract

Chromatography is an essential physical technique that allows the constituent components of a mixture to be identified, separated, and purified in preparation for qualitative examination. Paper chromatography (PC) is a sort of planar chromatography, which refers to a stationary phase that is a solid, flat surface. In this illustration stationary phase is a particular kind of paper (Whatman quantitative filter paper grade 41). The fundamental idea behind paper chromatography is the differential passage of a mixture's constituent parts through filter paper or chromatography paper. A quick method for separating mixtures of metal ions, amino acids, carbohydrates, colors, and pharmaceuticals is paper chromatography (PC). For this qualitative analysis, only a very small sample is needed. Metal cation separation has seen increased by the use of the PC approach. Here, the four experiments show how PC may be used to separate metal ions [(Pb2+ & Cu2+), (Ni2+ & Co2+), (Cu2+ & Fe3+), (Cu2+ & Co2+)] based on their colored spots and the retardation factors or retention factors (Rf) values by using different eluting solutions.

1. Introduction

The separation of chemical species is an important stage in many chemical operations and processes. Paper chromatography (PC) can be used to swiftly and efficiently separate materials such as pigments, metal ions, and other substances. Paper chromatography is used to separate the metal cations in the aqueous mixture. Nad et al. described the chromatographic separation and identification of Fe3+, Ni2+, Co2+,Cu2+, Pb2+, and Hg2+ 1. During this study, rubeanic acid, Dimethylglyoxime (DMG) and sodium sulphide were used as eluting solutions. S.C. Das 2 described the separation and identification of inorganic cations (Co2+, Ni2+, and Cu2+) by using ethanolic solution of rubeanic acid as spraying reagent.

Till now, no such works have been done by taking water as the universal mobile phase (developer) for the separation of group II metal ions (Pb2+ & Cu2+) with 10% KI solution as eluting agent; group IV metal ions (Ni2+ & Co2+) with 5% NH4OH solution as spraying agent; group II and group III metal ions (Cu2+ & Fe3+) with 100 ml, 1N aqueous solution of potassium ferrocyanide K4[Fe(CN)6] as spraying agent; and group II and group IV metal ions (Cu2+ & Co2+) with 10% NH4OH solution as eluting agent. Thus it was thought of interest to undertake four experiments of paper chromatography (PC) for the separation of metal ions [(Pb2+ & Cu2+), (Ni2+ & Co2+), (Cu2+ & Fe3+), (Cu2+ & Co2+)] for UG students.

2. PC Experiment-1: Separation of Group II Metal ions (Pb2+ & Cu2+) by 10% KI Solution

2.1. Materials and Method

i) Experimental

Requirements

A. Apparatus & chemical required

(i) Chromatographic jar ii) 10% KI Solution iii) Measuring cylinder iv) Lead nitrate Pb(NO3)2 v) Copper sulfate CuSO4.5H2O vi) Spotting capillaries vii) Small test tubes viii) 10ml and 250ml beaker ix) Whatman quantitative filter paper grade 41 x) Distilled water

(B) Solution required

(i) Metal salts solution: Prepared saturated solution of lead nitrate and copper sulfate by dissolving them in distilled water (1mg/mL) in the 10ml beaker.

(ii) Detector: Prepared 10% KI solution in distilled water in the 250ml beaker.

(C) Developer

200ml distilled water in the 250ml beaker.

ii) Procedure

The chromatographic jar had a suspended Whatman grade 41 filter paper strip. Place a dot on the side of the line that you drew on this stripe, around 0.5 cm from the bottom. Development will start at this end, which will be the strip's bottom. Using a small capillary to pass through two (02) places on the filter paper, the saturated solutions of Pb2+ and Cu2+ were applied separately. For every remedy, a brand-new capillary was used. The filter paper with the 02 spots was then allowed to dry outside. After that, the dried and stained filter paper strip was once more suspended in the distilled water-filled chromatographic jar, with the top end secured to the steel rod and the bottom end touching the developer (water). The strip is shown to be vertical. Always place the point above the level of the developer. As the developer (solvent front) approaches the upper end of the filter paper (Figure 1b), the developer (water) is let to climb along the filter paper (Figure 1a). After taking the filter paper out of the chromatography jar, the solvent front was indicated with a pen. The developer was then removed from the paper by drying it. 10% KI solution was taken in a sprayer and applied to the dry filter paper as a separating solvent or spraying reagent. With the KI reaction, one yellow and one brown colored spot appeared right away (Figure 1c), signifying the identification of Pb2+ and Cu2+ ions, respectively. Pencils were used to mark the colored zones.

2.2. Results and Analysis
2.2.1. Reactions Involved During Formation of Colour Spots by Interaction with Solute Zone

In a redox reaction, 10% potassium iodide (KI) added to a copper sulfate solution causes the copper sulfate to combine with the KI solution, the iodide ions reduce Cu(II) to Cu(I), and the iodide (I-) ion oxidizes to iodine (I2), forming a brown color spot on the Whatman 41 filter paper. The solute zone (Cu2+ ion) traveled a distance where the Cu2+ reaction with KI happened, and since I2 escaped quickly, this was immediately noted by marking the brown color spot with a pen.

However, potassium iodide (KI) and lead nitrate [Pb(NO3)2] interacted to form an ion exchange that resulted in the production of potassium nitrate (KNO3) and a yellow-colored spot of lead iodide (PbI2).


2.2.2. Data Analysis

Observed the colored spots corresponding to two different cations. Two cations (Pb2+ and Cu2+) were identified and separated by comparing color spots and retention factor values. The first spot appeared as brown due to the liberation of I2 after the reaction of KI with CuSO4.5H2O indicated the distance traveled by one solute zone as Cu2+ (ds1) and the second spot Pb2+ appeared as yellow indicating the distance traveled by another solute zone (ds2). Then, measured the distance of the color zones of each solute from the point of application. Also measured the distance between the solvent front (water) and the starting line, labeled this distance as distance traveled by the solvent (dm). Then calculated retardation factors or retention factors (Rf) values of each cation (Table 1) by the following equation:

3. PC Experiment-2: Separation of Group IV Metal ions (Ni2+ & Co2+) by 5% NH4OH solution

3.1. Materials and Method

i) Experimental

Requirements

A. Apparatus & chemical required

(i) Chromatographic jar ii) 5% NH4OH Solution iii) Measuring cylinder iv) Nickel nitrate hexahydrate Ni(NO3)2. 6H2O v) Cobalt nitrate Co(NO3)2.6H2O vi) Spotting capillaries vii) Small test tubes viii) 10ml, 100ml, 250ml beaker ix) Whatman quantitative filter paper grade 41 x) Distilled water

(B) Solution required

(i) Metal salts solution: Prepared saturated solution of both metal nitrates by dissolving them in distilled water (1mg/mL) in the 10ml beaker.

(ii) Detector: Prepared 5% NH4OH solution in distilled water in the 100ml beaker.

(C) Developer

200ml distilled water in the 250ml beaker.

ii) Procedure

Whatman grade 41 filter paper strip was suspended in the chromatographic jar. On this stripe drawn a line at about 1cm from the bottom and put dot in the side of the line. This end will be the bottom of the strip and development will take place from this end. The saturated solution of Ni2+ and Co2+ applied separately on the filter paper with help of a fine capillary through two (02) spots. A fresh capillary was used for each solution. Then, filter paper containing 02 spots was dried in open air. The spotted and dried filter paper strip was then suspended again in the chromatographic jar containing distilled water with the upper end pinned to the steel rod and lower end touching the developer (water). It is observed that the strip is vertical. The spot should always be above the developer level. The developer (water) is allowed to rise along the filter paper (Figure 2a) and wait till developer (solvent front) reaches near the upper end of the filter paper along with rise of two metal ions (Figure 2b).The filter paper was then removed from the chromatography jar and marked the solvent front with the help of pen. Then the paper was dried to evaporate the developer. As a separating solvent or spraying reagent 5% NH4OH solution was taken in a sprayer and scattered it on the dried filter paper. Green gel and bluish green colored spots developed immediately (Figure 2c) with the reaction of NH4OH corresponding to the identification of Ni2+ and Co2+ ions respectively. The coloured zones were marked with pen.

Attempt was made in the PC experiment initially by using 1% NH4OH solution but not achieved satisfactory result for Ni2+ (Figure 3).

3.2. Results and Analysis
3.2.1. Reactions Involved During Formation of Colour Spots by Interaction with Solute Zone

Nickel and cobalt (II) nitrate solutions are mixed with 5% NH4OH solution to generate metal hydroxide, which results of colored spots in the Whatman grade 41 filter paper that are green gel and bluish green, respectively 3, 4.


3.2.2. Data Analysis

Two cations (Ni2+ and Co2+) were identified and separated by comparing their color spots and retention factor values. First spot appeared as green gel due to formation of nickel (II) hydroxide Ni(OH)2 indicated the distance travelled by one solute zone as Ni2+ (ds3) and second spot Co2+ appeared as bluish green due to formation of cobalt (II) hydroxide Co(OH)2 indicated the distance travelled by another solute zone (ds4). Then calculated retardation factors or retention factors (Rf) values (Table 1).

4. PC Experiment-3: Separation of Group II and Group III Metal ions (Cu2+ & Fe3+) by 1(N) K4[Fe(CN)6] solution

4.1. Materials and Method

i) Experimental

Requirements

A. Apparatus & chemical required

(i) Chromatographic jar ii) Spraying bottle iii) 100 ml, 1N aqueous solution of potassium ferrocyanide K4[Fe(CN)6] iv) Ferric chloride, FeCl3 v) Copper sulfate pentahydrate CuSO4.5H2O vi) Spotting capillaries vii) Small test tubes viii) 100ml Measuring cylinder ix) 10ml, 250ml beaker x) Whatman quantitative filter paper grade 41 xi) Distilled water

(B) Solution required

(i) Metal salts solution: Prepared saturated solution of ferric chloride and copper sulfate by dissolving them in distilled water (1mg/mL) in the 10ml beaker.

(ii) Eluting solution: Prepared 100 ml, 1N aqueous solution of potassium ferrocyanide K4[Fe(CN)6] in the 250ml beaker.

(C) Developer

200ml distilled water in the 250ml beaker.

ii) Procedure

In the chromatographic jar, a strip of Whatman grade 41 filter paper was suspended. Place a dot to the side of the line you drew on this stripe, about 1 centimeter from the bottom. Development will start at this end, which is the bottom of the strip. Using a tiny capillary that passed through two (02) locations, the saturated solutions of Fe3+ and Cu2+ were applied individually to the filter paper. Every solution was applied to a brand-new capillary. The filter paper with the 02 spots was then allowed to dry outside. The filter paper strip that had been spotted and dried was then suspended once more in the chromatographic jar filled with distilled water, with the lower end coming into contact with the developer (water) and the top end being pinned to the steel rod. The strip is shown to be vertical. Always place the point above the level of the developer. Allow the developer (water) to rise along the filter paper (Figure 4a) and wait for the two metal ions to rise together with the developer (solvent front) to approach the upper end of the filter paper (Figure 4b).

After taking the filter paper out of the chromatography jar, the solvent front was indicated with a pen. The developer was then removed from the paper by drying it. Potassium ferrocyanide 1N aqueous solution was used as an eluting or spraying reagent; it was applied to the dry filter paper using a sprayer. Following the interaction with the aqueous solution of K4[Fe(CN)6], prussian blue and reddish-brown spots appeared right away (Figure 4c), signifying the identification of Fe3+ and Cu2+ ions, respectively. Pen was used to indicate the colored zones.

4.2. Results and Analysis
4.2.1. Reactions Involved During Formation of Color Spots by Interaction with Solute Zone

Ferric chloride solution was mixed with 1N aqueous solution of K4[Fe(CN)6] formed Prussian blue or Berlin blue coloration spot, iron(III)hexacyanidoferrate(II), Fe4[Fe(CN)6]3 in the Whatman grade 41 filter paper strip.

On the other hand, copper sulfate reacted with 1N aqueous solution of K4[Fe(CN)6] formed reddish brown coloration spot, cupric ferrocyanide, Cu2[Fe(CN)6] in the Whatman grade 41 filter paper strip.


4.2.2. Data Analysis

Observed the colored spots corresponding to two different cations (Cu2+ and Fe3+). Two cations (Cu2+ and Fe3+) were identified and separated by comparing their color spots and retention factor values. First spot appeared as prussian blue due to formation of iron(III)hexacyanidoferrate(II), Fe4[Fe(CN)6]3 indicated the distance travelled by one solute zone as Fe3+ (ds5) and second spot for Cu2+ appeared as reddish brown due to formation of cupric ferrocyanide, Cu2[Fe(CN)6] indicated the distance travelled by another solute zone Cu2+ (ds6). Then calculated retardation factors or retention factors (Rf) values (Table 1).

5. PC Experiment-4: Separation of Group II and Group IV Metal ions (Cu2+ & Co2+) by 10% NH4OH solution

5.1. Materials and Method

i) Experimental

Requirements

A. Apparatus & chemical required

(i) Chromatographic jar ii) 10% NH4OH Solution iii) Measuring cylinder iv) Copper sulphate CuSO4. 5H2O v) Cobalt nitrate Co(NO3)2.6H2O vi) Spotting capillaries vii) Small test tubes viii) 10ml, 100ml, 250ml beaker ix) Whatman quantitative filter paper grade 41 x) Distilled water xi) FT-IR spectrophotometer

(B) Solution required

(i) Metal salts solution: Prepared saturated solution of copper (II) sulfate and cobalt (II) nitrate by dissolving them in distilled water (1mg/mL) in the 10ml beaker.

(ii) Detector: Prepared 10% NH4OH solution in distilled water in the 100ml beaker.

(C) Developer

Taken 200ml distilled water in the 250ml beaker.

ii) Procedure

In the chromatographic jar, a strip of Whatman grade 41 filter paper was suspended. Place a dot to the side of the line you drew on this stripe, about 1 centimeter from the bottom. Development will start at this end, which is the bottom of the strip. Cu2+ and Co2+ saturated solutions were administered individually to the filter paper through two (02) locations using a tiny capillary. For every remedy, a brand-new capillary was used. The filter paper with the 02 spots was then allowed to dry outside. The filter paper strip that had been spotted and dried was then suspended once more in the chromatographic jar filled with distilled water, with the lower end coming into contact with the developer (water) and the top end being pinned to the steel rod. The strip is shown to be vertical. Always place the point above the level of the developer. Developer (water) is allowed to rise along the filter paper (Figure 5a); two metal ions rise along the filter paper as the developer (solvent front) approaches the upper end of the paper (Figure 5b). After taking the filter paper out of the chromatography jar, the solvent front was indicated with a pen. The developer was then removed from the paper by drying it. 10% NH4OH solution was used in a sprayer as a separating solvent or spraying reagent, and the dried filter paper was covered with it. As soon as 10% NH4OH was added, green and blue colored spots appeared (Figure 5c), signifying the presence of Co2+ and Cu2+ ions, respectively.

5.2. Results and Analysis
5.2.1. Reactions Involved During Formation of Colour Spots by Interaction with Solute Zone

When copper salt reacts with 10% NH4OH solution gives copper (II) hydroxide, Cu(OH)2, which results of blue colored spot in the Whatman grade 41 filter paper. When Co(II) nitrate reacts with 10% NH4OH solution gives Co(III) hydroxide, Co(OH)3, results green colored spots in the Whatman grade 41 filter paper instead of bluish green Co(II) hydroxide Co(OH)2, which obtained by the reaction of Co(II) nitrate with 5% NH4OH solution. The cobalt(II) ion is more stable because it cannot quickly oxidize to the far less stable cobalt(III) state. All cobalt(II) salts are therefore stable, however cobalt(II) is readily converted to cobalt(III) in basic solutions (50 ml 10% NH4OH) 5. With increasing concentration of NH4OH solution (5% to 10%), basic nature of the reaction medium increases and with increasing concentration of basic medium, air oxidation of cobalt(II) to cobalt(III) takes place relatively easily 5, 6. Thus, Co(II) hydroxide (bluish green) oxidizes to Co(III) hydroxide results green colored spot. That's why after eluting with 10% ammonium hydroxide solution bluish green coloured of Co(OH)2 immediately converted into green coloured Co(OH)3. It was further confirmed by the spot analysis of cobalt(II) nitrate solution with 5% and 10% NH4OH solution individually in the Whatman grade 41 filter paper (Figure 6.). It was observed that during spot test of cobalt (II) nitrate solution with 5% NH4OH, bluish green coloured developed (Figure 6b Left) and with 10% NH4OH the green colour developed immediately (Figure 6b Right).


5.2.2. FT-IR Analysis of Green colored Spot

FT-IR analysis of green spot carried out within the range 4000–400 cm−1 by Bruker Alpha II-E spectrophotometer. The stretching and bending vibrations of the OH (hydroxyl) group in Co(OH)3 typically occur in the infrared (IR) region of the electromagnetic spectrum. The strong broad band for -OH stretching vibrations typically occurs at 3384 cm-1, while strong bending vibrations occurs around 1653cm-1 7, suggesting the presence of –OH group in cobalt (III) hydroxide. IR frequency of a Co-O bond generally occurs within the range 400 to 600 cm-1. But in green spot, i.r. band for Co-O bond occurs at 620 cm-1. A positive shift in the IR frequency of a Co-O bond, typically happens when the cobalt atom is in a higher oxidation state, such as Co(III) or Co(IV). In these higher oxidation states, the Co-O bond becomes stronger, leading to a higher vibrational frequency 8. So the observe i.r. frequency of Co-O bond suggests the presence of (+3) oxidation state of cobalt in the cobalt hydroxide, Co(OH)3 for which green color spot developed.


5.2.3. Data Analysis

Two cations (Cu2+ and Co2+) were identified and separated by comparing their color spots and retention factor values. Observed the coloured spots corresponding to two different cations (Cu2+ and Co2+). First spot appeared as green due to formation of cobalt (III) hydroxide Co(OH)3 indicated the distance travelled by one solute zone, Co2+ (ds7), where in basic medium it is readily oxidized into Co3+ and second spot Cu2+ appeared as blue due to formation of copper (II) hydroxide Cu(OH)2 indicated the distance travelled by the another solute zone, Cu2+ (ds8). Then calculated retardation factors or retention factors (Rf) values (Table 1).

6. Conclusion

Using water as mobile phase (developer), separation of metal ions [(Pb2+ & Cu2+), (Ni2+ & Co2+), (Cu2+ & Fe3+), (Cu2+ & Co2+)] have been done by taking different eluting agents like aqueous solution of 10% KI, 5% NH4OH solution, 1N aqueous solution of K4[Fe(CN)6] and 10% NH4OH solution respectively based on their colored spots and the retardation factors or retention factors (Rf) values. Thus, by using these improved techniques, make paper chromatography easy to separate two cations from the same or different groups of the analytical table.

ACKNOWLEDGEMENT

Corresponding author, Arijit Das, would like to express his heartfelt gratitude to Dr. Sudhan Debnath, Principal, Netaji Subhash Mahavidyalaya, Udaipur, Tripura and Dr. Abhijit Bhattacharya, Associate Professor, Bir Bikram Memorial College, Agartala, Tripura for their valuable assistance regarding paper chromatography. As stated by the corresponding author, Arijit Das, financial support from the SERB, DST, Govt. of India, New Delhi is greatly appreciated (SERB's Sanction order No. EEQ/ 2021/000257 dated 25/02/2022). In continuing with his ongoing SERB project mentioned above, Arijit Das wrote this popular article specifically for a general scientific audience. It is a part of the SERB-SSR activity (category D).

References

[1]  A.K.Nad, B.Mahapatra and A.Ghoshal, An Advanced Course in Practical Chemistry, pp 82-86, 2007, ISBN: 81-7381-302-7.
In article      
 
[2]  S.C.Das, Advanced Practical Chemistry, 6th Edition, pp 417-419, 2017-18, ISBN:81-901944-0-2.
In article      
 
[3]  University of Colorado Boulder, Equilibrium – Complex ions – Metal + ammonia complexes, (Library webpage), Available at (), p. E740.
In article      
 
[4]  G.Svehla and B.Sivasankar, VOGEL’S Qualitative Inorganic Analysis, 7th Edition, p140, 2013, ISBN: 978-81-317-7371-0.
In article      
 
[5]  K. Kavitha. Int. J. Adv. Res. Ideas Innov. Technol. 4, 766-770, 2018, ISSN: 2454-132X.
In article      
 
[6]  J. Clark, Chemistry of cobalt. Available at (chem.libretexts.org)., (, (University of California, Davis, US), 2023.
In article      
 
[7]  The nature of vibrational spectroscopy, Michigan State University, (webpage), Available at
In article      
 
[8]  E. Andris, R. Navrátil, J. Jašík, M. Srnec, M. Rodríguez, M. Costas, J. Roithová, Angew. Chem. 2019, 131, 9721 – 9726, Wiley Online Library
In article      View Article
 

Published with license by Science and Education Publishing, Copyright © 2023 Arijit Das, Digvijoya Sarmaa, Paresh Debnath and Bijaya Paul

Creative CommonsThis work is licensed under a Creative Commons Attribution 4.0 International License. To view a copy of this license, visit https://creativecommons.org/licenses/by/4.0/

Cite this article:

Normal Style
Arijit Das, Digvijoya Sarmaa, Paresh Debnath, Bijaya Paul. Metal Ions Separation Via Paper Chromatography: Enhanced Methods Using Eluting Solutions. World Journal of Chemical Education. Vol. 11, No. 4, 2023, pp 134-140. https://pubs.sciepub.com/wjce/11/4/2
MLA Style
Das, Arijit, et al. "Metal Ions Separation Via Paper Chromatography: Enhanced Methods Using Eluting Solutions." World Journal of Chemical Education 11.4 (2023): 134-140.
APA Style
Das, A. , Sarmaa, D. , Debnath, P. , & Paul, B. (2023). Metal Ions Separation Via Paper Chromatography: Enhanced Methods Using Eluting Solutions. World Journal of Chemical Education, 11(4), 134-140.
Chicago Style
Das, Arijit, Digvijoya Sarmaa, Paresh Debnath, and Bijaya Paul. "Metal Ions Separation Via Paper Chromatography: Enhanced Methods Using Eluting Solutions." World Journal of Chemical Education 11, no. 4 (2023): 134-140.
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  • Figure 6. Spot analysis of cobalt(II) nitrate in the Whatman grade 41 filter paper (a) before addition of NH4OH (b) after addition of 5% and 10% NH4OH solution
[1]  A.K.Nad, B.Mahapatra and A.Ghoshal, An Advanced Course in Practical Chemistry, pp 82-86, 2007, ISBN: 81-7381-302-7.
In article      
 
[2]  S.C.Das, Advanced Practical Chemistry, 6th Edition, pp 417-419, 2017-18, ISBN:81-901944-0-2.
In article      
 
[3]  University of Colorado Boulder, Equilibrium – Complex ions – Metal + ammonia complexes, (Library webpage), Available at (), p. E740.
In article      
 
[4]  G.Svehla and B.Sivasankar, VOGEL’S Qualitative Inorganic Analysis, 7th Edition, p140, 2013, ISBN: 978-81-317-7371-0.
In article      
 
[5]  K. Kavitha. Int. J. Adv. Res. Ideas Innov. Technol. 4, 766-770, 2018, ISSN: 2454-132X.
In article      
 
[6]  J. Clark, Chemistry of cobalt. Available at (chem.libretexts.org)., (, (University of California, Davis, US), 2023.
In article      
 
[7]  The nature of vibrational spectroscopy, Michigan State University, (webpage), Available at
In article      
 
[8]  E. Andris, R. Navrátil, J. Jašík, M. Srnec, M. Rodríguez, M. Costas, J. Roithová, Angew. Chem. 2019, 131, 9721 – 9726, Wiley Online Library
In article      View Article