# Estimation of Iron Content in Water Using Conductometric Method

Abhijit Mallick, Debamalya Ghosh

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Abhijit Mallick, Debamalya Ghosh. Estimation of Iron Content in Water Using Conductometric Method. International Research Journal of Pure and Applied Chemistry, 2025, 26 (5), pp.105-112. 10.9734/irjpac/2025/v26i5948 . hal-05297438

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# Estimation of Iron Content in Water Using Conductometric Method

Abhijit Mallick a* and Debamalya Ghosh a

a Department of Chemistry Academy of Technology P.O. Aedconagar, Adisaptagram, Dist. Hooghly 712121, W.B., India.

## Authors' contributions

This work was carried out in collaboration between both authors. Both authors read and approved the final manuscript.

## Article Information

DOI: https://doi.org/10.9734/irjpac/2025/v26i5948

## Open Peer Review History:

This journal follows the Advanced Open Peer Review policy. Identity of the Reviewers, Editor(s) and additional Reviewers, peer review comments, different versions of the manuscript, comments of the editors, etc are available here: https://pr.sdiarticle5.com/review-history/144869

## Short Research Article

Received: 20/07/2025

Published: 27/09/2025

## ABSTRACT

Iron content is one of the important parameters of water quality. Permanganometric method is a very common technique to estimate Fe²⁺ ion. However, this technique fails to estimate Fe³⁺ ion but water sample contains both Fe²⁺ and Fe³⁺ ions. Colourimetric method is popular to estimate iron content in a given water sample. However, it has some limitations e.g., the method is sensitive to pH and temperature. Furthermore, the method is applicable to a limited concentration range. The present work proposed a novel technique, conductometric method, to estimate iron content in a given water sample. The method is based on change in ionic conductance of Fe²⁺ ion during formation of iron-phenanthroline complex. A calibration curve is obtained while plotting change in ionic conductance values against known concentrations of Fe²⁺ ion. Using this calibration curve unknown concentration of Fe²⁺ ion in a given sample water can be determined by measuring corresponding change in ionic conductance of Fe²⁺ ion in presence of 1,10 phenanthroline. This novel technique is applicable in a wide concentration range. In the present work two unknown samples with concentrations, 0.084 (N/100) and 0.20 (N/100), are used. Using the calibration

<footnote>*Corresponding author: E-mail: dramallick12@gmail.com;</footnote>
curves the corresponding concentrations are found to be 0.085 (N/100) and 0.19 (N/100) respectively, indicating that the experimental results are very close to the actual values. The other advantages of this method are: (a) it is simple and easy to perform anywhere, (b) it is cost-effective, (c) the accuracy of the method does not depend on either pH or temperature of experiment.

## GRAPHICAL ABSTRACT

### Iron estimation in water sample

Water Sample
[Fe²⁺ / Fe³⁺]

Permanganometry
Method

1. Fails to estimate
Fe³⁺ content

2. Fails in presence
of reducing agent

Colourimetric
Method

1. pH sensitive

2. Temperature sensitive

Conductometric
Method

1. Accuracy in estimation
of iron content

2. Independent of pH
and Temperature

<figure><img src="image_3.png" /></figure>

Keywords: Mohr's salt; Sulphuric acid; 1:10 phenanthroline; hydroxylamine hydrochloride; ferphenanthroline complex; conductivity-meter; conductance.

## 1. INTRODUCTION

Iron is an essential element for growth. However, presence of excess iron in drinking water causes disturbances in normal functionality of organs, causing health concern. So, iron content is one of the important parameters to specify drinking water quality. Excess iron content in water poses a threat on agricultural sector also. There are different methods to determine iron content in a given water sample, e.g., spectrophotometric method, atomic absorption spectrometric method, volumetric titration method. All these methods are based on ferrous iron (Fe²⁺). As iron remains both as Fe²⁺ and Fe³⁺ forms in water, it is required that a reducing agent be used to

convert Fe³⁺ to Fe²⁺ ion for accurate estimation of iron content. Different analytical methods for estimation of iron are well documented in the literature (Merli et al., 2012; Mohite, 2011). Baltzis et al. (2023) developed an optical sensor to determine speciation of iron (Fe²⁺/ Fe³⁺) using deferoxamine reagent. Several authors reported that UV-VIS spectrophotometric method is a useful tool to determine iron content in different water samples (Devi & Reddy, 2012; Balasubramanian et al., 2021; Peng et al., 2015). Pepper et al. reported a solvent extraction method to determine ferrous and ferric iron in aqueous samples (Pepper et al., 2010). It is documented that ferrous iron can be estimated in presence of ferric iron using F⁻ as complexing
agent, which masks Fe³⁺ ion (Zhu et al., 2018). Estimation of total iron by WCRM technique was reported by Lin et al. (Lin & Liu, 2022; Gonsalves et al. 2011) reported that iron content can be determined using UV-VIS spectrometry of hydrazine complex of Fe²⁺ ion (Gonsalves et al., 2011). It is documented that ferrous iron content in drug samples, containing ferrous fumarate, can be determined using redox titration method (Balarabe & Folashade, 2019). Kirakosyan & Davinyan, (2021) reported that ferric iron in drug samples can be estimated successfully by complexometric titration method using EDTA. It is documented that iron content in environmental water samples can be estimated by FIA-TLS method (Korte et al., 2019). Farhood and Taha, (2022) documented a new merging-zone flow injection system for estimation of iron content in water samples. Reverse flow injection analysis based method for determination of iron content in water is documented in the literature (Cooray & Pullin, 2022).

The present work puts forth a novel technique to estimate the iron content in a water sample using conductometric method, which helps measuring the change in ionic conductance of Fe²⁺ ion due to formation of Fe-Phenanthroline complex. This information is capitalised to obtain a calibration curve using several Mohr's salt solutions with known concentration of Fe²⁺ ion. Using this calibration curve iron content of an unknown water sample can be determined. This novel technique is neither temperature-sensitive nor pH-sensitive and believed to be applicable in a wide range of iron concentration in different water samples.

## 2. MATERIALS AND SAMPLE SOLUTIONS

### 2.1 Apparatus

(a) Conductivity meter (El-make).

(b) 10 ml Pipette.

(c) 100 ml Glass beakers.

(d) 100 ml Volumetric flask.

(e) 10 ml Measuring cylinder.

(f) 100 ml Reagent bottles.

### 2.2 Chemicals

1. Details of chemicals and Mohr's salt solutions, used in this work, are shown in the Table 1 and Table 2 respectively.

2. Two types of Mohr's salt solutions are prepared for the present work.

(a) Low concentration Mohr's salt solution.

(b) High concentration Mohr's salt solution.

### 2.3 Experimental Methods

#### 2.3.1 Sample preparation

All the samples are prepared at room temperature (25°C).

**Hydroxylamine hydrochloride solution:**
1.04 gm LR grade Hydroxylamine hydrochloride is dissolved in 50 ml double distilled water so that concentration of the solution is maintained at 0.3 M.

<table><caption>Table 1. Details of chemicals used in this research work</caption><thead><tr><th>Chemicals</th><th>Molecular Weight</th><th>Purpose</th></tr></thead><tbody><tr><td>Mohr's salt</td><td>392</td><td>To provide Fe<sup>2+</sup> ion in aqueous solution</td></tr><tr><td>Sulphuric acid</td><td>98</td><td>To stabilize Mohr's salt solution</td></tr><tr><td>Hydroxylamine hydrochloride</td><td>69.5</td><td>Reducing agent converting Fe<sup>3+</sup> ion to Fe<sup>2+</sup> ion</td></tr><tr><td>1.10 Phenanthroline monohydrate</td><td>198</td><td>Complexing agent</td></tr></tbody></table>

<table><caption>Table 2. Concentrations of Mohr's salt solutions</caption><thead><tr><th colspan="4">Mohr's salt solutions</th></tr><tr><th colspan="2">Low concentration samples</th><th colspan="2">High concentration samples</th></tr><tr><th>Serial No.</th><th>Concentration (N/100)</th><th>Serial No.</th><th>Concentration (N/100)</th></tr></thead><tbody><tr><td>1</td><td>0.025</td><td>1</td><td>0.16</td></tr><tr><td>2</td><td>0.034</td><td>2</td><td>0.25</td></tr><tr><td>3</td><td>0.040</td><td>3</td><td>0.34</td></tr><tr><td>4</td><td>0.050</td><td>4</td><td>0.50</td></tr><tr><td>5</td><td>0.067</td><td>5</td><td>0.65</td></tr></tbody></table>
Mohr's salt solutions

<table><thead><tr><th colspan="2">Low concentration samples</th><th colspan="2">High concentration samples</th></tr><tr><th>Serial No.</th><th>Concentration (N/100)</th><th>Serial No.</th><th>Concentration (N/100)</th></tr></thead><tbody><tr><td>6</td><td>0.075</td><td>6</td><td>0.80</td></tr><tr><td>7</td><td>0.094</td><td>7</td><td>1.00</td></tr><tr><td>8</td><td>0.100</td><td></td><td></td></tr></tbody></table>

**Mohr's salt solutions of known concentrations (for calibration):** 50 mg LR grade Mohr's salt is dissolved in 50 ml distilled water in a 100 ml volumetric flask. 1 ml 4(N) H₂SO₄ is added into it. 5 ml Hydroxylamine hydrochloride, as prepared above, is added into it. Double distilled water is added into it till the level reaches 100 mark. So, 100 ml (N/50) Mohr's salt solution is prepared. pH of the solution is measured as 4.25. This is considered as mother solution, from which 15 different Mohr's salt solutions, as mentioned in the Table 2, are prepared using double distilled water and stored in 15 different tagged reagent bottles. All these 15 solutions are required to prepare two calibration curves, one for low concentration samples and another for high concentration samples.

**Mohr's salt solutions of unknown concentrations:** Two other Mohr's salt solutions of concentrations [100 ml 0.084 (N/100) and 100 ml 0.2 (N/100)] are prepared separately. Few drops of 4(N) H₂SO₄ is added in each solution. 1 ml freshly prepared hydroxylamine hydrochloride solution is added in each solution. These two solutions are marked as unknown solutions.

**1,10 Phenanthroline solution:** 40 mg 1,10 phenanthroline crystals is dissolved in 80 ml slightly warm double distilled water with stirring. Concentration of the solution is 2.5 (M/100) or 2.5 × 10⁻² M.

### 2.3.2 General procedure

(a) Conductivity-meter is calibrated. Conductance is expressed in µS.

(b) Low concentration samples, as mentioned in the Table 2, are considered first. 10 ml of the 1st solution, i.e., 0.025 (N/100) is taken in a 100 ml beaker using 10 ml pipette. Double distilled water is added to it up to the mark 80 ml. The solution is placed under the conductivity-meter and the electrode-set is dipped slowly into it. Stir the solution slowly and wait till the conductance reading reaches a constant value. Take the reading of conductance value. The electrode-set is

taken out and washed properly with double distilled water.

(c) The step (b) is repeated for the remaining 7 low concentration samples (Table 2).

(d) So 8 blank readings, i.e., without addition of 1,10 phenanthroline solution, are collected and noted down. The readings are shown in the Table 3.

(e) 10 ml of the 1st solution, i.e., 0.025 (N/100) is taken in a 100 ml beaker using 10 ml pipette. 5 ml freshly prepared 1,10phenanthroline solution is added into it. The solution turns intense red-orange in colour. Stir the solution gently. Double distilled water is added to it up to the mark 80 ml. The solution is placed under the conductivity-meter and the electrode-set is dipped slowly into it. Stir the solution slowly and wait till the conductance reading reaches a constant value. Take the reading of conductance value. The electrode-set is taken out and washed properly with double distilled water.

(f) The step (e) is repeated for the remaining 7 low concentration samples (Table 2).

(g) So 8 readings with addition of 1,10 phenanthroline solution are collected and noted down. The readings are shown in the Table 3.

(h) Step (b) is repeated for the high concentration samples (mentioned in the Table 2) without addition of 1,10 phenanthroline solution.

(i) So 7 blank readings, i.e., without addition of 1,10 phenanthroline solution, are collected and noted down. The readings are shown in the Table 4.

(j) Step (e) is repeated for the high concentration samples (mentioned in the Table 2) with addition of freshly prepared 1,10 phenanthroline solution in each case.

(k) So 7 readings, i.e., with addition of 1,10 phenanthroline solution, are collected and noted down. The readings are shown in the Table 4.

## 3. RESULTS AND DISCUSSION

Iron in Fe²⁺ state forms a complex with 1,10phenanthroline (represented as phen) as given in equation (1).
$$Fe^{2+} + 3Phen \rightarrow [Fe(phen)_{3}]^{2+} \cdots (1)$$

The complex appears as intense red-orange colour. The size of $[Fe(phen)_{3}]^{2+}$ ion is expected to be much larger than that of $Fe^{2+}$ ion and hence ionic conductance of $[Fe(phen)_{3}]^{2+}$ ion is believed to be less than that of $Fe^{2+}$ ion. In presence of phen ligand $Fe^{2+}$ mostly remains as $[Fe(phen)_{3}]^{2+}$. So, it is expected that ionic conductance of any solution, containing $Fe^{2+}$ ion, should decrease in presence of phen ligand. Using this concept calibration curve for standard Mohr's salt solutions can be obtained by measuring decrease in conductance value of $Fe^{2+}$ ion in presence of phen ligand. As iron usually remains in $Fe^{3+}$ state in water sample, it is mandatory to use a reducing agent to convert $Fe^{3+}$ ion to $Fe^{2+}$ ion. In this method hydroxylamine hydrochloride is used as reducing agent.

## 3.1 Low concentration samples

There are 8 low concentration Mohr's salt solutions and one unknown concentration, listed in the Table 2. The details of their conductance values are shown in the Table 3.

$\Delta C$ values are plotted against concentrations of Mohr's salt solution. The plot is shown in the Fig. 1, which is called calibration curve for low concentration Mohr's salt solutions. Mohr's salt solution of unknown concentration shows $\Delta C$ value of 75 $\mu S$ (Table 3). According to the Fig. 1, the corresponding unknown concentration of Mohr's salt solution is 0.085 (N/100). However, the actual value is 0.084 (N/100). Thus iron content of a given sample water can be determined with sufficient accuracy using the conductometric calibration curve.

<table><caption>Table 3. Conductance values for low concentration Mohr's salt solutions</caption><thead><tr><th>Serial No.</th><th>Concentration (N/100)</th><th>Conductance (Blank value) (C<sub>1</sub> in µS)</th><th>Conductance (with 1,10 phenanthroline) (C<sub>2</sub> in µS)</th><th>Diff. in conductance (ΔC in µS)</th></tr></thead><tbody><tr><td>1</td><td>0.025</td><td>45.5</td><td>34.1</td><td>11.40</td></tr><tr><td>2</td><td>0.034</td><td>66.0</td><td>44.4</td><td>21.60</td></tr><tr><td>3</td><td>0.040</td><td>80.0</td><td>51.3</td><td>28.70</td></tr><tr><td>4</td><td>0.050</td><td>103.0</td><td>61.3</td><td>41.70</td></tr><tr><td>5</td><td>0.067</td><td>133.2</td><td>80.5</td><td>52.70</td></tr><tr><td>6</td><td>0.075</td><td>168.6</td><td>104.6</td><td>64.00</td></tr><tr><td>7</td><td>0.094</td><td>201</td><td>117.6</td><td>83.40</td></tr><tr><td>8</td><td>0.100</td><td>217</td><td>127</td><td>90.00</td></tr><tr><td>9</td><td>Unknown</td><td>186.4</td><td>111.4</td><td>75.00</td></tr></tbody></table>

<figure><img src="image_4.png" /><figcaption>Fig. 1. Calibration curve for low concentration Mohr's salt solutions</figcaption></figure>
<table><caption>Table 4. Conductance values for high concentration Mohr's salt solutions</caption><thead><tr><th>Serial No.</th><th>Concentration (N/100)</th><th>Conductance (Blank value) (C<sub>1</sub> in µS)</th><th>Conductance (with 1,10 phenanthroline) (C<sub>2</sub> in µS)</th><th>Diff. in conductance (ΔC in µS)</th></tr></thead><tbody><tr><td>1</td><td>0.16</td><td>359</td><td>199</td><td>160</td></tr><tr><td>2</td><td>0.25</td><td>518</td><td>278</td><td>240</td></tr><tr><td>3</td><td>0.34</td><td>709</td><td>379</td><td>330</td></tr><tr><td>4</td><td>0.50</td><td>1000</td><td>565</td><td>435</td></tr><tr><td>5</td><td>0.65</td><td>1325</td><td>790</td><td>535</td></tr><tr><td>6</td><td>0.80</td><td>1773</td><td>1123</td><td>650</td></tr><tr><td>7</td><td>1.00</td><td>2010</td><td>1220</td><td>790</td></tr><tr><td>8</td><td>Unknown</td><td>423</td><td>243</td><td>180</td></tr></tbody></table>

<figure><img src="image_5.png" /><figcaption>Fig. 2. Calibration curve for high concentration Mohr's salt solution</figcaption></figure>

## 3.2 High concentration samples

There are 7 high concentration Mohr's salt solutions and one unknown concentration, listed in the Table 2. The details of their conductance values are shown in the Table 4.

$ΔC$ values are plotted against concentrations of Mohr's salt solution. The plot is shown in the Fig. 2, which is called calibration curve for high concentration Mohr's salt solutions. Mohr's salt solution of unknown concentration shows $ΔC$ value of 180 µS (Table 4). According to the Fig. 2, the corresponding unknown concentration of Mohr's salt solution is 0.19 (N/100). However, the actual value is 0.20 (N/100). The result supports the accuracy of this method in determining iron

content of a given sample water. Furthermore, $ΔC$ value is independent of pH of the solution and temperature of the experiment.

## 4. CONCLUSION

1. Iron content of a given water sample can be estimated accurately using conductometric method.

2. This novel technique of iron estimation obviates any use of external indicators, eliminating human errors.

3. Both high and low concentrations of $Fe^{2+}$ ion in a given water sample can be estimated accurately using this conductometric method.

4. This novel technique of iron estimation is expected to explore future research works based on conductivity-meter.
## DISCLAIMER (ARTIFICIAL INTELLIGENCE)

The Authors hereby declare that no generative AI technologies such as Large Language Models (ChatGPT, COPILOT, etc.) and text-to-image generators have been used during the writing or editing of this manuscript.

## COMPETING INTERESTS

Authors have declared that no competing interests exist.

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