Determination of trace iron ions in water by UV-1200 spectrophotometer - Master's thesis - Dissertation

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Determination of Trace Iron Ions in Water by Spectrophotometer

Key words: spectrophotometer; trace iron ion; mass spectrometer; V-1200; o-phenanthroline, absorbance, hydroxylamine hydrochloride 1. Foreword With the rapid development of urbanization and industrialization, although people's living standards have significantly improved, environmental issues have become increasingly serious. Among these problems, water pollution has emerged as a major concern. This study focuses on the determination of trace iron ions in water using a spectrophotometric method. 2. Experimental Theoretical Analysis 2.1 Experimental Analysis Iron typically exists in the Fe³⁺ state. Hydroxylamine hydrochloride is used to reduce it to Fe²⁺ through the following reaction: 2Fe³⁺ + 2NH₂OH·HCl → 2Fe²⁺ + N₂ + 4H⁺ + 2H₂O + 2Cl⁻ Fe²⁺ forms a stable orange-red complex with o-phenanthroline at pH 2–9, with maximum absorption at 508 nm. The molar absorptivity (ε₅₀₈) is 1.01 × 10⁴ L/(mol·cm), and the stability constant lgK is 21.3. For accurate measurement, the solution’s pH should be around 5. If the acidity is too high or too low, it can affect the reaction rate or cause hydrolysis of the ions, which may interfere with color development. The experimental formula for absorbance is given as: A = εmax * L * C Where: - A = absorbance - εmax = molar absorptivity (L/(mol·cm)) - L = path length (cm) - C = concentration of iron (mol/L) 2.2 Experimental Ideas 3. Experimental Section 3.1 Instruments and Reagents

Instrument nameSpecificationQuantity
SpectrophotometerV-1200 type1
Phenanthrolineanalytical pure (AR)1
pH meterpHS-25 type1
Hydroxylamine hydrochlorideanalytical pure (AR)1
Measuring cylinder5mL1
NaAcanalytical pure (AR)4
Volumetric flask100mL4
NaOHanalytically pure (AR)4
NH₄Fe(SO₄)₂·12H₂Oanalytically pure (AR)1
Plastic dropper11
Concentrated HClPipette 1mL1
pH buffer solvent2mL1
5mL11
10mL11
Wash bottle11
Colorimetric tube50mL8
Sticks100mL2
200mL11
Suction ear11
Glass rod11
Support scale0.1g1
Analytical balance0.0000g1
Filter papera pack of1
pH test paper11
3.2 Preparation of Solution 3.2.1 100g/L Hydroxylamine Hydrochloride Solution Weigh 10g of hydroxylamine hydrochloride crystal, dissolve in 100mL distilled water. If not fully dissolved, dissolve first in ethanol before diluting. 3.2.2 1.5g/L Phenanthroline Solution Weigh 0.3750g of o-phenanthroline, add a small amount of water and 4 drops of concentrated HCl, then transfer to a 250mL volumetric flask and dilute to volume. 3.2.3 NaAc (1mol/L) Dissolve 8.2g of NaAc in a beaker, transfer to a 100mL volumetric flask and dilute with water. 3.2.4 NaOH (1mol/L) Dissolve 4.0g of NaOH in a beaker, transfer to a 100mL volumetric flask and dilute with water. 3.2.5 HCl (6mol/L) Dilute concentrated HCl with an equal volume of water. 3.2.6 Iron Standard Solution Weigh 0.2059g of NH₄Fe(SO₄)₂·12H₂O in a 100mL beaker, add 20mL of 6mol/L HCl, dissolve, and transfer to a 1L volumetric flask. Dilute to the mark and shake well. This gives a 100μg/mL iron standard solution. For a working solution, take 10mL of this solution and dilute to 100mL with water. 3.3 Experimental Procedure 3.3.1 Conditional Test (1) Absorption Curve and Measurement Wavelength Pipette 0 and 1.0 mL of iron standard solution into two 50mL flasks, add 1mL of hydroxylamine hydrochloride, 2mL of phenanthroline, and 5mL of NaAc. Dilute to the mark and measure absorbance at 440–560 nm every 10 nm, and near 490–520 nm every 5 nm. The maximum absorption wavelength was found to be 510 nm. (2) Selection of Solution Acidity Take 7 50mL flasks, add 1mL of iron standard solution, 1mL of hydroxylamine hydrochloride, and 1mL of NaOH solution. Measure absorbance at selected wavelength. The optimal pH range was found to be around 5.4. (3) Determination of Color Developer Amount Add varying volumes of phenanthroline to 7 flasks and measure absorbance. The optimal volume was found to be 0.6mL, with a complex ratio of 1:3. (4) Selection of Color Development Time Measure absorbance at different times after adding reagents. The best time was found to be 10 minutes. 3.3.2 Determination of Iron Content (1) Preparation of Standard Series Solution Prepare 6 solutions with 0, 2.0, 4.0, 6.0, 8.0, and 10.0 mL of iron standard solution. Measure absorbance and plot a standard curve. The linear relationship was A = 0.246C. (2) Sample Analysis Measure the absorbance of the sample solution and determine the iron content using the standard curve. The average iron content in drinking water was found to be 0.050 μg/mL, which is below the national standard of 0.3 mg/L. 4. Conclusions Based on the results, the most suitable absorption wavelength is 510 nm, the optimal pH is 5.4, the best developer volume is 0.6 mL, and the optimal reaction time is 10 minutes. The iron content in the sample meets the national drinking water standard.

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