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

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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, despite the people's living standards There has been a big improvement, but environmental problems have become more serious. Among the many environmental problems, the problem of water pollution is particularly prominent, so the problem of water pollution has become a focus of attention today. 2 Experimental theoretical analysis 2.1 Experimental analysis: In general, iron exists in the Fe ³⁺ state, and hydroxylamine hydrochloride can reduce it to Fe ²⁺ : 2Fe ³⁺ + 2NH ₂ OHÂ·HCl = 2 Fe ²⁺ + N ₂ + 4H ⁺ 2H ₂ O + 2Cl ^- Fe ²⁺ and phenanthroline form a stable 1:3 orange-red complex at pH 2-9, with maximum absorption at 508n, Îµ508=101 104L/(mol Â· cm), lgK = 21.3. When measuring, it is preferred to control the acidity of the solution at a pH of about 5. When the acidity is high, the reaction is slow; the acidity is too low, and the ions are easily hydrolyzed, which affects color development. Experimental calculation formula: absorbance A = ÎµmaxLCÎµmax - molar absorptivity (representing the absorbance of a solution of 1 mol / L, the thickness of the liquid layer is 1 cm, the unit is L / (mol Â· cm) C - the concentration of iron in the solution, the unit Is mol/L - the content of iron in the solution, the unit is Î¼g / mLL - the thickness of the solution, the content of iron per unit cm (Î¼g / mL) = = 2.2 Experimental ideas: 3 Experimental Section 3.1 Instruments and Reagents:

Instrument name specification quantity drug name specification spectrophotometer V-1200 type 1 phenanthroline analytical pure (AR) pH meter pHS-25 type 1 hydroxylamine hydrochloride analytical pure (AR) measuring cylinder 5mL 1 NaAc analytical pure (AR) Volumetric flask 100mL 4 NaOH Analytically pure (AR) 250mL 4 NH4Fe(SO ₄ ) ₂ ?12H ₂ O Analytically pure (AR) Plastic dropper 1 Concentrated HCl Pipette 1mL 1 pH buffer solvent 2mL 1 5mL 1 10mL 1 wash bottle 1 colorimetric tube 50mL 8 sticks 100mL 2 200mL 1 suction ear 1 glass rod 1 support scale 0.1g 1 analytical balance 0.0000g 1 set of filter paper a pack of pH test paper

3.2 Preparation of solution 3.2.1 Preparation of 100g/L hydroxylamine hydrochloride solution Weigh 10g hydroxylamine hydrochloride crystal [Hydroxylamine hydrochloride (also known as hydroxylamine chloride) Molecular formula: NH2OHÂ·HCL Physical and chemical properties: This product is white crystal, strong hygroscopicity. Soluble in water alcohol, easy to decompose when exposed to moisture, stable at room temperature, non-flammable] Dissolved in 100mL distilled water. If it is not dissolved, dissolve it first in ethanol and then dilute it. 3.2.2 Preparation of 1.5g/L phenanthroline solution Weigh 0.3750g of o-phenanthroline (AR) in a beaker, add a small amount of distilled water and 4 drops of concentrated hydrochloric acid, then transfer to a 250mL volumetric flask, add distilled water. Rong. 3.2.3 NaAc (1mol / L) Weigh 8.2g NaAc solid dissolved in a beaker with a small amount of distilled water, transferred to a 100mL volumetric flask, diluted with water. 3.2.4 NaOH (1mol / L) Weigh 4.0g NaOH solids in a beaker with a small amount of distilled water dissolved, transferred to a 100mL volumetric flask, diluted with water. 3.2.5 HCl (6mol/L) diluted with concentrated hydrochloric acid (1+1) 3.2.6 100Î¼g/mL or 1.791mmol/L iron standard solution [weigh 0.2059g analytical pure NH ₄ Fe(SO ₄ ) ₂ ?12H ₂ O In a 100 mL beaker, add 20 mL of 6 mol/L HCl solution and a small amount of water, dissolve and transfer to a 1 L volumetric flask, dilute to the mark and shake well], 10 Î¼g/mL of iron standard working solution (accurately absorb 100 Î¼g/mL of iron) 10 mL of standard solution in a 100 mL volumetric flask, add 2 mL of 6 mol/L HCl solution, dilute to the mark with water and shake the masking agent: AI/Fe (triethanolamine) Mg (pH 12.5 / NaOH) Cu Zn (KCN\Na ₂ S Masking) Mn (hydroxylamine hydrochloride masking) 3.3 Experimental procedure 3.3.1 Conditional test (1) Drawing of absorption curve and determination of measurement wavelength Pipette 0, 1.0 mL of iron standard working solution into two 50 mL volumetric flasks, each with a pipette Add 1 mL of hydroxylamine hydrochloride solution and shake well, then add 2 mL of phenanthroline and 5 mL of NaAc solution, dilute with water to the mark and shake well. After standing for 10 min, use 1 cm cuvette, with reagent blank as reference, at wavelength 440-560 nm The absorbance was measured every 10 nm, near the maximum absorption wavelength (490 to 520), every 5 nm. The absorbance is measured once. The absorption curve is plotted with the wavelength Î» as the abscissa and the absorbance A as the ordinate. The appropriate wavelength of the iron is selected from the absorption curve, and the maximum absorption wavelength is generally selected. Wavelength / nm 440 450 460 470 480 490 495 500 A 0.185 0.194 0.204 0.225 0.236 0.239 0.246 0.252 Wavelength / nm 505 510 515 520 530 540 550 560 A 0.257 0.258 0.246 0.226 0.164 0.106 0.054 0.026

(2) Select the acidity of the solution. Take 7 50mL volumetric flasks, add 1ml of iron standard working solution, add 1mL hydroxylamine hydrochloride separately with a pipette, shake well, then add 2mL of phenanthroline and shake well. Add 1 mL/L NaOH solution 0 mL, 0.5 mL, 1.0 mL, 2.0 mL, 2.5 ml, and 3.0 mL with a 5 mL pipette, dilute to the mark with water, and shake well. After standing for 10 min, the absorbance of each solution was measured at a selected wavelength using a 1 cm cuvette with distilled water as a reference, and the pH of each solution was measured with a pH meter. The acidity influence curve of the relationship between the absorbance A and the pH value is plotted on the abscissa of pH value and the absorbance A as the ordinate, and the suitable acidity range of the determined iron is determined. No. 1 2 3 4 5 6 7 V(NaOH)/mL 0 0.5 1.0 1.5 2.0 2.5 3.0 pH 3.46 5.35 6.17 6.88 11.8 12.06 12.30 A 0.173 0.327 0.175 0.175 0.151 0.141 0.095

(3) Determination of the amount of color developer In 7 50mL volumetric flasks, accurately add 1mL of iron standard working solution, 1mL of hydroxylamine hydrochloride solution, and shake well. Then add 0.2mL, 0.4mL, 0.6mL, 0.8mL, 1.0mL, 1.5mL and 2.0mL phenanthroline and 5mL NaAc solution, dilute with water to the mark and shake. After standing for 10 min, the absorbance of each solution was measured at a selected wavelength using a 1 cm cuvette with distilled water as a reference. The volume of the adjacent phenanthroline is plotted on the abscissa and the absorbance A is plotted on the ordinate. The intersection is found by the tangent method at the inflection point of the curve to determine the optimum amount of the developer and its complexation ratio. No. 1 2 3 4 5 6 7 V phenanthroline/mL 0.2 0.4 0.6 0.8 1.0 1.5 2.0 A 0.046 0.117 0.158 0.159 0.161 0.155 0.158

(4) Selection of color development time Use a pipette to remove 1 mL of iron standard working solution, place it in a 50 mL volumetric flask, 1 mL of hydroxylamine hydrochloride solution, shake well, then add 2.0 mL of phenanthroline and 5 mL of NaAc solution, dilute with water until Scale and shake. The absorbance of each solution was measured immediately at a selected wavelength using a 1 cm cuvette with distilled water as a reference. The spectrophotometers placed for 5 min, 10 min, 30 min, 60 min, 120 min or even longer were then measured in turn. Taking the time t as the abscissa and the absorbance A as the ordinate, the color time influence curve of the relationship between A and t is plotted to determine the appropriate time required for the complete reaction of iron with phenanthroline. Color development time t/min 5 10 30 60 120 A 0.152 0.157 0.156 0.155 0.155

3.3.2 Determination of iron content (1) Configuration and determination of standard series solution In 6 50mL volumetric flasks, accurately add 0, 2.0mL, 4.0mL, 6.0mL, 8.0mL, 10.0mL iron standard with pipette The solution (10 Î¼g/mL) was added to 1 mL of hydroxylamine hydrochloride solution and shaken. Add 2 mL of phenanthroline and 5 mL of NaAc solution, dilute to the mark with water, and shake well. After 10 min, the absorbance of each solution was measured at the selected wavelength using a 1 cm cuvette with the reagent blank as a reference. Taking the concentration c of iron as the abscissa, the absorbance A as the ordinate to draw a standard curve and calculating the molar absorptivity Îµmax No. 1 2 3 4 5 6 Iron standard solution volume / mL 0 2 4 6 8 10 Iron concentration / Î¼g / mL 0 0.4 0.8 1.2 1.6 2.0 A 0 0.121 0.221 0.273 0.405 0.484

(2) Determination of iron content in the sample Accurately absorb the appropriate amount of water sample to be tested in a 50 mL volumetric flask, add various reagents according to the drawing procedure of the standard curve (can be performed simultaneously with drawing a standard curve), and then measure the absorbance A. The A value of each test solution was recorded, and the iron content in the test solution was found on the standard curve (unit: Î¼g/mL). Can be drawn and calculated by computer. A 0 0.011 0.012 0.014 Average c(fe)/Î¼g/ml 0 0.045 0.049 0.057 0.050

4 Conclusions (1) According to (Fig. 1) absorption curve: due to the maximum absorbance of iron ions at this wavelength, the most suitable absorption wavelength (ie maximum wavelength) is 510 nm. (2) According to (Figure 2) acidity influence curve: Because the maximum absorbance of iron ions at pH=5.4, the pH value of the solution should be controlled at about 5.4. (3) According to (Fig. 3) developer dosage curve: when the volume of iron ion is 1 mL, the optimum dosage of the developer is 0.6 mL, and the complex ratio is iron ion/o-phenanthroline=0.36 (about 1: 3). (4) According to (Fig. 4) the selection curve of color development time: when the color development time is 10 min, the absorbance is the largest, so the suitable time required for the complete reaction of the color developer is 10 min. (5) According to (Figure 5) standard curve of iron ion content: absorbance A = 0.246C _(Fe3+) (6) According to the iron standard curve: the average iron ion content in the drinking water is 0.050Î¼g / mL according to the national standard GB The iron limit of the sanitary standard for drinking water in 5749-2006 is 0.3mg/L, and the iron content of the drinking water is less than this value, so the drinking water meets the national standard. Key words: spectrophotometer; trace iron ion; mass spectrometer ; V-1200; phenanthroline, absorbance, hydroxylamine hydrochloride

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