**Spectrophotometric Determination of Chlorine Dioxide**
**Keywords**: Spectrophotometry; Chlorine Dioxide (ClOâ‚‚); US Analytical Instrument; V-1200
This method describes a reliable and accurate procedure for the spectrophotometric determination of chlorine dioxide in water samples. The process involves the preparation of a standard solution, construction of a calibration curve, and subsequent measurement of unknown samples.
**Preparation of Chlorine Dioxide Standard Stock Solution:**
To prepare the stock solution, 300 mL of distilled water is placed in a glass bottle labeled A. One end of a glass tube is connected to an air compressor, while the other end is attached to another glass bottle labeled B. Bottle B is a high-strength borosilicate glass container with three glass tubes at its mouth. The first tube is positioned 5 mm above the bottom to introduce air. The second tube is connected to a separating funnel, with the lower end extending below the liquid surface. The third tube is used to release excess gas into a third bottle, labeled C.
Next, 10 g of sodium chlorite is dissolved in 750 mL of distilled water and transferred to bottle B. A 20 mL portion of 10% sulfuric acid is added to the separating funnel. Bottle C contains a saturated sodium chlorite solution, while bottle D, a 2L borosilicate glass collection bottle, holds 1500 mL of distilled water to absorb the generated ClOâ‚‚. Any excess gas is vented through an exhaust pipe. The entire setup is placed inside a fume hood for safety.
Once the system is set up, the air compressor is turned on. Every 5 minutes, 5 mL of sulfuric acid is added from the separating funnel. After the final addition, the airflow is maintained for an additional 30 minutes. The resulting yellow-colored solution is collected in a brown bottle and stored at 4°C. The concentration of the stock solution should be between 250 mg/L and 600 mg/L.
**Preparation of Chlorine Dioxide Standard Solution:**
Before use, a measured volume of the stock solution is diluted with double-distilled water to achieve a concentration of 250 mg/L.
**Construction of the Calibration Curve:**
In a 100 mL volumetric flask, various volumes of the standard solution (0.0 mL, 4.0 mL, 10.0 mL, 20.0 mL, 40.0 mL, 60.0 mL, 80.0 mL, and 100.0 mL) are added, and the total volume is adjusted to 100 mL with double-distilled water. This produces concentrations ranging from 0 mg/L to 250 mg/L. The absorbance of each solution is measured at 430 nm using distilled water as the blank. A linear regression is performed between the mass of ClOâ‚‚ and the corresponding absorbance values, and a calibration curve is plotted.
**Sample Measurement:**
For sample analysis, the disinfectant solution or its diluent is measured directly. The absorbance at 430 nm is recorded using distilled water as the reference. The concentration of ClOâ‚‚ in the sample is then determined using the equation derived from the calibration curve.
**Calculation:**
The formula used for calculating the chlorine dioxide content is:
$$ X = \frac{\rho \times V_1}{V_2} $$
Where:
- $ X $: Chlorine dioxide content, mg/L
- $ \rho $: Concentration calculated from the calibration curve, mg/L
- $ V_1 $: Volume of the diluted disinfectant, mL
- $ V_2 $: Volume of the original disinfectant, mL
The detection limit of this method is 10 mg/L, and the linear range of the calibration curve spans from 10 mg/L to 250 mg/L. The average recovery rate is 103.3%, and the relative standard deviation is less than 10%, indicating good precision and accuracy.
**Keywords**: Spectrophotometry; Chlorine Dioxide (ClOâ‚‚); US Analytical Instrument; V-1200
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