**Determination of Sodium Benzoate by Spectrophotometry**
Spectrophotometric methods are widely used for the analysis of food additives, including sodium benzoate. This experiment focuses on determining the concentration of sodium benzoate in carbonated beverages using UV-1300 spectrophotometry. The method involves the conversion of sodium benzoate to benzoic acid under acidic conditions, followed by extraction and spectrophotometric measurement at a specific wavelength.
**Introduction to Sodium Benzoate**
Sodium benzoate (C₆H₅COONa) is the sodium salt of benzoic acid and is commonly used as a preservative in food and pharmaceutical products. It prevents microbial growth and extends shelf life. However, concerns about its potential toxicity have led to restrictions in some countries. Sodium benzoate is white, odorless, and slightly sweet. It dissolves well in water but is poorly soluble in organic solvents. Its antimicrobial activity is most effective in acidic environments, with optimal performance between pH 2.5 and 4.0.
**Principle of the Method**
In this experiment, sodium benzoate is first converted to benzoic acid by adding hydrochloric acid. The resulting benzoic acid is then extracted into an organic solvent, such as ethanol. After evaporation, the residue is dissolved in deionized water, and the solution is analyzed using a UV-1300 spectrophotometer. The absorbance at 223 nm is measured, and the concentration of sodium benzoate is calculated based on a standard curve.
**Experimental Procedure**
1. **Preparation of Deionized Water**: Boil deionized water to remove dissolved COâ‚‚, cool it, and use for subsequent steps.
2. **Sample Pretreatment**: Carbonated beverages are heated to remove COâ‚‚, and sodium benzoate is extracted using HCl and NaCl. The extract is then titrated with a standardized NaOH solution.
3. **Standard Curve Preparation**: Prepare a series of sodium benzoate solutions with known concentrations and measure their absorbance at 223 nm to construct a calibration curve.
4. **Sample Analysis**: Measure the absorbance of the sample solution and calculate the sodium benzoate content using the standard curve.
**Instrumentation and Reagents**
- Instruments: UV-1300 spectrophotometer, burettes, volumetric flasks, separatory funnels, and pipettes.
- Reagents: HCl (1+1), NaOH (4%), potassium hydrogen phthalate, phenolphthalein (PP), ethanol, and deionized water.
**Results and Discussion**
The results from the spectrophotometric method are compared with those obtained from acid-base titration. The spectrophotometric method offers higher accuracy and sensitivity, especially for low-concentration samples. The minimum detection limit of sodium benzoate is 0.0014 g/L, making it suitable for quality control in food industries.
**Conclusion**
UV-1300 spectrophotometry provides a reliable and efficient method for determining sodium benzoate in food samples. This technique is particularly useful for analyzing complex matrices like carbonated drinks, where traditional titration may be less accurate due to solubility issues. The method ensures precise quantification and supports compliance with food safety regulations.
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