Spectrophotometric Determination of Hexavalent Chromium in Water by Diphenylcarbazide - Master's thesis - Dissertation
**Spectrophotometric Determination of Hexavalent Chromium in Water Using Diphenylcarbazide**
**Keywords:** spectrophotometry; hexavalent chromium; analytical instrument; UV-1100; UV-1200
This method is designed for the accurate determination of hexavalent chromium (Cr(VI)) in surface water and industrial wastewater. It is particularly suitable for samples with low concentrations of Cr(VI), offering a detection limit of 0.004 mg/L when using a 30 mm cuvette, and up to 1.0 mg/L when using a 10 mm cuvette. The method involves the formation of a stable, purple-red complex between hexavalent chromium and diphenylcarbazide, which is then quantified at a wavelength of 540 nm.
The procedure is straightforward and reliable, with minimal interference from common contaminants such as iron, molybdenum, and mercury, provided their concentrations remain below certain thresholds. However, vanadium may cause some interference at higher levels (above 4 mg/L), though this can often be mitigated through proper timing and reaction conditions.
Reagents used include sulfuric acid, phosphoric acid, sodium hydroxide, zinc sulfate, potassium permanganate, and various standard solutions of chromium. The preparation of reagents is critical to ensure accuracy and consistency in results. For instance, the diphenylcarbazide developer must be stored properly to avoid degradation and maintain its effectiveness.
Instruments required for the analysis include a spectrophotometer such as the UV-1100 or UV-1200, along with appropriate glassware. All glassware should be clean and free from contamination, avoiding any contact with potassium dichromate wash solutions that could introduce errors.
Sample collection and preparation are essential steps. Water samples should be collected in glass bottles and adjusted to a pH of approximately 8 before analysis. If necessary, pretreatment methods such as zinc hydroxide co-precipitation or potassium permanganate oxidation can be applied to remove interferences and improve measurement accuracy.
The calibration curve is prepared by measuring absorbance values of known chromium concentrations, allowing for the quantification of unknown samples. Proper blank tests are also conducted to account for background absorption and ensure the reliability of results.
Overall, this method provides a robust and widely applicable approach for the determination of hexavalent chromium in environmental water samples, ensuring precise and reproducible results.
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