determination of oil and grease in water by gravimetric method

Determination of Oil and Grease in Water by Gravimetric Method

Oil and grease are common pollutants in water bodies and can pose significant environmental hazards. They originate from various sources, including industrial discharges, urban runoff, and oil spills. The presence of oil and grease in water can adversely affect aquatic life, disrupt ecosystems, and impair the quality of drinking water. Therefore, the accurate quantification of oil and grease concentrations is crucial for monitoring water quality and formulating regulations to protect our water resources. One of the reliable techniques for determining the concentration of oil and grease in water is the gravimetric method.

Overview of the Gravimetric Method

The gravimetric method for determining oil and grease in water involves collecting a known volume of water sample, extracting the oil and grease, and then measuring the mass of the extracted substances. This method is favored for its simplicity, accuracy, and reproducibility, making it a standard procedure in many environmental laboratories.

Sample Collection and Preparation

The process begins with the collection of water samples from the area of interest. It is crucial to use clean, non-contaminating containers to prevent external contamination. Samples should be taken in a way that minimizes agitation and exposure to air, which could lead to the volatilization of lighter hydrocarbons. Once collected, the samples should be stored in a cool, dark place and analyzed as soon as possible to minimize degradation or changes in composition.

Extraction Procedure

The next step in the gravimetric method involves the extraction of oil and grease from the water sample. This is typically achieved using organic solvents, such as hexane, dichloromethane, or petroleum ether. The sample is first filtered to remove particulate matter, which may interfere with the extraction process. The filtrate is then mixed with the chosen organic solvent in a separatory funnel. The mixture is shaken vigorously to enhance the transfer of oil and grease into the solvent.

After sufficient mixing, the mixture is allowed to settle, and the organic layer containing the oil and grease is carefully separated from the water phase. To ensure maximum recovery, the extraction process may be repeated several times with fresh solvent, combining all organic extracts into a single vessel.

Evaporation and Weighing

Once the oil and grease have been effectively extracted, the organic solvent must be removed to obtain a dry residue. This is accomplished using a rotary evaporator or a simple evaporation setup, where the solvent is gently heated to vaporize it, leaving behind the oil and grease. The resulting residue is then dried to a constant weight in an oven at a controlled temperature to eliminate any residual solvent.

After the drying process, the mass of the oil and grease is measured using an analytical balance. The concentration of oil and grease in the original water sample can be calculated based on the mass of the residue and the volume of the water sample taken.

Advantages and Limitations

The gravimetric method offers several advantages, including its simplicity and the ability to provide accurate quantitative results. It does not require complex instrumentation and can be performed with relatively basic laboratory equipment. Moreover, it can be applied to a wide range of water types, including wastewater, surface water, and even groundwater.

However, the method does have limitations. It may not distinguish between different types of oils and greases, and lighter hydrocarbons may be lost during extraction due to volatility. Additionally, the presence of high concentrations of dissolved organic matter can interfere with the extraction and measurement processes, necessitating careful sample preparation and handling.

Conclusion

The determination of oil and grease in water by the gravimetric method remains a fundamental technique in environmental monitoring and analysis. Despite its limitations, it provides a crucial tool for assessing water quality and ensuring compliance with environmental regulations. As industries continue to evolve and environmental concerns grow, methods like gravimetric analysis will play a vital role in safeguarding our water resources and protecting aquatic ecosystems from harmful pollutants. With ongoing advancements in extraction and analytical technologies, the precision and reliability of this method are expected to improve, further enhancing its applicability in the field.