determination of oil and grease in water by gravimetric method

Determination of Oil and Grease in Water by Gravimetric Method

The presence of oil and grease in water bodies has raised considerable environmental concerns due to their detrimental effects on aquatic ecosystems and human health. Accurate monitoring of these pollutants is critical for pollution control and management strategies. A widely accepted method for measuring oil and grease concentrations in water is the gravimetric method, which allows for a precise quantitative assessment of these contaminants.

The gravimetric method involves several key steps, beginning with the collection of water samples. Samples should be collected from various sites to obtain a representative analysis of the water body. It is essential to use clean, uncontaminated containers to avoid introducing additional oils or greases into the samples. The samples must be analyzed promptly or preserved according to standard procedures to prevent degradation of the oils present.

Once the samples are collected, the first step in the gravimetric analysis involves filtering the water through a filter paper. This process is crucial for removing solid particles that could interfere with the measurement. After filtration, the resulting filtrate is subjected to a series of extraction steps. Typically, a suitable organic solvent, such as hexane or dichloromethane, is added to the filtered sample. The choice of solvent is essential because it should effectively dissolve the oil and grease while remaining immiscible with water.

After the addition of the organic solvent, the mixture is agitated, often using a mechanical shaker, to promote the extraction of oils from the aqueous phase into the organic phase. Following agitation, the two phases are allowed to separate, and the organic phase, which contains the dissolved oil and grease, is carefully collected.

The next critical step involves evaporating the solvent from the collected organic phase. This is typically achieved using a rotary evaporator, which facilitates the removal of the solvent under reduced pressure and controlled temperature. Care must be taken during this step to ensure that the oils and greases are not decomposed or lost due to excessive heat or prolonged evaporation.

Once the solvent has been completely removed, the remaining residue, which represents the oil and grease content, is weighed. The weight of the residue is then used to calculate the concentration of oil and grease in the original water sample. This is often expressed in milligrams per liter (mg/L). To ensure accuracy and reliability, it is crucial to conduct replicate analyses and include blanks to account for any potential contamination and procedural errors.

The gravimetric method is preferred for its simplicity and effectiveness. It has the ability to provide a direct measurement of total oil and grease content without the complications associated with some other analytical techniques, such as gas chromatography. However, it is important to acknowledge its limitations. The method may not distinguish between different types of oils or compounds, and its sensitivity may not be sufficient for very low concentrations.

In conclusion, the determination of oil and grease in water using the gravimetric method is a valuable procedure for environmental monitoring. It provides an essential tool for assessing the quality of water bodies affected by oil spills, industrial discharges, and urban runoff. The simplicity and reliability of this method continue to make it a staple in environmental laboratories, contributing to efforts aimed at protecting and preserving aquatic ecosystems. By quantifying oil and grease levels, stakeholders can make informed decisions about pollution control measures and ensure a healthier environment for all.