1.3. Liquid-Liquid Extraction

So, the first thing is the extraction, we look about extraction. Extraction means, we are talking about something which is at very low levels, typically, we are talking about nanogram per liter or microgram per liter that level of concentration. So, we want to pull it out.

Liquid-liquid extraction (LLE) is a technique used to isolate a substance from a sample, typically when the concentration of that substance is very low, such as nanograms or micrograms per liter. The goal of extraction is to effectively separate and concentrate the desired substance (denoted as 'A') from a complex mixture.

Imagine trying to extract a few drops of flavor from a large pot of soup. The flavor is subtle and mixed with many ingredients, similar to how certain substances are present in low concentrations in water samples. By using a technique like LLE, we can pull out just the flavor, much like we would extract the target substance 'A' from the water.

So, one of the common methods in which people do this is, one is your water sample which contains A to which they add another solvent. This is another liquid and then A will transfer to this. So, this is directly using what is called as liquid - liquid extraction. So the second solvent liquid that we use, by definition if you are going to do liquid - liquid extraction it must be immiscible in water predominantly.

In LLE, a second solvent is added to the water sample, which helps to transfer the desired substance ('A') from the water into the solvent. For effective extraction, this second solvent must be immiscible with water, meaning it does not mix with water. Common solvents used include hexane and dichloromethane, which are effective at dissolving organic compounds.

Think about oil and water. If you pour oil into a glass of water, the oil does not mix and instead sits on top. This is similar to how we want our extracting solvent to behave in our extraction process to effectively capture and separate the target substance.

So, if you add 100 ml or 50 ml of solvent to 1 liter of water, you can recover most of it, 40 ml you can recover at least. So, we did that calculation last time.

During the LLE process, when a suitable solvent is added to the water, a portion of the desired substance will dissolve into the solvent. While not all of the substance can be extracted, a significant amount can be recovered, often around 40%, depending on the amount and type of solvent used. This makes solvent selection critical for successful extraction.

Imagine using a sponge to soak up water from the floor. The sponge can only hold a certain amount before it becomes saturated and can hold no more. Similarly, in LLE, the solvent can only extract a certain amount of the desired substance before it becomes saturated.

Dichloromethane is a chlorinated organic solvent but this is one of the strongest solvents that there is, many of the chlorinated solvents organic solvents are very powerful, they will extract a lot of things. Okay, but they also are listed among, if you go and look at the priority chemicals of concern organic, you will find some of them there.

Dichloromethane is a strong solvent known for its effective extraction capabilities. However, it is also hazardous and is classified as a priority chemical due to its potential health and environmental impacts. Therefore, when selecting solvents for LLE, it is crucial to consider both the effectiveness of extraction and the safety and environmental implications.

Consider a cleaning agent like bleach. It can effectively remove tough stains but poses health risks if not handled properly. Similarly, while potent solvents like dichloromethane are beneficial in extraction, they must be used responsibly to avoid environmental contamination.

When I am analyzing water, I want concentration of A, in water alone. If this is associated with solids, and I know I am getting the wrong information. Yeah.

Interferences can occur during LLE, especially if the water sample contains other substances or solids. These interferences can affect the accuracy of the analysis related to the target substance ('A'). It is important to understand that interference is relative to what is being analyzed, meaning that substances present can confuse the results if they are not accounted for beforehand.

Imagine trying to find a specific coin in a jar full of mixed coins. If you just shake the jar and look for your coin, other coins may block your view, making it hard to find the one you're looking for. Here, those other coins represent interferences in the extraction process.

So, before this you have to do liquid - liquid extraction, if you don’t want that information, you have to filter the samples.

To minimize interference, it’s essential to filter the sample before performing liquid-liquid extraction. Filtration removes suspended solids and larger particles from the water, ensuring that only the target substance remains for extraction. This step is crucial to obtaining accurate concentration results of the target analyte.

Think about making juice from fruits. If you leave the pulp in the juice, it can alter the taste and texture. Straining the juice removes the pulp, ensuring you have a clear beverage. Filtration in LLE serves a similar purpose—removing unwanted particles and solids for a clearer analysis.

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