1.2. Extraction Methods

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.

Extraction is the process of separating a substance (A) from a mixture, often at very low concentrations, such as nanograms or micrograms per liter. This means that the substance we are interested in is present in the water in very small quantities, making it challenging to measure directly. The goal of extraction is to increase the concentration of this substance so it can be analyzed more easily.

Imagine trying to find a single grain of sand on a vast beach. It's nearly impossible to find it directly, but if you collect a handful of sand and sift through it, you can more readily discover that grain. Similarly, in extraction, we gather more of the substance to make it easier to analyze.

So, as if you recall the objectives of extraction are, use of compatible solvent for exchange of A to compatible solvent matrix, that is compatible means it to the instrument. Second, it gives you an opportunity to concentrate the sample.

When performing extraction, two main objectives must be achieved: First, we need to use a solvent that won't interfere with our analytical instruments—this is known as a 'compatible solvent'. Second, the extraction process should result in a concentration of the target substance, making it easier to measure and analyze.

Think of making a cup of coffee. You use hot water (the compatible solvent) to extract flavor from the coffee grounds. The goal is to concentrate the coffee flavor in the water so that when you drink it, you get a rich taste. Similarly, in extraction, we want to pull out the essential substances from water into another medium.

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.

Liquid-liquid extraction is a method in which a water sample containing the target substance (A) is mixed with a second non-miscible solvent. This means that the two liquids do not mix, allowing A to move from the water into the solvent where it is more soluble. This method is commonly used in chemical analysis because it efficiently separates substances based on their solubility in different liquids.

Think of oil and vinegar in a salad dressing. They do not mix well, and if you shake them together, eventually, the oil will separate out and sit on top of the vinegar. In a similar manner, liquid-liquid extraction allows us to separate our target substance from water by transferring it into a different liquid.

So, by definition if you are going to do liquid - liquid extraction it must be immiscible in water predominantly. So, use an immiscible solvent when we say immiscible, we are not talking from environmental point of view, all of them have some solubility, but bulk in solubility is very small.

For liquid-liquid extraction to be effective, the second solvent must be predominantly immiscible with water. This ensures that when mixed, the two liquids will separate cleanly, with one containing the desired extraction while the other retains the remaining water. While all substances have some degree of solubility in each other, we want to choose solvents that minimize this to achieve better separation.

Consider oil and water again. They don't mix well, which is why you see them separating into layers when you let them sit. In the same way, when we use an immiscible solvent for extraction, we benefit from the clear separation between our target substance and the water.

Typical extraction solvents are hexane, Dichloromethane. These are 2 very commonly used. Dichloromethane is a chlorinated organic solvent but this is one of the strongest solvents that there is.

When choosing a solvent for extraction, hexane and dichloromethane are popular choices due to their effectiveness in dissolving a wide range of organic compounds. However, it is crucial to note that dichloromethane is a hazardous substance, which necessitates careful handling and disposal.

Think of dichloromethane like a powerful cleaner you might use at home. It can remove tough stains, but because it's so strong and potentially harmful, you need to be careful with where and how you use it. Similarly, while effective, solvents like dichloromethane require responsible use and disposal.

And that is why you have a section in your analysis method it’s called waste management which means you will end up at the end with some Dichloromethane or hexane which is not supposed to be there and you can’t throw it down the drain. You have to dispose it properly.

Any extraction method that uses solvents such as dichloromethane or hexane generates waste that must be managed responsibly. These solvents cannot be disposed of carelessly, as they can have harmful environmental impacts. Appropriate waste management procedures must be followed to ensure safety and compliance with regulations.

Imagine cleaning your home with harsh chemicals. Once you're done, you can't just pour the leftover cleaner down the drain; it could harm the water supply. In the same manner, when we use solvents in extraction, we need to ensure they are disposed of properly to prevent environmental harm.

So, when you extract water as it is raw water, sometimes you will get everything, all the interferences in your sample and this is true mostly for samples that are coming from waste water treatment plants or sewage treatment plants.

When extracting raw water, especially from complex sources like wastewater treatment plants, the extracted sample may contain many substances that can interfere with the analysis. This means that in addition to the target substance we want to measure, we may also extract unwanted materials that can affect the results.

Think of it like trying to find a piece of gold in a pile of mixed metals. If you just take a chunk of that pile, you’ll get a lot of other metals too, making it hard to isolate just the gold. This is similar to how unwanted materials can interfere with our desired analysis in a water sample.

So, here comes the definition of an interference very interesting now, because if your goal is to find out what is there in the water whatever is there in the water is going to come out so none of it is really an interference.

Interference in analytical chemistry refers to any substance that might affect the measurement of the target analyte. However, interference can be relative to what you are trying to measure. If multiple substances are extracted from water, they may or may not affect the analysis depending on whether they are relevant to the specific measurement being conducted.

Imagine taking a photo of a beautiful landscape, but there are also some people in the background. If the focus is on the landscape, those people might be viewed as distractions but aren’t significant to the overall picture. Similarly, other substances in the water can distract from or interfere with our analysis of the target substance.

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

To avoid unwanted interferences in the liquid-liquid extraction process, it is often necessary to filter the water sample first. This step ensures that solid particles and substances that might interfere with the analysis are removed, resulting in a cleaner extract.

Think of filtering coffee grounds before pouring coffee into your cup. By removing the grounds, you’re ensuring that what you drink is a pure cup of coffee and not a gritty mixture. Similarly, filtering a water sample helps achieve a cleaner analysis.

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