3.3. Adsorption

Third one is adsorption. So, the adsorption occurs through any solid surface during the processing, collection and processing, and one of the solid surfaces that you can generally see is solid surfaces we are looking at adsorption is the container itself, container of sample collection and storage.

Adsorption is a process where molecules of a substance adhere to the surface of a solid. In environmental analysis, this can frequently occur when samples are collected and stored in containers. The surface of the container can attract and hold onto the molecules of interest from the sample, leading to a decrease in the amount of analyte available for analysis. This issue is particularly significant if the container interacts with the analyte.

Think of adsorption like a sponge soaking up water. When you pour water onto a sponge (the solid surface), the sponge holds onto some of the water. In our case, the container (sponge) 'holds onto' some of the analyte in the sample, meaning that when we analyze the sample later, we find less analyte than we actually collected.

Again, adsorption is a kinetic process. It means that if you look at the adsorption, the way adsorption occurs, the volatilization reaction occurs they are all kinetic processes until there is an equilibrium.

Adsorption is considered a kinetic process because it happens over time; there is a rate at which molecules adhere to the surfaces. Initially, the concentration of the analyte decreases as it adsorbs, but as more molecules are adsorbed, a point of equilibrium is reached where the rate of adsorption equals the rate of desorption. This means that until equilibrium is achieved, we experience continuous analyte loss, which can skew the results of analyses.

Imagine filling a glass with sugar and water. At first, the sugar dissolves rapidly, but as more sugar gets added, the rate of dissolution drops until no more sugar can dissolve (equilibrium). In adsorption, as the time passes, the rate of analyte loss decreases until it stabilizes, similar to how the sugar reaches saturation point.

So, when you look at the design of the sample collection and the analysis processes, to reduce these three things, we keep this in mind when we are designing processes for sample collection.

To minimize adsorption and its effects during sample collection and analysis, the process must be carefully designed. For example, the materials selected for sample containers can significantly impact the degree of adsorption. Using non-reactive materials, like glass for organic compounds, can help to reduce the loss of analytes due to adsorption.

Think about using different types of shopping bags for groceries. If you want to keep your fruits fresh, you might prefer breathable cotton bags over plastic ones that trap moisture and can lead to spoilage. Similarly, the choice of sample container can help prevent the 'spoilage' of chemical analytes through adsorption on surfaces.

In addition keeping the temperature low for sample storage and sample transportation sometimes, it will also reduce biodegradation if there is happening.

Keeping samples at low temperatures during storage and transport can minimize both adsorption losses and the potential for biochemical reactions such as biodegradation. Lower temperatures slow down the kinetic processes that lead to both adsorption and decomposition of analytes, ensuring more accurate results when samples are finally analyzed.

Consider how ice cream melts. If you leave it outside in a warm environment, it melts quickly and loses its form. However, if you store it in a freezer, it stays solid and unchanged. Similarly, keeping samples cooler prevents them from changing and losing their important components during transport.

Therefore, the collection vessel, this collection and storage containers should be inorganic. In other words, the one of the most common inorganic containers is glass.

Choosing the right container material is crucial for minimizing adsorption. For instance, when handling organic compounds, using inorganic materials like glass can significantly reduce the loss due to adsorption, while for inorganic analytes, a different approach may be needed such as using plastics. The choice should be dictated by the chemical nature of the analyte being tested.

Think of how certain foods are stored. If you put acidic foods in a metal container, they may react with the metal and lead to off-flavors. In contrast, using glass keeps the flavors intact. Similarly, for chemical samples, the correct containers help preserve the integrity of analytes.

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