7.1. Measurement Procedure

So, the next question that you will have and there’s also number of samples and all that. So, number of samples. So what is the definition of sample? So we discussed that definition of a sample is a quantity, it is amount. So what is our goal of sampling? So, our goal of sampling is eventually we would like to get some measure of concentration. This is our goal, concentration. Concentration means concentration is mass by volume or mass. It is a mass fraction or a mass concentration.

In this section, we learn that the main goal of sampling in environmental monitoring is to measure concentration, which can be defined as mass per volume. The concentration can represent various components being studied: it could be the amount of a chemical substance in air, water, or soil, expressed as a fraction of mass over volume. For example, if we want to know how much pollutant is in a liter of water, we are looking to measure its concentration.

Think of concentration like how sweet a glass of lemonade is. If you add more sugar (mass) to a fixed amount of water (volume), the lemonade becomes sweeter, and its concentration increases. Similarly, when monitoring air or water quality, scientists aim to determine how much of a pollutant is present in a specific volume.

So, if we want to get this, this is the information we want, we need this and this. So, this brings us, this denominator here is what we would call as the sampling volume, the sample volume, we will come back to this in a minute after this discussion.

The concept of sampling volume is introduced as a crucial part of the measurement procedure. The sampling volume refers to the amount of liquid, gas, or solid that we are analyzing to determine concentration. This volume is essential because the results are directly related to the volume of sample collected; if too little volume is taken, it may not provide a reliable reading since it may contain insufficient particles or pollutants to measure accurately.

Imagine trying to understand the overall taste of a soup by only tasting a tiny spoonful. That minor sample might not reflect the soup's actual flavor, just like a small volume of water might not give accurate results of pollutants.

Let me take an example of one of the analysis methods. So, what do I need to do in order to measure the solids, suspended solids? ... I need to filter filter. What am I doing when I am filtering? Separating the solids from the liquids. So I am separating, this is the separation of the solids from the water.

This chunk focuses on a practical example: measuring Total Suspended Solids (TSS) in water. The procedure involves taking a water sample, filtering it to separate solids from the liquid, and then measuring the mass of the separated solids. The grams of solids (mass) collected on the filter paper are then divided by the initial water volume to determine the concentration of suspended solids, giving crucial information about the water quality.

Envision this process like trying to filter out tea leaves from a brewed cup of tea. By using a tea strainer, you separate the leaves (solids) from the liquid tea (water). The remaining tea can then be enjoyed, while the leaves give an idea of how much 'solid' was present to begin with.

If I take 1 liter of water okay, what is the condition under which I can make this measurement using this method I have described? ... The question that we're posing is if mf0 is the same as mf1, are you sure that TSS is 0?

This section addresses the challenges faced when measuring low concentrations of suspended solids. It raises the question of whether a measurement indicates truly zero solids if the amounts measured before and after filtering are the same. The text explains that mere appearances can be misleading; just because something looks 'clean' doesn’t mean it is free from particulates or pollutants. The detection limit refers to the smallest amount of substance that can be reliably measured.

Consider searching for hidden dirt in a seemingly clean room. Just because the floor looks clean doesn’t guarantee there’s no dust; you can only tell when you check with a vacuum. The same way, a clean water sample might have low levels of suspended solids that are undetectable by simple measurement methods.

This feature of sensitivity when you see sensitivity, when you look at instruments listing characteristics, specifications, you will see sensitivity and it is listed as a lowest concentration.

Here, the concept of sensitivity in analytical instruments is discussed. Sensitivity determines how small a change in concentration an instrument can detect. A more sensitive instrument can pick up smaller amounts of a substance. For accurate contamination assessment, having highly sensitive instruments is preferable because they can detect lower concentrations that might otherwise remain unnoticed.

Think of sensitivity in measurement as akin to hearing: some people can hear faint sounds that others cannot. A sensitive instrument is like a person with superior hearing; it can pick up faint signals (low concentrations) that less sensitive instruments may miss.

So what do we do in our example, coming back to our example, if you are not able to see a difference, what can you do to check if there is a difference?

This final chunk emphasizes the importance of selecting an appropriate sample volume based on the detection limits of the instrument being used. When the concentration of a substance is low, increasing the volume of the sample collected may improve the chances of detecting that substance. A practical relationship is drawn between the expected concentration, detection limits, and sample volume. Understanding this ensures accurate analysis, allowing researchers to adapt their sampling strategies accordingly.

Imagine you're trying to find a rare book in a library. If you search in just a few shelves (small sample volume), your chance of finding the book is low. But if you search through many shelves (large sample volume), your chances increase significantly. Similarly, inanalysis, a larger sample can increase the likelihood of detecting low concentrations of substances.

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