Standard addition is a method used in chemical analysis to determine the concentration of a substance in a complex sample. It involves adding a known amount of the substance to a portion of the sample and comparing the results to the original sample. This allows chemists to accurately assess the concentration of the substance of interest in the sample.
Some scientific analytical techniques are designed to find the amount of individual substances in a mixture. Sometimes this is straightforward, but some samples interfere with the technique’s ability to assess the true concentration of a substance in a mixture. Standard addition is a way of finding the actual concentration of a material in a mixture by comparing it to an identical mixture with more material added. By comparing the result received with the known amount of substance, the analyst can understand how much substance is present in the first sample.
Chemical products tend to interact with each other, in different ways, depending on the characteristics of the individual materials. Generally, a chemical in a simple solution, such as sodium chloride (NaCl) in water (H2O,) can be recognized by an analytical technique to evaluate the amount of NaCl present in a sample of the solution. The NaCl concentration is not masked by the presence of other chemicals that interfere with the sensitivity of the assay.
Some complex samples, such as standing water, contain a variety of different molecules. The actual concentration of the substance of interest in the sample can be masked by the presence of these other chemicals. For example, the characteristics of the target substance may be altered by interaction or binding with other constituents, resulting in recorded levels of the substance that are too low. Since the point of evaluation of the concentrations of the individual components of a sample is accuracy, this poses a problem for chemists.
One way to solve the problem is to compare the concentration of the unknown sample with a known set of results for a similar sample. However, this involves a lot of primary testing and samples can vary widely in composition, so a set of standard known results can be impractical. Instead of using this complicated and perhaps expensive method, chemists may choose to use standard addition.
This method of analysis involves dividing the sample into two or more portions. One remains unchanged, but the chemist adds a chemical to the other portions. The chemical to be added is exactly the same as the substance in the sample whose concentration the chemist wants to know. Adds a known amount of the chemical to the second portion of the sample and tests this and the original sample. For greater accuracy, additional portions may also be tested, with varying concentrations of chemical added.
Since the analyst knows how much extra chemical he has put into the altered samples, the original sample can be compared to the standard-spiked portions. This comparison of results can tell the analyst how much of the substance was in the original sample. Typically, mathematical calculations or a graph of the standard addition results are used to calculate the initial concentration in the sample. Standard addition is a common analytical technique in chemical analysis, where it is also known as “spiking the sample”.
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