The question of how critical sample preparation is “depends” on what the sample is and what you are analyzing. Generally speaking, the more accurate the result required, the more critical the sample preparation will be. In some cases, the analysis will not even be possible without preparation, as tests will not detect the analyte without some initial preparatory reaction. Chemical analysis should be regarded as a multi-step process where measurement is a step near the end of the process. All steps in the preparation process must be carried out carefully and correctly to get an accurate representative result.
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Analytical chemistry is a tool used to monitor the environment and changes in environmental conditions. Analytical Chemistry can monitor and prevent dangerous chemical discharges and pollution. It is also often an important quality control tool in many processes and quality assurance of components, materials, and products in many industries. It’s a vital tool in forensics and many medical procedures and disease detection and monitoring. Analytical chemistry can be carried out in laboratories, but also, in many cases, field tests are carried out to get near-real-time results.
The type of analysis required may influence preparation. Some inaccuracy may be tolerated for qualitative analysis as the presence or absence of a substance is all the required information. However, accurate preparation will significantly affect the measured results for quantitative analysis. Lower standards of accuracy may be acceptable in some cases for field analysis to get quick results.
What is Sample Preparation?
Let us first investigate what is meant by sample preparation. Sample preparation in analytical chemistry encompasses processes during which a representative sample is extracted from a larger amount of material and readied for analysis. Sampling and sample preparation have particular importance in analytical chemistry. Samples may be solid, gas, liquid or solutions, biological matter or cells, or mixtures. Errors in any preparation stage can lead to inaccuracies, which are compounded in the analytical process.
Sampling
Correct sampling for analytical chemistry is a vitally important link in the preparation chain. All subsequent steps in the process rely on accurate sampling. It is vital to get the right sample and ensure it is representative of what you want to test. You may need to get a sample from the edge of the subject, and in some cases, you may wish to get a sample from the middle. You may even want to take a composite sample of many mixed samples to give an average sample. Obtaining a sample requires thought and preparation to ensure that it is possible to get the correct analysis.
The method of sampling and the storage of the sample is also critical. Spotlessly cleaning sampling equipment and sample storage containers are essential to prevent contamination. The materials used to collect and store samples are also necessary to prevent the sample from reacting with the storage container. For example, keeping an acidic sample in an iron container would create iron salts by the reaction. Accurate labeling of samples is also crucial to prevent mix-ups.
In many cases, a sample will need to be transported to a laboratory, so the correct transport and storage are required to prevent sample spillage or spoilage. Once in a lab, the sample must be registered and scheduled for analysis. If it is not used straight away, it must be stored correctly to prevent further reaction, degradation, or contamination. Once it is scheduled for analysis, it must be removed from storage safely and correctly to prevent contamination or degradation.
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Lab Analysis
Samples are sometimes analyzed as they are, which makes preparation reasonably simple. A small amount of sample is measured and analyzed. Care must be taken to use measuring containers of suitable materials that are scrupulously clean. Occasionally, a solid, liquid, or gas sample component will need to be extracted from the mixture before analysis. In analytical chemistry, sample preparation refers to how a sample is treated before it is analyzed. Preparation is an essential step in some analytical techniques because the sample will not respond to the analyte in its natural form. Analytical results can be distorted by interfering species. Knowing your chemical reaction may be critical in the preparation of samples. To get an accurate result, it may be necessary to precipitate or extract potential contaminants that interfere with the analytical reaction.
The material must be correctly treated and prepared before any sample can be analyzed using advanced scientific equipment and instruments, like chromatography or mass spectrometry. This preliminary step is an essential stage of the overall analysis process as it helps prevent contamination, improve accuracy and minimize the risk of results distortion.
On line Analysis
If analytical chemistry is used to monitor discharges from manufacturing or treatment plants, it may be carried out automatically online. This requires the design of automatic sampling equipment, which will take the sample and then prepare the sample for analysis. This preparation could be as simple as filtration before adding reagents but may be more complex.
The prepared and treated sample will then be analyzed to determine the analyte levels. The analysis could be a simple colorimetric instrument or may involve more complex procedures such as mass spectrometry or chromatography. Companies like Hach and many others produce equipment that will carry out continuous online testing, often using titrants and colorimetry.
Cleanliness
One key aspect of sample preparation is cleanliness. It is critical that all sampling, storage, and handling equipment is spotlessly clean to avoid contamination of samples. Laboratory glassware cleaning equipment is an industry in itself. Companies like Cole-Palmer, Camlab, Fisher Scientific, and many others have extensive cleaning sampling product lines.
Sample preparation from initial sampling through sample handling to final analysis preparation is critical. The accuracy of steps in the preparation process will influence the final analytical result, and any inaccuracies can be multiplied by further steps. Some analytical methods like chromatography analysis cannot take place without a significant amount of preparation to get the sample into a usable form.
Further Reading