Sample preparation is a crucial first step in many analytical processes. It involves a series of steps to transform a raw sample into a form suitable for analysis. The specific steps depend heavily on the sample type (solid, liquid, gas) and the analytical technique being used.
Key Steps in Sample Preparation
While the exact procedures vary, several common steps are frequently involved:
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Sampling: This initial step involves carefully selecting a representative portion of the larger sample. The goal is to ensure the selected portion accurately reflects the composition of the whole. For instance, in analyzing soil composition, multiple soil samples from different locations within a field might be combined to create a composite sample. This step is crucial as a biased sample leads to inaccurate results. Britannica emphasizes the importance of obtaining a representative sample.
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Homogenization: This involves making the sample uniform in composition. For solid samples, this might involve grinding or blending. Liquid samples may require mixing or stirring. The EPA uses a single lab to homogenize samples in their fish tissue study to control variability. EPA Fish Tissue Study
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Extraction: This step isolates the analyte(s) of interest from the sample matrix. Different extraction methods exist, like solid-phase extraction (SPE) or liquid-liquid extraction (LLE). This step is crucial for removing interfering substances and enriching the target analytes for better detection. For example, in preparing samples for Next-Generation Sequencing (NGS), the extraction of DNA is an essential part of the preparation process. Frontline Genomics
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Purification: This step removes any remaining unwanted substances from the extracted analyte(s). Techniques employed may include chromatography or filtration, ensuring a "cleaner" sample for analysis. The use of additives to protect sample integrity is also mentioned as a technique. Organomation
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Concentration: This step increases the concentration of the analyte(s) if necessary, improving detection sensitivity, especially if the concentration is initially low. This can involve evaporation or other concentration methods. Sample preparation kits often incorporate optimized extraction protocols for PCR tests. Roche Custom Biotech
Specific Examples:
- Electron Microscopy: Sample preparation for electron microscopy often includes fixation to stabilize the tissue. Science Learn This helps preserve the sample's structure before imaging. Further steps might involve sectioning the sample to achieve the required thinness.
- Dynamic Light Scattering (DLS): Sample preparation for DLS needs careful consideration of the solvent and its purity. Colorado State University
- Next Generation Sequencing (NGS): Sample preparation for NGS involves multiple steps from sample collection to nucleic acid extraction. Roche Sequencing Store
The error introduced during sampling and sample preparation can be substantial; therefore, careful control and standardization are vital for accurate analytical results. EPA 402-B-04-001B-12
