Intermediate Topic 943 of 1102 Analytical, Lab & Spectroscopy
Sampling
Collecting representative portions of material for analysis.
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In-depth explanation of Sampling
Sampling collects a small portion of material that is representative of the whole, and it is often the largest source of uncertainty in an analysis. A representative sample is taken randomly or as a composite of many increments across the batch, in an amount large enough to cover the heterogeneity of the material. Samples must be preserved between collection and analysis by cooling, acidification or storage in clean inert containers to prevent changes in composition. Labelling, chain of custody and documentation are important for legal and regulatory work. Sampling error is frequently larger than the measurement error of the analytical method itself.
Going deeper: Sampling
Key ideas: Choose a sample mass large enough for the particle size and heterogeneity, reduce it by coning and quartering or riffle splitting, then grind and homogenize before analysing. For liquids, flush the container and avoid headspace. Use blanks to test contamination from sampling gear. Preservation examples: acidify metals to pH below 2, cool microbial samples to 4 C, and use amber glass for light-sensitive analytes.
Common mistakes and connections: Students think that analytical precision makes up for a bad sample. A grab sample may not represent a changing stream, and a hot spot can mislead. Contamination from containers (metals from glass, plasticizers from plastic) and loss of volatiles are common. Documenting time, place and handling is part of the result. Related to quality control, error analysis and environmental monitoring.
Worked example and use case
Water is collected at several depths in a lake and combined to represent the average composition.
Frequently asked questions about Sampling
What is Sampling?
Collecting representative portions of material for analysis.
Is Sampling a beginner, intermediate or advanced topic?
Sampling is a intermediate topic in Analytical, Lab & Spectroscopy. It builds on the vocabulary of beginner topics in this area.
What should I learn before Sampling?
Study these earlier topics in Analytical, Lab & Spectroscopy first: Error Analysis, Standard Deviation, Detection Limit.
What comes after Sampling?
The next topics in Analytical, Lab & Spectroscopy are Quality Control and Electrophoresis.
Can I practise Sampling with quizzes?
Yes. The interactive lesson includes a self-check question on Sampling, and the Analytical, Lab & Spectroscopy quiz draws on every topic in this area.
Where Sampling fits in Analytical, Lab & Spectroscopy
Sampling is topic 67 of 99 in Analytical, Lab & Spectroscopy.