The sampling , and sampling is, the taking of a sample according to a defined procedure. It is used to make reliable statements about the quality, nature or composition of a certain material. The process of taking a sample produces a sample, but these samples can be combined again to form collective or mixed samples or divided accordingly using a sample divider. It makes sense to generate a representative sample that is as reproducible as possible. There are methods in statistics to prove this .
Sampling is colloquial in the original sense of taking samples on a trial basis in order to try something out or to determine properties in further subsequent analyzes .
Currently, the term sampling (in Switzerland, sampling) is also used as a generic term for the entire area
- Taking individual samples
- Mixing to bulk samples or parts to partial samples
- Preparation, if necessary comminution, sieving, division ... up to a laboratory sample, which may be reprocessed in a laboratory, into an analysis sample.
Practical significance and implementation in technology and natural sciences
For analytical tests in the laboratory, it is important to have a laboratory sample that is as representative as possible. This means that the mostly small amount examined in the laboratory should provide analysis and measurement results that are meaningful for a significantly larger batch (content of a wagon , a shipload, the soil of a property in environmental analysis, etc.). The physical state of the part to be examined often plays an important role.
In the case of wagon or ship loads, the samples are taken during loading and / or unloading. A single sample is taken from each delivery unit and mixed to form a mixed sample (= initial sample). The mixed sample is pulverized in grinding machines ( pan mill , jaw crusher , ball mill, etc.) and then “rejuvenated”, ie divided into partial samples. A partial sample (for example 15% of the initial sample) is ground even finer and then rejuvenated. In this way a sample is obtained that makes up about 1% of the original sample. Further comminution processes and rejuvenation can follow, so one finally receives an analysis sample. The described sample division (tapering) can be done by hand, with a sample spike or with the help of machine sample dividers. Large amounts of sample or large material flows are z. B. shared with a rotary pipe divider. So-called laboratory sample dividers are common in the laboratory.
In the case of homogeneous liquids, sampling is easy, you take some partial quantities and combine them in a bottle to form a mixed sample, which is then examined in the laboratory. Sampling suspensions is more difficult. Sealed, automatically operating sampling systems are sometimes used to obtain representative samples for wastewater analysis in industrial companies.
The sampling of gases is usually carried out by sucking in the gas using an aspirator . Gas samples are stored in gas collecting tubes ( gas mice , gas sausages ) which are closed at both ends with a ground joint tap . Due to the inertness of the Tedlar material , bags made from it are also used to collect gas samples for subsequent analysis.
When measuring emissions in a guided, dust-laden exhaust gas , a partial flow is often taken using isokinetic sampling and fed to the measuring device. The sampling location is of decisive importance for immission measurements and depends on the measurement task. Depending on the measuring task and measuring method, the duration of the sampling can vary between a few minutes and several weeks. The measurement methods for immission measurement can be enriching or non-enriching, with enriching methods usually being used for measurements in the outside air.
Sampling in biotechnology
In biotechnology , bioreactors and fermenters are used to produce a wide variety of products from microorganisms . Installed sensors only record some of the interesting process values, so samples have to be taken for external analyzes. Here, have contamination of the culture suspension is essential to prevent to growth and product quality is not negatively influenced. At the same time, possible internals for sampling must be designed sterile and free of dead spaces in order to prevent the formation of biofilms .
Manual sampling from bioreactors and fermenters
Manual sampling is one of the regular activities in production in biotechnology. There are various options that are selected depending on the reactor type and size:
- Piercing membrane : A syringe-like cannula is used to pierce a membrane to the medium on the side or in the lid of a reactor vessel and the desired amount is drawn up into a syringe. The outside of the membrane is coated with a chemical, e.g. B. alcohol , or disinfected by flaming with a gas burner.
- Sampling tube: A tube is built into the lid of a reactor vessel and extends into the vessel as far as the culture medium. The tube is filled with a sterile barrier medium until it is released from the outside and sample medium flows in from the inside and is collected. After the end of the process, the remaining material is pressed back with the sterile barrier medium.
- Sampling valve: A valve with connections for steam is installed in a container nozzle below the liquid level . Before a sample is taken, the valve body and all components in contact with the medium are sterilized with sterile steam. The sample can then be poured into a vessel held under the valve.
While sampling valves are used from small laboratory reactors to industrial fermenters, the other two methods are mostly limited to the laboratory scale.
Automatic sampling from bioreactors and fermenters
With the automatic sampling, a higher degree of automation is achieved, which is desired in biotechnology for reasons of process control, security and predictability. Various methods have been developed that allow the formation of so-called atline measurements, i.e. H. In contrast to sensors that measure online directly in the medium, they enable external measurements to be carried out automatically with direct feedback to the automation. For the successful sampling with subsequent analysis , sometimes complex devices have to be installed in order to ensure sterility in the culture vessel and at the same time to deliver full-fledged measurement results.
- Automatic sampling valve: In the variation of the manual solution, the valves for the steam, opening the sampling valve and filling into a vessel are equipped with an automatic drive. Permanently piped and automated, there is no contact with the environment and contamination can be excluded.
- Probes with an integrated valve: A valve is opened in the culture medium itself, which was also sterilized during the sterilization of the entire system and then pressurized with sterile compressed air . By closing and opening the compressed air supply, an exact amount of sample can be taken and dosed into a prepared container.
- Filter probes: A probe with filter ceramic is installed in the culture medium . Culture medium is drawn through the ceramic into a tube, whereby the cultivated microorganisms remain on the ceramic surface. The medium can then be examined for its components.
In principle, the automatic methods can also be used in many other fields of application for sampling liquids, for example in the chemical industry or petroleum processing. In biotechnology, the sterility requirement justifies the installation of complex sampling systems.
Sampling for quality control in the pharmaceutical industry
For the sampling of packaging , medicinal products and finished medicinal products in the pharmaceutical industry, there are detailed sampling instructions and plans, the use of which is monitored by the responsible state authorities.
Sampling already existed in the Middle Ages as a so-called "stitch". A small amount was taken from a larger amount (see sample ).
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