Sampling from Gases

The gas phase is the most difficult phase to sample due to its inherent properties sample.

Sampling Methods and Equipment

Sampling Gases Flowing Through Pipes

This device consists of a thin series tube of varying length, positioned so that its tip aligns with the axis of the pipe through which the gas flows. This device is primarily used for discrete sampling.

Sampling Gas from Tanks

A gas sampling system consists of a pressure gauge speed measurement flask gas meter pressure control meter and pressure gauge. One end of the device is connected to an aspirator and the other end to the substance from which the sample is to be taken. The aspirator facilitates gas extraction. During sampling the pressure reading on the pressure gauge is adjusted to 20–25 mm Hg by moving the tube in the control device up and down movement. If the gas is under pressure the aspirator pressure control device and pressure gauge components are not used.

Sampling Using a Gas Sample Container

A gas sample container is a tubular vessel made of borosilicate glass with suitable chemical and thermal properties. The gas inlet and outlet pipes of this container are fitted with single-valve stopcocks whose tightness is verified by a vacuum device. This type of container is frequently used for sampling gases from Tank. The procedure for sampling using a gas sample container is as follows:

• The gas sample container is connected to the tank sampling valve at the inlet.
• The outlet valve of the sample container is closed.
• The inlet valve of the sample container is opened.
• The tank sampling valve is opened.
• The container is allowed to fill completely.
• The inlet valve of the sample container is closed.
• The tank sampling valve is closed.
• The sample container is disconnected from the tank.
• The sample is labeled.
• The sample is sent to the laboratory for analysis.
• The analysis results received from the laboratory are recorded and a report is prepared.

Sampling Safety Rules

• All personnel except those assigned to sampling must be removed from the area during gas sampling.
• Samples must be transported in a manner that minimizes the risk of breakage.
• All equipment and containers must be suitable for the substance being sampled and the intended purpose.
• Adequate headspace must be left at the top of the container to accommodate potential expansion of the sample. However for substances easily degraded by air this headspace must not be excessive.
• Immediately before or after sampling the sample container must be labeled according to the nature of the substance and its associated risks.
• The person collecting the sample must be fully informed of potential hazards and necessary precautions.
• A second person must accompany the sample collector when necessary to ensure safety.
• Eye protection devices must be used when sampling chemical substances.
• A mask appropriate to the sampled substance must be worn.

Sample Storage Methods

During storage physical chemical and biological changes occur in the sample. Preservation techniques delay the natural chemical and biological changes that continue after the sample is removed from its source only. It is difficult to preserve samples in their original state. Most preservation agents react with the sample and therefore require blank analysis immediately. If samples are to be analyzed in a day refrigerated storage at +4°C is the best method. Chemical preservatives may be used if they do not interfere with the intended analysis. When preservatives are used they must be added to the sample container in advance and thoroughly mixed with all collected samples. The choice of preservation and storage methods depends on the intended analysis. Sample preservation and storage methods are limited and primarily aim to delay biological activity and hydrolysis of chemical compounds and complexes and reduce volatility of components. Preservation and storage methods typically involve pH control addition of chemical substance cooling and freezing. Samples must be delivered to the laboratory in the shortest possible time short duration. This period must not exceed 24 hours. During transport appropriate measures must be taken to prevent samples from being exposed to foreign odors direct sun light or temperatures above 25°C.

Sample Labeling

Identifying the sample is as important as collecting it. Immediately after sampling the sample must be labeled with legible identifying information using waterproof ink or an appropriate label. Sample identification can also be performed electronically using barcode labels.

Recording Measurement Results

Recording measurement results after analysis is essential for maintaining production continuity. Reoccurrence of errors detected during analysis can be identified by reviewing records. Recurring error recorded in the logs indicate a malfunctioning device or personnel failing to perform their duties. Storing measurement results rather than the physical samples is a simpler and more practical approach. Measurement results are recorded by the analyzing personnel in the plant logbook or computer system. The following information is also recorded alongside the results:

1. Date and time (hour and minute if necessary)
2. Definition of the sampling point
3. Name code or lot number barcode number of the sample
4. Name of the person who collected the sample

Error Detection

During trials and test productions certain set values are determined for each process. Parameters such as pressure temperature flow level and other variables are established. Changes may occur in these values due to malfunctions or other causes. Such errors lead to undesirable changes in product quality. It must be known in advance which errors cause which changes in product characteristics. The error indicated by the deviation detected through analysis of the sample is identified. The field personnel are informed of the error and corrective action is taken. A new sample is then collected and reanalyzed. This process is repeated until the product quality reaches the desired values.

Directing Production Based on Measurement Results

Results obtained from samples provide the most valuable information for guiding production. To monitor the Production process and implement appropriate corrective interventions when necessary the following procedures must be followed.

Acceptance of routine and additional samples collected from the facility for process control

• Samples are collected by designated personnel according to the sampling instructions and delivered to the laboratory.
• The person delivering the sample hands it over to the laboratory technician. Explanations are provided if necessary such as for delayed or additional samples. These explanations are recorded by the shift laboratory technician in the logbook.
• If the shift laboratory technician receives a sample that does not meet requirements such as being contaminated improperly contained or insufficient in quantity they request a new sample to be collected and invalidate the original sample.

Analysis of routine samples collected from the facility for process control

• The shift laboratory technician performs analyses according to the specified analytical methods.
• If the shift laboratory technician has doubts about any analysis result they repeat the analysis. If deemed necessary they request a new sample.
• Results are recorded on the appropriate forms.
• The shift laboratory technician enters the analysis results into the computer system. If results fall outside the established limits they notify the relevant unit operators by phone.
• Residual portions of samples after analysis are not immediately discarded. The sampling instructions specify how long and for which samples storage is required. Samples are retained accordingly for the specified duration.
• After the results of out-of-limit analyses are communicated to the relevant unit additional samples are requested from the unit after each corrective action to monitor whether the defect in the intermediate product or final product persists.
• Additional samples received are reanalyzed as described in the previous section.