Sampling from Gases

The gas phase is the most difficult phase for sampling due to its properties.

This device consists of a series of fine tubes of varying lengths and is installed so that the longest tube aligns with the axis of the pipe through which the gas flows. This device is primarily used for discrete sampling.

^{Device for sampling gases from pipes}

The device consists of a pressure gauge, a velocity measurement flask, a gas meter, a pressure control meter, and a pressure scale. 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 scale is adjusted to 20–25 mm Hg by moving the tube in the control device up and down. If the gas is under pressure, the aspirator, pressure control device, and pressure scale components are not used.

^{Device for sampling gas from a tank}

A gas sample container is a tubular vessel made of borosilicate glass suitable for the chemical and thermal properties of the gas. The inlet and outlet pipes of this container are fitted with single-valve stopcocks whose tightness is verified by a vacuum device.

It is frequently used for sampling gases from tanks. The procedure for sampling using a gas sample container is as follows:

• Connect the inlet of the sample container to the tank sample valve.
• Close the outlet valve of the sample container.
• Open the inlet valve of the sample container.
• Open the tank sample valve.
• Wait until the sample container is filled.
• Close the inlet valve of the sample container.
• Close the tank sample valve.
• Disconnect the sample container from the tank.
• Label the sample.
• Send the sample to the laboratory for analysis.
• Record the analysis results from the laboratory and prepare a report.

^{Gas sample container}

• 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.
• When storing samples, leave a specified space at the top of the container to accommodate potential expansion. However, for substances easily degraded by air, this space must not be excessive.
• Immediately before or after sampling, label the sample container 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.
• When necessary, a second person accompanies the sampler to ensure their safety.
• Eye protection devices must be used when sampling chemical substances.
• A mask appropriate for the sampled substance must be worn.

During storage, physical, chemical, and biological changes occur in the sample. Preservation techniques only delay the natural chemical and biological changes that continue after the sample is removed from its source. Complete preservation of samples is difficult. Since most preservation agents react with the sample, analysis must be performed immediately. If samples are to be analyzed within a day, storage at low temperatures (+4°C) is the best method. Chemical preservatives may be used if they do not interfere with the intended analysis. When used, preservatives must be placed in the sample container beforehand and thoroughly mixed with the collected sample. The choice of preservation and storage methods must be determined by the type of analysis to be performed. Sample preservation methods are limited and aim to delay biological activity and hydrolysis of chemical compounds and complexes, as well as reduce volatility of components. Preservation and storage methods typically involve pH control, addition of chemical substances, cooling, and freezing. Samples must be delivered to the laboratory in the shortest possible time, and this period must not exceed 24 hours. During transport, precautions must be taken to prevent samples from being exposed to foreign odors, direct sunlight, or temperatures above 25°C.

Defining the sample is as important as collecting it. Immediately after sampling, identifying information must be written legibly with water- and oil-resistant ink or labeled on the container. Sample identification may also be performed electronically using barcode labels.

After analysis, recording measurement results is essential for maintaining continuous production. Reoccurrence of errors detected during analysis can be identified by reviewing historical records. Recurring errors recorded in the data indicate malfunctioning equipment or personnel failing to perform their duties. It is easier and more practical to store measurement results than to store the samples themselves. Measurement results are recorded by the analyzing personnel in the operational logbook or computer system. The following information must also be recorded along with the results:

1. Date and time (and hour and minute if necessary)
2. Definition of the sampling point
3. Sample name, code/lot number, barcode number
4. Name of the person collecting the sample

During process trials and production tests, certain set values are determined for each process. Values for pressure, temperature, flow, level, and other variables are established. These values may change due to malfunctions or other reasons. Such deviations cause adverse changes in product quality. It must be known in advance which errors lead to which changes in product characteristics. The error indicated by the deviation detected through sample analysis is identified. The field personnel are informed of the error so that corrective action can be taken. A new sample is then collected and reanalyzed. This process is repeated until product quality reaches the desired values.

Results obtained from samples provide the most valuable information for directing production. To monitor the production process and implement appropriate corrective actions when needed, the following procedures must be followed.

• 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. If necessary, explanations are provided—for example, if the sample is delayed or additional. These explanations are recorded by the shift laboratory technician in the logbook.
• If the shift laboratory technician finds a sample unsuitable upon receipt—for example, contaminated, improperly contained, or insufficient in quantity—they instruct that a new sample be collected and cancel the original sample.

• 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.
• If results are obtained, they record them on the appropriate forms.
• The shift laboratory technician enters the analysis results into the computer system. If the results fall outside the established limits, they notify the relevant unit operator by phone.
• The remaining portions of the samples are not immediately discarded. The sampling instructions specify how long each type of sample must be retained in the laboratory. Samples are stored for the specified duration accordingly.
• After the unit is notified of out-of-limit results, additional analysis samples are requested from the unit after each corrective action to monitor whether the defect in the intermediate or final product has been resolved.
• The additional sample is reanalyzed as described in the previous section.