Common Problems In Water Quality Analysis

There are many indicators for environmental water quality monitoring. In addition to physical and chemical indicators, there are also many parameters such as inorganic, organic and microbial parameters that are often used as standards for measuring environmental water quality. Faced with so many indicators, what problems should be paid attention to in the process of water quality analysis?

Collection of water samples

1. Prepare the sampling device and sample container before sampling. The sampling devices currently used include buckets, various water collectors, etc. If the sampling device is made of plastic or glass, it can be cleaned and set aside according to the general washing method of the container; if it is made of iron, it must first be thoroughly cleaned with detergent to remove oil or oil, then rinsed with tap water, dried and set aside, but the water samples taken cannot be used for analysis of metals such as iron and nickel.

2. Sampling volume The sample volume depends on the measurement project. Different measurement projects have different requirements for the amount of water samples and storage conditions. Therefore, the required amount should be calculated according to the actual situation of the measurement project and 20~30% should be added as the actual sampling volume. Suppose the volume of the sampling container is limited and one sampling cannot meet the required sample volume. In that case, you can collect multiple samples and mix them in a larger container before putting them into the sample container.

3. Sampling method The water sample collection method is extremely important for the analysis results. The water samples collected must be representative so that the water samples can truly reflect the water quality of the entire water body.

4. Before water quality analysis, the collected water samples should be shaken or otherwise stirred to avoid problems such as precipitation caused by long-term placement.

5. Water sample collection during water pollution survey When conducting a pollution survey on a water system, it is necessary to consider the entire water area, reasonably set up sampling points, and establish a water pollution monitoring network to report the pollution situation and the dynamic changes of various harmful substances in the water area in a timely and accurate manner.

Transportation and storage of water samples

Water samples of various water qualities will take a certain amount of time from collection to analysis and determination. The time difference may range from a few minutes to a few hours, and sometimes they will even be left for several days. Due to changes in environmental conditions, the influence of microbial metabolic activities and chemical reactions, some physical parameters and chemical components of water samples will change, resulting in inaccurate water quality analysis results. To minimize these changes, it is necessary to shorten the transportation time as much as possible, analyze and measure as quickly as possible, and take necessary protective measures; some items must be measured at the sampling site.

Transportation of water samples

For each water sample collected, a record should be kept, and a label should be attached to the sampling bottle and transported to the laboratory. During transportation, the following points should be noted:

1. The stopper of the sampling container should be tightly plugged, and if necessary, it should be sealed with sealing glue or paraffin (water samples for oil testing cannot be sealed with paraffin).

2. To avoid loss or contamination of water samples due to vibration and collision during transportation, it is best to pack the sample bottles and squeeze them tightly with foam plastic or paper strips.

3. For samples that need to be refrigerated, a special insulated container should be equipped with a refrigerant and the sample bottle should be placed in it.

4. Insulation measures should be taken in winter to prevent the sample bottle from freezing and cracking.

Storage of water samples

The container for storing water samples may adsorb the components to be measured or be contaminated with water samples, so containers made of materials with stable performance and low impurity content should be selected. Commonly used container materials include borosilicate glass, quartz, polyethylene and polytetrafluoroethylene. Among them, quartz and polytetrafluoroethylene have less impurities, but are expensive. Polyethylene and borosilicate glass containers are widely used in general water quality analysis. For water samples that cannot be transported or analyzed as soon as possible, appropriate preservation methods should be adopted according to the requirements of different monitoring projects. The transportation time of water samples is usually 24 hours as the maximum allowable time.

Laboratory analysis stage

The sample pretreatment process is different for different types of water quality and different monitoring projects. Many water quality analysis projects of groundwater and surface water can be directly measured without pretreatment. For industrial wastewater and domestic sewage with more serious pollution, different monitoring projects may require pretreatment operations such as filtration, precipitation, digestion, distillation, and extraction, which must not be omitted. Otherwise, there will be large errors in the analysis process and analysis results. When each batch of samples is analyzed, standard samples from the National Environmental Monitoring Center or the Provincial Environmental Monitoring Center are brought in. It is generally believed that as long as the analysis results of the standard samples are within the allowable error range, the sample analysis is qualified, while the calibration of the measuring instrument is ignored. Generally speaking, the larger the capacity of the measuring instrument, the smaller the relative error of its capacity. Therefore, large-capacity containers should be used as much as possible. In addition, when choosing glassware, grade A glass measuring instruments should be used as much as possible to avoid using measuring instruments of different grades.

Conclusion

As one of the important links in environmental protection, water quality analysis should be taken seriously, not just to meet environmental protection requirements. We need to cherish this career from the bottom of our hearts, strengthen our own operational capabilities and theoretical knowledge, and make water quality analysis more accurate.