When analyzing organic pollutants by gas chromatography , the water sample must be sent to the laboratory for measurement as soon as possible after collection. Under normal circumstances, the water sample transportation time should not exceed 24h. During transportation, it should be noted that the inner and outer covers of the water sample container should be tightly closed before packing, and the glass-grinding bottle of the water-like sample should be covered with polyethylene film to cover the bottle mouth and be thin. The rope fastens the bottle stopper to the bottle neck; when the box is packed with foam or corrugated cardboard to prevent vibration, the sample bottles at the same sampling point should be installed in the same box as much as possible.
Sunlight should be avoided during transportation, and appropriate measures should be taken when the temperature is abnormally high or low. For testing organic contaminated samples, it should be kept away from light and refrigerated at low temperature.
The main methods for preservation of water samples are as follows:
1 Refrigeration and freezing
The main role of refrigeration and freezing is to inhibit microbial activity, slow down physical effects, and rate chemical reactions. Common storage conditions are 2~5°C refrigeration and -18~-22°C freezing.
2 filtration and centrifugation
Water turbidity not only affects the results of the analysis, but also accelerates the change of the water sample. If the dissolved component is determined, the water sample can be filtered with a 0.45 um microporous membrane to remove algae and bacteria and improve the stability of the water sample. In order to reduce the filtration adsorption loss, a glass fiber or polytetrafluoroethylene filter is generally used for the determination of organic items. Sediment type water samples can be separated by centrifugation; water samples containing more organic matter can be filtered by filter paper or sand core funnel.
3 Add preservative
The method of adding preservative mainly includes adjusting the pH value of water sample, adding biological inhibitor, oxidant or reducing agent, etc. The main concern is that the addition of preservative can not interfere with the subsequent determination, and the preservative is prepared by applying excellent grade pure reagent, and needs to be done at the same time. The corresponding blank test is used to correct the measurement results.