Ⅰ. Overview
Anions, cations and organic acid ions in water vapor samples are important indicators for studying the quality of soda water. These indicators in water vapor samples are constantly changing with time, and their distributions are different in different water vapors. We can effectively prevent thermal system corrosion, scaling and other problems by studying its source and the law of material transfer process, and by changing the operation mode. With the rapid development of power technology, high-parameter large units have been put into operation for power generation, and their requirements for water vapor indicators are getting higher and higher, and stricter requirements for sampling and testing are also put forward. At present, the most commonly used method for the trace analysis of water vapor in power systems is ion chromatography. The accuracy of ion chromatography trace analysis is more susceptible to various factors than conventional analysis. For example, changes in environmental conditions, the performance of ion chromatography itself, and the purity of standard substances are all important factors that affect the accuracy of trace analysis. Some of these factors are controllable by instrument analysts and can be dealt with through system errors. We can do uncertainty analysis of ion chromatography to determine it. In order to obtain accurate and valuable data, the experimenters will be committed to taking strict prevention and control measures in the above-mentioned links and have made substantial progress. However, in the trace analysis of soda water, due to the extremely low ion content in soda water samples, in a large number of experimental analyzes we found that these samples generally have errors caused by various pollutions in the process of collection, transportation and pretreatment. In this regard, our research group conducted specific experiments, and finally found that most of the problems were the influence of the sample bottle material, pretreatment, packaging and other processes on the experimental analysis results. In order to ensure the accuracy of the experimental analysis results, this paper will focus on the selection, cleaning, packaging and control of samples for the ion chromatography analysis of soda samples.
Ⅱ. Sampling bottle selection
According to the nature of the sample taken and the components to be tested, the corresponding sampling bottle should be selected, so as to avoid the loss and contamination of the sample, or the analysis results will be affected due to the material of the sampling bottle.
At present, most of the power plants choose plastic sampling bottles. The sample sampling bottles received by our laboratory are generally “three-no products”, that is, there is no production plant name, no production site, and no production hygiene license code, and there is no material description and use guarantee. This is very difficult for trace analysis. Ion chromatographic analysis is a precision analytical instrument, and if the error in the sampling process is not resolved, it will result in half the effort of the experimental analysis work.
2.1 Material and volume of sampling bottle
(1) The polyvinyl chloride sampling bottle will release chloride ions during the storage of water vapor samples, and cannot be used for the collection and storage of trace anion analysis in water vapor systems;
(2) ETFE fluoroplastic sampling bottles will release fluoride ions, and are not recommended for the collection and storage of trace anions in water vapor systems;
(3) If the material of the plastic bottle is not clear, it is not recommended to collect samples of trace anions in the water vapor system. If a plastic sampling bottle is selected, a dissolution test should be fully carried out to determine whether there is dissolution of impurity ions, and then determine whether it can be used to collect samples;
(4) The sampling bottle should be an airtight container with a lid. Do not use a beaker or measuring cylinder that is in contact with the air to avoid contamination.
