In the national economy, petrochemical products occupy an important position. There are many varieties of these products, but most of them have an important indicator that must be tested-moisture content. Which method to choose in the test, how to choose the instrument, and how to determine its qualification is a major event in many laboratory tests. As a type of measuring instrument for measuring the moisture content of a substance, there are currently a variety of instruments such as the drying method, Karl Fischer (Karl Fischer, hereinafter referred to as the Karl Fischer) volume method, and the Karl Fischer Coulomb method. But for most substances, the most economical and accurate method is the Karl Coulomb method. This article discusses its principle and application scope with reference to KAF-2010 series automatic trace moisture analyzer developed and produced by Shanghai Hegong Scientific Instrument Co., Ltd., based on the Karl Coulomb method. And with the experience of using the instrument for several years to promote the application of the Karl Coulomb method instrument and promote the development of experimental work in the multidisciplinary field.
Moisture does not exist in one form in the substance. Common forms include free water and dissolved water. And several forms of water exist almost simultaneously. The molecular weight of water is relatively small, and it is inevitable to be contained by the molecules of petrochemical products. Relatively speaking, free water is better measured. When the sample is injected, the electrolysis rate increases rapidly and then decreases rapidly in about 30 seconds. The water content during this period is mainly free water in the substance. However, the measurement time of dissolved water is long, and the precipitated water can only be determined after the substance is dissolved by the force of the molecular bond in the reagent. When the Huakun instrument measured the electrolysis speed fell below 1μg / s but did not reach the end point, this period of time was mainly to measure the dissolved water (about 30 seconds). If there is more dissolved water, the simple way is to control the injection volume. Reducing the amount of sample injection allows the molecular bond in the reagent to quickly open the sample molecular cluster in a short period of time to rapidly precipitate the dissolved water. The other method is to use the principle of similar compatibility of substances to quickly dissolve the sample. Take an experiment I encountered in practice as an example: to determine the moisture content of vinylene carbonate, according to the product standard, the moisture content of the substance is 10-6, and it is a colorless solid crystal below 15 ℃. It gradually dissolves into a colorless liquid above 15 ° C, with low viscosity. When the room temperature is less than 20 ° C, it gradually returns to a solid crystalline state. When the moisture content is measured at room temperature, it is just near the critical point of the solid-liquid transition of the substance. When the first sample (1ml) is injected, the measurement time is 65 seconds, the second sample measurement time is 130 seconds, and the third sample measurement time is 260 seconds. As process control, this is obviously undesirable, and the longer the time, the greater the deviation from the true value. Can only be solved by the loss of reagents. One sample and one pool of reagents, the process is very cumbersome and uneconomical. After repeated thinking, we have adopted solubilization measures based on the principle of similar compatibility of chemical products. After the reagents are equilibrated, 1 ml of tetrahydrofuran is injected first, and after being equilibrated, the samples are injected. The result of the test was 60 seconds for the first sample, and the subsequent samples were measured for a slightly longer time but not more than 70 seconds. The problem is solved. The reason for this is that at room temperature, the Köhler reagent alone cannot completely dissolve the vinylene carbonate, and it cannot completely dissolve out the water. The dissolved water of each sample accumulates in turn, causing time to increase, which is solved by the principle of similar compatibility There are not many literature reports on this kind of problem, which can be used as a reference. This case also illustrates a problem, as long as it is a substance without side effects
For this products Line, We collect and introduce the customer all style of products can easy life, we organize three main products range from Easy Organizer, Easy take, Folding products, We are try our efforts to found and develop the new creative products, wish can improve the Life Quality and easy your life.
Shoes Rack Organizer,Rain Proof Umbrella,Notebook Water Bottle,Plastic Shoe Slot Organizer
NINGBO DAC ARTS & CRAFTS COMPANY , http://www.dacpets.com