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There are several problems in its operation steps: First, the temperature control of the electric furnace in the digestion process is inaccurate, the digestion time is too long, and one sample needs more than 1h, resulting in low work efficiency. If there are multiple samples that need to be measured, corresponding digestion equipments need to be added, which not only increases the workload, but also increases the experimental cost. Second, there are some problems in the semi-micro distiller design used in the distillation process. In the course of the research, we commissioned the glassware manufacturer to make a set of the same distillation device. However, during the experiment, it was found that the Kjeldahl distillation vessel was not designed with a liquid outlet, that is, after the distillation, the residual liquid could only pass through the upper end of the earmould. Aspiration, operation is very inconvenient, the liquid must be cleaned in the same way to suck out. In addition, the concentration of sodium hydroxide solution in the raffinate is very large, and the risk factor is larger when sucked out. In view of the above deficiencies, this research carried out research and improvement on the experimental method. The digestion furnace was used instead of the temperature-controlled electric furnace for digestion, and the Kjeldahl apparatus was used to replace the Kjeldahl nitrogen apparatus for distillation, and then the titration analysis was performed. A batch of samples was determined by an improved method and compared with the semi-micro open method measurement results.
The automatic Kjeldahl nitrogen analyzer first uses ammonia-free water instead of the sample for distillation, and the distillate is used to wash the instrument pipeline. Subsequently, distillation of the blank test and the sample test was performed in order. When distilling, add 20ml of boric acid absorbing solution to a 150ml Erlenmeyer flask, deepen the end of the device's condenser tube to 1cm below the absorbing liquid surface, start the instrument, until the distillate volume is about 50ml, measure the distillate with a pH test paper. Distillation is completed on neutral (continue distillation if neutral) and the ends of the condenser tube are washed with a small amount of boric acid solution. A methyl red-o-cresol green indicator is added to the distillate, the distillate is titrated with a calibrated hydrochloric acid standard solution, the solution is changed from green to lavender, the hydrochloric acid standard solution used is recorded, and the total nitrogen content is calculated. Complete blank test. The blank experiment was performed simultaneously with the determination of the sample. Except for the absence of the sample, the rest of the operation steps were determined by the same sample. The volume of the hydrochloric acid standard solution consumed by the blank should not exceed 0.1 mL in general.
The semi-micro Kelvin method for the determination of total nitrogen has been studied and improved in municipal solid waste installations. The first one is the numerical control melting furnace instead of the tempering furnace digestion, precise temperature control and digestion, which greatly reduces the time resolution; secondly, automatic The Kjeldahl nitrogen analyzer replaces the automatic distillation of the Kelvin distillation unit to facilitate the clean addition of samples and equipment, and the numerical control melting furnace greatly improves the efficiency of the experiment. The use of improved methods for the determination of actual samples, and methods with national standards, and proved that the improved measurement method is feasible, the operation of the experiment is convenient, accurate, and the experimental efficiency is high and the effect is good.
Automatic Kjeldahl determination and semi-micro determination of the total nitrogen content of solids
The determination of total nitrogen content in solid wastes by the semi-micro open method is a long-standing process. The semi-micro open method measurement steps mainly include the three processes of sample digestion, distillation, and titration. The principle is that after treatment of solid waste samples in the catalyst (ie potassium sulfate, copper sulfate pentahydrate and selenium powder mixture), when digested with concentrated sulfuric acid, various nitrogen-containing organic compounds undergo complex pyrolysis The reaction is converted to ammonium nitrogen, and after the alkalized and distilled ammonia is absorbed by boric acid, it is titrated with an acid standard solution to calculate the total nitrogen content of the domestic waste (excluding all nitrate nitrogen). In modern determination methods, the application of automatic Kjeldahl determination is becoming more and more common. This is mainly because semi-micro methods have certain deficiencies.