1. Prepare 6 Kjeldahl flasks, numbered. Add 1.0 mL of the appropriate concentration of protein solution to the flasks 1, 2, and 3, and add the sample to the bottom of the flask. Do not stick it on the bottle neck or bottle neck. Then, 0.3 g of potassium sulfate-copper sulfate contact agent, 2.0 mL of concentrated sulfuric acid, and 1.0 mL of 30% hydrogen peroxide were sequentially added. The 4, 5, and 6 flasks were used as blank controls to determine the trace amount of nitrogenous substances that may be contained in the reagents, and the samples were calibrated. To the flasks 4, 5, and 6 was added 1.0 mL of distilled water instead of the sample solution, and the remaining reagents were the same as those of the No. 1, 2, and 3 flasks. 2. Place the flasks with the reagents on the digesting rack and connect the pumping device. First, heat it with a slight heat. At this time, the material in the flask becomes carbonized and black, and a large amount of foam is generated. Care must be taken to prevent bubbles from rushing out of the nozzle. After the foam disappears and stops, increase the firepower and keep the liquid in the bottle slightly boiling. After the solution is clarified, continue heating to make the digestive juice boil for 15 minutes. The flask should be rotated at any time during the digestion process so that the adhesive material on the inner wall can flow into the bottom to ensure complete digestion of the sample. The gas released during digestion contains SO2, which is highly irritating. Therefore, the pump should be turned on and the gas is pumped into the tap water from the beginning. The entire digestion process should be carried out in a fume hood. After the digestion was complete, the flame was turned off and the flask was allowed to cool to room temperature.
Folding distillation absorption
Distillation and absorption were carried out in a micro-Kjeldahl instrument. There are many types of Kjeldahl distillation plants, which are generally composed of three parts: steam generation, ammonia distillation and ammonia absorption.
1. Washing of the instrument
Before the instrument is installed, all parts need to be cleaned by the general method. The rubber tube and plug should be immersed in 10% NaOH solution, boiled for about 10 minutes, washed with water, boiled for 10 minutes, washed several times, then installed and fixed on an iron. On the stand. Before the instrument is used, all the traces of the pipeline must be washed with steam to remove the ammonia that may remain in the pipeline. The instrument being used can be washed for 5 minutes before each sample. For instruments that have not been used for a long time, repeat the steam wash, no less than three times, and check that the instrument is normal. Carefully inspect the connections to ensure that there are no air leaks. First, add about 2/3 volume of distilled water to the steam generator, add a few drops of sulfuric acid to keep it acidic, to avoid the ammonia in the water being distilled out to affect the result, and put a little zeolite (or capillary, etc.) to prevent explosion. Add about 20 mL of distilled water along the wall of the small glass to allow water to flow into the reaction chamber through the cannula, but the water in the glass should not be exposed, plug the rod-shaped glass stopper, keep the water seal and prevent air leakage. Immediately after the steam occurs, the switch on the waste liquid discharge pipe is closed, so that the steam can only enter the reaction chamber, causing the water in the reaction chamber to boil rapidly. The steam is distilled out from the upper port of the reaction chamber through the nitrogen-fixing ball into the condenser to be cooled, in the condensation tube. Place a conical flask on the lower end to receive the condensate. Start from the time when the nitrogen ball is hot, continue to cook for 5 minutes, then remove the gas lamp. After the flushing is completed, the connecting rubber tube between the steam generator and the collector is clamped. Since the gas cooling pressure is lowered, the waste liquid in the reaction chamber is automatically drawn into the reaction chamber casing, and the waste liquid discharge port clamp is opened to discharge the waste liquid. So clean 2~3 times, then exchange a conical flask containing boric acid-indicator mixture under the condenser tube to completely immerse the bottom of the condenser tube in the solution, distill for 1~2min, observe the solution in the conical flask. Whether it is discolored. If it does not change color, it means that the inside of the distillation unit has been cleaned. Remove the conical flask, distill for another 1-2 min, rinse the condenser bottom with distilled water, turn off the gas lamp, and the instrument can be used for sample measurement.
2. Distillation absorption of inorganic nitrogen standard samples
Due to the cumbersome operation of nitrogen determination, in order to be familiar with the operation techniques of distillation and titration, beginners should first perform repeated exercises with inorganic nitrogen standard samples, and then determine the unknown samples of organic nitrogen. It is tested three times with standard ammonium sulfate of known concentration. Take 5 clean 100mL conical flasks, add 20mL of 2% boric acid solution, 3~4 drops of methylene blue-methyl red mixed indicator (purple red), and cover the bottle for use. Take one of the conical flasks to the lower end of the condenser and immerse the outlet of the condenser in the solution. Note: The collector piston must be opened before this operation to prevent the liquid in the conical flask from sucking back. Accurately absorb 2mL ammonium sulfate standard solution into the glass cup, carefully lift the rod-shaped glass stopper to slowly flow the ammonium sulfate solution into the distillation flask, rinse the small glass cup with a small amount of distilled water 3 times, and put it into the distillation bottle. Then, 10 mL of 30% NaOH solution was added to the small glass via the measuring cylinder, and the lye was slowly flowed into the distillation bottle, and the rod-shaped glass stopper was tightly closed when the alkali solution had not completely flowed in. Add about 5 mL of distilled water to the small glass cup, and then slowly open the glass stopper, so that half of the water flows into the distillation bottle, and half is left in the small glass cup for water sealing. The collector piston is closed, the steam generator is heated, and distillation is performed. The boric acid-indicator mixture in the conical flask changes from magenta to green due to absorption of ammonia. From the time of discoloration, distill for another 3 to 5 minutes, move the conical flask so that the liquid level in the bottle leaves the lower mouth of the condenser tube about 1 cm, and rinse the lower end of the condenser tube with a small amount of distilled water, then continue to distill for 1 min, remove the conical flask, and cover it. , ready to titrate. After one distillation is completed, the gas lamp is removed, the rubber tube between the steam generator and the collector is clamped, the reacted waste liquid is removed, the small glass cup is washed several times with water, and the waste liquid is removed. After repeated rinsing, the next sample can be distilled. Repeat twice with standard ammonium sulfate as above. Another 2 mL of distilled water was used instead of the standard ammonium sulfate for the blank measurement twice. Each of the distilled conical flasks was titrated together.
3. Unknown sample and blank distillation absorption
Three samples of the digested protein were prepared, and three blank control solutions were sequentially subjected to distillation absorption. Add 5mL of hot distilled water to the digested sample or blank control solution, add it to the reaction chamber through a small glass cup, and then wash the small glass cup 3 times with hot distilled water. The water consumption is about 3mL each time, and the washing liquid is poured together. In the reaction chamber. The rest of the operation was carried out by distillation of standard ammonium sulfate. Due to the high concentration of potassium sulfate in the digestive juice, it is viscous and difficult to pour out from the Kjeldahl flask. It must be diluted with 5 mL of hot distilled water. If crystals are precipitated, it must be slightly heated and added to the glass to make it hot. Flow into the reaction chamber. In addition, it should be noted that the sample or blank control solution is added immediately when the instrument wash has not been completely cooled, otherwise the digestive juice is easily precipitated and crystallized through the cooled pipe, causing clogging.
Folding titration
After the sample and the blank are distilled, the titration is carried out together. The receiving cap was opened, and the acid microtiter tube was titrated with a standard hydrochloric acid solution of 0.0100 mol/L. When the solution to be dripped into the bottle is dark gray, rinse the inner wall of the conical flask with distilled water once. If the green color is reproduced after shaking, carefully drop half of the standard hydrochloric acid solution, shake the color change of the solution in the bottle, and the dark gray does not change within one or two minutes, when it is deemed to reach the end of the titration. If it is pink, indicating that the end point of the titration has been exceeded, 0.02 mL can be subtracted from the amount of standard hydrochloric acid solution that has been titrated. The color of the nitrogen determination endpoint of each sample must be identical. The blank control solution accepts the color of the solution in the bottle unchanged or slightly changed and has not appeared green, and may not be titrated. Record the number of milliliters of standard hydrochloric acid solution used for each titration for calculation
Lightweight and portable camping burner, barbecue stove.
Very suitable for BBQ and small parties.
High thermal efficiency, pocket bellows and air vents for good ventilation and efficient burning.Made of stainless steel, the adjustable legs can be retracted. Very small and easy to put in the trunk of the car.
ARC USA camping stove gives you an environmental and simple way to enjoy camping.You can get twigs,leaves,dry grass,pinecones as original fuel from nature naturally, which is very safe and environmentally friendly.
ARC Advanced Royal Champion , https://www.arcimportcorp.com