Determination of Nitrogen Content in Pu'er Tea by Kjeldahl Analyzer
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Strengthen the alkali in the digestion solution, heat distillation, absorb free ammonia with boric acid to titrate with hydrochloric acid standard solution. GB5009.5-2010 first method 6.1 is semi-micro full glass distillation} 6.2 is Kjeldahl method (according to different instruments Set different conditions), GB/T5511-2008 for the whole method (full glass distillation or Kjeldahl determination of nitrogen). Using the Kjeldahl nitrogen analyzer under the operating conditions of HZSO, one HzOz digestion Pu'er tea samples to determine the nitrogen content (Excluding nitrate nitrogen), and a comparison of digestion methods and determination of NHQ-N in digestive liquids, precision experiments, and spike recovery experiments.
Kjeldahl nitrogen analyzer (including programmable thermostat and automatic lifting device digester with matching digestive tube); digested catalyst KZSOQ+CuS04 (uniform mass ratio of 9:1); HzOz (30%); HzS04 (p =1.84g/L); c(HCl)-0.1000mol/L; Absorption solution H3B03} 4%); NaOH} 40%); Indicator: Methyl red (0.1%) + orochlor green (0.1%) Add 7:10 mixture to the absorption solution, add the amount: methyl red 0.7%, acetochlor green 1%; reagents are of analytical grade, water is ammonia-free deionized water. HzSOQ+I}zSOQ+CuSO, digestion method Weigh the Pu'er tea sample (mixed and smashed over 1mm standard sieve) 0.5g in 250mL digestive tube, add 5g KZSOQ + CuS04 mixed catalyst, rinse tea with a small amount of water on the bottle wall and add 10mLHzS04, after program temperature control heating, end of heating After the digestion furnace cooling, digestive liquid cooling standby, while doing blank experiments. The entire digestion process time is about 4h (high temperature and long time consumption).
Kjeldahl test procedures, weighed Pu'er tea samples (mixed and crushed over 1mm standard sieve) 0.5g in 250mL digestive tube, rinse with a small amount of water on the wall of the tea after adding 5mLHzOz, plus 10mLHzSO, after the program control After heating, after the end of heating, the digester cools, and the digester cools down. At the same time, a blank experiment is performed. The entire digestion process takes about 3 hours. The digestive tube containing the digestive fluid is loaded into the instrument, and the sample determination procedure is performed. The blank is first tested. Sample start. A single sample takes about 6min.
The Kjeldahl nitrogen determination method for determining the nitrogen content of Pu-erh tea is feasible. The method has high precision, good accuracy, and is easy to operate. It saves time and greatly improves the time compared with the semi-micro method and full-glass distillation method. Work efficiency can be applied to the determination of nitrogen content in many plant samples or foods.