Protein determination problem

I am a novice, in the laboratory determination of crude protein, the digested substance does not change color, the solution is clear blue, done several times, do not know where the problem is, please help analyze what is the reason? -- I don't understand. Does it mean that the liquid after digestion and distillation will not change color when it encounters alkali? 510228206 add the following at 09:41 on 2009-9-14. We absorb it with boric acid, how to use alkali? I don't understand-- what's the result? When we do it, we don't change color all the time, sometimes it's blue, sometimes it's brown. The composition will not be the same according to different raw materials and finished products and different formulations. If anyone knows the specific principle reaction, give a chemical reaction formula, that would be very grateful! Looking forward to it! -- Yes, the digested and distilled liquid met a constant color [ts] jiangwenbo119 at 2009-9-14 10:49 to add the following [/ ts] 372637000. The result is incorrect. Basically no ammonia is produced-- digested and decomposed with concentrated sulfuric acid (H2SO4) (that is, all organic matter is decomposed into a transparent solution with concentrated sulfuric acid), so that all forms of nitrogen-containing compounds (proteins, amino acids, etc.) are converted into ammonium ions (NH4+). In this way, the nitrogen content can be determined by the classical acid-base titration, and then multiplied by a certain conversion coefficient is the protein content. The conversion coefficients of different substances are slightly different, including 6.38 for dairy products, 5.95 for rice, 5.46 for peanuts, 5.70 for flour, 6.24 for corn and sorghum, 5.71 for soybeans and their products, 6.25 for meat and meat products, 5.83 for barley, millet, oats, rye, 5.30 for sesame and sunflower (which is related to the protein structure). Converted to protein content: W (protein) = w (N) * coefficient. -- I don't understand what the problem is. To be clear, the determination of protein is very simple. What kind of equipment do you use? nitrogen meter or Kjeldahl distillation? -- the national standard is to absorb with boric acid! Is there something wrong with the way you do it? According to the national standard, there will be no problem!-- the digestive juice after digestion has been kept for too long, and the digestive juice is too cold. Just add alkali to the steam for a while-adding alkali in protein distillation sometimes does not change color, sometimes it is brown-black flocs, sometimes it is blue. Whether there is a problem depends on your result, the result is too low may be the amount of alkali is not enough. -- agree with the upstairs point of view that the result is not only the lack of alkali, but also the concentration error of the standard liquid. Has it been verified by ammonium sulfate?-- We have also encountered such a situation. It should be the problem of the sample itself, as long as there is little difference in the results, there is not much problem-learning! Study! study! Study! study! Study! study! Study! study! Study! study!