【作者】 王磊；

【导师】 张忠远；

【作者基本信息】 东北农业大学 ， 动物营养与饲料科学， 2015， 硕士

【摘要】 本试验将从盐酸溶液浓度的标定方法、蒸馏仪器的选择、饲料中亚硝酸盐含量等方面对饲料中粗蛋白质含量测定时产生的影响以及饲料中亚硝酸盐含量测定方法的比较及改进进行研究。凯氏定氮法是食品和饲料中测定粗蛋白质应用最广泛也是最经典的方法,其中盐酸溶液浓度的标定是凯氏定氮法中至关重要的一步,盐酸溶液浓度的标定方法分为无水碳酸钠法和硼砂法。无水碳酸钠标定法需要在270℃~300℃干燥至恒重,操作较费时费事,且指示剂颜色不易把握;而硼砂标定法中只说是干燥的硼砂,并未说明干燥程度以及如何干燥。蒸馏装置是凯氏定氮法中的重要仪器,分为半微量蒸馏装置和全自动凯氏定氮仪等类型,不同蒸馏装置对测定结果的影响尚无报道。试验表明:无水碳酸钠须在270℃~300℃干燥至恒重才可标定盐酸。380℃干燥至恒重的硼砂在标定盐酸时计算式中的硼砂分子式要按无水硼砂计算;100℃干燥的硼砂不可以用于盐酸标定;正常室温密闭存放的硼砂更适于北方地区实验室进行盐酸标定(因为南方湿度较大)。全自动凯氏定氮仪较半微量蒸馏装置测定准确性更好。亚硝酸钠存在于饲料原料及配合饲料中,尤其在鱼粉、肉骨粉及青绿饲料中含量较大,目前没有试验研究表明饲料中亚硝酸盐对其粗蛋白质含量测定是否产生影响,但是通过人为向标准样品硫酸铵中加入一定浓度梯度的亚硝酸钠后,发现测出的硫酸铵中的氮含量减少,损失的氮含量与亚硝酸钠的添加量呈现一定的线性关系。向牛血清白蛋白和饲料中加入亚硝酸钠后会出现同样的线性关系。试验表明:亚硝酸盐的存在会对凯氏定氮法测定粗蛋白质时产生一定的副作用,会与部分含氮化合物反应,降低蛋白含量的真实值,严重影响粗蛋白质测定的准确性。草酸是最简单的有机二元酸之一,结构简式HOOCCOOH。NO2-中的N为+3价,所以既有氧化性,又有还原性,在酸性介质中呈现较强的氧化能力。与很弱的草酸、乙酸均可反应。可能的反应为:2NO2-+2H+=NO+NO2↑+H2O。向加有不同浓度梯度亚硝酸钠的硫酸铵混合物中分别加入0.1mol/l、0.5mol/l、1mol/l的草酸溶液,待反应充分后加入浓硫酸。经过试验结果分析得出:草酸溶液的加入不能消除亚硝酸钠对粗蛋白质测定的影响,所测出的硫酸铵中的氮含量与亚硝酸钠的添加量仍然呈现一定的线性关系。为了对饲料中亚硝酸盐含量进行有效的检测,首先要确定比较可靠、准确的测定方法。饲料中亚硝酸盐的测定方法分别为GB/T 13085—2005版和GB 13085—91版两种。试验采用两版国标法对同一样品进行检测,分别对两种方法的准确度和精确度进行比较。同时对2005版前处理方法进行改进,探讨用于青绿饲料的测定。试验表明:亚硝酸盐国标检测方法中2005版的精确度和准确度均高于1991版,用2005版测定青绿饲料中亚硝酸盐时加入1g活性炭可提高亚硝酸盐的回收率,增强其测定的准确性。更多还原

【Abstract】 The concentration of hydrochloric acid solution from the test calibration method was studied from the calibration method、choosing the distillation equipment、feed and other effects of nitrite content generated when the dietary crude protein content was measured and comparisons and improved method for the determination of nitrite in feed.Kjeldahl method is widely used in measuring crude protein and it is the most classic, in which the concentration of hydrochloric acid solution Calibration Kjeldahl method is a crucial step, the concentration of hydrochloric acid solution is divied into no calibration method water,sodium carbonate and borax Law Act. Anhydrous sodium carbonate calibration method requires270℃ ~ 300℃drying to constant weight, the more time-consuming and cumbersome operation,and the indicator color is not easy to grasp; and the borax is just called dried borax in the borax calibration method.But it doesn’t explain how the degree of drying and how to dry. Distillation unit Kjeldahl method is an important instrument,it divided into semi-micro distillation unit and automatic Kjeldahl instrument, such as the type, the effects of different distillation unit of measurement results have not been reported. Experiments showed: anhydrous sodium carbonate must be dried between 270℃ ~ 300℃ to constant weight before calibration hydrochloric acid.From 380℃ drying to constant weight of borax in the calibration formula HCl in anhydrous borax,borax is calculated according to the formula; 100℃ drying borax can not be used for calibration of hydrochloric acid; properly stored airtight at room temperature is more suitable for the northern region of borax laboratory hydrochloric acid were calibrated(because the South humidity).Automatic Kjeldahl nitrogen analyzer accuracy better than the semi-micro determination of the distillation unit.Sodium nitrite was present in feed materials and compound feed, especially in fish meal,bone meal, and a large green feed content, there is no experimental studies which show that whether the feed crude protein content of nitrite in their determination impacts or not, but after adding a certain standard sample concentration gradient of ammonium sulfate sodium nitrite by man was found that the nitrogen content in ammonium sulfate lessens,and it shows some linear relationship between the addition of sodium nitrite nitrogen content and presentation of certain losses. After bovining serum albumin and feeding will appear the same linear relationship to sodium nitrite. Experiments show that: the presence of nitrite Kjeldahl method will produce the determination of crude protein certain side effects, will react with some nitrogen compounds,reduce the real value of the protein content, seriously affect the accuracy of the determination of crude protein.Oxalic acid, i.e. acetic acid, one of the simplest organic dibasic acid. The simple structure isHOOCCOOH. N+3 in NO2-is a positive trivalent, so both oxidation, but also reduction, showing a strong oxidizing power in acidic media. With weak acid, acetic acid can be reacted. Possible reaction: 2NO2-+2H+=NO+NO2↑+H2O. The mixture was added with ammonium sulfate to different concentrations of sodium nitrite were added to 0.1mol/l、0.5 mol/l、1mol/l oxalic acid solution until the reaction after addition of concentrated sulfuric acid sufficiently. After analyzing the test results obtained: adding oxalic acid solution can not eliminate the influence of sodium nitrite on the crude protein determination, the measured amount of ammonium sulfate is added sodium nitrite nitrogen content and still showing a linear relationship. So to find a way to eliminate the effect of nitrite on the determination of crude protein content has to be studied further experiments.In order to feed the nitrite content for effective detection, we must first determine a more reliable and accurate measurement method. Determination of nitrite in feed were GB/T13085-2005 and GB 13085-91 edition version of the two. Test uses two editions of the national standard method for testing the same sample, respectively for the accuracy and precision of the two methods were compared. While the 2005 edition of pretreatment methods is improved determination to explore for green feed. experiments showed:nitrite 2005 edition national standard test method precision and accuracy are higher than the 1991 version, 1g of activated carbon can improve the recovery of nitrite measured nitrite green feed with the 2005 edition, to enhance its determination accuracy. Nitrite in some common feed ingredients and feed content,such as soybean meal, rice bran, corn bran, cottonseed meal, broiler complete feed, pig feed full price,is lower,it meets feed hygiene standards allowable amount of nitrite.更多还原