Determination of the Uncertainty of Nitrogen Content in Soy Sauce by Automatic Kjeldahl Determination of Nitrogen

The purpose of food inspection is to determine the results of the samples tested. This has a very important influence on the evaluation of product quality and is also the basic condition for the survival of test laboratories. However, there are more or less uncertainties in the measurement process, which requires a certain assessment to ensure the accuracy and reliability of the evaluation test results. One of the most important indicators for the quality of soy sauce is its total nitrogen content. However, in the past, the evaluation of the uncertainty of the total nitrogen content of soy sauce was relatively rare using an automatic Kjeldahl apparatus.

The national standard implemented in June 2010 has included the automatic Kjeldahl determination of protein (nitrogen) content in national standards. The automatic Kjeldahl tester is used to determine the total nitrogen in GB 18186-2000 Brew Soy Sauce. The uncertainty of the measurement result of total nitrogen in soy sauce was evaluated. By analyzing and quantifying the uncertainty components that affect the measurement results of the sample, the standard uncertainty and extended uncertainty that are measured are obtained, and the measurement results are expressed.

The sources of uncertainty in determination of total nitrogen content in soy sauce by the automatic Kjeldahl nitrogen analyzer mainly include: the uncertainty introduced by the pipette to absorb the volume of the sample, the uncertainty introduced by the titration volume of the standard solution, and the introduction of hydrochloric acid standard solution concentration The degree of certainty, the uncertainty introduced by the numerical revision, and the uncertainty introduced by measuring the repeatability of the sample.

After accurate tests, the determination using the automatic Kjeldahl analyzer can be summarized. The main sources of uncertainty are the sample volume removal and repeatability tests, and also the concentrations of the standard solutions. Sample volume removal and reproducibility test are the main sources of uncertainty. Special attention should be paid to the pipette selection and the standard operation of removing the sample during the test. At the same time, attention should be paid to the digestion and distillation process of the sample and automatic titration of the nitrogen determination device. The working condition of the system. As the secondary source of uncertainty, the standard solution concentration is the main influencing factor for the uncertainty of the reference substance. Therefore, the reference substance must be accurately weighed during the calibration process in order to better meet the test requirements. , Weighing with higher precision balance can be used.

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