Fast neutron activation analysis for simultaneous determination of nitrogen and phosphorus content in biological materials

Abstract

Nitrogen and phosphorus are the most important macronutrients among 17 nutrients required for optimal plant growth and reproduction. These elements are always present in cereal crops and play a determining role in the quality of plant products. For this reason, methods for determining their content simultaneously are of immediate interest in connection with monitoring grain quality.Fast neutron activation analysis is the most suitable method for determining nitrogen and phosphorus content in grain, pulse, and other agricultural crops [1,2]. This article presents the results of additional studies of a method for simultaneous determination of nitrogen and phosphorus in grain, pulse, hulled, and kernel crops using the NG-150 neutron generator at the Institute of Nuclear Physics of the Academy of Sciences of the Republic of Uzbekistan [2][3][4].The nuclear reaction 31 P(n, α) 28 Al was used to determine phosphorus content (Table 1). Aluminum is used as a monitor for checking the neutron flux [2]. The nuclear reaction 28 Si(n, p) 28 Al is an interfering reaction when determining phosphorus, and the reaction 29 Si(n, p) 29 Al is used to take account of this interfering effect on the method [5].The neutron activation method was developed to determine the nitrogen and phosphorus content in samples of certain grain, pulse, hulled, and kernel crops -wheat, millet, beans, buckwheat, dried apricots, apricots, pistachios, and peaches. Samples with mass 19-22 g were weighed and packed in 40 mm in diameter, 35 mm high cylindrical polyethylene containers. A polyethylene top tightly sealed a container. A 35-50 mg, 0.1 mm thick aluminum monitor was secured to the top for monitoring the fast-neutron flux. Some nitrogen and phosphorus compounds served as comparison samples. The test procedure for standard nitrogen is described in detail in [2,3]. The phosphorus content in the plants is 0.1-0.6% [6]. For this reason, the comparison samples were prepared from compounds in which the phosphorus mass falls approximately within these limits. The samples were irradiated in identical fast neutron fluxes. The time regimes of irradiation of the samples and measurement of their induced activity were also identical. Figure 1 displays the dependence of the variation of the 28 Al activity (in this case the number of counts recordedthe area of the photo-peak of the γ-ray 1778.8 keV line) versus the phosphorus mass in the comparison samples. This dependence is rectilinear within the limits of the chosen phosphorus concentration range, whence it follows that the method can be used to determine correctly the content of the element in biological materials. It is evident that for some samples the deviation of the data from rectilinearity is substantial (>30%). Such a deviation could be due to possible mass losses as a result of long-term storage of chemical compounds or sorption of water from air. For this reason, compounds which fell on the rectilinear sections of the plot were used as the comparison samples. Thus, the approach for developing a method...