Determination of Organic Selenium Compounds in Crops by Liquid Chromatography-Quadrupole/Electrostatic Field Orbitrap High-resolution Mass Spectrometry

Abstract

BACKGROUND As more attention is paid to selenium-rich products, the research on the determination of selenium content in crops has become more and more significant. However, existing methods for determining organic selenium has interferences of the matrix effect and polyatomic ion, which affect the accuracy of the measurement. OBJECTIVES To establish a rapid method to determine selenium species pf organic selenium in agricultural products by liquid chromatography-quadrupole/electrostatic field orbitrap high-resolution mass spectrometry (LC-Q Exactive Orbitrap MS). METHODS The selenium species were extracted using an ultrasonic extraction system with a mixture of protease XIV. The separation was carried out on a Waters Symmetry RP18 column by gradient elution with water and acetonitrile as mobile phases. The selenomethionine, selenocystine and methylselenocysteine were simultaneously analyzed in switching positive and negative modes. The quantitative and qualitative analyses were carried out by high-resolution mass spectrometry with electrospray ionization (ESI) source in negative ion acquisition mode under Full MS/dd-MS2 mode. RESULTS Under the optimal conditions, good linearity was obtained in the respective concentration ranges. The limits of detection for three compounds were in the range of 1.0-4.7μg/kg. The recoveries ranged from 76.4% to 116.0% with relative standard deviations less than 6.5%. CONCLUSIONS Compared with existing methods, this method has a wider linear range and is suitable for the analysis of a variety of grain and vegetable samples. The established method has been applied to the determination of the edible part of a variety of crops in Heilongjiang, which is the main grain production area in China. The results show that selenomethionine is the main ingredient in cereals, and methylselenocysteine is the main ingredient in vegetables, and that the organic selenium content of crops in this area is at a low level. Therefore, selenium supplementation is urgently needed.

Keywords

• organic selenium
• crop
• quadrupole/obitrap high-resolution mass spectrometry
• ultrasonic enzyme extraction