Extraction and Analysis of Available Boron Isotopes in Soil Using Multicollector Inductively Coupled Plasma Mass Spectrometry.

As a result of the important roles of boron (B) in the growth of plants, the uptake of B by plants is dependent upon the existing form and content of available B in soil, which can bring about the local cycle of B isotope equilibrium. A method using water-heating extraction combined with three-step ion-exchange chromatography was developed for the extraction and isotopic analysis of available B in soil. The extraction efficiency and fractionation of B isotopic composition in the procedure were investigated. The results showed that, in the upper layers of soils, the change of δ11B values was opposite that of the mass concentration and a similar variation between δ11B and content occurred in the lower layers. The isotope of available B in soil can create a featured isotopic signature to further understand the geochemical details related to the soil properties and molecular mechanism of B uptake in plants.

Differentiation analysis of boron isotopic fractionation in different forms within plant organ samples.

As a critical micronutrient, boron (B) plays an important role in plant growth and embryonic development. To further understand the effects of B uptake, transportation and isotopic fractionation, the contents and isotopic compositions of hydro-soluble B in the sap and structural B fixed in the cell within individual plant tissues were investigated. The B isotope ratio was determined by multi-collector inductively coupled plasma mass spectrometry. The δ11B values in hydro-soluble and structural B in the investigated plant samples ranged from -1.57‰ to +11.30‰ and from +6.57‰ to +16.64‰, respectively. Different fractionation factors of the B isotopes, in the range of 0.9954-1.0150, were observed in these samples, indicating that in most plant tissues, the heavy isotope (11B) was preferentially enriched in structural B, which was fixed into the cell. However, there was a reversal in the fractionation of B isotopic compositions in the fruit samples compared with the other plant tissue samples. It is more powerful to examine the molecular mechanisms of B transport, uptake and utilization than the use of limited plant organ samples containing a mixture of hydro-soluble and structural B within different intra-plant compartments and in inter-plant interactions. These isotopic shifts, which may be used as important isotopic indicators, contribute to the surface processes interactions in the plant-soil system and the knowledge of the molecular mechanisms of B in the uptake and absorption by different plant species in nature.

Separation and Analysis of Boron Isotope in High Plant by Thermal Ionization Mass Spectrometry.

Knowledge of boron and its isotope in plants is useful to better understand the transposition and translocation of boron within plant, the geochemical behavior in the interface between soil and plant, and the biogeochemical cycle of boron. It is critical to develop a useful method to separate boron from the plant for the geochemical application of boron and its isotope. A method was developed for the extraction of boron in plant sample, whose isotope was determined by thermal ionization mass spectrometry. The results indicated that this method of dry ashing coupled with two-step ion-exchange chromatography is powerful for the separation of boron in plant sample with large amounts of organic matters completely. The ratios of boron isotope composition in those plant tissue samples ranged from -19.45‰ to +28.13‰ (total range: 47.58‰) with a mean value of 2.61 ± 11.76‰ SD. The stem and root isotopic compositions were lower than those in flower and leaf. The molecular mechanism of boron isotope may be responsible for the observed variation of boron isotopic composition and are considered as a useful tool for the better understanding of boron cycling process in the environment and for the signature of living systems.

Major factors affecting the isotopic measurement of chlorine based on the Cs2Cl+ ion by thermal ionization mass spectrometry.

The factors that affect isotopic measurement of chlorine based on Cs2Cl+ ion by thermal ionization mass spectrometry were studied. Graphite is essential for the emission of Cs2Cl+ ion from CsCl. No Cs2Cl+ ions are detected in the absence of graphite on the filament. The emission of Cs2Cl+ ion and the measured 37Cl/35Cl ratio were affected by different varieties of graphite, the pH value of the sample solution, and impurities in the solution. High-precision isotopic measurement of chlorine based on Cs2Cl+ ion is achieved only by using graphite with a perfect crystal structure. The measured 37Cl/35Cl ratios were much higher, and even the emission of Cs2Cl+ ion becomes impossible when pH values of the sample solution were higher than 6, corresponding to the presence of excess Cs. The measured 37Cl/35Cl ratios were higher when SO4(2-) and NO3- anions were present. The results show that the measured 37Cl/35Cl ratios are weakly related to the amount of chlorine on filament in a range from 1 to 500 microg.