Method for determining boron isotopic composition by PTIMS—static double collection

#The following pertains to the field of mass-spectrometric technique and relates to a method for determining boron isotopic composition, particularly to a method for accurately determining boron isotopic composition by simultaneously collecting 133Cs211B16O2+ ion (m/e=309) and 133Cs210B16O2+ ion (m/e=308) using two Faraday Cups.

#In the nature, boron isotope (δ11B) varies in a large range and the isotopic composition of boron differs significantly in different environmental and geological process. For this reason, boron isotopic composition is widely applied in the fields of crust-mantle evolution, mineral deposits, hydrochemistry, environmental geochemistry, marine environment and paleoenvironment. With the improvement in the determination methodology and analyzing accuracy, boron isotope as a sensitive and reliable indicator has been employed in various scientific fields, paleooceanography, paleoenvironment, environmental monitoring, pollution sources identification etc. Boron isotope is the most promising tools in the research field of geochemistry in the recent two decades.

#Due to the remarkable indicative significance of boron isotopic composition for the changes of environmental and geological processes, the purification-separation procedure and the analytical methods for boron isotopes have been significantly developed and improved to deal with natural samples with rich organic matter, complex matrix and low boron content.

#FIG. 1 is a schematic diagram for the principle of the method for determining boron isotopic composition by TIMS-static double collection;

#FIG. 2 is a schematic diagram of the method for determining boron isotopic composition by static double collection (PTIMS-Cs2BO2+-Static);

#FIG. 3 is a peak scan diagram of the method for determining boron isotopic composition by PTIMS-Cs2BO2+-Static;

#According to the method of the present invention, the boron isotopic composition in NIST 951 boron isotope standard materials is determined on TIMS (Triton Ti) by static double collection.

#As shown in FIG. 2, the method for determining boron isotopic composition by static double collection includes the following steps: (1) Selecting cup H3 and cup H4 in the Faraday collector to collect m/e309 and m/e308 boron isotope ions, respectively, and setting cup distance as the minimum value available in the instrument; (2) Adjusting Focus Quad and Dispersion Quad parameters in Zoom Optics of the ion source, and optimizing the parameters by the iterative method till the peaks of 133Cs211B16O2+(m/e=309) ion and 133Cs210B16O2+(m/e=308) ion are fully collected by two parallel Faraday cups, Cup H4 and Cup H3, and both two ion peaks are perfect flat peaks without any tailing peak and prepeak and fully superposed. (3) Determining the collection mass number of cup C in the Faraday collector till instrument baseline has no noise, peak 309 and peak 308 are fully collected and the center positions of the peaks are right; (4) Performing peak scanning, and data acquisition and data evaluation.

#In the foregoing step (2), parameters are optimized by the iterative method. Its flow chart is shown in FIG. 4 and includes the following steps: (1) Setting Focus Quad (x1) and Dispersion Quad (x2) parameters as default value (0, 0); (2) Setting x1 as default value (0), and adjusting x2 within the range of instrument parameter values to x2+iΔx2, wherein i is a natural number and Δx2 is a 50-unit value; checking the peak shape and peak superposition of the two ions, and determining an optimal value x2-1 from the foregoing x2 parameter values; (3) Setting x1 as minimum value (−30), and adjusting x2 within the range of instrument parameter values to x2+iΔx2, wherein i is a natural number and Δx2 is a 50-unit value; checking the peak shape and peak superposition of the two ions, and determining an optimal value x2-2 from the foregoing x2 parameter values; (4) Setting x1 as maximum value (+30), and adjusting x2 within the range of instrument parameter values to x2+iΔx2, wherein i is a natural number and Δx2 is a 50-unit value; checking the peak shape and peak superposition of the two ions, and determining an optimal value x2-3 from the foregoing x2 parameter values; (5) Comparing the peak shape and peak superposition of the two ions under the foregoing three parameter conditions of (0,x2-1), (x1min, x2-2) and (x1max, x2-3), and determining the combination of the two parameters; (6) Setting Focus Quad (x1) and Dispersion Quad (x2) parameters as the parameter values determined in step (5), adjusting the two parameters by a step of 2˜5 units, and checking the peak shape and peak superposition of the two ions till the optimal parameter combination is found.