Determination of Bromine Stable Isotopes Using Continuous-Flow Isotope Ratio Mass Spectrometry

Abstract

A new methodology for bromine stable isotope determination by continuous-flow isotope ratio mass spectrometry (CF-IRMS) was developed. The technique was tested on inorganic samples. Inorganic bromide was precipitated in the form of silver bromide by using silver nitrate in a standard methodology. Bromine stable isotope analysis was carried out on methyl bromide (CH3Br) after converting silver bromide to methyl bromide by reacting it with methyl iodide (CH3I). The system used in this study is an IsoPrime IRMS, with analytical capabilities of both dual-inlet and continuous-flow modes coupled with an Agilent 6890 GC equipped with a CTC Analytics CombiPAL autosampler. This new technique measures samples as small as 0.2 mg of AgBr (1 micromol of Br-). The bromine stable isotope analysis using continuous flow technology showed excellent precision and accuracy. The internal precision using pure methyl bromide gas is better than +/-0.03 per thousand (+/-SD); the external precision using seawater standard is better than +/-0.06 per thousand (+/-SD) for n = 12. Moreover, the sample analysis time is 16 min, as compared to 75 min needed in previous techniques. This allows for 50 samples to be analyzed in 1 day, as compared to 8 samples using the conventional techniques. A series of natural saline formation waters and brines from sedimentary and crystalline rock environments was measured by this new methodology to test the potential natural range of delta81Br. The bromine isotopic composition of the samples ranged from 0.00 to +1.80 per thousand relative to standard mean ocean bromide (SMOB). Initial trends and distinctive isotopic difference were noticed between crystalline shield brines and sedimentary formation brines.

Atomic weights of the elements 2011 (IUPAC Technical Report)

“…2). The standard atomic weight was determined by combining (1) the best calibrated isotope-ratio measurement of bromine in SRM977 NaBr isotopic reference material [25,26], formerly known as NBS106 [25], (2) the relative isotope-ratio difference between SRM977 and bromide in ocean water [27], and (3) the relative isotope-ratio differences between other materials and ocean-water bromide [2,28]. Bromide in ocean water is isotopically homogeneous and serves as the international measurement standard for bromine [26], standard mean ocean bromide (SMOB).…”

“…The standard atomic weight was determined by combining (1) the best calibrated isotope-ratio measurement of bromine in SRM977 NaBr isotopic reference material [25,26], formerly known as NBS106 [25], (2) the relative isotope-ratio difference between SRM977 and bromide in ocean water [27], and (3) the relative isotope-ratio differences between other materials and ocean-water bromide [2,28]. Bromide in ocean water is isotopically homogeneous and serves as the international measurement standard for bromine [26], standard mean ocean bromide (SMOB). Bromine relative isotope-ratio differences, also called bromine isotope delta values, have been reported with the symbol δ 81 Br [26][27][28] and are defined by the relation [20] where N( 81 Br) P and N( 79 Br) P are the numbers of atoms of the two isotopes 81 Br and 79 Br in material P and equivalent parameters follow for bromine in SMOB.…”

“…Bromide in ocean water is isotopically homogeneous and serves as the international measurement standard for bromine [26], standard mean ocean bromide (SMOB). Bromine relative isotope-ratio differences, also called bromine isotope delta values, have been reported with the symbol δ 81 Br [26][27][28] and are defined by the relation [20] where N( 81 Br) P and N( 79 Br) P are the numbers of atoms of the two isotopes 81 Br and 79 Br in material P and equivalent parameters follow for bromine in SMOB. The minimum and maximum δ 81 Br values of saline waters and salt deposits (Fig.…”

“…Their measurement has been accepted as a "best measurement" of isotopic abundance. The isotope ratios recommended for acceptance as a Magnesium relative isotope-ratio differences, also called magnesium isotope-delta values, have been reported with the symbol δ 26 Mg [31][32][33][34][35][36][37][38] and are defined by the relation [28] where N( 26 Mg) P and N( 24 Mg) P are the numbers of atoms of the two isotopes 26 Mg and 24 Mg in material P and equivalent parameters follow for magnesium in the standard (Std). Many of the δ 26 Mg measurements reported herein were made using DSM3 as the standard.…”

Assessment of international reference materials for isotope-ratio analysis (IUPAC Technical Report)

“…Br SMOB value of −0.64 ‰ for NIST SRM 977 [220]. This will become necessary as instrumentation improves and authors report variations in bromine isotopic composition of seawater bromide with geographic location.…”