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Mass spectrometric methods (MC-ICP-MS and TIMS) are without doubt the working horse of stable isotope analysis. However, drawbacks of these methods include the high costs for instruments and their operation, experienced operators and elaborate chromatographic sample preparation which are time consuming.
We propose a lower-cost and faster optical alternative for the analysis of isotope ratios of selected elements: high-resolution continuum source molecular absorption spectrometry (HR-CS-MAS). Stable isotope amount compositions of boron (B) and magnesium (Mg) were determined based on the absorption spectra of in-situ generated mono-hydrides and halide (MH and MX) using graphite furnace HR-CS-MAS. The use of a modular simultaneous echelle spectrograph (MOSES) helps to find the maximal isotope shift in the diatomic molecular spectra produced in a graphite furnace by using isotopic spike solutions. Isotopes of boron (10B and 11B) were studied via their hydrides for the electronic transition X 1Σ+ → A 1Π. The spectrum of a given sample is a linear combination of the 10BH molecule and its isotopologue 11BH. Therefore, the isotopic composition of samples can be calculated by a partial least square regression (PLS). For this, a spectral library was built by using samples and spikes with known isotope composition. Boron isotope ratios measured by HR-CS-MAS are identical with those measured by mass spectrometric methods at the 0.15 ‰ level. Similar results were obtained for a multiple isotope system like Mg (24Mg, 25Mg, and 26Mg), where isotope shifts of their isotopologues can be resolved in the MgF molecule for the electronic transition X 2Σ → A 2 Πi. The extension of this methodology to other elements like Li, Ca, Cu, and Sr is discussed.
Boron isotope amount ratios n(10B)/n(11B) have been determined by monitoring the absorption spectrum of boron monohydride (BH) in a graphite furnace using high-resolution continuum source molecular absorption spectrometry (HR-CS-MAS). Bands (0→0) and (1→1) for the electronic transition X1Σ+ → A1Π were evaluated around wavelengths 433.1 nm and 437.1 nm respectively. Clean and free of memory effect molecular spectra of BH were recorded. In order to eliminate the memory effect of boron, a combination of 2% (v/v) hydrogen gas in argon and 1% trifluoromethane in argon, an acid solution of calcium chloride and mannitol as chemical modifiers was used. Partial least square regression (PLS) for analysis of samples and reference materials were applied. For this, a spectral library with different isotopes ratios for PLS regression was built. Results obtained around the 433.1 nm and 437.1 nm spectral regions are metrologically compatible with those reported by mass spectrometric methods. Moreover, for the evaluated region of 437 nm, an accuracy of 0.15‰ is obtained as the average deviation from the isotope reference materials. Expanded uncertainties with a coverage factor of k = 2 range between 0.15 and 0.44‰. This accuracy and precision are compatible with those obtained by mass spectrometry for boron isotope ratio measurements.
Boron presents two stable isotopes, 10B and 11B and due to their relatively large mass difference (~ 10%) isotope fractionation leads to considerable isotope amount ratio variations n(10B)/n(11B) in natural occurrence. These have been used as a proof of provenance of mineral and biological samples, to estimate a contamination source and to the determination of geological processes by erosion or subduction. Additionally, boron is employed in the nuclear industry due to the capability of its isotope 10B to thermal-neutron capture and therefore 10B enriched boric acid solutions are used in the cooling system of thermonuclear facilities and in the alloying of steel and carbides for protective shielding. Usually, isotope ratio variations are determined by mass spectroscopic methods.
Here an alternative faster and low cost method for isotope ratio determination is proposed: high-resolution continuum source molecular absorption spectrometry (HR-CS-MAS). Boron isotope amount ratios have been determined by monitoring the absorption spectrum of boron monohydride (BH) in graphite furnace HR-CS-MAS. Bands (0→0) and (1→1) for the electronic transition X1Σ+ → A1Π were evaluated around wavelengths 433.1 nm and 437.1 nm respectively. Partial least square regression (PLS) for analysis of samples and reference materials were applied. For this, a spectral library with different isotopes ratios for PLS regression was built. Results obtained around the 433.1 nm and 437.1 nm spectral regions are metrologically compatible with those reported by mass spectrometric methods. Moreover, a precision and accuracy of the method of ± 0.5 ‰ for the evaluated spectral region around 437.1 nm is reported here. This accuracy and precision is comparable with those obtained by thermal ionization mass spectrometry (TIMS) and multiple collector inductively coupled plasma mass spectrometry (MC-ICP-MS) for boron isotope ratio measurements.
Boron presents two stable isotopes, 10B and 11B and due to their relatively large mass difference (~ 10%) isotope fractionation leads to considerable isotope amount ratio variations n(10B)/n(11B) in natural occurrence. These have been used as a proof of provenance of mineral and biological samples, to estimate a contamination source and to the determination of geological processes by erosion or subduction. Additionally, boron is employed in the nuclear industry due to the capability of its isotope 10B to thermal-neutron capture and therefore 10B enriched boric acid solutions are used in the cooling system of thermonuclear facilities and in the alloying of steel and carbides for protective shielding. Usually, isotope ratio variations are determined by mass spectroscopic methods.
Here an alternative faster and low cost method for isotope ratio determination is proposed: high-resolution continuum source molecular absorption spectrometry (HR-CS-MAS). Boron isotope amount ratios have been determined by monitoring the absorption spectrum of boron monohydride (BH) in graphite furnace HR-CS-MAS. Bands (0→0) and (1→1) for the electronic transition X1Σ+ → A1Π were evaluated around wavelengths 433.1 nm and 437.1 nm respectively. Partial least square regression (PLS) for analysis of samples and reference materials were applied. For this, a spectral library with different isotopes ratios for PLS regression was built. Results obtained around the 433.1 nm and 437.1 nm spectral regions are metrologically compatible with those reported by mass spectrometric methods. Moreover, a precision and accuracy of the method of ± 0.5 ‰ for the evaluated spectral region around 437.1 nm is reported here. This accuracy and precision is comparable with those obtained by thermal ionization mass spectrometry (TIMS) and multiple collector inductively coupled plasma mass spectrometry (MC-ICP-MS) for boron isotope ratio measurements.