Online Determination of Boron Isotope Ratio in Boron Trifluoride by Infrared Spectroscopy
Online Determination of Boron Isotope Ratio in Boron Trifluoride by Infrared Spectroscopy
Zhang, Weijiang;Tang, Yin;Xu, Jiao
2018-12-06 00:00:00
applied sciences Article Online Determination of Boron Isotope Ratio in Boron Trifluoride by Infrared Spectroscopy Weijiang Zhang, Yin Tang and Jiao Xu * School of Chemical Engineering & Technology, Tianjin University, Tianjin 300072, China; wjzh@tju.edu.cn (W.Z.); tangyin0001@163.com (Y.T.) * Correspondence: xujiaohh@163.com; Tel.: +86-022-27402028 Received: 17 September 2018; Accepted: 3 December 2018; Published: 6 December 2018 Abstract: Enriched boron-10 and its related compounds have great application prospects, especially in the nuclear industry. The chemical exchange rectification method is one of the most important 10 11 ways to separate the B and B isotope. However, a real-time monitoring method is needed because this separation process is difficult to characterize. Infrared spectroscopy was applied in the separation device to realize the online determination of the boron isotope ratio in boron trifluoride (BF ). The possibility of determining the isotope ratio via the 2 band was explored. A correction factor was introduced to eliminate the difference between the ratio of peak areas and the true value of the boron isotope ratio. It was experimentally found that the influences of pressure and temperature could be ignored. The results showed that the infrared method has enough precision and stability for real-time, in situ determination of the boron isotope ratio. The instability point of the isotope ratio can be detected with the assistance of the online determination method and provides a reference for the production of boron isotope. Keywords: isotope; boron; infrared spectroscopy; online determination 1. Introduction Boron in naturally occurring compounds is composed of two isotopes, one of mass 10 and the other of mass 11. B at a relative abundance of 18.8%, has an unusually large cross section for the capture of low energy neutrons [1]. Therefore, in high concentrations, it is particularly valuable for neutron shielding [2,3]. The design and realization of the isotopes separation processes of boron began as early as the Second World War. A large industrial plant with a productivity of up to 300 kg per year of elemental boron with 95% B content was put into operation in 1944 [4]. At present, the most common methods for the separation of boron isotopes include the distillation method [5], chemical exchange rectification [6,7], ion exchange [8,9], and laser isotope separation [10,11], among others. Chemical 10 11 exchange rectification is the simplest and most productive method for the separation of B and B isotopes at concentrations of 95% and over [12]. Figure 1 shows the principal scheme of the apparatus 10 11 for the separation of boron isotopes using the chemical exchange rectification method. B and B can be extracted from the separation and the complex parts of the apparatus, respectively [13]. The internal variations in this separation process tend to be very complex, making it necessary to frequently track any changes in the isotope ratio obtained. Appl. Sci. 2018, 8, 2509; doi:10.3390/app8122509 www.mdpi.com/journal/applsci Appl. Sci. 2018, 8, 2509 2 of 10 Appl. Sci. 2018, 8, x FOR PEER REVIEW 2 of 10 Figure 1. Principal scheme of the apparatus for the separation of boron isotopes using the chemical Figure 1. Principal scheme of the apparatus for the separation of boron isotopes using the chemical exchange rectification method. exchange rectification method. The mass spectrometry (MS) method is one of the most important ways of analyzing the boron The mass spectrometry (MS) method is one of the most important ways of analyzing the boron isotope ratio. Analysis comes from the peaks with mass-to-charge ratios (m/e ) equal to 10 and isotope ratio. Analysis comes from the peaks with mass-to-charge ratios (m/e ) equal to 10 and 11 11 [14]. Porteous [15] et al. determined the isotopic ratio of boron in samples of groundwater by [14]. Porteous [15] et al. determined the isotopic ratio of boron in samples of groundwater by inductively coupled plasma mass spectrometry (ICP-MS) to evaluate possible levels of boron pollution inductively coupled plasma mass spectrometry (ICP-MS) to evaluate possible levels of boron from anthropogenic inputs into natural aqueous systems. The matrix effect was reduced by the pollution from anthropogenic inputs into natural aqueous systems. The matrix effect was reduced by preconcentration and ion-exchange of the sample. Compared with the standard material, the precision the preconcentration and ion-exchange of the sample. Compared with the standard material, the of the method achieved 0.13% (natural abundance). However, the sampling and preparation for precision of the method achieved 0.13% (natural abundance). However, the sampling and this method are very complex, so it is difficult to achieve real-time tracking for this process during preparation for this method are very complex, so it is difficult to achieve real-time tracking for this actual production. Infrared spectroscopy (IR) is a traditional technology that has been used for on-line process during actual production. Infrared spectroscopy (IR) is a traditional technology that has been detection. For instance, Hepburn [16] et al. established a method using online FTIR spectroscopy to used for on-line detection. For instance, Hepburn [16] et al. established a method using online FTIR determine the siloxane content in bio-gas. Both the precision and the detection limit for siloxane were spectroscopy to determine the siloxane content in bio-gas. Both the precision and the detection limit satisfactory when using this online FTIR technology. for siloxane were satisfactory when using this online FTIR technology. The vibrational spectra of BF has been studied by Herrebout [17,18] et al.and Sluyts [19] et al. The vibrational spectra of BF3 has been studied by Herrebout [17,18] et al.and Sluyts [19] et al.. The results were obtained by dissolving BF in liquid Argon. The infrared absorption bands changed The results were obtained by dissolving BF3 in liquid Argon. The infrared absorption bands changed depending on the change in the boron isotope ratio. Thus, the bands could be used to measure depending on the change in the boron isotope ratio. Thus, the bands could be used to measure the the boron isotopic ratio in BF . Despite having a good signal-noise ratio in the region, such a 3 3 boron isotopic ratio in BF3. Despite having a good signal-noise ratio in the ν3 region, such a high high dilution factor was difficult to realize via changing optical paths in the industrialized process. dilution factor was difficult to realize via changing optical paths in the industrialized process. Although the 2 is a weak IR absorption band for BF , the difference in absorbance peaks was about 3 3 Although the 2ν3 is a weak IR absorption band for BF3, the difference in absorbance peaks was about 1 10 11 112 cm between BF and BF at the 2 bands, which means that there is good resolution for this −1 10 3 11 3 3 112 cm between BF3 and BF3 at the 2ν3 bands, which means that there is good resolution for this measurement. In this paper, the IR method was applied to determine the boron isotope ratio based on measurement. In this paper, the IR method was applied to determine the boron isotope ratio based calculating the BF infrared spectrum at 2 . Further, an infrared spectrophotometer was installed in a 3 3 on calculating the BF3 infrared spectrum at 2ν3. Further, an infrared spectrophotometer was installed boron separation device to monitor the separation process online. in a boron separation device to monitor the separation process online. 2. Experimental Method 2. Experimental Method 2.1. Instruments and Reagents 2.1. Instruments and Reagents The BF was purchased from LiuFang Gas Corporation (Dalian, LN , China) with a stated purity The BF3 was purchased from LiuFang Gas Corporation (Dalian, LN , China) with a stated purity of 99.95%. Small amounts of SiF were present as an impurity in the BF but these were ignored 4 3 of 99.95%. Small amounts of SiF4 were present as an impurity in the BF3 but these were ignored in this 10 11 in this study. NIST SRM 951a isotopic reference material of boric acid ( B/ B is 0.2473 0.0002) 10 11 study. NIST SRM 951a isotopic reference material of boric acid ( B/ B is 0.2473 ± 0.0002) was was purchased from the National Institute of Standards and Technology (Gaithersburg, MD, USA). purchased from the National Institute of Standards and Technology (Gaithersburg, MD, USA). A gas A gas cell (TianGuang Optical Instrument Co. Ltd., Tianjin, TJ, China) was equipped with the cell (TianGuang Optical Instrument Co. Ltd., Tianjin, TJ, China) was equipped with the CaF2 CaF windows ('40 5 mm). The optical path length of this gas cell was 100 mm. An infrared windows (φ40 × 5 mm). The optical path length of this gas cell was 100 mm. An infrared spectrophotometer (Xintian Optical Analytical Instrument Co. Ltd., Tianjin, TJ, China) with an spectrophotometer (Xintian Optical Analytical Instrument Co. Ltd., Tianjin, TJ, China) with an 10 11 accuracy of transmittance lower than or equal to 0.2%T. (TJ270-30A, Tianjin, China). The B/ B 10 11 accuracy of transmittance lower than or equal to ±0.2%T. (TJ270-30A, Tianjin, China). The B/ B ratio ratio was measured as a reference by an ICP-MS X7 (Thermo Electron Corporation, Waltham, MA, was measured as a reference by an ICP-MS X7 (Thermo Electron Corporation, Waltham, MA, USA) USA) series mass spectrometer manufactured by the Thermo Electron Corporation. series mass spectrometer manufactured by the Thermo Electron Corporation. 2.2. Procedure for Offline Measurement 2.2. Procedure for Offline Measurement The procedure for the offline experiment is shown in Figure 2. BF gas samples with different The procedure for the offline experiment is shown in Figure 2. BF3 gas samples with different amounts of boron were collected from the chemical exchange rectification device or feed gas cylinder. amounts of boron were collected from the chemical exchange rectification device or feed gas cylinder. The outlet of the gas cell was linked to a buffer bottle and an absorber bottle filled with sodium The outlet of the gas cell was linked to a buffer bottle and an absorber bottle filled with sodium hydroxide solution to prevent BF3 gas from escaping. BF3 was filling into the gas cell, which was replaced by N2 to remove the air (especially the water in air) inside of the gas cell beforehand. This Appl. Sci. 2018, 8, 2509 3 of 10 Appl. Sci. 2018, 8, x FOR PEER REVIEW 3 of 10 Appl. Sci. 2018, 8, x FOR PEER REVIEW 3 of 10 hydroxide solution to prevent BF gas from escaping. BF was filling into the gas cell, which was 3 3 was allowed to continue for at least 1–2 min, and the operation was stopped when the inside of the replaced by N to remove the air (especially the water in air) inside of the gas cell beforehand. This was allowed to continue for at least 1–2 min, and the operation was stopped when the inside of the ga was s ce allowed ll was full to continue y replacefor d by atB least F3. The 1–2v min, alves and of th the e ga operation s cylindwas er an stopped d gas cewhen ll were the clo inside sed inof turn the f gas or gas cell was fully replaced by BF3. The valves of the gas cylinder and gas cell were closed in turn for about 10 min before use. The infrared spectra were acquired from scanning the contents of the gas cell was fully replaced by BF . The valves of the gas cylinder and gas cell were closed in turn for about about 10 min before use. The infrared spectra were acquired from scanning the contents of the gas −1 −1 ce 10 llmin at a befor scann ein use. g spe The ed infrar of 1 cm ed spectra /s and awer scan e n acquir ing raed nge from of 40 scanning 00 to 400the cmcontents . of the gas cell at a −1 −1 cell at a scanning speed of 1 cm /s and a scanning range of 4000 to 400 cm . 1 1 scanning speed of 1 cm /s and a scanning range of 4000 to 400 cm . Figure 2. Diagram of offline experiment. Figure 2. Diagram of offline experiment. Figure 2. Diagram of offline experiment. 2.3. Procedure for Online Measurement 2.3. Procedure for Online Measurement 2.3. Procedure for Online Measurement The online isotopic ratio determination system was set on the device used for boron isotope The online isotopic ratio determination system was set on the device used for boron isotope The online isotopic ratio determination system was set on the device used for boron isotope separation, as shown in Figure 3. The BF3 gas was extracted from a pipe where the gas flow and the separation, as shown in Figure 3. The BF gas was extracted from a pipe where the gas flow and the separation, as shown in Figure 3. The BF3 gas was extracted from a pipe where the gas flow and the pipeline can be controlled by valve. The BF3 flowed through a gas cell that was equipped with two pipeline can be controlled by valve. The BF3 flowed through a gas cell that was equipped with two pipeline can be controlled by valve. The BF3 flowed through a gas cell that was equipped with two CaF2 windows because the weatherability and corrosion resistance of CaF2 are superior to KBr under CaF windows because the weatherability and corrosion resistance of CaF are superior to KBr under 2 2 CaF2 windows because the weatherability and corrosion resistance of CaF2 are superior to KBr under atmospheric and BF3 conditions. The whole gas cell was fitted to the IR spectrophotometer by which atmospheric and BF conditions. The whole gas cell was fitted to the IR spectrophotometer by which atmospheric and BF3 conditions. The whole gas cell was fitted to the IR spectrophotometer by which the infrared spectrogram could be obtained directly. the infrared spectrogram could be obtained directly. the infrared spectrogram could be obtained directly. Figure 3. Diagram of boron isotope ratio online determination system. Figure 3. Diagram of boron isotope ratio online determination system. Figure 3. Diagram of boron isotope ratio online determination system. 2.4. Testing method of ICP-MS 2.4. Testing method of ICP-MS 2.4. Testing method of ICP-MS The ICP-MS was used to determine the isotope ratio as a reference. The BF gas was absorbed by The ICP-MS was used to determine the isotope ratio as a reference. The BF3 gas was absorbed The ICP-MS was used to determine the isotope ratio as a reference. The BF3 gas was absorbed a small amount of ethanol and diluted to samples containing 0.1 g/mL of boron with ultrapure water. by a small amount of ethanol and diluted to samples containing 0.1 μg/mL of boron with ultrapure by a small amount of ethanol and diluted to samples containing 0.1 μg/mL of boron with ultrapure The operation method and experimental conditions of the ICP-MS experiments were similar to the water. The operation method and experimental conditions of the ICP-MS experiments were similar water. The operation method and experimental conditions of the ICP-MS experiments were similar method found in [15]. After each test, the system pipeline was alternately washed three times with to the method found in [15]. After each test, the system pipeline was alternately washed three times to the method found in [15]. After each test, the system pipeline was alternately washed three times 2% HNO and 0.1 mol/L ammonia water solution to reduce any errors due to memory effect. The with 2% HNO3 and 0.1 mol/L ammonia water solution to reduce any errors due to memory effect. 10 11 with 2% HNO3 and 0.1 mol/L ammonia water solution to reduce any errors due to memory effect. specific parameters used for the ICP-MS experiments to determine the boron isotope ratios ( B/ B) The specific parameters used for the ICP-MS experiments to determine the boron isotope ratios The specific parameters used for the ICP-MS experiments to determine the boron isotope ratios ar 10 e 11 shown in Table 1. ( B/ B) are shown in Table 1. 10 11 ( B/ B) are shown in Table 1. Appl. Sci. 2018, 8, x FOR PEER REVIEW 4 of 10 Table 1. Experimental conditions and parameters of inductively coupled plasma mass spectrometry Appl. Sci. 2018, 8, 2509 4 of 10 (ICP-MS). Counts per Second (CPS); Atomic Mass Unit (AMU). Item Parameter Item Parameter Table 1. Experimental conditions and parameters of inductively coupled plasma mass spectrometry −1 6 Microconcentric Sensitivity/s 1.759 × 10 Nebulizer (ICP-MS). Counts per Second (CPS); Atomic Mass Unit (AMU). −1 −1 Nebulizer (μg·L ) CPS Spray chamber Item Parameter Item Parameter 3 Scanning mode Peak-jump temperature/°C Microconcentric Sensitivity/s −1 Nebulizer 1.759 10 CPS Nebulizer gas flow/L· min 0.93 Dwell time/ms 10 1 1 Nebulizer (gL ) −1 Auxiliary gas flow/L· min 0.9 Acquisition degree 10 Spray chamber temperature/ C 3 Scanning mode Peak-jump −1 Nebulizer Cool gas f gas lo flow/L w/L· mmin in 0.93 10 Dwell Acqui time/ sition ms time/s 10 20 Auxiliary gas flow/Lmin 0.9 Acquisition degree 10 Channels per Plasma power/W 1250 3 10 Acquisition time/s 20 Cool gas flow/Lmin AMU Plasma power/W 1250 Channels per AMU 3 Resolution Standard Runs/replicates 3 Resolution Standard Runs/replicates 3 −1 Sample uptake rate/mL· min 1 Sample depth/mm 104 Sample uptake rate/mLmin 1 Sample depth/mm 104 Ionization lens parameters L1 3.8; L2 31.8; L3 189.8 - - Ionization lens parameters L1 3.8; L2 31.8; L3 189.8 - - 3. Results and Discussion 3. Results and Discussion 3.1. Calculation and Correction of the Isotope Ratio 3.1. Calculation and Correction of the Isotope Ratio Fi Figur gure e 4 4 shows shows the the comparison comparison of of the the IR IR spectr spectro ograms grams in in the the 2 2 ν3 r re egions gions between between natural natural abundance BF and enriched BF . The peaks at these regions are more complex than peaks in the abundance BF3 and enriched BF3. The peaks at these regions are more complex than peaks in the ν3 3 3 3 re regions. gions. Fo Fortunately rtunately, , th the e peak peak changes changes h had ad no no significant significant overlap overlap of of the the two two bands. bands. B By y co contrast, ntrast, th the e 10 1 10 −1 absorption band of 2 for BF (the range being about 3270–3170 cm ) was significantly reduced, absorption band of 2ν3 for BF3 (the range being about 3270–3170 cm ) was significantly reduced, 3 3 which which pr pr oved ovedthat thathis t thiabsorption s absorptio band n bais nd influenced is influence byd the by amount the am of oun BF t ofthat BF is 3 pr thesent. at is pr Inese contrast, nt. In 11 1 11 −1 the absorption peaks in the 2 band for BF (the range being about 3170–3070 cm ) varied regularly contrast, the absorption peaks in the 2ν3 band for BF3 (the range being about 3170–3070 cm ) varied 3 3 with regulchanging arly with concentrations changing conceof ntrati BF on.s Thus, of BF it 3.was Thus, feasible it was to fea calculate sible to the calcul isotope ate the ratio isoto based pe rati on o comparing the peak areas of these two absorption bands. based on comparing the peak areas of these two absorption bands. Figure 4. Comparison of the IR spectrograms. (A) Natural abundance BF ; (B) Enriched 11 BF . Figure 4. Comparison of the IR spectrograms. (A) Natural abundance BF 33; (B) Enriched BF3 3. The NIST SRM 951a boric acid standard sample was used to investigate the accuracy of the The NIST SRM 951a boric acid standard sample was used to investigate the accuracy of the ICP- ICP-MS. Before testing by ICP-MS, the standard boric acid sample was dissolved and diluted to a MS. Before testing by ICP-MS, the standard boric acid sample was dissolved and diluted to a solution solution containing 0.1 g/mL of boron with ultrapure water. The relative error between the result containing 0.1 μg/mL of boron with ultrapure water. The relative error between the result from the from the ICP-MS and the standard value is shown in Table 2. ICP-MS and the standard value is shown in Table 2. Table 2. Accuracy experiment of ICP-MS. 10 11 10 11 B/ B Results of ICP-MS Mean Relative B/ B Value of Value Error/% Standard Material 1 2 3 4 5 6 0.2471 0.2464 0.2469 0.2468 0.2469 0.2475 0.2469 0.2473 0.0002 0.16 Appl. Sci. 2018, 8, x FOR PEER REVIEW 5 of 10 Table 2. Accuracy experiment of ICP-MS. 10 11 10 11 B/ B Results of ICP-MS Mean B/ B Value of Relative Value Standard Material Error/% 1 2 3 4 5 6 Appl. Sci. 2018, 8, 2509 5 of 10 0.2471 0.2464 0.2469 0.2468 0.2469 0.2475 0.2469 0.2473 ± 0.0002 0.16 The The re relative lative er err roor r betwee between n ththe e expe experimental rimental resul result t from fr om the ICP the -ICP-MS MS and th and e iso the topic isotopic ratio oratio f the standard material was less than 0.16%. This result indicated that the ICP-MS, which was used to of the standard material was less than 0.16%. This result indicated that the ICP-MS, which was used determi to n determine e the boron the isobor topon e raisotope tio in soratio lution in ha solu s a h tion igh has accur a ahigh cy, an accuracy d could ,band e used could to ca be libused rate th to e isotope ratio of boron in BF3. In Figure 4, the isotopic ratio values of the samples were calibrated by calibrate the isotope ratio of boron in BF . In Figure 4, the isotopic ratio values of the samples were 10 11 10 11 11 11 calibrated ICP-MS. The by ICP-MS. B/ B raThe tios ofB/ the B na ratios tural of abun the dnatural ance BFabundance 3 and enriched BF and BF3enriched samples were BF samples 0.2473 ± 3 3 0.0009 and 0.0526 ± 0.0011, respectively. were 0.2473 0.0009 and 0.0526 0.0011, respectively. 10 10 11 11 BF3 and BF3 could be regarded as two distinct forms of matter. As is shown in Figure 5, the BF and BF could be regarded as two distinct forms of matter. As is shown in Figure 5, the 3 3 10 10 10 10 graph shape of A10 represents peaks of 2ν3 of BF3. Similarly, A11 represents 2ν3 peaks for BF3. The graph shape of A represents peaks of 2 of BF . Similarly, A represents 2 peaks for BF . 10 3 3 11 3 3 baselines of the spectrograms were adjusted to zero before calculation. The experiments were The baselines of the spectrograms were adjusted to zero before calculation. The experiments were processed at room temperature (25 ± 3 °C). processed at room temperature (25 3 C). Figure 5. Schematic of the calculation method. Figure 5. Schematic of the calculation method. It is obvious that the difference in the peak integration value is significant between the A /A 10 11 It is obvious that the difference in the peak integration value is significant between the A10/A11 10 11 10 11 and the true value of 10B/11 B, and this is most likely due to 10BF and 11BF having different molar 3 3 and the true value of B/ B, and this is most likely due to BF3 and BF3 having different molar absorption coefficients at the 2 band. According to Lambert-Beer theory: absorption coefficients at the 2ν3 band. According to Lambert-Beer theory: lg(I0/I) = ε × b × c (1) lg(I /I) = # b c (1) where, ε is the molar absorption coefficient, c is the molarity of the substance (mol/L), b is the optical where, # is the molar absorption coefficient, c is the molarity of the substance (mol/L), b is the optical length (cm), and lg(I0/I) is the absorbance at the specific wavenumber. A10 or A11 could be regarded as length (cm), and lg(I /I) is the absorbance at the specific wavenumber. A or A could be regarded 0 10 11 the addition of several fixed number of absorptions roughly: as the addition of several fixed number of absorptions roughly: nn A / A lg I / I / lg I / I n n 10 11 0 10 0 11 ii A / A =ii11 å lg( I / I ) / å lg( I / I ) 10 11 0 10 0 11 i i i=1 i=1 (2) (2) n n nn = # b c / # b c å å 10i 10i 10i 11i 11i 11i b c / b c 10i 10i 10i 11i 11i 11i i=1 i=1 ii11 For b = b , c /c is a constant for the same gas (fixed concentration). Then: 10 11 10i 11i For b10 = b11, c10i/c11i is a constant for the same gas (fixed concentration). Then: nn n n AA // AA =(( # // # ) )(c(c /c/ c) ) (3) (3) 10 11 å 10i å 11i 10 11 10 11 10ii 11 10 11 ii11 i=1 i=1 n n n n Let # / # = K. K, which is the correction factor, then: å å 10i 11i i1 i1 i=1 i=1 Let ε10i/ ε11i = K. K, which is the correction factor, then: K = A /A c /c (4) 11 10 10 11 and c /c = A /A K (5) 10 11 11 10 Appl. Sci. 2018, 8, 2509 6 of 10 The correction factor, K, is the ratio of the addition of a series of molar absorption coefficients in essence according to Equations (1)–(5). So, boron isotope ratio can be calculated by the peak areas of A and A . The correction factor can be obtained by testing the BF gas of a known isotope 10 11 3 ratio. Table 3 shows the continuous determination results of the A /A ratio for the normal, natural 10 11 10 11 abundance BF sample. The ICP-MS result of B/ B for this sample is 0.2473. While, the isotope ratio 10 11 of B/ B is equal to c /c , based on the ICP-MS result and Equation (5), the value of correction 10 11 factor K is 0.5431. Table 3. Investigation of the correction factor by continuous determination of the ratio of A /A of 10 11 the natural abundance BF . 10 11 1 A /A (by IR Method) Mean Value RSD/% B/ B (by ICP-MS ) K 10 11 0.4508 0.4513 0.4634 0.4585 0.4601 0.4512 0.2473 0.0009 0.4553 1.16 0.5431 0.4535 0.4498 0.4515 0.4626 mean and standard deviation were obtained from 3 determinations. 3.2. Precision Experiment for the IR Method The precision experiment was achieved by continuous measurements of a group of samples of a known isotope ratio, and the results are shown in Table 4. The relative standard deviation (RSD) was calculated by Equation (6), (x x) i=1 n 1 RSD = 100% = 100% (6) x x where, S is the standard deviation, x is the mean value of the results of n tests, and n is the number of tests. The RSD of the samples with the higher levels of isotope ratio were less than 2.00%. Although 10 11 the RSD of the sample where the B/ B ratio was 0.0506 (by ICP-MS) was more than 5.00%, the mean value of the IR method was close to the results from the ICP-MS experiments. These results indicated that the IR method is more precise when determining the boron isotope ratio. Table 4. Precision experiment for the IR method. 10 11 10 11 Sample ( B/ B, by IR Method) B/ B Mean S RSD/% (by ICP-MS) Value 1 2 3 4 5 6 1.2351 1.2290 1.2382 1.2401 1.2320 1.2355 1.2413 1.2360 0.0048 0.39 0.2473 0.2405 0.2428 0.2451 0.2422 0.2506 0.2472 0.2447 0.0037 1.52 0.0506 0.0559 0.0532 0.0485 0.0511 0.0463 0.0509 0.0510 0.0034 6.64 3.3. Influence of the Pressure and Temperature Due to the effect of the concentration of BF , absorbance values grew with an increase in pressure. In addition, an increase in the temperature made the peak pattern wilder. Figure 6A,B show the 10 11 influence of pressure and temperature on the isotope ratio of B/ B, with the ranges of pressure and temperature being the possible interval values for the chemical exchange rectification operation. It was found that both the pressure and temperature have little impact on the isotope ratio determination results. Nevertheless, the optimum operation temperature was in the range of 278 to 298 K, because the errors might increase significantly when the temperature is higher than 303 K. Appl. Sci. 2018, 8, x FOR PEER REVIEW 7 of 10 Appl. Sci. 2018, 8, x FOR PEER REVIEW 7 of 10 pressure and temperature being the possible interval values for the chemical exchange rectification operation. It was found that both the pressure and temperature have little impact on the isotope ratio pressure and temperature being the possible interval values for the chemical exchange rectification determination results. Nevertheless, the optimum operation temperature was in the range of 278 to operation. It was found that both the pressure and temperature have little impact on the isotope ratio 298 K, because the errors might increase significantly when the temperature is higher than 303 K. determination results. Nevertheless, the optimum operation temperature was in the range of 278 to Appl. Sci. 2018, 8, 2509 7 of 10 298 K, because the errors might increase significantly when the temperature is higher than 303 K. 10 11 Figure 6. Influence of pressure and temperature on the isotope ratio of B/ B. (A) Influence of 10 11 pr Figure essure;6. (BInfluence ) Influence ofopr f tem essur per e a and turetemperatur . e on the isotope ratio of 10 B/ 11B. (A) Influence of Figure 6. Influence of pressure and temperature on the isotope ratio of B/ B. (A) Influence of pressure; (B) Influence of temperature. pressure; (B) Influence of temperature. 3.4. Investigation of the Enriched BF3 Gas by IR 3.4. Investigation of the Enriched BF Gas by IR 3.4. Investigation of the Enriched BF3 Gas by IR 10 11 Figure 7 shows the IR spectrograms for an enriched BF3 sample and an enriched BF3 sample. 10 11 Figure 7 shows the IR spectrograms for an enriched BF sample and an enriched BF sample. 3 3 10 10 11 It is clea Firl gure y ob 7 ser sh v oed ws i n th Fi e g IR ure spec 7A tro th gra at w mh s en forth an e co enn rice ched ntra ti BF on 3 o sa f mB pl d e ec an re da a sed n e,n tri hched e abso rp BFti 3 o sa nm pe pl ae. ks It is clearly observed in Figure 7A that when the concentration of B decreased, the absorption peaks ofIt Ai10 s cl were earl y re o d buce serv ded an id n th Fig e ure A11 7 pe Aa th ks a t in w cr hea en sed the . co Sim nce ila nrl tra y, tith on e o af b so Brp dti ec o re n a pe sed aks , th oe f a A b11 so were rptio n re pe du ace ks d of A were reduced and the A peaks increased. Similarly, the absorption peaks of A were reduced 10 11 11 of A10 were reduced and the A11 peaks increased. Similarly, the absorption peaks of A11 were reduced and the A10 peaks were increased in Figure 7B. The calculation results for the samples in Figure 7A,B and the A peaks were increased in Figure 7B. The calculation results for the samples in Figure 7A,B and the A10 peaks were increased in Figure 7B. The calculation results for the samples in Figure 7A,B were 0.0120 and 0.7536, respectively. All of the results were in good agreement with the ICP-MS as a were 0.0120 and 0.7536, respectively. All of the results were in good agreement with the ICP-MS as a were 0.0120 and 0.7536, respectively. All of the results were in good agreement with the ICP-MS as a reference standard (the isotope ratios for Figure 7A,B were 0.0102 and 0.7546, respectively) for each reference standard (the isotope ratios for Figure 7A,B were 0.0102 and 0.7546, respectively) for each reference standard (the isotope ratios for Figure 7A,B were 0.0102 and 0.7546, respectively) for each sample, which proved the validity of the IR method. A series of enriched BF 3 samples, with their sample, which proved the validity of the IR method. A series of enriched BF samples, with their sample, which proved the validity of the IR method. A series of enriched BF 3 samples, with their isotopic ratios determined by IR, are listed in Table 5, with the mean and standard deviation obtained isotopic ratios determined by IR, are listed in Table 5, with the mean and standard deviation obtained isotopic ratios determined by IR, are listed in Table 5, with the mean and standard deviation obtained from 10 determinations. By comparing the results of the IR method and the ICP-MS method, the from 10 determinations. By comparing the results of the IR method and the ICP-MS method, the errors from 10 determinations. By comparing the results of the IR method and the ICP-MS method, the errors of measurement increased slightly when determining the ratio of high abundance samples. of measurement increased slightly when determining the ratio of high abundance samples. This could errors of measurement increased slightly when determining the ratio of high abundance samples. This could be attributed to the decline in the signal-noise ratio (SNR), which was caused by the be attributed to the decline in the signal-noise ratio (SNR), which was caused by the decrease in the This could be attributed to the decline in the signal-noise ratio (SNR), which was caused by the decrease in the absorbance value. absorbance value. decrease in the absorbance value. Figure 7. IR spectrograms of enriched BF3. (A) Spectrogram of an enriched BF sample; Figure 7. IR spectrograms of enriched BF3. (A) Spectrogram of an enriched BF3 sample; (B) Figure 7. IR spectrograms of enriched BF3. (A) Spectrogram of an enriched BF3 sample; (B) (B) Spectrogram of an enriched BF sample. Spectrogram of an enriched BF3 sample. Spectrogram of an enriched BF3 sample. Appl. Sci. 2018, 8, x FOR PEER REVIEW 8 of 10 Appl. Sci. 2018, 8, 2509 8 of 10 Appl. Sci. 2018, 8, x FOR PEER REVIEW 8 of 10 Table 5. Comparison of the results from the IR method and ICP-MS method. Table 5. Comparison of the results from the IR method and ICP-MS method. 10 11 Table 5. Comparison of the results from the IR method and ICP-MS method. Isotope Ratio of B/ B Series No. 10 11 Results ofI I sot R Me opet h R od ati o of Re su B/ lts B of ICP-MS 10 11 Isotope Ratio of B/ B Series No. Series No. 1 1.6385 ± 0.0043 1.6390 ± 0.0006 Results of IR Method Results of ICP-MS Results of IR Method Results of ICP-MS 2 0.7536 ± 0.0045 0.7546 ± 0.0010 1 1.6385 ± 0.0043 1.6390 ± 0.0006 1 1.6385 0.0043 1.6390 0.0006 3 0.4815 ± 0.0038 0.4832 ± 0.0009 2 0.7536 ± 0.0045 0.7546 ± 0.0010 2 0.7536 0.0045 0.7546 0.0010 4 0.0915 ± 0.0059 0.0905 ± 0.0010 3 0.4815 ± 0.0038 0.4832 ± 0.0009 3 0.4815 0.0038 0.4832 0.0009 5 0.0504 ± 0.0063 0.0488 ± 0.0012 4 0.0915 ± 0.0059 0.0905 ± 0.0010 4 0.0915 0.0059 0.0905 0.0010 5 6 0.0504 0.01 200.0063 ± 0.0079 0.01 0.0488 02 ± 0 .00.0012 007 5 0.0504 ± 0.0063 0.0488 ± 0.0012 6 0.0120 0.0079 0.0102 0.0007 6 0.0120 ± 0.0079 0.0102 ± 0.0007 3.5. Online Determination of Boron Isotope Ratio 3.5. Online Determination of Boron Isotope Ratio 3.5. Online Determination of Boron Isotope Ratio Figure 8 illustrates the online determination results from the separation part of a chemical exchFigur ange e re8 ctiillustrates fication dev the iceonline , showin determination g the enrichedr st esults age, th fre om stab the ility separation stage, andpart an in of staa bichemical lity point Figure 8 illustrates the online determination results from the separation part of a chemical exchange (where thr e ectification isotope rati device, o sudden showing ly drops) the . Wi enriched th the astage, ssistan the ce o stability f IR spec stage, trosco and py, th ane instability instability point point exchange rectification device, showing the enriched stage, the stability stage, and an instability point (wher can be e the foun isotope d and tratio hus esuddenly ncourage dr coops). rrectiW on ith ofthe the assistance operation.of FiIR gure spectr 9 sh oscopy ows th , e the isoinstability tope ratio point curve (where the isotope ratio suddenly drops). With the assistance of IR spectroscopy, the instability point of the complex part where the BF3 was enriched on the same isotope separation device. The errors can be found and thus encourage correction of the operation. Figure 9 shows the isotope ratio curve of can be found and thus encourage correction of the operation. Figure 9 shows the isotope ratio curve the of d complex etermina part tion wher resule tsthe wereBF a littl was e la enriched rger when t on h the e iso same tope isotope ratio bec separation ome smaldevice. ler withThe the err dec ors reaof se of the complex part where the BF3 was enriched on the same isotope separation device. The errors in SNR. The sampling stage experiments lasted for 12 h and the sampling interval was 2 h. The curve determination results were a little larger when the isotope ratio become smaller with the decrease in of determination results were a little larger when the isotope ratio become smaller with the decrease shows the change of the isotope ratio in the process of product collection. The overtopping (exceeding SNR. The sampling stage experiments lasted for 12 h and the sampling interval was 2 h. The curve in SNR. The sampling stage experiments lasted for 12 h and the sampling interval was 2 h. The curve limit value) point indicated that the sampling operation should be stopped at that moment, because shows the change of the isotope ratio in the process of product collection. The overtopping (exceeding shows the change of the isotope ratio in the process of product collection. The overtopping (exceeding 11 10 11 the limit of the isotope ratio for B product ( B/ B ≤ 0.0204) has been exceeded. limit value) point indicated that the sampling operation should be stopped at that moment, because limit value) point indicated that the sampling operation should be stopped at that moment, because 11 10 11 11 10 11 the limit of the isotope ratio for B product ( B/ B 0.0204) has been exceeded. the limit of the isotope ratio for B product ( B/ B ≤ 0.0204) has been exceeded. Figure 8. Online determination results of the separation part of a chemical exchange rectification device. Figure Figure8. 8.Online Onlindetermination e determinatio rn esults result ofs the of separation the separapart tion of pa art chemical of a chemic exchange al exc rh ectification ange rectifi device. cation device. Figure 9. The curve of isotope ratio about the complex part of a chemical exchange rectification device. Figure 9. The curve of isotope ratio about the complex part of a chemical exchange rectification device. Figure 9. The curve of isotope ratio about the complex part of a chemical exchange rectification device. Appl. Sci. 2018, 8, 2509 9 of 10 4. Conclusions A method was established to determine the isotope ratio of boron based on calculating the 2 region of BF in infrared spectra used in a boron separation device to monitor the separation process online. The results showed that this has many benefits for a chemical exchange rectification device with the assistance of the online IR method. Response speed and measuring precision might be enhanced with further improvements such as the use fiber-optic technology. Author Contributions: W.Z. and J.X. conceived and designed the experiments; Y.T. performed the experiments; Y.T. and J.X. analyzed the data; W.Z. contributed reagents/materials/analysis tools; Y.T. wrote the paper. Funding: This research received no external funding. Conflicts of Interest: The authors declare no conflicts of interest. References 1. Zhang, L.; Zhang, W.J.; Xu, J.; Ren, X. Synthesis of enriched 10B boric acid of nuclear grade. Trans. Tianjin Univ. 2014, 6, 458–462. [CrossRef] 2. Zhang, W.J.; Liu, T.Y.; Xu, J. Preparation and characterization of 10B boric acid with high purity for nuclear industry. Springerplus 2016, 1, 1202–1212. [CrossRef] [PubMed] 3. Ferreira, T.H.; Miranda, M.C.; Rocha, Z.; Leal, A.S.; Comes, D.A.; Sousa, E.M.B. An Assessment of the Potential Use of BNNTs for Boron Neutron Capture Therapy. Nanomaterials 2017, 4, 82–92. 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