Online Determination of Boron Isotope Ratio in Boron Trifluoride By

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; [email protected] (W.Z.); [email protected] (Y.T.) * Correspondence: [email protected]; 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 ways to separate the 10B and 11B 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 (BF3). The possibility of determining the isotope ratio via the 2ν3 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. 10B 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% 10B 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 exchange rectification is the simplest and most productive method for the separation of 10B and 11B isotopes at concentrations of 95% and over [12]. Figure1 shows the principal scheme of the apparatus for the separation of boron isotopes using the chemical exchange rectification method. 10B and 11B 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 exchange rectification rectiﬁcation method.

The m massass spectrometry (MS) method is is one of the most important ways of analy analyzingzing the boron + isotopeisotope ratio. ratio. Analysis Analysis comes comes from from the the peaks peaks with with mass mass-to-charge-to-charge ratios ratios (m/e (m/e+) equal) equal to 10 to and 10 and 11 [14].11 [14 Porteous]. Porteous [15] [ 15et] etal. al.determined determined the the isotopic isotopic ratio ratio of of boron boron in in samples samples of of groundwater groundwater by by inductivelyinductively coupled coupled plasma plasma mass mass spectrometry spectrometry (ICP-MS) (ICP-MS) to evaluate to evaluate possible possible levels of levels boron of pollution boron pollutionfrom anthropogenic from anthropogenic inputs into inputs natural into natural aqueous aqueous systems. systems. The matrix The matrix effect effect was was reduced reduced by theby thepreconcentration preconcentration and ion-exchange and ion-exchange of the of sample. the sample. Compared Compared with the with standard the standard material, material, the precision the precisionof the method of the achieved method 0.13% achieved (natural 0.13% abundance). (natural However, abundance). the However, sampling and the preparation sampling and for preparationthis method for are this very method complex, are sovery it is complex, difficult so to achieveit is difficult real-time to achiev trackinge real for-time this tracking process for during this processactual production. during actual Infrared production. spectroscopy Infrared (IR) spectroscopy is a traditional (IR) technology is a traditional that technology has been used that for has on-line been useddetection. for on For-line instance, detection. Hepburn For instance, [16] et Hepburn al. established [16] et a al. method established using a online method FTIR using spectroscopy online FTIR to spectroscopydetermine the to siloxane determine content the sil inoxane bio-gas. content Both thein bio precision-gas. Both and the the precision detection and limit the for detection siloxane werelimit forsatisfactory siloxane whenwere satisfactory using this online when FTIRusing technology. 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 BF33 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 on the the change change in in the the boron boron isotope isotope ratio. ratio. Thus, Thus, the the bands bands could could be used be used to measure to measure the the boron isotopic ratio in BF . Despite having a good signal-noise ratio in the ν region, such a boron isotopic ratio in BF3. Despite3 having a good signal-noise ratio in the ν3 region,3 such a high dilutionhigh dilution factor factor was was difficult difficult to realize to realize via via changing changing optical optical path pathss in in the the industrialized industrialized process. process. Although the 2ν is a weak IR absorption band for BF , the difference in absorbance peaks was about Although the 2ν3 is a weak IR absorption band for BF33, the difference in absorbance peaks was about −1 10 11 ν 112 cm−1 betweenbetween 10BFBF3 3andand 11BFBF3 at3 at the the 2ν 23 bands,3 bands, which which means means that that there there is is good good resolution resolution for for this this measurement. In this paper,paper, thethe IRIR method method was was applied applied to to determine determine the the boron boron isotope isotope ratio ratio based based on ν oncalculating calculating the the BF3 BFinfrared3 infrared spectrum spectrum at 2 at3 2ν. Further,3. Further, an infraredan infrared spectrophotometer spectrophotometer was was installed installed in a inboron a boron separation separation device device to monitor to monitor the separationthe separation process process online. online. 2. Experimental Method 2. Experimental Method 2.1. Instruments and Reagents 2.1. Instruments and Reagents The BF3 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 SiF4 were present as an impurity in the BF3 but these were ignored of 99.95%. Small amounts of SiF4 were present as an impurity in the BF3 but these were ignored in this in this study. NIST SRM 951a isotopic reference material of boric acid (10B/11B is 0.2473 ± 0.0002) study. NIST SRM 951a isotopic reference material of boric acid (10B/11B 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 CaF2 windows (ϕ40 × 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 accuracy of transmittance lower than or equal to ±0.2%T. (TJ270-30A, Tianjin, China). The 10B/11B accuracy of transmittance lower than or equal to ±0.2%T. (TJ270-30A, Tianjin, China). The 10B/11B 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 Figure2. BF 3 gas samples with different amountsThe procedure of boron were for collectedthe offline from experiment the chemical is shown exchange in Figure rectification 2. BF3 gas device samples or feed with gas different cylinder. amountsThe outlet of ofboron the were gas cell collected was linked from the to achemical buffer bottleexchange and rectification an absorber device bottle or filled feed withgas cylinder. 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 BF3 gas from escaping. BF3 was ﬁlling into the gas cell, which was wasreplaced allowed by Nto2 continueto remove for the at airleast (especially 1–2 min, theand waterthe operation in air) inside was stopped of the gas when cell beforehand.the inside of Thisthe was allowed to continue for at least 1–2 min, and the operation was stopped when the inside of the gaswas cell allowed was fully to continue replaced for by at BF least3. The 1–2 valves min, and of the the gas operation cylinder was and stopped gas cell when were the closed inside in of turn the for gas gas cell was fully replaced by BF3. The valves of the gas cylinder and gas cell were closed in turn for aboutcell was 10 fullymin before replaced use. by The BF3 .infrared The valves spectra of the were gas cylinderacquired and from gas scanning cell were the closed content in turns of for the about gas about 10 min before use. The infrared spectra were acquired from scanning the contents of the gas cell10 minat a beforescanning use. speed The infraredof 1 cm−1 spectra/s and a werescanning acquired range from of 4000 scanning to 400the cm contents−1. of the gas cell at a cell at a scanning speed of 1 cm−1/s and a scanning range of 4000 to 400 cm−1. scanning speed of 1 cm−1/s and a scanning range of 4000 to 400 cm−1.

Figure 2. Diagram of offline experiment. Figure 2. Diagram of offlineoffline experiment.experiment. 2.3.2.3. Procedure Procedure for for Online Online Measurement Measurement 2.3. Procedure for Online Measurement TheThe online online isotopic isotopic ratio ratio determination determination system system was was set set on on the the device device used used for for boron boron isotope isotope The online isotopic ratio determination system was set on the device used for boron isotope separation,separation, as as shown shown in in Figure Figure 33.. The BF 33 gasgas was was extracted extracted from from a a pipe pipe where where the the gas gas flow flow and and the the separation, as shown in Figure 3. The BF3 gas was extracted from a pipe where the gas flow and the pipelinepipeline can can be be controlled controlled by by valve. valve. The The BF3 BF3 flowed flowed t throughhrough a a gas gas cell cell that that was was equipped equipped with with two two pipeline can be controlled by valve. The BF3 flowed through a gas cell that was equipped with two CaFCaF22 windowswindows because because the the weatherability weatherability and and corrosion corrosion resistance resistance of of CaF CaF22 areare superior superior to to KBr KBr under under CaF2 windows because the weatherability and corrosion resistance of CaF2 are superior to KBr under atmosphericatmospheric and and BF BF33 conditions.conditions. The The whole whole gas gas cell cell was was fitted fitted to to the the IR IR spectrophotometer spectrophotometer by by which which atmospheric and BF3 conditions. The whole gas cell was fitted to the IR spectrophotometer by which thethe infrared infrared spectrogram spectrogram c couldould be be obtained obtained directly. directly. the infrared spectrogram could be obtained directly.

FigureFigure 3 3.. DiagramDiagram of of boron boron isotope isotope ratio ratio online online determination determination system. system. Figure 3. Diagram of boron isotope ratio online determination system. 2.4.2.4. Testing Testing method method of of ICP ICP-MS-MS 2.4. Testing method of ICP-MS TheThe ICP ICP-MS-MS was was used to determinedetermine thethe isotopeisotope ratio ratio as as a a reference. reference. The The BF BF3 gas3 gas was was absorbed absorbed by bya smalla smallThe amount ICP amount-MS of was ethanolof ethanol used and to and diluteddetermine diluted to samples theto samples isotope containing containingratio as 0.1 a µreference. g/mL0.1 μg/mL of boronThe of boronBF with3 gas ultrapurewith was ultrapure absorbed water. water.Theby a operationsmall The operationamount method of method ethanol and experimental and and experimental diluted conditions to samples conditions of containing the o ICP-MSf the 0.1ICP experiments μg/mL-MS experiments of boron were with similarwere ultrapure similar to the tomethodwater. the method The found operation found in [15 in]. method After[15]. After each and test,each experimental thetest, system the system conditions pipeline pipeline wasof the alternatelywas ICP alternately-MS experiments washed washed three were three times similar times with to the method found in [15]. After each test, the system pipeline was alternately washed three times with2% HNO 2% HNO3 and3 and 0.1 mol/L 0.1 mol/L ammonia ammonia water water solution solution to reduce to reduce any any errors error dues due to memory to memory effect. effect. The 10 11 Thespeciﬁcwith specific 2% parameters HNO parameters3 and used0.1 mol/L used for the forammonia ICP-MS the ICP experimentswater-MS experimentssolution to determineto reduce to determine any the boronerror thes isotope due boron to ratiosmemory isotope ( B/ ratioseffect.B) (areThe10B/11 shown specificB) are inshown parametersTable in1. Table used 1. for the ICP-MS experiments to determine the boron isotope ratios (10B/11B) 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.(ICP2018-MS, 8),. 2509Counts per Second (CPS); Atomic Mass Unit (AMU). 4 of 10

Item Parameter Item Parameter Table 1. Experimental conditions andMicroconcentric parameters of inductively coupledSensitivity/s plasma−1 mass spectrometry1.759 × 106 Nebulizer (ICP-MS). Counts per Second (CPS); AtomicNebulizer Mass Unit (AMU). (μg·L−1)−1 CPS Spray chamber Item Parameter3 Scanning Item mode Peak Parameter-jump temperature/°C Microconcentric Sensitivity/s−1 Nebulizer −1 1.759 × 106 CPS Nebulizer gas flow/L·min Nebulizer0.93 (Dwellµg·L−1 )time/ms−1 10 SprayAuxiliary chamber gas temperature/flow/L·min−◦1C 30.9 ScanningAcquisition mode degree Peak-jump10 NebulizerCool gas gas flow/L·min flow/L·min−1 −1 0.9310 DwellAcquisition time/ms time/s 1020 −1 Auxiliary gas flow/L·min 0.9 AcquisitionChannels degree per 10 Plasma power/W· −1 1250 3 Cool gas flow/L min 10 AcquisitionAMU time/s 20 Plasma power/W 1250 Channels per AMU 3 ResolutionResolution StandardStandard Runs/replicatesRuns/replicates 33 SampleSample uptake rate/mLrate/mL·min·min−−11 11 SampleSample depth/mm depth/mm 104104 IonizationIonization lens lens parameters L1L1 3.8; 3.8; L2 L2 31.8; 31.8; L3 L3 189.8 189.8 --- -

3. Results and Discussion

3.1. Calculation and Correction of the Isotope Ratio

Figure 44 shows shows the the comparison comparison of of the the IR IR spectrograms spectrograms in in the the 2 2νν33 regions between natural 11 abundance BF3 and enriched 11BFBF33. .The The peaks peaks at at these these regions regions are are more more complex than peaks inin thethe νν33 regions. Fortunately, the peak changes ha hadd no significantsignificant overlap of the two bands. By contrast, the 10 −1 absorption band of 22νν33 for 10BF33 (the(the range range being about 3270–31703270–3170 cmcm−1)) was was significantly significantly reduced reduced,, 10 which proved proved that that this this absorption absorption band band is influenced is influenced by the by amount the amount of BF of3 that 10BF is3 present.that is present. In contrast, In 11 −1 cothentrast, absorption the absorption peaks in the peaks 2ν3 inband the for2ν3 bandBF3 (thefor 11 rangeBF3 (the being range about being 3170–3070 about 3170 cm –3070) varied cm− regularly1) varied 11 11 withregularly changing with concentrationschanging concentrations of BF3. Thus,of BF it3. wasThus, feasible it was to feasible calculate to thecalculate isotope the ratio isotope based ratio on basedcomparing on comparing the peak areasthe peak of these areas two of these absorption two absorp bands.tion bands.

11 FigureFigure 4.4. ComparisonComparison ofof thethe IRIR spectrograms.spectrograms. ((AA)) NaturalNatural abundanceabundance BFBF33;(; (B)) EnrichedEnriched 11BF33..

The NIST NIST SRM SRM 951a 951a boric boric acid acid standard standard sample sample was was used used to investigate to investigate the accuracy the accuracy of the of ICP the- MS.ICP-MS. Before Before testing testing by ICP by-MS, ICP-MS, the standard the standard boric acid boric sample acid samplewas dissolved was dissolved and diluted and to diluted a solution to a containingsolution containing 0.1 μg/mL 0.1 ofµ borong/mL with of boron ultrapure with ultrapurewater. The water. relative The error relative between error the between result thefrom result the ICPfrom-MS the and ICP-MS the standard and the standardvalue is shown value isin shown Table 2. in Table2.

Table 2. Accuracy experiment of ICP-MS.

10B/11B Results of ICP-MS Mean 10B/11B Value of Relative 1 2 3 4 5 6 Value Standard Material Error/% 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.

10B/11B Results of ICP-MS Mean 10B/11B Value of Relative 1 2 3 4 5 6 Value Standard Material Error/% 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 relative relative error error between between the the experimental experimental result result from from the ICP the- ICP-MSMS and the and isotopic the isotopic ratio of ratio the ofstandard the standard material material was less was than less 0.16%. than 0.16%.This result This indicated result indicated that the thatICP- theMS, ICP-MS, which was which used was to useddetermine to determine the boron the isotope boron ratio isotope in solution ratio in has solution a high hasaccuracy, a high and accuracy, could be and used could to calibrate be used the to calibrateisotope ratio the isotopeof boron ratio in BF of3. boronIn Figure in BF 4,3 the. In isotopic Figure4 ,ratio the isotopic values of ratio the valuessamples of were the samples calibrated were by 10 11 10 11 11 11 calibratedICP-MS. The by ICP-MS.B/ B ratios The ofB/ the Bnatural ratios ofabundance the natural BF abundance3 and enriched BF3 andBF3enriched samples wereBF3 samples0.2473 ± were0.0009 0.2473 and 0.0526± 0.0009 ± 0.0011, and 0.0526 respectiv± 0.0011,ely. respectively. 10 1111 BFBF33 andand BFBF3 3couldcould be be regarded regarded as as two two distinct distinct forms forms of of matter. matter. As As is is shown shown in in Figure Figure 55,, thethe 10 10 10 10 graph shape of of AA1010 representsrepresents peaks peaks of of 2ν 2ν3 3ofof BFBF3. Similarly,3. Similarly, A11A represents11 represents 2ν3 2peaksν3 peaks for forBF3. BFThe3. Thebaselines baselines of the of thespectrograms spectrograms were were adjusted adjusted to to zero zero before before calculation. calculation. The The experiments were processed at room temperaturetemperature (25(25 ±± 33 °C).◦C).

Figure 5. Schematic of the calculation method.

It is obviousobvious thatthat thethe differencedifference inin thethe peakpeak integration integration value value is is signiﬁcant significant between between the theA A1010//AA1111 10 11 10 11 and the truetrue valuevalue ofof 10B/B/11B,B, and and this this is most likely duedue toto 10BFBF33 and 11BF3 having different molar ν absorption coefﬁcientscoefficients at the 22ν33 band. According According to Lambert Lambert-Beer-Beer theory:

lg(lg(I0/II)0/I =) ε= ×ε ×b b× ×c c (1) where, ε is the molar absorption coefficient, c is the molarity of the substance (mol/L), b is the optical where, ε 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 the addition of several0 fixed number of absorptions roughly: 10 11 as the addition of several fixed number of absorptions roughly: nn AAIIII/ lgn / /n lg / 10 11 0 10ii 0 11  A10/A11 =ii11∑ lg(I0/I10)i/ ∑ lg(I0/I11)i i=1 i=1 (2) nnn n (2) = ∑bε10 cib10i/c10i/ ∑ bε11 cib11i c11i i10=i1 10 i 10 ii= 111 i 11 i 11 i ii11

For b10 == bb1111, c, 10c10i/ci11/ic is11 iais constant a constant for forthe thesame same gas gas (fixed (ﬁxed concentration). concentration). Then: Then:

nnnn A/(/)(/) A c c A1010/A11 11= (∑ε 10 10iii/∑ ε11 i 11) × (c10 10/c11) 11 (3) i=ii111i=1

nn n Let ∑ ε10i/ ∑ ε11i = K. K, which is the correction factor, then: i 1 Let i= 1 ε10i/ i=1ε11i = K. K, which is the correction factor, then:

K = A11/A10 × c10/c11 (4)

and c10/c11 = A11/A10 × K (5) 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 A10 and A11. The correction factor can be obtained by testing the BF3 gas of a known isotope ratio. Table3 shows the continuous determination results of the A10/A11 ratio for the normal, natural 10 11 abundance BF3 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 c10/c11, based on the ICP-MS result and Equation (5), the value of correction factor K is 0.5431.

Table 3. Investigation of the correction factor by continuous determination of the ratio of A10/A11 of the natural abundance BF3.

10 11 1 A10/A11 (by IR Method) Mean Value RSD/% B/ B (by ICP-MS ) K 0.4508 0.4513 0.4634 0.4585 0.4601 0.4512 0.4553 1.16 0.2473 ± 0.0009 0.5431 0.4535 0.4498 0.4515 0.4626 1 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 Table4. The relative standard deviation (RSD) was calculated by Equation (6),

s n 2 ∑ (xi−x) i=1 S 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 the RSD of the sample where the 10B/11B 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.

10B/11B Sample (10B/11B, by IR Method) Mean S RSD/% (by ICP-MS) 1 2 3 4 5 6 Value 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 BF3, absorbance values grew with an increase in pressure. In addition, an increase in the temperature made the peak pattern wilder. Figure6A,B show the influence of pressure and temperature on the isotope ratio of 10B/11B, 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 pressureAppl. Sci. and2018, temperature8, x FOR PEER REVIEW being the possible interval values for the chemical exchange rectification7 of 10 operation. It was found that both the pressure and temperature have little impact on the isotope ratio determinationpressure and results.temperature Nevertheless, being the the possible optimum interval operation values temperaturefor the chemical was exchange in the range rectification 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 pressure;FigureFigure 6. 6.(B Influence)Influence Influence of of of pressure pressure temperature and and temperature. temperature onon the the isotope isotope ratio ratio of of 10B/B/11B. ( (AA)) Influence Influence of of pressure;pressure; ((BB)) Influence Influence of of temperature. temperature. 3.4. Investigation of the Enriched BF3 Gas by IR 3.4. Investigation of the Enriched BF3 Gas by IR 3.4. Investigation of the Enriched BF3 Gas by IR 10 11 Figure 7 shows the IR spectrograms for an enriched10 BF3 sample and an enriched11 BF3 sample. Figure7 shows the IR spectrograms for an enriched BF3 sample and an enriched BF3 sample. It is clearlyFigure observed 7 shows in the Figure IR spectrograms 7A that when for the an concentrationenriched 10BF3 ofsample 10B decreased, and an enriched the absorption 11BF3 sample. peaks It is clearly observed in Figure7A that when the concentration of 10B decreased, the absorption peaks ofIt A is10 clearlywere reduced observed and in theFigure A11 7peaksA that increased. when the concentrationSimilarly, the ofabsorption 10B decreased, peaks the of absorptionA11 were redu peaksced of A10 were reduced and the A11 peaks increased. Similarly, the absorption peaks of A11 were reduced andof theA10 wereA10 peaks reduced were and increased the A11 peaks in Figure increased. 7B. The Similarly, calculation the resultsabsorption for thepeaks sample of A11s inwere Figure redu 7cedA,B and the A10 peaks were increased in Figure7B. The calculation results for the samples in Figure7A,B wereand 0.0120 the A10 and peaks 0.7536, were respectively. increased in FigureAll of the 7B. resultsThe calculation were in good results agreement for the sample withs the in FigureICP-MS 7A as,B a were 0.0120 and 0.7536, respectively. All of the results were in good agreement with the ICP-MS as a referencewere 0.0120 standard and 0.7536, (the isotope respectively. ratios Allfor ofFigure the results 7A,B werewere 0.0102in good and agreement 0.7546, respectively)with the ICP- MSfor aseach a reference standard (the isotope ratios for Figure7A,B were 0.0102 and 0.7546, respectively) for each sample,reference which standard proved (the the isotope validity ratios of thefor FigureIR method. 7A,B wereA series 0.0102 of andenriched 0.7546, BF respectively)3 samples, with for eachtheir sample, which proved the validity of the IR method. A series of enriched BF3 samples, with their sample, which proved the validity of the IR method. A series of enriched BF3 samples, with their isotopicisotopic ratios ratios determined determined by by IR, IR, are are listed listed in in Table Table5 5,, withwith the the mean mean and and standard standard deviation deviation obtained obtained isotopic ratios determined by IR, are listed in Table 5, with the mean and standard deviation obtained fromfrom 10 10 determinations. determinations. ByBy comparingcomparing the the results results of theof the IR method IR method and theand ICP-MS the ICP method,-MS method, the errors the from 10 determinations. By comparing the results of the IR method and the ICP-MS method, the errorsof measurement of measurement increased increased slightly slightly when determining when determining the ratio ofthe high ratio abundance of high abundance samples. This samples. could errors of measurement increased slightly when determining the ratio of high abundance samples. Thisbe attributed could be to attributed the decline to in the the decline signal-noise in the ratio signal (SNR),-noise which ratio was (SNR) caused, which by the was decrease caused in by the the This could be attributed to the decline in the signal-noise ratio (SNR), which was caused by the decreaseabsorbance in the value. absorbance value. decrease in the absorbance value.

11 FigureFigure 7. 7. IR IR spectrograms spectrograms of of enriched enriched BF3. BF3. (A) ( A Spectrogram) Spectrogram of of an an enriched enriched 11BF3BF sample;3 sample; (B) Figure 7. IR spectrograms of enriched BF3. (A) Spectrogram of an enriched 11BF3 sample; (B) 10 Spectrogram(B) Spectrogram of an of enriched an enriched 10BF3 sample.BF3 sample. Spectrogram of an enriched 10BF3 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. Table 5. Comparison of the resultsIsotope from the Ratio IR method of 10B/ and11B ICP-MS method. Series No. Results ofIsotope IR Method Ratio ofResults 10B/11B of ICP-MS Series No. Isotope Ratio of 10B/11B Series No. 1 Results1.6385 of ±IR 0.0043 Method Results1.6390 of ± 0.0006ICP-MS Results of IR Method Results of ICP-MS 21 0.75361.6385 ± 0.00450.0043 0.75461.6390 ± 0.00100.0006 ± ± 132 1.63850.48150.75360.0043 ± 0.00380.0045 0.48320.7546 1.6390 ± 0.00090.00100.0006 2 0.7536 ± 0.0045 0.7546 ± 0.0010 4 0.0915 ± 0.0059 0.0905 ± 0.0010 33 0.48150.4815± 0.0038 ± 0.0038 0.4832 0.4832 ± 0.0009± 0.0009 454 0.09150.05040.0915± 0.0059 ± 0.00630.0059 0.04880.0905 0.0905 ± 0.00120.0010± 0.0010 565 0.05040.01200.0504± 0.0063 ± 0.00790.0063 0.01020.0488 0.0488 ± 0.00070.0012± 0.0012 66 0.01200.0120± 0.0079 ± 0.0079 0.0102 0.0102 ± 0.0007± 0.0007 3.5. Online Determination of Boron Isotope Ratio 3.5. Online Determination of Boron Isotope Ratio 3.5. OnlineFigure Determination 8 illustrates of the Boron online Isotope determination Ratio results from the separation part of a chemical exchangeFigureFigure rectification8 8illustrates illustrates device, the the online onlineshowing determination determination the enriched results resultsstage, fromthe from stability the the separation separation stage, and part partan instability of of a a chemical chemical point exchange(exchangewhere the rectiﬁcationrectification isotope ratio device,device, sudden showingshowingly drops). thethe With enrichedenriched the assistance stage,stage, thethe of stabilitystability IR spectroscopy, stage,stage, andand the anan instabilityinstability pointpoint (wherecan(where be thefound the isotopeisotope and thus ratio ratio encouragesuddenly suddenly drops). correctiondrops). WithWith of thethe assistanceassistanceoperation. of ofFigure IRIR spectroscopy,spectroscopy, 9 shows the thethe isotope instabilityinstability ratio pointcurvepoint canofcan the bebe foundcomplex found and and part thus thus where encourage encourage the 11BF correction correction3 was enriched of of the the operation. on operation. the same Figure Figure isotope9 shows 9 showsseparation the the isotope isotopedevice. ratio ratioThe curve errorscurve of 11 theof determinationthe complex complex part part whereresults where the were theBF a 11 little3BFwas3 waslarger enriched enriched when on the on the isotopethe same same isotope ratio isotope become separation separation smaller device. device.with The the The errorsdecrease errors of determinationinof SNR.determination The sampling results results were stage were a experiments little a little larger larger whenlasted when the for the isotope12 isotopeh and ratio the ratio becomesampling become smaller interval smaller with was with the 2 h.the decrease The decrease curve in SNR.showsin SNR. The the The sampling change sampling of stagethe stage isotope experiments experiments ratio inlasted the lasted process for for 12 of12 h product andh and the the collection sampling sampling. intervalThe interval overtopping was was 2 2 h. h. (exceeding The Thecurve curve showslimitshows value) thethe changechange point ofofindicated thethe isotopeisotope that ratioratio the sampling inin thethe processprocess operation ofof productproduct should collection.collection be stopped. TheThe at overtoppingovertopping that moment, (exceeding(exceeding because limitthelimit limit value)value) of the pointpoint isotope indicatedindicated ratio that thatfor 11 thetheB product samplingsampling (10 operationB/operation11B ≤ 0.0204) shouldshould has be bebeen stoppedstopped exceeded. atat thatth at moment, moment, becausebecause thethe limitlimit of of the the isotope isotope ratio ratio for for11 11BB productproduct ((1010B/1111BB ≤ ≤0.0204)0.0204) has has been been exceeded. exceeded.

Figure 8. Online determination results of the separation part of a chemical exchange rectification Figuredevice.Figure 8. 8.Online Online determination determination results results of the of separationthe separation part of part a chemical of a chemical exchange exchange rectiﬁcation rectification device. device.

FigureFigure 9.9. TheThe curvecurve ofof isotope ratio about the complex part of a chemical exchange rectiﬁcationrectification device.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 2ν3 region of BF3 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.

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