Boron-11 NMR for Quantitative Boron Analysis (PDF)

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Analyst View Article Online PAPER View Journal | View Issue Pushing the frontiers: boron-11 NMR as a method for quantitative boron analysis and its application Published on 05 September 2018. Downloaded by Brock University on 12/15/2024 3:03:19 AM. Cite this: Analyst, 2018, 143, 4707 to determine boric acid in commercial biocides† Luis Manuel Aguilera-Sáez, José Raúl Belmonte-Sánchez, Roberto Romero-González, José Luis Martínez Vidal, Francisco Javier Arrebola, Antonia Garrido Frenich * and Ignacio Fernández * Quantitative boron-11 NMR (11B qNMR) spectroscopy has been introduced for the first time as a method to determine boric acid content in commercial biocides. Validation of the method affords a limit of detec- tion of 0.02% w/w and a limit of quantification of 0.04% w/w, which are low enough to determine boric acid in commercial biocides. Other figures of merit such as linearity (R2 > 0.99), recovery (93.6%–106.2%), intra- and inter-day precision (from 0.7 to 2.0%), uncertainty (3.7 to 4.4%) and matrix effects were also evaluated. This method was successfully applied to determine boric acid in five different commercial bio- cides in a wide range of concentrations ( 1/2) have barely been introduced probably due to funda- mixture can be determined by comparing its relative inte- mental differences in the governing factors of the nuclear mag- netic relaxation processes compared to dipolar nuclei. In fact, to the best of our knowledge, there are only a few reports Department of Chemistry and Physics, Research Centre CIAIMBITAL, Agrifood where a quadrupolar nucleus has been measured for quantifi- Campus of International Excellence, ceiA3, University of Almería, Ctra. Sacramento, cation purposes. Maki et al. have described the use of 27Al s/n, 04120, Almería, Spain. E-mail: [email protected] † Electronic supplementary information (ESI) available. See DOI: 10.1039/ qNMR (I = 5/2) for the quantification of various hydrolyzed c8an00505b species of Al3+ ions, such as [Al(H2O)6]3+, the trinuclear This journal is © The Royal Society of Chemistry 2018 Analyst, 2018, 143, 4707–4714 | 4707  View Article Online Paper Analyst complex Al(OH)4− and K–Al13.17 Furthermore, there is a study accurate determination of boric acid content in commercial that reported the use of 14N qNMR (I = 1) for the determination biocide pellets in extensive use in agrochemical applications. of nitrate, urea and ammonium in aqueous solutions.16 All these reports provided a comprehensive overview of the often overlooked capabilities of quadrupolar qNMR. Inspired by Experimental section these authors, we envisaged the possibility of extending this Chemicals and materials methodology to another quadrupolar nucleus such as boron-11. This nucleus is considered active from an NMR point of A total of 5 biocide pellets were acquired from different local view and it is present in the structure of boric acid and its commercial suppliers (Almería, Spain). Boric acid (H3BO3, salts. It has two stable isotopes, 10B and 11B, with spin- purity >99%) was purchased from Panreac (Barcelona, Spain), Published on 05 September 2018. Downloaded by Brock University on 12/15/2024 3:03:19 AM. quantum numbers of 3 and 3/2, respectively. 11B is more suit- sodium tetraborate (Borax, purity 99%) was obtained from able for NMR because of its higher sensitivity associated with Sigma-Aldrich (St Louis, MO, USA) and deuterium oxide (D2O, its higher natural abundance (80.1 vs. 19.9%), higher gyromag- D ≥ 99.9%) and Norell™ thin-wall natural quartz NMR sample netic constant (8.58 × 107 vs. 2.87 × 107 rad s−1 T−1), lower tubes (0.025 M), highly water- using quartz NMR tubes. NMR spectra were collected using soluble polyborate ions such as [B3O3(OH)4]−, [B4O5(OH)4]2– the following acquisition parameters: number of FID data and [B5O6(OH)4]− are formed.39,40 points (TD) = 64 K, acquisition time (AQ) = 0.6 s, relaxation As far as we know, 11B qNMR has never been used for the delay (D1) = 0.1 s, FID resolution (FIDRES) = 0.58 Hz, number quantitative analysis of boric acid-containing substances. of scans (NS) = 64 and pre-scan delay (DE) = 6.5 µs. The Therefore, we report herein the development and validation of Lorentzian line-broadening factor of 1.5 Hz was applied to the a rapid, sensitive, and reliable qNMR-based method that takes total FID prior to Fourier transformation. The spectra were advantage of the quadrupolar nature of boron-11 towards the automatically phased, baseline-corrected and integrated using 4708 | Analyst, 2018, 143, 4707–4714 This journal is © The Royal Society of Chemistry 2018  View Article Online Analyst Paper TOPSPIN software (version 3.5). Automatic integration was tice is to use quartz NMR tubes that contain low quantities of carried out using the multi_integ3 command. The spectro- boron (