The combination of inorganic phosphate and pyrophosphate 31P-NMR for the electrodeless pH determination in the 5–12 range

IF 1.9 3区 化学 Q3 CHEMISTRY, MULTIDISCIPLINARY Magnetic Resonance in Chemistry Pub Date : 2024-01-20 DOI:10.1002/mrc.5429
Paola Carta, Mariano Andrea Scorciapino
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Abstract

Potentiometry is the primary pH measurement method, but alternatives are sought beyond glass electrodes operative limitations. In nuclear magnetic resonance (NMR) experiments, electrodeless pH sensing is important to track changes along titrations, during chemical reactions or inside compartmentalized environments inaccessible to electrodes, for instance. Although several interesting NMR pH indicators have been already presented, the potential of inorganic phosphate is overlooked, despite its common presence in NMR samples as the buffer main component. Its use for electrodeless pH determination can be expanded by exploiting all its three proton dissociations. This study was aimed at verifying the use of inorganic phosphate 31P chemical shift to sense pH variations, and at exploring the complementary use of pyrophosphate ions to cover a wide pH range. A simple set of equations is presented to utilize both phosphate and pyrophosphate 31P chemical shift in combination for accurate pH determination without a glass electrode over the 5–12 pH range, and without affecting the spectrum of other nuclei. The present study demonstrated an average deviation of 0.09 (maximum <0.2) pH unit from glass electrode measurements. The trimethylphosphate can be used as a suitable chemical shift reference for both 31P and 1H (also 13C), with its hydrolysis being significant only at pH > 12. The method was also demonstrated by determining the pKa of three distinct molecules in a mixture and by comparing the results to those obtained when the glass electrode was used to measure the pH. The approach shown here can be easily tuned to different experimental conditions.

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结合无机磷酸盐和焦磷酸盐 31 P-NMR 进行 5-12 范围内的无电极 pH 值测定。
电位计是测量 pH 值的主要方法,但除了玻璃电极的操作限制外,人们还在寻求其他方法。在核磁共振(NMR)实验中,无电极 pH 值感应对于跟踪滴定过程、化学反应过程或电极无法进入的分隔环境中的变化非常重要。尽管已经介绍了几种有趣的核磁共振 pH 指示剂,但无机磷酸盐的潜力却被忽视了,尽管它作为缓冲剂的主要成分普遍存在于核磁共振样品中。通过利用无机磷酸盐的三种质子解离,可以扩大其在无电极 pH 值测定中的应用。本研究旨在验证利用无机磷酸盐 31 P 化学位移来感知 pH 值变化,并探索焦磷酸离子的互补使用,以覆盖较宽的 pH 值范围。本研究提出了一套简单的方程,结合使用磷酸盐和焦磷酸 31 P 化学位移,在 5-12 pH 范围内无需玻璃电极即可准确测定 pH 值,且不会影响其他核素的光谱。本研究表明,该方法的平均偏差为 0.09(31 P 和 1 H(也包括 13 C)的最大值),其水解作用仅在 pH 值大于 12 时才显著。通过测定混合物中三种不同分子的 pKa,并将结果与使用玻璃电极测量 pH 值时的结果进行比较,也证明了该方法的有效性。这里展示的方法很容易根据不同的实验条件进行调整。
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来源期刊
CiteScore
4.70
自引率
10.00%
发文量
99
审稿时长
1 months
期刊介绍: MRC is devoted to the rapid publication of papers which are concerned with the development of magnetic resonance techniques, or in which the application of such techniques plays a pivotal part. Contributions from scientists working in all areas of NMR, ESR and NQR are invited, and papers describing applications in all branches of chemistry, structural biology and materials chemistry are published. The journal is of particular interest not only to scientists working in academic research, but also those working in commercial organisations who need to keep up-to-date with the latest practical applications of magnetic resonance techniques.
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