Hu W, Hasebe K, Iles A, Tanaka K
Division of Chemistry, Graduate School of Science, Hokkaido University, Sapporo 060-0810, Japan.
Analyst. 2001 Jun;126(6):821-4. doi: 10.1039/b102292j.
An ion chromatographic (IC) method was developed for the high-resolution determination of a sample's free hydrogen ion concentration (H+). Highly purified lithium dodecyl sulfate was used as the stationary phase, a slightly acidified aqueous LiCl solution was used as the mobile phase and conductivity was used for analyte detection. An electrical double layer (EDL) containing H+ was established on the stationary phase by using a slightly acidified electrolyte solution as the eluent. H+ in the EDL protonated any weak acid groups (i.e., silanols) on the stationary phase so that H+ from the sample could be retained/separated purely by dodecyl sulfate. The optimum molar ratio of H+:Li+ in the EDL for this IC system was obtained by using an aqueous solution containing 40.0 mM LiCl and 0.07 mM H2SO4 as the eluent. After separation, H+ was detected by direct conductimetric measurement. An H+ detection limit of better than 8.2 x 10(-6) M was obtained from the analysis of standard aqueous H2SO4 solutions. Other monovalent cations could also be separated with this method, giving detection limits of 7.4 x 10(-5), 4.3 x 10(-5) and 4.2 x 10(-5) M for Na+, NH4+ and K+, respectively. The method was applied to the simultaneous determination of H+, Na+, NH4+ and K+ in acid rain. The results obtained showed a significant improvement in reproducibility when compared with those from a conventional pH-meter. Acid rain samples with a pH < 5 could be analyzed with this IC system.
开发了一种离子色谱（IC）方法，用于高分辨率测定样品中的游离氢离子浓度（H⁺）。使用高纯度十二烷基硫酸锂作为固定相，用微酸化的LiCl水溶液作为流动相，并用电导率检测分析物。通过使用微酸化的电解质溶液作为洗脱液，在固定相上建立了含有H⁺的双电层（EDL）。EDL中的H⁺使固定相上的任何弱酸基团（即硅醇）质子化，从而使样品中的H⁺能够仅通过十二烷基硫酸盐被保留/分离。通过使用含有40.0 mM LiCl和0.07 mM H₂SO₄的水溶液作为洗脱液，获得了该IC系统中EDL中H⁺与Li⁺的最佳摩尔比。分离后，通过直接电导测量检测H⁺。通过对标准H₂SO₄水溶液的分析，获得了优于8.2×10⁻⁶ M的H⁺检测限。其他单价阳离子也可以用该方法分离，Na⁺、NH₄⁺和K⁺的检测限分别为7.4×10⁻⁵、4.3×10⁻⁵和4.2×10⁻⁵ M。该方法应用于酸雨样品中H⁺、Na⁺、NH₄⁺和K⁺的同时测定。与传统pH计的结果相比，所得结果的重现性有显著提高。pH < 5的酸雨样品可以用该IC系统进行分析。
