The substance Tris (or THAM, 2-amino-2-hydroxymethyl-1,3-propanediol, CAS 77–86-1), and its protonated form TrisH⁺, is used in the preparation of pH buffer solutions for applications in seawater chemistry. The development of an acid-base chemical speciation model of buffer solutions containing Tris, TrisH⁺, and the major ions of seawater is desirable so that: (i) the effects of changes in the composition of the medium on pH can be calculated; (ii) pH on the free (a measure of [H⁺]) and total (a measure of ([H⁺] + [HSO₄⁻])) scales can be interconverted; (iii) approximations inherent in the definition of the total pH scale can be quantified; (iv) electrode pairs such as H⁺/Cl⁻ and H⁺/Na⁺ can more easily be calibrated for the measurement of pH. As a first step towards these goals we have extended the Pitzer-based speciation model of Waters and Millero (Mar. Chem. 149, 8–22, 2013) for artificial seawater to include Tris and TrisH⁺, at 25 °C. Estimates of the variances and covariances of the additional interaction parameters were obtained by Monte Carlo simulation. This enables the total uncertainty of any model-calculated quantity (e.g., pH, speciation) to be estimated, as well as the individual contributions of all interaction parameters and equilibrium constants. This is important for model development, because it allows the key interactions to be identified. The model was tested against measured EMFs of cells containing Tris buffer in artificial seawater at 25 °C, and the mean deviation was found to be 0.13 ± 0.070 mV for salinities 20 to 40. Total variances for calculated electromotive forces of the buffer solutions are dominated by contributions from just a few interaction parameters, making it likely that the model can readily be improved. The model was used to quantify the difference between various definitions of total pH and –log₁₀([H⁺] + [HSO₄⁻]) in Tris buffer solutions at 25 °C, for the first time (item (iii) above). The results suggest that the total pH scale can readily be extended to low salinities using the established approach for substituting TrisH⁺ for Na⁺ in the buffer solutions, especially if the speciation model is used to quantify the effect on pH of the substitution. The relationships between electromotive force (EMF), and pH on the total scale, with buffer molality in artificial seawater at constant salinity are shown to be linear above about 0.01 to 0.02 mol kg⁻¹ buffer molality. The pH of Tris buffers containing ratios of TrisH⁺ to Tris that vary from unity can be calculated very simply. Technical aspects of the total pH scale, such as the extrapolation of pH to zero buffer (at constant salinity), are clarified. Recommendations are made for further work to extend the model to the temperature range 0–45 °C, and improve accuracy, so that requirements (i) to (iv) above can be fully met.

物质 Tris（或 THAM，2-amino-2-hydroxymethyl-1,3-propanediol，CAS 77–86-1）及其质子化形式 TrisH ⁺用于制备用于海水化学的 pH 缓冲溶液. ^{需要开发含有 Tris、TrisH +}和海水主要离子的缓冲溶液的酸碱化学形态模型，以便： (i) 可以计算介质组成变化对 pH 值的影响；(ii) 自由（[H ⁺ ] 的量度）和总（([H ⁺ ] + [HSO ₄ ^- ]) 的量度）尺度上的 pH 值可以相互转换；(iii) 总 pH 标度定义中固有的近似值可以量化；(iv) 电极对，例如 H ⁺/Cl ^-和 H ⁺ /Na ⁺可以更容易地校准以测量 pH 值。作为实现这些目标的第一步，我们扩展了基于 Pitzer 的 Waters 和 Millero 物种形成模型（Mar. Chem. 149, 8-22, 2013），用于人工海水，包括 Tris 和 TrisH ⁺，在 25 °C。附加相互作用参数的方差和协方差的估计是通过蒙特卡罗模拟获得的。这使得可以估计任何模型计算量（例如，pH、物种形成）的总不确定性，以及所有相互作用参数和平衡常数的个体贡献。这对于模型开发很重要，因为它允许识别关键交互。该模型在 25 °C 的人造海水中针对含有 Tris 缓冲液的细胞的测量 EMF 进行了测试，发现平均偏差为 0.13 ± 0.070 mV，盐度为 20 至 40。缓冲溶液的计算电动势的总方差占主导地位通过来自几个交互参数的贡献，使得模型很可能很容易得到改进。₁₀ ([H ⁺ ] + [HSO ₄ ^- ]) 在 Tris 缓冲溶液中，在 25 °C 下，第一次（上文第 (iii) 项）。结果表明，使用已建立的在缓冲溶液中用 TrisH ⁺代替 Na ⁺的方法，可以很容易地将总 pH 范围扩展到低盐度，特别是如果使用物种形成模型来量化替代对 pH 的影响。电动势 (EMF) 与总规模的 pH 值之间的关系，在盐度恒定的人造海水中，缓冲摩尔浓度在约 0.01 至 0.02 mol kg ^-1缓冲摩尔浓度以上呈线性关系。^{含有比例 TrisH +}的 Tris 缓冲液的 pH 值与单位不同的 Tris 可以非常简单地计算出来。阐明了总 pH 值标度的技术方面，例如将 pH 值外推至零缓冲液（在恒定盐度下）。建议进一步将模型扩展到0-45°C的温度范围，并提高精度，以充分满足上述（i）至（iv）的要求。