A STUDY OF SOME PROBLEMS IN DETERMINING STOICHEIOMETRIC PROTON DISSOCIATION CONSTANTS OF COMPLEXES BY POTENTIOMETRIC TITRATIONS USING A GLASS ELECTRODE
A STUDY OF SOME PROBLEMS IN DETERMINING STOICHEIOMETRIC PROTON DISSOCIATION CONSTANTS OF COMPLEXES BY POTENTIOMETRIC TITRATIONS USING A GLASS ELECTRODE
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DOI：
10.1016/s0003-2670(01)80616-4
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发表时间：
1967-01-01
影响因子：
6.2
通讯作者：
PETTIT, LD
中科院分区：
文献类型：
--
作者：
IRVING, HM;MILES, MG;PETTIT, LD
讨论了用电位滴定技术测定酸离解常数时可能存在的误差，特别是氮三乙酸(NTA)和乙二胺四乙酸(EDTA)。当使用已用标准缓冲溶液校准过的饱和甘汞参比电极的玻璃电极进行pH测量时，可能会出现未知的结电位。酸解离常数的计算精度也会受到阳离子物种(如H4L4)的存在、总酸强度、常数的绝对值和水的自离解常数值(Kw)的影响。所有这些因素都已被定量考虑，并注意到它们对由这些酸解离常数计算出的金属络合物形成常数的影响。NtA的阳离子物种(即H4L+)的质子离解常数在20°时pK_0=0.80，μ=0.10M。
Possible errors in the measurement of acid dissociation constants by potentiometric titration techniques have been considered, with particular references to nitrilotriacetic acid (NTA) and ethylenediaminetetraacetic acid (EDTA). Unknown junction potentials can arise when pH measurements are carried out using a glass electrode with saturated calomel reference electrode which have been previously calibrated with a standard buffer solution. The magnitude of the influence of these unknown potentials has been demonstrated and an experimental procedure recommended which gives meaningful results.The precision of calculated acid dissociation constants will also be influenced by the presence of cationic species (e.g. H4L4), the total acid strength, the absolute values of the constants and the value accepted for the auto-dissociation constant of water (Kw). All these factors have been considered quantitatively and their effect on metal complex formation constants, calculated from these acid dissociation constants, noted. The proton dissociation constant of the cationic species of NTA (i.e. H4L+) has been found to have the value of pK0=0.80 at 20° and μ=0.10M.