Thermodynamics of the second dissociation constant and standards for pH of 3-(N-morpholino) propanesulfonic acid (MOPS) buffers from 5 to 55°C
Thermodynamics of the second dissociation constant and standards for pH of 3-(N-morpholino) propanesulfonic acid (MOPS) buffers from 5 to 55°C
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DOI：
10.1023/a:1022692629289
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发表时间：
1998-01-01
影响因子：
1.2
通讯作者：
Wu, YC
中科院分区：
文献类型：
--
作者：
Roy, RN;Mrad, DR;Wu, YC
用氢电极和银-氯化银电极测量无液结电池的电动势，在5 ~ 55 ℃的8个温度下测定了3-（N-吗啉代）丙磺酸（MOPS）的第二离解常数pK（2）。pK（2）在25 ℃时的值为7.18 +/- 0.001，在37 ℃时为7.044 +/- 0.002。热力学量Δ G度、Δ H度、Δ S度和Δ C-p（0）已从pK（2）的温度系数导出。该缓冲液的离子强度I = 0.16 mol·kg（-1），接近血清的离子强度，已被推荐作为测量生理液体的有用的二级pH标准。制备具有以下组成的五种缓冲溶液：（a）MOPS的等摩尔混合物，（0.05 mol·kg（-1））+ NaMOPS，（0.05 mol-kg（-1））;（B）MOPS（0.05 mol-kg（-1））+ NaMOPS（0.05 mol-kg（-1））+ NaCl（0.05 mol-kg（-1））;（c）MOPS（0.05 mol-kg（-1））+ NaMOPS（0.05 mol-kg（-1））; + NaCl（d）MOPS（0.08 mol·kg（-1））+ NaMOPS（0.08 mol·kg（-1））;和（e）MOPS（0.08 mol·kg（-1））+ NaMOPS（0.08 mol·kg（-1））+ NaCl（0.08 mol·kg（-1））。将通过使用pH计+玻璃电极组件获得的pH值与从用KCl饱和的流动结甘汞池（池B）测量的那些pH值以及从在25和37 ℃下没有液体结的池（A）获得的那些pH值进行比较。对于生理磷酸盐参比溶液以及上述MOPS缓冲液（d）和（e），已经在25和37 ℃下获得了液体接界电位E-j的常规值。
The second dissociation constant pK(2) of 3-(N-morpholino)propanesulfonic acid (MOPS) has been determined at eight temperatures from 5 to 55 degrees C by measurements of the emf of cells without liquid junction, utilizing hydrogen electrodes and silver-silver chloride electrodes. The pK(2) has a value of 7.18 +/- 0.001 at 25 degrees C and 7.044 +/- 0.002 at 37 degrees C. The thermodynamic quantities Delta G degrees, Delta H degrees, Delta S degrees, and Delta C-p(0) have been derived from the temperature coefficients of the pK(2). This buffer at ionic strength I = 0.16 mol-kg(-1) close to that of blood serum, has been recommended as a useful secondary pH standard for measurements of physiological fluids. Five buffer solutions with the following compositions were prepared: (a) equimolal mixture of MOPS (0.05 mol-kg(-1)) + NaMOPS, (0.05 mol-kg(-1)); (b) MOPS (0.05 mol-kg(-1)) + NaMOPS (0.05 mol-kg(-1)) + NaCl (0.05 mol-kg(-1)); (c) MOPS (0.05 mol-kg(-1)) + NaMOPS (0.05 mol-kg(-1)); + NaCl (0.11 mol-kg(-1)); (d) MOPS (0.08 mol-kg(-1)) + NaMOPS (0.08 mol-kg(-1)); and (e) MOPS (0.08 mol-kg(-1)) + NaMOPS (0.08 mol-kg(-1)) + NaCl (0.08 mol-kg(-1)). The pH values obtained by using the pH meter + glass electrode assembly are compared with those measured from a flow-junction calomel cell saturated with KCI (cell B), as well as those obtained from cell (A) without liquid junction at 25 and 37 degrees C. The conventional values of the liquid junction potentials E-j have been obtained at 25 and 37 degrees C for the physiological phosphate reference solution as well as for the MOPS buffers (d) and (e) mentioned above.