Elfsson B, Wallin I, Eksborg S, Rudaeus K, Ros A M, Ehrsson H
Karolinska Pharmacy, Box 160, S-171 76, Stockholm, Sweden.
Eur J Pharm Sci. 1999 Jan;7(2):87-91. doi: 10.1016/s0928-0987(98)00009-8.
The chemical stability of 5-aminolevulinic acid (ALA) was studied in aqueous solution as a function of concentration, pH, temperature and in the presence of ethylenediaminetetraacetic acid (EDTA). The degradation of ALA was followed by reversed-phase liquid chromatography using a pH where ALA is protonated (pKa1=3.90; pKa2=8. 05, as determined potentiometrically). ALA was degraded by a reaction following second order kinetics. Stock solutions of 1% (60 mM) ALA were incubated at 50 degrees C. At pH 2.35, ALA was stable during the whole incubation period (37 days). The half-lives for the second-order decomposition of 1% ALA at pH 4.81 and 7.42 were 257 and 3.0 h, respectively. The degradation rate increased about 1.5 times with each 10 degrees C rise in temperature at pH 7.53 within the range studied (37-85 degrees C). The energy of activation, Ea, for the second-order decomposition of ALA was 43.7 kJmol-1. EDTA did not influence the degradation of ALA when a mixture of 1% ALA and 1% EDTA was incubated at pH 7.42.
研究了5-氨基乙酰丙酸（ALA）在水溶液中的化学稳定性，考察了其浓度、pH值、温度以及乙二胺四乙酸（EDTA）存在时对稳定性的影响。采用反相液相色谱法监测ALA的降解情况，检测时的pH值设定在ALA呈质子化状态（通过电位滴定法测定，pKa1 = 3.90；pKa2 = 8.05）。ALA的降解遵循二级动力学反应。将1%（60 mM）的ALA储备溶液在50℃下孵育。在pH 2.35时，ALA在整个孵育期（37天）内保持稳定。在pH 4.81和7.42条件下，1% ALA二级分解反应的半衰期分别为257小时和3.0小时。在所研究的温度范围（37 - 85℃）内，在pH 7.53条件下，温度每升高10℃，降解速率约增加1.5倍。ALA二级分解反应的活化能Ea为43.7 kJmol-1。当1% ALA与1% EDTA的混合物在pH 7.42条件下孵育时，EDTA不影响ALA的降解。
