Çelebİer Mustafa, Nennİ Merve, Kaplan Ozan, Akgeyİk Emrah, Kaynak Mustafa Sinan, Şahİn Selma
Hacettepe University Faculty of Pharmacy, Department of Analytical Chemistry, Ankara, Turkey.
Çukurova University Faculty of Pharmacy, Department of Analytical Chemistry, Adana, Turkey.
Turk J Pharm Sci. 2020 Oct;17(5):535-541. doi: 10.4274/tjps.galenos.2019.82335. Epub 2020 Oct 30.
The aim of this study was to determine the acid dissociation constant (pKa) of piroxicam using high performance liquid chromatography (HPLC) and ultraviolet-visible (UV-Vis) spectrophotometry, and to determine the partition coefficient (Log P), distribution coefficient (Log D), and "Log kw" values of piroxicam using HPLC.
The HPLC studies were performed on a reversed-phase ACE C18 (150x4.6 mm ID, 5 μm) column at a flow rate of 1.0 mL min. The detector was set to 360 nm. Log D at different pH values (3.0-6.5) was examined with a phosphate buffer (20 mM) and acetonitrile (30:70 v/v) mixture as the mobile phase. For pKa determination, HPLC studies were performed with a mixture of phosphate buffer (20 mM) and methanol within the pH range of 3.50-6.00. Log kw measurements were performed with phosphate buffer (20 mM) and MeOH (from 20:80 v/v to 10:90 v/v) mixtures within the pH range of 3.50-6.00. UV-Vis spectrophotometric pKa measurements were performed at 285 nm wavelength.
The pKa value of piroxicam was found to be 5.3 by HPLC and 5.7 by UV-Vis spectrophotometry. Log P of piroxicam was determined as 1.58 in our experimental conditions. Log D values were 1.57, 1.57, 1.44, 1.13, and 0.46 for pH values of 3.17, 3.79, 4.44, 5.42, and 6.56, respectively.
In the literature, different Log P (3.1, 2.2, and 0.6) and pKa (6.3 and 4.8) values were reported for piroxicam. The Log P (1.58) and pKa (5.3 and 5.7) values obtained for piroxicam in our study were within the range of the literature values. All these results indicate that different experimental approaches used for the determination of physicochemical properties could provide different values. Although UV spectrophotometry is easy to apply, HPLC is a unique technique for simultaneous determination of pKa, Log D, and Log P values of compounds.
本研究旨在使用高效液相色谱法（HPLC）和紫外可见（UV-Vis）分光光度法测定吡罗昔康的酸解离常数（pKa），并使用HPLC测定吡罗昔康的分配系数（Log P）、分布系数（Log D）和“Log kw”值。
HPLC研究在反相ACE C18（内径150x4.6 mm，5μm）柱上进行，流速为1.0 mL/min。检测器设置为360 nm。以磷酸盐缓冲液（20 mM）和乙腈（30:70 v/v）混合物为流动相，检测不同pH值（3.0 - 6.5）下的Log D。为测定pKa，在pH值3.50 - 6.00范围内，用磷酸盐缓冲液（20 mM）和甲醇的混合物进行HPLC研究。在pH值3.50 - 6.00范围内，用磷酸盐缓冲液（20 mM）和甲醇（从20:80 v/v到10:90 v/v）混合物进行Log kw测量。UV-Vis分光光度法pKa测量在285 nm波长下进行。
通过HPLC测得吡罗昔康的pKa值为5.3，通过UV-Vis分光光度法测得为5.7。在我们的实验条件下，吡罗昔康的Log P值测定为1.58。pH值为3.17、3.79、4.44、5.42和6.56时的Log D值分别为1.57、1.57、1.44、1.13和0.46。
文献中报道的吡罗昔康的Log P值（3.1、2.2和0.6）和pKa值（6.3和4.8）各不相同。我们研究中获得的吡罗昔康的Log P值（1.58）和pKa值（5.3和5.7）在文献值范围内。所有这些结果表明，用于测定物理化学性质的不同实验方法可能会提供不同的值。虽然紫外分光光度法易于应用，但HPLC是同时测定化合物pKa、Log D和Log P值的独特技术。
