Extraction of Alkaloids by the Micellar Phase of Sodium Dodecyl Sulfate for their Further Chromatographic Determination

Abstract

The influence of the main parameters of hydrophobicity (log P), structure (PSA), and protolytic properties (pKa) of some alkaloids on their distribution into modified micellar extraction system based on sodium dodecyl sulfate (SDS-NaCl-H2Sal) was established. The proposed prognostic regression D= 941 – 4.09∙PSA – 27.3∙log P – 44.5∙рКа is characterized by satisfactory indexes (R-squared 99.9, F-ratio 242, standard error 7.19, mean absolute error 2.38). The accuracy of the alkaloid distribution prediction by this regression is well correlated with accuracy of the measurement of the extraction parameters. The predicted D value for novocaine is 257 (R = 93 %), and the experimentally found D value is 202 (R = 91 %). For lidocaine, the predicted and experimental D values are practically the same and equal 386 (R = 95 %) and 380 (R = 95 %), respectively. The possibility of quantitative extraction of positively charged hydrophilic (logP < 0) organic bases into the micellar phase of SDS is shown. The developed hybrid HPLC technique for determining papaverine in urine with its cationic form (pH=2) preconcentration by modified micellar SDS phase is characterized by sufficient sensitivity and accuracy (DL= 0.01 μg/ml, Sr ≤ 0.08, R > 99 %, K = 10). Only alkaloids with log P > 1.4 can be determined by this technique because otherwise, the chromatographic peaks of salicylic acid and alkaloid cannot separate.