Fundamental studies in reversed-phase liquid-solid extraction of basic drugs; III: Sample matrix effects.

Area of Science:

• Analytical Chemistry
• Pharmacokinetics

Background:

• Direct analysis of plasma simplifies sample preparation for drug and metabolite quantification.
• Reversed-phase liquid-solid extraction (RPSLSE) is a common technique for isolating analytes from biological matrices.
• Understanding factors influencing RPSLSE from plasma is crucial for method development.

Purpose of the Study:

• To investigate factors affecting the extraction of basic solutes from plasma using RPSLSE.
• To establish optimal sample application conditions for direct plasma analysis.
• To understand the influence of plasma components on extraction efficiency.

Main Methods:

• Studied 13 basic solutes with controlled pKa, log P, and plasma protein binding.
• Investigated direct application of plasma samples to reversed-phase cartridges.
• Evaluated the effect of sample acidification and wash solvents on extraction recovery.
• Assessed the impact of lipophilicity (log D at pH 7.4) on optimal application conditions.

Main Results:

• Direct plasma analysis is feasible by optimizing sample application conditions based on lipophilicity and protein binding.
• Lipophilic compounds (log D > 2.03) require acidified plasma, while polar compounds (log D < 0.9) are best applied untreated.
• Optimal conditions for intermediate lipophilicity compounds could not be predicted.
• Cationic plasma components, not proteinaceous ones, influence extraction, potentially by attenuating cation exchange, leading to easier elution.

Conclusions:

• Sample application conditions are critical for successful direct plasma extraction via RPSLSE.
• Lipophilicity and protein binding are key predictors for optimizing sample preparation.
• Further research is needed to predict optimal conditions for compounds with intermediate lipophilicity.