EVALUATION OF SOLID PHASE EXTRACTION PROTOCOLS FOR ISOLATION OF ANALGESIC COMPOUNDS FROM BIOLOGICAL FLUIDS PRIOR TO HPLC DETERMINATION

Abstract

A comparative study of various sorbents, reversed phase silica based C18, C8, and copolymeric hydrophilic-lipophilic balanced, from different manufacturers and various eluting solvents (methanol, acetonitrile, and isopropanol) was conducted for optimization of isolating the constituents of multi-component analgesic mixtures by means of Solid Phase Extraction (SPE). Optimized SPE protocols were subsequently applied to human serum and urine samples. Traditional minicolumns and disc formats of C18 sorbent were studied as well. The effect of sorbent bed conditioning was also investigated when using novel copolymeric sorbent materials, such as OASIS and NEXUS, as both claim to function under no conditioned sorbent bed as being water wettable. An analgesic mixture containing paracetamol, caffeine, and codeine was selected as a model for this survey, since they very often co-exist in pharmaceutical formulations. Analytes were monitored at 240 nm, after isocratic elution from a C8 Inertsil analytical column. The mobile phase was a mixture of methanol and ammonium acetate (0.05 M) at a volume ratio of 40:60. Statistical evaluation revealed satisfactory accuracy, repeatability, and intermediate precision. Pharmaceutical formulation analysis yielded high recoveries ranging from 95.4 to 107.5%. Various recovery rates were obtained when the different protocols were applied. Reversed phase C18 sorbent yielded a 80–90% recovery, while copolymeric sorbents reached the 100% of analyte concentration in optimizing extraction conditions concerning the activation step and the eluting solvent.