DETERMINATION OF THEOPHYLLINE IN SERUM BY MOLECULARLY IMPRINTED SOLID-PHASE EXTRACTION WITH PULSED ELUTION

The technique of molecular imprinting is used to produce an extensivel y cross-linked poly(methacrylic acid-co-ethylene dimethacrylate) mater ial that contains theophylline as a print molecule. After Soxhlet extr action of the theophylline, binding sites are formed in the polymer wi th complementary size, shape, and positioning of chemical functionalit ies. The molecularly imprinted polymer's (MIP) high theophylline selec tivity, chemical stability, and physically robust nature make it an id eal stationary-phase material in columns for HPLC separation of theoph ylline from other structurally related drug compounds, Mobile-phase te sts confirm that a retention mechanism typical of normal-phase chromat ography governs the separation, and selectivity of the MIP column can be controlled by a combination of the mobile phase and the sample solv ent. Under optimal conditions, the MIP column functions like a solid-p hase sorbent for theophylline extraction. Rapid elution of the bound t heophylline can be accomplished in a pulsed format through injection o f 20 mu L of a solvent that has the proper polarity and protic nature to disrupt the electrostatic interactions and hydrogen bonding between theophylline and binding sites. A concentration detection limit of 12 0 ng/mL is obtained using direct UV absorption detection at 270 nm, wh ich corresponds to a mass detection limit of 2.4 ng, This new techniqu e, molecularly imprinted solid-phase extraction with pulsed elution (M ISPE-PE), permits on-line preconcentration of theophylline from a larg e volume of dilute sample solution. Using a sample volume of 300 mu L, a 40 ng/mL standard solution produces a detectable peak signal. Appli cation of MISPE-PE in serum analysis further demonstrates the high cap ability of the MIP column to selectively isolate theophylline from oth er matrix components for fast, accurate determination.