Wm. Mullett et Epc. Lai, DETERMINATION OF THEOPHYLLINE IN SERUM BY MOLECULARLY IMPRINTED SOLID-PHASE EXTRACTION WITH PULSED ELUTION, Analytical chemistry (Washington), 70(17), 1998, pp. 3636-3641
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.