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An. R. Acad. Nac. Farm., 2009, 75 (1): 25-41

ARTÍCULO

Mono and biexponential models in radioimmunoassay
of insulin

Ricardo Díez Montoro1, M.ª Teresa Salabert Salvador1, José Luis
Moreno Frigols1,2,*

1 Dpt. of Physical Chemistry. Faculty of Pharmacy. Valencia, Spain.
2 Radioisotope Service. Hospital Clínico Universitario. Valencia, Spain.
Recibido el 1 de julio de 2008.

ABSTRACT

Radioimmunoassay (RIA) is a principal method for quantifying
serum Insulin concentration. We studied the influence of initial con-
centration of 125I-labeled antigen (M) and unlabeled Insulin (Q), vis-
cosity and temperature on the substitution reaction between Q and
the immunocomplex (PM) formed by M and the anti-Insulin antibody
(P). The accuracy of this method is critically dependent on such fac-
tors. In addition, we propose a kinetic model for this reaction. We
used a commercially available RIA kit for Insulin, a gamma counter,
and a viscosimeter to study the effect of initial concentration of M,
ionic strength, viscosity, and temperature on the substitution reaction
between M and Q. Data were analyzed using Statistica software. The
apparent rate constant for the reaction between PM and Q is depend-
ent on the initial concentrations of M and Q, and the viscosity of the
reaction medium, and temperature, and independent of the ionic
strength.

A kinetic model for the displacement of the 125I-Insulin by the
Insulin in its union to a specific antibody is proposed. Such model
adjusts satisfactorily to the results and shows the influence of the va-
riables studied on the sensitivity of the method of RIA on which the
analytical determination of the Insulin is based.

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