Radioimmunoassay: Instrumentation

 INSTRUMENTATION

The two most vital equipments essentially required for radioimmunoassay (RIA) are, namely :

 

(i) Centrifuge, and

 

(ii) Radioactive Counters.

 

These two equipments shall now be discussed briefly as follows :

 

 

1. CENTRIFUGE

 

A centrifuge which is capable of generating 1200-2500 rpm using swing-bucket-rotor or 3500 to 4000 rpm using a fixed-angle-head rotor can be employed effectively. However, the former type is preferred because of the fact that here the pellet is formed at the bottom of the test tube and the supernatant layer is more easily removed in comparison to the latter type where the pellet is formed at an angle. In case, a centrifuge having relatively less gravitational force is employed then it is absolutely necessary to enhance the centrifugation time until suitable pellets are formed duly.

 

 

2. RADIOACTIVE COUNTERS

 

In usual practice, two types of radioactive counters are mainly employed depending on the type of radioactive substance used, namely :

 

(a) Gamma Counters, and

 

(b) Scintillation Counters.

 

2.1. Gamma Counters

 

These are used invariably for the gamma-energy emitting isotopes, for instance : 125I-the more com-mon iodine-isotope.

 

2.2. Scintillation Counters

 

These are mostly used for counting beta-energy-emitting isotopes, such as : tritium 3H and 14C-(Carbon-14) isotopes.

 

First and foremost, radioimmunoassays were universally based on the 3H or 14C isotope labelling tech-nique, but this has the main disadvantage of using liquid-scintillation counting. Therefore, the comparatively much simpler technique of gamma-ray counting by labelling compounds with 124I, 125I, or 131I is now being increasingly utilized wherever such labelling is practically feasible.