Types of Chemical Labelling: Qualitative and Quantitative | Radioactive Tracer

After reading this article you will learn about qualitative and quantitative types of chemical labelling.

Qualitative Chemical Labelling:

It is also known as in vivo or surface measurement. Through this qualitative measurement, the rate of movement and uptake pattern of plant nutrients viz. p, k etc. by plants—can be made. Circulation times ‘in normal and diseased humans by using Na-24, thyroid function using 1-131 can also be measured.

In addition, gross rates of movement to provide information on the dynamics of transfer of biological material, rates of translocation of different plant nutrients, effect of temperature variation, respiratory poisons, killing of stem of streams etc. can also be measured successfully.

Quantitative Chemical Labelling:

It is measure based on the principles that the amount of radioactivity is proportional to the amount of radioisotopes present. The radioactive isotopes behave similarly to that of stable counterpart before start of decay.

However, when two or more sources are present, the assessment for the contribution of a labeled source towards the production of end product is possible. In addition, the assessment of unknown element or compound in a system without its quantitative separation is possible.

From the quantitative point of view, radioisotopes are being used to assess the contribution of particular source when two or more sources contribute towards the final end product. As for as example, one of the contributing sources is labeled to a known specific activity (Si).

A known quantity of the labeled source (Y) is added to the system and the system containing unlabeled source (X) reacts with labeled system resulting final product.

The specific activity (sf) is then determined after isolation of the final product as follows:

where, x and y are the amounts found in the final product derived from sources X and Y respec­tively.

Specific activity of the product (Sf) = Activity/Mass = x(Si)/x + y)

.^.. x/y + x = Sf/Si = Specific activity of the product/Specific activity of the labeled source

The specific activities in the plant (Sf) and fertilizer (Si) are determined, and the following relationships will hold well in case of a plant growing in a soil to which fertilizer labeled ³²P has been added:

(a) Phosphorus in the plant derived from fertilizer (Pdff)

= Specific activity of the plant/Specific activity of fertilizer

= Sf/Si = A

(b) Total P in the plant derived from the fertilizer

= Specific activity of plant (Sf) × Total P in the plant Specific activity of fertilizer (Si)

= A × Total P in the plant = B

(c) % utilization of P applied = B/Amount of applied P × 100

Radioisotopes are used in agriculture to follow up or to trace the movement of plant nutrient from bulk soil to rhizosphere as well as translocation of nutrients within the plant. The radioisotopes are traced in the plant body by means of radio-autographs. A classic example of this is the absorption of phosphorus by plants from the phosphates in the soil or phosphatic fertilizers tagged with radio phosphorus ³²P.

Radioisotopes are also used in medicine both for diagnosis as well as medical treatment. Radio cobalt ⁶⁰Co has of late come into use as a source of radiation for cancer treatment. Radio phosphorus is used to control certain blood disorders such as polycythemia vera in which the bone marrow produces an excess of red blood corpuscles.

Iodine is known to be selectively absorbed by the thyroid gland. Radio iodine is found to be preferentially absorbed by tumorous growth, a fact that has been made use of in locating brain tumours. Besides these, radioisotopes are finding ever growing application in technology.

(c) Per cent utilization of the applied fertilizer

= Total P in plant/Amount of applied fertilizer × Sp. activity of the plant/Sp. activity of the fertilizer × 100

= B/Amount of applied P fertilizer × 100

[^._.^. B = Sp. act of the plant/Sp. act of the fertilizer × Total P in the Plant]