NEPHELOMETRY: WHAT IT CONSISTS OF AND APPLICATIONS - CHEMISTRY - 2025

The nephelometry involves measurement of the radiation caused by particles (in solution or suspension) and measuring the power of the scattered radiation at an angle to the direction of the incident radiation.

When a suspended particle is hit by a beam of light, there is a portion of the light that is reflected, another portion is absorbed, another is deflected, and the rest is transmitted. This is why when the light hits a transparent medium in which there is a suspension of solid particles, the suspension appears cloudy.

What is nephelometry?

Dispersion of radiation by particles in solution

At the moment in which a light beam hits the particles of a suspended substance, the direction of propagation of the beam changes its direction. This effect depends on the following:

1.Dimensions of the particle (size and shape).

2. Characteristics of the suspension (concentration).

3.Wavelength and intensity of light.

4.Incident light distance.

5. Angle of detection.

6. Refractive index of the medium.

Nephelometer

The nephelometer is an instrument used to measure suspended particles in a liquid sample or in a gas. Thus, a photocell placed at a 90 ° angle to a light source detects radiation from particles present in the suspension.

Likewise, the light reflected by the particles towards the photocell depends on the density of the particles. Diagram 1 presents the basic components that make up a nephelometer:

Figure 1. Basic components of a nephelometer.

TO.

In nephelometry it is of vital importance to have a radiation source with a high light output. There are different types, ranging from xenon lamps and mercury vapor lamps, tungsten halogen lamps, laser radiation, among others.

B.

This system is located between the radiation source and the cuvette, so that in this way radiation with different wavelengths compared to the desired radiation is avoided on the cuvette.

Otherwise, fluorescence reactions or heating effects in the solution would cause measurement deviations.

C.

It is a generally prismatic or cylindrical container, and it can have different sizes. In this is the solution under study.

D.

The detector is located at a specific distance (generally very close to the cuvette) and is in charge of detecting the radiation scattered by the particles in the suspension.

AND.

Generally it is an electronic machine that receives, converts and processes data, which in this case are the measurements obtained from the study carried out.

Deviations

Every measurement is subject to a percentage of error, which is mainly given by:

Contaminated cuvettes: in the cuvettes, any agent external to the solution under study, whether inside or outside the cuvette, reduces the radiant light on the way to the detector (defective cuvettes, dust adhering to the walls of the cuvette).

Interferences: the presence of a microbial contaminant or turbidity disperses the radiant energy, increasing the intensity of the dispersion.

Fluorescent compounds: these are those compounds that, when excited by incident radiation, cause erroneous and high scattering density readings.

Reagent Storage: Inadequate system temperature could cause adverse study conditions and could lead to the presence of cloudy or precipitated reagents.

Fluctuations in electrical power: to prevent incident radiation from being a source of error, voltage stabilizers are recommended for uniform radiation.

Metrological characteristics

Since the radiant power of the radiation detected is directly proportional to the mass concentration of the particles, nephelometric studies have, in theory, a higher metrological sensitivity than other similar methods (such as turbidimetry).

Furthermore, this technique requires dilute solutions. This allows both absorption and reflection phenomena to be minimized.

Applications

Nephelometric studies occupy a very important position in clinical laboratories. Applications range from the determination of immunoglobulins and acute phase proteins, complement and coagulation.

Immune complex detection

When a biological sample contains an antigen of interest, it is mixed (in a buffer solution) with an antibody to form an immune complex.

Nephelometry measures the amount of light that is scattered by the antigen-antibody reaction (Ag-Ac), and in this way immune complexes are detected.

This study can be carried out by two methods:

End Point Nephelometry:

This technique can be used for end-point analysis, in which the antibody of the biological sample studied is incubated for 24 hours.

The Ag-Ac complex is measured using a nephelometer and the amount of scattered light is compared with the same measurement carried out before the complex was formed.

Kinetic nephelometry

In this method, the rate of complex formation is continuously monitored. The reaction rate depends on the concentration of the antigen in the sample. Here the measurements are taken as a function of time, so the first measurement is taken at time "zero" (t = 0).

Kinetic nephelometry is the most widely used technique, since the study can be carried out in 1 hour, compared to the long period of time of the end point method. The dispersion ratio is measured just after adding the reagent.

Therefore, as long as the reagent is constant, the amount of antigen present is considered directly proportional to the rate of change.

Other apps

Nephelometry is generally used in the analysis of the chemical quality of water, to determine clarity and to control its treatment processes.

It is also used to measure air pollution, in which the concentration of the particles is determined from the dispersion they produce in an incident light.

References

1. Britannica, E. (nd). Nephelometry and turbidimetry. Recovered from britannica.com
2. Al-Saleh, M. (nd). Turbidimetry & Nephelometry. Retrieved from pdfs.semanticscholar.org
3. Bangs Laboratories, Inc. (nd). Recovered from technochemical.com
4. Morais, IV (2006). Turbidimetric and Nephelometric Flow Analysis. Obtained from repository.ucp.p
5. Sasson, S. (2014). Principles of nephelometry and turbidimetry. Recovered from notesonimmunology.files.wordpress.com
6. Stanley, J. (2002). Essentials of Immunology & Serology. Albany, NY: Thompson Learning. Obtained from books.google.co.ve
7. Wikipedia. (sf). Nephelometry (medicine). Recovered from en.wikipedia.org