Nephelometry measures the light-
Ans. is 'c' i.e., Scattered* When particles are suspended in a solution in a cuvette, they make the solution unclear (turbid). Incident light entering the cuvette will be subjected to three reactions :i) Some of the light will be absorbed by the particlesii) Some will be transmitted through the cuvetteiii) Some will be scattered in various directions.Turbidimetry* Turbidimetry is involved with measuring the amount of transmitted light (and calculating the absorbed light) by particles in suspension to determine the concentration of the substance in question.* Amount of absorbed light, and therefore, concentration is dependent on# Number of particles# Size of particles* Measurements are made using light spectrophotometers* Clinical Applications# Determination of the concentration of total protein in biological fluids such as urine and CSF which contain small quantities of protein (mg/L quantities) using trichloroacetic acidNephelometry* Principle# Nephelometry is concerned with measurement of scattered light from a cuvette containing suspended particles in a dilute solution.* The components of a nephelometer are the same as a light spectrophotometer except that the detector is placed at a specific angle from the incident light. The detector is a photomultiplier tube placed at a position to detect forward scattered light. Detectors may be placed at 90o, 70o or 37o depending on the angle at which most scattered light are found.* Since the amount of scattered light is far greater than the transmitted light in a turbid suspension, nephelometry offers higher sensitivity than turbidimetry.* For most clinical applications, the light source is a tungsten lamp giving light in the visible region. For higher sensitivity and for applications that determine the size and number of particles in suspension, laser light nephelometers is used.* Clinical applications of nephelometry.# Widely used to determine concentrations of unknowns where there is antigen-antibody reactions such as-* Determination of immunoglobulins (total, IgG, IgE, IgM, IgA) in serum and other biological fluids.* Determination of the concentrations of individual serum proteins; hemoglobin, haptoglobin, transferring, c-reactive protein, a1-antitrypsin, albumin (using antibodies specific for each protein).# Turbidity is measured as Nephalometric Turbidity units (NTU) or as Formazin Turbidity unit (FTU). Formazin Turbidity Unit is the International Standard Unit. Both measure the light scattered at 90o. NTU uses white light with peak spectral output at 400 to 680nm as light source. FTU uses Infrared monochromatic light with peak output at 780 to 900nm as light source.
Absorbed
transmitted
Scattered
Refracted
Miscellaneous (Bio-Chemistry)