Chemistry · MU Pleven

Photometric analysis – principles and position in clinical laboratory and biochemistry.

Explains photometric analysis as a way of measuring light absorption to quantify substances such as glucose, bilirubin and enzymes, starting from the Beer–Lambert relationship between absorbance, concentration and path length. It then covers the spectrophotometer's main components, the calibration and measurement procedure, and the clinical and biochemical applications. A summary table links common analytes such as glucose, bilirubin, urea, creatinine and liver enzymes to their samples and clinical uses.

Inside: 9 sections · 2 labelled pictures · 1 table · 15 flashcards · 4 min

Topic 24 of 47 in the MU Pleven syllabus for Chemistry (Medicine, Year 1). The free AceMed note covers it in 9 sections, about 573 words (4 min of reading), with 15 flashcards.

In this note

  1. Photometric Analysis – Principles and Position in Clinical Laboratory and Biochemistry
  2. Introduction
  3. Principle
  4. Position in Clinical Laboratory and Biochemistry
  5. Apparatus
  6. Procedure of Photometric Analysis
  7. Diagram Explanation
  8. Applications in Clinical Biochemistry
  9. Conclusion

Introduction

Photometric analysis is a branch of analytical chemistry that involves the measurement of light absorption or emission by a substance. It is widely used in clinical laboratories and biochemistry for the quantitative determination of biological substances such as proteins, enzymes, glucose, bilirubin, hemoglobin, and other metabolites. The technique relies on the principle that the intensity of light absorbed by a solution is proportional to the concentration of the absorbing substance.

Principle

The principle of photometric analysis is based on Beer–Lambert’s Law:

Where:

  • (A) = Absorbance of the solution (no units)
  • (\varepsilon) = Molar absorptivity (L·mol⁻¹·cm⁻¹)
  • (l) = Path length of the cuvette (cm)
  • (c) = Concentration of the analyte (mol·L⁻¹)
  • A solution absorbs light of a specific wavelength, and the absorbed light is measured using a photometer or spectrophotometer.
  • The absorbance is directly proportional to the concentration of the solute, allowing quantitative determination.

Position in Clinical Laboratory and Biochemistry

Photometric analysis is an essential tool in clinical diagnostics and biochemistry. Its main roles include:

  1. 1. Clinical Laboratory Applications
  2. a. Measurement of blood glucose levels for diabetes management
  3. b. Determination of serum bilirubin, urea, creatinine, and cholesterol
  4. c. Estimation of enzymes such as AST, ALT, and ALP
  5. d. Assessment of electrolytes like sodium, potassium, and calcium
  6. 2. Biochemistry Applications
  7. a. Quantification of proteins and amino acids
  8. b. Enzyme kinetics and activity studies
  9. c. Analysis of nucleic acids (DNA/RNA) and their concentration
  10. d. Monitoring metabolic pathways in research

Advantages in clinical and biochemical settings:

  • High sensitivity and accuracy
  • Rapid and reproducible results
  • Minimal sample required
  • Automated analysis possible with modern spectrophotometers

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