Instrumental Analysis Lecture 7 PDF

Instrumental analysIs lecture 7 JUNE 30, 2024 2ND YEAR PHARMACY Dr. Anwar Salem Non-Spectroscopic Analysis: Turbidimetry 1. Introduction Definition: Turbidimetry is an analytical technique used to measure the turbidity (cloudiness or haziness) of a fluid due to the p...

Instrumental analysIs lecture 7 JUNE 30, 2024 2ND YEAR PHARMACY Dr. Anwar Salem Non-Spectroscopic Analysis: Turbidimetry 1. Introduction Definition: Turbidimetry is an analytical technique used to measure the turbidity (cloudiness or haziness) of a fluid due to the presence of suspended particles. The basic principle of turbidimetry is to measure the loss of intensity of light due to the scattering effect of the suspended particles in the sample. Importance: Applications in various fields such as environmental monitoring, medical diagnostics, and industrial processes. 2. Principle of Turbidimetry Basic Principle: Measures the loss of intensity of light due to scattering by suspended particles in the sample. Comparison with Absorbance: Unlike absorbance, which measures light absorbed by a sample, turbidimetry measures light scattered by particles. 3. Instrumentation A. Components: Light Source: Typically a tungsten or LED lamp. Sample Holder: Cuvette or sample cell. Detector: Photodetector to measure scattered light. B. Instrument Calibration and Maintenance Calibration Standards: Regular calibration using standard turbidity solutions, like formazin or AMCO-AEPA standards, is essential. Light Source Stability: The stability of the light source should be ensured, as fluctuations can lead to erroneous readings. Detector Sensitivity: The detector should be checked regularly for sensitivity and accuracy. Cleanliness: The sample cuvette or cell must be clean and free from scratches, as these can affect light transmission. 4. Measurement Process A. Sample Preparation: Homogeneity: The sample should be well-mixed to ensure uniform distribution of particles. Particle Size: Ideally, particles should be uniformly distributed in size. Large or irregular particles can affect the accuracy of the measurements. Filtration: Samples with very high turbidity might need dilution or filtration to bring them within the measurable range of the instrument. Avoiding Settling: Suspended particles should not settle during measurement. If settling occurs, it can lead to inaccurate readings. B. Measurement Technique: Wavelength Selection: The appropriate wavelength of light should be chosen based on the sample’s properties. For most turbidimetric measurements, a wavelength in the visible range is used. Path Length: The path length of the light through the sample (i.e., the cuvette size) should be suitable for the expected turbidity range. Blank Measurement: A blank (a clear sample with no particles) should be measured to set a baseline for zero turbidity. 5. Applications of Turbidimetry Environmental Monitoring: Measuring water quality by detecting suspended solids. Medical Diagnostics: Quantifying bacterial growth, protein concentrations, etc. Pharmaceutical Industry: Employed for quality control to check the clarity of solutions, suspensions, and other liquid formulations. Here is how the results from turbidimetry are generally interpreted: Direct Relationship: There is a direct relationship between the concentration of the suspended particles and the turbidity of the solution. As the concentration increases, the solution becomes more turbid, and less light passes through.  Calibration Curve: To quantify the concentration of particles, a calibration curve is often used. This is created by measuring the turbidity of standard solutions with known concentrations and plotting a graph of turbidity against concentration. Sample Measurement: The turbidity of the test sample is measured, and the corresponding concentration is determined by referring to the calibration curve. Low Turbidity: If the measured turbidity is low, it suggests a low concentration of the particles in the solution. High Turbidity: Conversely, a high turbidity reading indicates a high concentration of particles. Interferences: The presence of color or other substances that absorb light can affect turbidimetric measurements. These factors need to be considered when interpreting results. Nephelometry Comparison: Unlike nephelometry, which measures the light scattered by the suspended particles at a certain angle to the incident light, turbidimetry measures the decrease in the intensity of light transmitted directly through the sample. 6. Advantages and Limitations A. Advantages: Simple and quick. Non-destructive to samples. B. Limitations: Sensitivity to particle size and shape. Requires careful calibration and sample handling. 7. Conclusion Turbidimetry is a valuable tool in various fields for its ability to quickly and effectively measure the concentration of suspended particles in a solution. Its ease of use and non-destructive nature make it a popular choice for routine analysis in environmental monitoring, biological research, and quality control in manufacturing processes. Summary: In this lecture we learnt about: