Turbidity meter
Measures how cloudy a liquid is by shining light through it and measuring the light scattered by tiny particles. Results are given in NTU or FNU and are used for clarity and opalescence tests.
- Pharmaceutical
- Biotech
- Water treatment
- Food & beverage
- Brewing
- Environmental testing
Test your Turbidity meter knowledge
Multiple-choice questions
Pick an answer to see whether you are right and why.
Q1. A nephelometer measures scattered light at an angle of:
basicQ2. The primary standard used to calibrate turbidity meters is:
basicQ3. How much 4000 NTU formazin stock is needed to make 500 mL of a 40 NTU standard?
intermediateQ4. A scratch on the cuvette will make the turbidity reading:
intermediateQ5. Which chemical used to prepare formazin needs special care because it is toxic?
intermediateQ6. What is the main purpose of the ratio design in a turbidity meter?
advanced
Viva questions
Think of your answer first, then open it to compare.
1. List the main sources of error when measuring turbidity.
Air bubbles, scratched or dirty cuvettes, fingerprints, condensation on cold samples, wrong cuvette orientation, settling particles and stray light. Good cuvette handling and indexing control most of these.
2. Why are dilute formazin standards prepared fresh on the day of use?
Dilute formazin suspensions are not stable; the particles settle and aggregate, so the turbidity changes. The concentrated stock is more stable. Stabilised commercial standards last longer.
3. How does an instrumental method improve the pharmacopoeial clarity test?
The visual test compares the sample with reference suspensions by eye, which depends on the analyst and lighting. A turbidity meter gives an objective number that can be trended, while the limits are still based on the same formazin reference suspensions.
Keep every Turbidity meter in control: usage logs, calibration and maintenance schedules, and automatic blocking of overdue instruments.