Determination of the Ascorbic Acid Content of a Food (2)

Determination of the Ascorbic Acid Content of a Food

Scurvy: Known as the “scourge of the navy.”
- Historical Context:
  - Vasco da Gama's 1497-1499 expedition: Half of the crew lost to scurvy.
  - Sir Richard Hawkins: Witnessed 10,000 deaths due to scurvy in 20 years at sea.
Symptoms of Scurvy:
- Bleeding gums, loss of teeth, foul breath, skin blotches, swelling of limbs, bloody diarrhea, rotting flesh, exhaustion, delirium.
Interesting Fact: Outbreaks of scurvy ceased when ships reached land.

Historical Remedies:
- 1617: John Woodall claimed lemon juice could prevent scurvy.
- James Lind advocated for green vegetables and ripe fruits.
Conditions on Ships:
- Poor living conditions: filthy, dark, crowded, inadequate ventilation, unchanged bedding, rotten food.
Captain James Cook: Promoted cleanliness and ensured crew received malt, sauerkraut, lemons, and oranges to prevent scurvy.
1795 Regulation: British Admiral mandated lemon juice for sailors on English ships.

Discovery: In 1933, the antiscorbic component in foods was identified as ascorbic acid.
Dietary Importance: Vitamin C is essential in human diet today.

Objective: To determine vitamin C content in food/liquid.
Types of Assays:
- Qualitative Assay: Identifies the presence of a substance (e.g., color change).
- Quantitative Assay: Measures concentration of a substance.
- Titration Assay: Involves adding solution drop-by-drop to achieve desired reaction.

Standardization:
- Determine volume of known vitamin C solution needed to change color of indophenol from blue to straw-yellow.
Procedure: Add vitamin C solution (unknown concentration) to indophenol solution until color changes.
Calculating Concentration: Use results to determine vitamin C concentration in unknown solution based on volume needed for color change.

Lab Activity Goals:
- Perform titration assay to standardize vitamin C amount required to change indophenol color.
- Gain practical skills to determine vitamin C content in an unknown juice sample.

Assay Reagents: Prepare 0.05% indophenol and 0.2% vitamin C solutions.
Standardizing Assay Procedure:
- Set up burette, ensure valve is closed, fill with ascorbic acid solution, and adjust to the 0 mL mark.

Measure and prepare 10 mL of indophenol solution, conduct titration until the color changes from blue to straw yellow.
Record the volume of ascorbic acid solution used. Repeat for three trials and average results.

Determine volume of ascorbic acid needed to change 10 mL of indophenol solution.
- Fill in data for three trials and calculate the average volume used for color change.

Calculate mass of vitamin C needed from titration results.
- Use the formula: average volume (mL) x 0.002 g/mL = g of vitamin C.
- Convert to mg for final data.

Follow similar procedure to determine the volume of practice solution that changes the color of indophenol.
- Record trial data and average for accuracy.

Use formula to determine concentration of vitamin C in practice solution:
- Grams of vitamin C = mass needed to change indophenol solution / volume of practice solution (mL).

Analyze unknown solution coded with a number, perform same procedures to determine vitamin C content.

Repeat standardization procedure with unknown solution. Record adjustments for each trial.

Perform titration with unknown solution, recording volumes and averaging for analysis.
Calculate the concentration in g/mL and convert to mg/mL for results.