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

Determination of the Ascorbic Acid Content of a Food

Page 1

• Title: Determination of the Ascorbic Acid Content of a Food

Page 2: Introduction to Scurvy

• 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.

Page 3: Scurvy Prevention

• 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.

Page 4: Ascorbic Acid

• Discovery: In 1933, the antiscorbic component in foods was identified as ascorbic acid.

• Dietary Importance: Vitamin C is essential in human diet today.

Page 5: Activity Overview

• 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.

Page 6: Analysis for Vitamin C Content

• 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.

Page 7: Learning Objectives

• 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.

Page 8: Procedure – Session I

• 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.

Page 9: Procedure – Continuation of Session I

• 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.

Page 10: Standardization Section A

• 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.

Page 11: Standardization Calculation

• 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.

Page 12: Section B – Practice Solution Titration

• Follow similar procedure to determine the volume of practice solution that changes the color of indophenol.

  • Record trial data and average for accuracy.

Page 13: Practice Solution Concentration Calculation

• 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).

Page 14: Session II – Unknown Solution

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

Page 15: Section C – Unknown Solution Standardization

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

Page 16: Section C – Concentration Calculation

• Perform titration with unknown solution, recording volumes and averaging for analysis.

• Calculate the concentration in g/mL and convert to mg/mL for results.