Toxicology Practicum: Detailed Guide to Chemical Reactions

Toxicology Practicum: Detailed Guide to Chemical Reactions

I. Formaldehyde (HCHO)

1. Isolation of HCHO:

• Method: Steam distillation.

• Role of H3PO4: Converts HCHO from its bound form to its free form, making the distillation process more efficient.

2. Qualitative Analysis of HCHO:

• Reaction with chromotropic acid:

• Detection limit: 0.5mg/kg solid sample.

• Color: Violet.

• Reaction with 1% Phloroglucinol/alkali:

• Color: Red.

• Reaction with phenol/acid:

• Phenomenon: Pink color appears at the interface.

3. Semi-quantitative Analysis of HCHO:

• Reagent: Chromotropic acid.

• Difference between test tubes: Concentration of HCHO.

II. Hydrogen Cyanide (HCN)

1. Qualitative Analysis of HCN:

• Guignard’s reaction:

• Reagent: Picric acid/alkali.

• Product: Isopurpurin, orange-yellow color.

• Grignard’s reaction:

• Components of test paper: Picric acid, Na2CO3.

• Phenomenon: Picric acid-soaked paper changes from yellow => orange-yellow => brown.

• Role of HCl: Added to allow HCN to evaporate, avoiding the alkaline environment from affecting the paper.

• Prussian blue reaction:

• Precipitate: Fe II and Fe III sulfate/alkali.

• Prussian blue: The precipitate turns blue when acidified.

• Alkalizing the sample solution: NaOH 50% – Converts cyanide to ionized form (CN-).

• Maximum duration for determination: 48 hours.

2. Quantitative Analysis of HCN:

• Method: Argentometry.

III. Phenol

1. Isolation of Phenol:

• Method: Steam distillation.

• Detection of phenol in distillate: p-nitroaniline diazotization/alkali. Measure the absorbance of the formed product and compare it to the standard solution.

2. Phenol in urine:

• Form of existence: Phenyl sulfonic acid.

• Treatment: Hydrolyze with H2SO4 => free phenol.

3. Quantitative Analysis of Phenol:

• Method: Iodometry (determining the amount of excess bromine after reaction with phenol).

• Role of chloroform: Dissolves the tribromophenol precipitate.

• Form of bromine: Bromide-bromate solution.

IV. Ethanol (C2H5OH)

1. Qualitative Analysis of Ethanol:

• Reaction with Sulphomolybdic Acid:

• Color: Deep blue.

• Reaction to form iodoform:

• Sensitivity: 0.04mg/mL.

• Environment: Alkali (NaOH or K2CO3 10%).

• Temperature: Not exceeding 50 degrees Celsius.

• I2: 1% iodine solution.

• Reaction to form ethyl acetate:

• Sensitivity: 15-20 mg/mL.

• Identification: Characteristic smell of the reaction between ethanol and acetic acid catalyzed by H2SO4 acid.

2. Quantitative Analysis of Ethanol:

• Nicloux’s method:

• Oxidizing agent: Potassium bichromate/concentrated sulfuric acid.

• Color change: Blue (excess ethanol) => green (excess potassium bichromate).

• Role of picric acid: Precipitates protein.

• Maximum amount of potassium bichromate: 1.1mL.

• Applicable sample: Fresh samples: blood, brain… not yet decomposed. Add NaF to preserve decomposed blood.

V. Methanol (CH3OH)

1. Qualitative Analysis of Methanol:

• Schiff’s reagent: Based on the oxidation product, Formaldehyde.

• Reaction with 1% resorcin:

• Environment: Alkali.

• Color: Pink or crimson.

• Reaction with Schiff’s reagent:

• Environment: Acid.

• Color: Blue or blue-violet.

• Esterification reaction: Add the test solution + 0.03g salicylic acid and 2-3 drops of concentrated H2SO4, heat. If methanol is present, there will be a hot oil smell.

VI. Arsenic (As)

1. Isolation of Arsenic:

• Inorganicization:

• Wet inorganicization: sulfo-nitric + H2O2/HClO4.

• Dry inorganicization: MgO-MgNO3.

2. Qualitative Analysis of Arsenic:

• Bougault’s reaction:

• Reagent: H3PO2/HCl.

• Catalyst: High temperature, an iodine spot.

• Sensitivity: 10 mcg.

• Phenomenon: Brown precipitate – As metal.

VII. Bismuth (Bi)

1. Qualitative Analysis of Bismuth:

• Leger’s reaction:

• Environment: Weak acid.

• Phenomenon: Red-orange precipitate of iodobismuthite quinine soluble in organic solvents.

VIII. Chromium (Cr)

1. Qualitative Analysis of Chromium:

• Cazeneuve’s reaction:

• Reagent: 1% Diphenylcarbazide/alcohol.

• Phenomenon: Pink-purple solution, unstable.

IX. Manganese (Mn)

1. Qualitative Analysis of Manganese:

• Marshall’s reaction:

• Phenomenon: The solution appears pink-purple.

X. Lead (Pb)

1. Qualitative Analysis of Lead:

• Reaction with Dithizone:

• Phenomenon: The solution turns purple-pink.

• Reaction with KI:

• Phenomenon: PbI2, a yellow precipitate, is formed.

• Reaction with K2Cr2O7:

• Phenomenon: PbCrO4 precipitate is formed, which has a yellow color.

XI. Mercury (Hg)

1. Isolation of Mercury:

• Method: Inorganicization with sulfo-nitric.

2. Quantitative Analysis of Mercury:

• Method: Formation of the Cu2I2 complex. Compare to the standard solution with a known concentration.

XII. General Notes:

• Sensitivity of the reaction: Note the sensitivity of each reaction to determine the minimum amount of toxic substance that can be detected.

• Environmental conditions: Chemical reactions are often dependent on the environment (acid, alkali, temperature…). Follow the instructions carefully so that the reaction takes place effectively.

• Chemical safety: Always use safe protective measures when working with hazardous chemicals.

• Practical techniques: The practical operations need to be accurate and careful to avoid errors.

Note: This document provides basic information on chemical reactions in toxicology practicum. To understand more about each reaction, please refer to other professional documents.