16. ESSENTIAL TRACE ELEMENTS

Introduction to Essential Trace Elements

Essential trace elements are naturally occurring inorganic substances required by the human body in very small amounts (less than 100 mg/day). They are vital for maintaining normal physiological processes such as growth, development, enzyme function, and regulation of body metabolism.

In the human body, apart from carbon, hydrogen, nitrogen, and oxygen, several other elements are required for structural and biochemical functions. These are broadly classified as major elements and trace (minor) elements.

Classification of Dietary Elements

1. Major Elements (Macronutrients):

Required in larger amounts and include:

  • Calcium (Ca)
  • Phosphorus (P)
  • Potassium (K)
  • Sodium (Na)
  • Magnesium (Mg)
  • Chlorine (Cl)
  • Sulfur (S)

2. Trace (Minor) Elements:

Required in small (trace) amounts, usually a few milligrams or less per day. These include:

  • Iron (Fe)
  • Iodine (I)
  • Fluorine (F)
  • Zinc (Zn)
  • Copper (Cu)
  • Cobalt (Co)
  • Chromium (Cr)
  • Manganese (Mn)
  • Molybdenum (Mo)
  • Selenium (Se)

Classification Based on Biological Role

  • Essential Elements: Iron, Zinc, Copper, Cobalt, Chromium, Fluorine, Iodine, Manganese, Molybdenum, Selenium.
  • Probably Essential Elements: Nickel, Tin, Vanadium, Silicon, Boron.
  • Non-Essential Elements: Aluminium, Arsenic, Barium, Bismuth, Cadmium, Mercury, Lead, Silver, Titanium, etc.

Subclassification

  • Trace Elements: Iron, Zinc, Copper
  • Ultra Trace Elements: Manganese, Selenium, Cobalt, Chromium, Fluorine, Iodine, Molybdenum

Important Essential Trace Elements and Their Compounds

1. Iron (Fe)

Atomic Number: 26    Atomic Weight: 55.845

Iron plays a crucial role in the formation of hemoglobin and is vital for oxygen transport and cellular respiration. Iron deficiency leads to anemia.

Official Compounds of Iron:

  • Ferrous Sulphate I.P
  • Ferric Ammonium Citrate I.P
  • Ferric Chloride
  • Iron Sorbitex Injection (B.P)

a) Ferrous Sulphate (FeSO₄·7H₂O)

  • Preparation: Formed by dissolving iron filings in dilute sulfuric acid, filtering, and crystallizing.
  • Properties: Pale bluish-green crystals, efflorescent in dry air; soluble in water, insoluble in alcohol.
  • Assay: Redox titration with 0.1 N potassium permanganate (KMnO₄).
  • Uses: As a hematinic for treating iron deficiency anemia.
  • Dose: 200 mg 2–3 times daily.

b) Ferric Ammonium Citrate

  • Preparation: Obtained by reacting ferric sulphate with sodium hydroxide, followed by addition of citric acid and ammonia.
  • Properties: Brownish-red scales; soluble in water; affected by light.
  • Assay: Redox titration involving KMnO₄ and sodium thiosulphate.
  • Uses: Used as hematinic and iron supplement.
  • Dose: 1–3 g/day.

c) Ferric Chloride (FeCl₃·6H₂O)

  • Properties: Yellowish-brown crystals; acidic solution to prevent hydroxide precipitation.
  • Assay: Iodometric titration using sodium thiosulphate and starch indicator.
  • Uses: Used as a hematinic and laboratory reagent.

d) Iron Sorbitex Injection

  • Composition: Contains 4.75–5.25% ferric iron complexed with sorbitol and citric acid.
  • Uses: Administered intramuscularly to treat anemia in patients unresponsive to oral therapy or during pregnancy.

2. Copper (Cu)

Atomic Number: 29    Atomic Weight: 63.546

Official Compound: Copper Sulphate (CuSO₄·5H₂O)

  • Properties: Deep blue triclinic crystals; efflorescent in dry air.
  • Preparation: By treating copper with hot concentrated sulfuric acid.
  • Assay: Iodometric titration using sodium thiosulphate and starch indicator.
  • Uses: As a fungicide, algicide, and astringent; also used in laboratory reagents like Fehling’s and Benedict’s solutions.

3. Zinc (Zn)

Atomic Number: 30    Atomic Weight: 65.38

Official Compound: Zinc Sulphate (ZnSO₄·7H₂O)

  • Preparation: By reacting zinc carbonate or zinc oxide with sulfuric acid.
  • Properties: Colorless or white crystals; odorless and water-soluble.
  • Assay: Complexometric titration with disodium EDTA using eriochrome black T as indicator.
  • Uses: Used as topical astringent and wound-healing agent; also supports immune and skin health.

4. Iodine (I)

Atomic Number: 53    Atomic Mass: 126.9045

Official Compounds:

  • Sodium Iodide (NaI)
  • Potassium Iodide (KI)

a) Sodium Iodide (NaI)

  • Properties: White crystalline solid; highly soluble in water and alcohol; hygroscopic.
  • Preparation: Formed by reacting iodine with sodium hydroxide and reducing the resulting sodium iodate with carbon.
  • Assay: Titrated with potassium iodate using amaranth indicator.
  • Uses: Used as iodine supplement and expectorant in goiter and respiratory conditions.
  • Dose: 3–5 g/day.

b) Potassium Iodide (KI)

  • Properties: White crystalline solid; soluble in water and alcohol; less hygroscopic than sodium iodide.
  • Preparation: Similar to NaI, via reduction of potassium iodate with carbon.
  • Assay: Titrated with potassium iodate using chloroform as visual aid for end point.
  • Uses: Acts as iodine supplement and expectorant; used in goiter management and antifungal therapy.
  • Dose: 3–6 g/day.

Detailed Notes:

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