Analytical Chemistry Basics

Analytical Chemistry

• Branch of science dealing with separation, identification, and determination of components in a sample.

Types of Analytical Chemistry

• Qualitative Analysis is a method for finding elemental composition of inorganic compounds and functional groups of organic compounds
• Quantitative Analysis involves measurements of the amounts of substances in reactions.

Accuracy and Precision

• Accuracy refers to the agreement of experimental results with true value.
• Precision is the measure of reproducibility of data within a series of results.

Significant Figures

• Non-zero digits (1-9) are always significant.
• Leading zeros are never significant.
• Confined zeros between nonzero digits are always significant.
• Trailing zeros are significant only with an explicitly shown decimal point.

Classification of Analysis

• Classification can be based on sample size, extent of determination, nature of methods, and materials used.

Based on Sample Size

• Ultramicroanalysis uses less than 1 mg.
• Microanalysis uses 1 mg - 10 mg.
• Semi-microanalysis uses 10 mg - 100 mg.
• Macroanalysis uses 100 mg - 1 g and above.

Based on the Extent of Determination

• Proximate analysis determines the total amount of a group of active plant principles in a sample.
  • It includes moisture content, volatile matter, fixed carbon, and ash content.
• Ultimate analysis measures the amount of a specific chemical species in a sample.
  • Carbon represents the combustible portion.
  • Hydrogen contributes to combustibility.
  • Nitrogen may contribute to pollutants.
  • Sulfur can lead to sulfur dioxide emissions.
  • Oxygen is often calculated via difference.

Based on Nature of Methods

• Classical methods.
• Instrumental methods.
• Miscellaneous or special methods.

Classical Method

• Also known as General, Chemical, Wet, or Stoichiometric method
• Gravimetric Analysis measures the mass of a substance formed from a chemical reaction.
• Volumetric Analysis (Titration) involves solution of known concentration reacting with a solution of the analyte.
• Colorimetric methods measure the intensity of color formed in a reaction.
• Potentiometric methods measure the voltage of a solution or the potential difference between two electrodes to determine concentration of ions.
• Chromatography early forms are considered classical methods.

Instrumental Method

• Spectroscopy involves interaction of electromagnetic radiation with matter.
• Mass Spectrometry (MS) measures the mass-to-charge ratio of charged particles.
• Electroanalytical Methods measure electrical properties to obtain information about a sample.

Miscellaneous or Special Methods

• Acid value measures the amount of acidic substances present, expressed as milligrams of potassium hydroxide (KOH) needed to neutralize acids in one gram of the sample.
• Ash content measures the total mineral content or inorganic residue after subjecting a sample to high temperatures, typically through combustion.
• Water content (moisture content) measures the amount of water present in a substance or material.

Based on Materials Used

• Chemical.
• Physical.
• Biological.

Types of Quantitative Analysis

• Volumetric Analysis involves measuring the volume of a solution of known concentration needed to react with the desired constituent.
  • Divisions include: Neutralization, Precipitation, Compleximetry, Oxidation-reduction.
• Gravimetric Analysis involves accurately measuring the weight of a substance isolated in pure form or converted to another substance of known composition.
• Special Methods are analysis techniques for crude drugs, assay of fats/fixed oils, assay of volatile oils, and assay of alkaloids.
• Physico-Chemical Methods are analysis based on physical or chemical properties using instruments like spectrophotometers, chromatographs, polarographs, polarimeters, and fluorometers.

Specialized Analytical Methods & Equipment

• Distillation purifies liquids and separates components based on boiling points.
• Microscopy visualizes and analyzes samples at microscopic and nanoscopic levels.
• Polarimeter measures the angle of rotation of plane-polarized light passing through an optically active substance.
• Refractometer measures the refractive index of a substance, giving information about concentration or purity.
• Desiccator dries and preserves moisture-sensitive substances.
• Oven provides controlled temperature environments for drying, heating, and thermal treatments.
• Moisture Balance (moisture analyzer/meter) determines the moisture content of a sample.
• Chromatography involves measuring the current flowing in an electrochemical cell as a function of applied potential.
• Spectroscopy
• Polarography studies electroactive species and their concentration/redox behavior.
• Biological tests use living organisms or their components to detect, identify, or quantify specific substances.

Qualitative Inorganic Analysis

• Detecting Cations: Cations are classified into five groups based on their properties.
  • The goal is to determine composition without necessarily quantifying the amounts of each constituent.
• Detecting Anions: Halides are precipitated by silver nitrate, and can then be identified by color.
• Detecting Cations using Group Reagents
  • I: Cold dilute hydrochloric acid with Ag+, Pb++, Hg2++ ions results in Chlorides that are insoluble in cold dilute HCl.
• II: Hydrogen sulfide in presence of hydrochloric acid (0.2-0.3 M) with subgroup IIA (Cu++, Cd++, Hg++, Bi++, Pb+) and subgroup IIB (Sn++, Sn4+, Sb3+, As3+, As5+) leads to precipitate as Sulfides in acidic medium (0.2-0.3 M HCl).
• III: Ammonium hydroxide in presence of ammonium chloride with Al3+, Cr3+, Fe3+ results in precipitate as Hydroxides by Ammonium Hydroxide in presence of excess Ammonium Chloride.
• IV: Hydrogen Sulfide in presence of Ammonium Hydroxide with Ni, Co, Mn, Zn results in precipitate as Sulfides by Hydrogen Sulfide from ammoniacal solution in presence of Ammonium Chloride
• V: (NH4)2CO3 in presence of Ammonium Hydroxide and Ammonium Chloride wiht Ba++, Ca++, Sr++ results in precipitate as Carbonates in alkaline medium by Ammonium Hydroxide in presence of Ammonium Chloride.
• VI: No particular reagent with Na+, K+, NH+4, Mg+ results in ions not precipitated in previous groups.
• Detecting Anions using Group Reagents to produce Gases evolves or Precipitates
  • I: Carbonates, hydrogen carbonate, sulphite, thiosulphate, sulphide, nitrite using dilute HCl leads to CO2, SO2, H2S, NO2,HCN.
  • II: Fluoride, chloride, Bromide, iodide, nitrate, Chlorate, perchlorate, Permanganate and organic anions using conc. H2SO4 leads to HF, HCl, HBr, HI.
• III: Sulphates and phosphates leads to Barium Chloride.

Modern Techniques

• Qualitative inorganic analysis is primarily used as a pedagogical tool.
• Modern techniques used in its place include atomic absorption spectroscopy and ICP-MS.