Cbio 55 - LEC Chap 1 - Analytical Chemistry

Sample Analyses

• Macro sample: > 100 mg, > 100 µL
• Semi-micro sample: 10-100 mg, 50-100 µL
• Micro sample: 1-10 mg, < 50 µL
• Ultra-micro sample: < 1 mg, 1% of the sample
• Minor constituent: 0.01-1% of the sample
• Trace constituent: 0.001-0.01% of the sample
• Ultra-trace constituent: < 0.001% of the sample

Analytical Reactions

• Dry method: sample and analytical reagent in solid state, subjected to high temperature heating
• Wet method: performed in qualitative analysis, involves precipitation, titration, and colorimetric methods
  • Accompanied by external effects:
    • Changing of solution coloration
    • Forming or dissolving precipitation
    • Evolution of gas

Dry Method Flame Test

• Involves introducing sample to hot, non-luminous flame and observing the color that appears

Bead Test

• Reactions for borax bead formation – sodium tetraborate (Na2B4O7 ∙10H2O)
• When heated, combines with colored transition metal oxides (e.g., Co, Ni, Cr, Cu, Mn) to form metaborates with characteristic colors

Charcoal Cavity Test

• Cations converted to metal carbonate in charcoal cavity, which decomposes on heating to metal oxide or metal

Errors in Chemical Analysis

• Gross errors: human errors leading to outliers
• Systematic (instrumental and personal) errors: minimized by:
  • Periodic calibration of equipment
  • Careful, disciplined laboratory work
  • Checking instrument readings, notebook entries, and calculations
  • Choosing the analytical method or using an automated procedure
• Systematic (method) errors: difficult to detect, estimated by analyzing Standard Reference Materials (SRMs)

Errors and Statistics

• Central tendency:
  • Mean (x): average value of measurements
  • Median: middle value in a set of data
• Personal errors: result from carelessness, inattention, or personal limitations
• Number bias: preference for certain digits or numbers
• Random errors (indeterminate error): cause data to scatter around a mean value
• Precision: reproducibility of measurements, closeness of data to other data obtained in exactly the same way
• Accuracy: closeness of a measurement to its true or accepted value

Analytical Chemistry

• Definition: science of methods to study material composition
• Branch of chemistry that deals with the operation and analysis of a chemical substance
• Divisions:
  • Qualitative chemistry/analysis: determination of actual constituents present
  • Quantitative chemistry/analysis: determination of amount of constituent present
• Importance:
  • Establishing economic value
  • Determining health hazards
  • Diagnosing disease
  • Controlling quality
  • Relating properties to composition and structure
  • Conducting research
• Classification of methods of analysis:
  • Gravimetric method: mass of sample or compounds chemically related to it is determined
  • Volumetric method: amount of analyte is determined by measuring volume of solution of known concentration
  • Instrumental method: employs instruments other than those used in gravimetric and volumetric methods
• Classification of analyses:
  • Complete or exact analysis: amount of each constituent of the sample is determined
  • Ultimate analysis: amount of each element is determined
  • Proximate or partial analysis: amount of a certain selected constituent in a sample is determined

Explore the fundamental concepts of analytical chemistry, including qualitative and quantitative analysis methods. Learn about the nature of analytical chemistry and how it is applied in studying material composition.