Chemical and Instrumental Analysis Quiz

Chemical Analysis

• Determination of substance's identity or amount
• Steps:
  • Collecting samples
  • Treating the sample
  • Performing measurements
  • Mathematical calculations
  • Reporting results
• Classification:
  • Qualitative: Identifying substances
  • Quantitative: Determining amount/concentration
  • Destructive: Changes sample composition
  • Non-destructive: Doesn't change composition
  • Instrumental: Uses analytical instruments to measure sample properties
  • Classical: Uses common lab equipment (depends on chemical reactions)

Instrumental Analysis

• Divided into categories based on measured property
  • Spectral: Measures radiation absorption, emission, or scattering
  • Electroanalytical: Applies electric signals to monitor sample solution's electrical properties (amperometry, voltammetry, potentiometry, conductimetry, coulometry, electrogravimetry)
  • Separative: Separates mixtures based on physical and chemical properties (chromatography, electrophoresis)

Classical Analysis

• Volumetric analysis: Quantitative method for determining analyte concentration in a solution
  • Titrant: Reagent added to a solution containing the analyte (known concentration)
  • Titrate: Unknown solution or analyte (known volume) + indicator
  • End point (N1V1 = N2V2): Calculate titrant volume and analyte concentration
• Gravimetric analysis: Based on measuring the weight of a pure compound related to analyte
  • Precipitation gravimetry
  • Volatilization gravimetry
  • Electrogravimetry
  • Thermogravimetry

Quantitative Organic Micro Analysis

• Determining percentages of elements in a new compound
• Verifying proposed molecular formula
• Determining purity of organic compounds
• Methods:
  • Classical (chemical reactions)
  • Instrumental (element analyzer)

Element Analyzer

• Instruments to determine element concentration & percentage in a compound
• Often use oxidative combustion methods
• Sample converted to oxidation products by decomposition or vaporization and oxidation

Accuracy and Precision

• Accuracy: Closeness of measurement to the true value
• Precision: Closeness of multiple measurements to each other

Determination Method Quantification of C,H

• Single-point calibration method: Compares signal of unknown with known standard
• Multiple-point calibration method: Uses signals from multiple standards to create a curve.

Element Analyzer Types (C, H, N....)

• C/H analyzer (Dumas & Pregl): Sample combustion in O2, CO2 & H2O measured
• C/H/N analyzer (Simon): Measures C,H,N by using reagents to remove interferences (Halogens, S, P)

Total Analyzers (N, S, C, H)

• Methods for determining the total amount of nitrogen, or sulfur, or carbon and hydrogen in organic or inorganic samples
• General procedure using thermal conductivity detectors and specialized detectors using chemiluminescence
• Different chemical methods may be used based on the analyzer types or compounds.

Total Carbon Analyzers

• Measurement of total carbon content in a solution.
• Using coulometric or other methods
• Differentiates between total carbon and total inorganic carbon and total organic carbon

Mercury Analysis

• Measures mercury concentration using AAS (atomic absorption spectrometry) or FAS (atomic fluorescence spectrometry)
• Using optical cells made of silica
• Uses a mercury discharge lamp for measurement

Kjeldahl Method

• Measures nitrogen content in organic products
• Digestion process involves boiling concentrated sulfuric acid and other chemicals in a sample solution
• Distillation process converts ammonia into ammonium in a separate solution
• Titration measures the amount of ammonia.
• Calculation of nitrogen percentage

Oxygen Flask Method

• Determination of halogens using combustion with oxygen
• Specific preparation of solid or liquid samples
• Combustion steps and resulting calculation for specific sample and analysis

Determination of Amino Group

• Amino groups react with acetic anhydride in the presence of pyridine
• The reaction forms acetic acid, measured by titration with sodium hydroxide
• Calculation of percent amino group in sample

Determination of Carboxyl Group

• In organic acids, carboxyl groups react with barium hydroxide.
• Measurement using titration
• Calculation to determine percentage of carboxyl group (COOH) in the sample

Amplification Reactions

• Involves reactions where the measured amount of element or compound proportionally increases
• Alternative reactions or methods that result in more favorable equivalence ratio
• Various multiplication reactions are possible (like with iodine or other elements)