analytical chem

• Analytical chemistry is the study of the separation, identification, and quantification of the chemical components of natural and artificial materials
• Analytical chemistry


  • It is a measurement science consisting of a set of powerful ideas and methods that are useful in all fields of science and medicine
• Qualitative analysis reveals the identity of the elements and compounds in a sample
• Quantitative analysis indicates the amount of each substance in a sample
• Analytical chemistry is applied throughout industry, medicine, and all the sciences
• Quantitative analytical measurements play a vital role in chemistry, biochemistry, biology, geology, physics, and other sciences
• Many scientists devote much time in the laboratory gathering quantitative information about systems that are important and interesting to them
• Results of a typical quantitative analysis are computed from two measurements

  • 1. Mass or volume of sample to be analyzed
  • 2. Measurement of some quantity that is proportional to the amount of analyte in the sample, such as mass, volume, intensity of light, or electrical charge
• Classifying Quantitative Analytical Methods

  1. Gravimetric methods determine the mass of the analyte or some compound chemically related to it

  2. Volumetric methods determine the volume of a solution containing sufficient reagent to react completely with the analyte

  3. Electroanalytical methods involve the measurement of electrical properties such as voltage, current, resistance, and quantity of electrical charge

  4. Spectroscopic methods are based on the measurement of the interaction between electromagnetic radiation and analyte atoms or molecules or on the production of such radiation by analytes

  5. Miscellaneous methods include mass-to-charge ratio, rate of radioactive decay, heat of reaction, rate of reaction, sample thermal conductivity, optical activity, refractive index
• Flow diagram showing the steps in a quantitative analysis
• Copyright © 2011 Cengage Learning
• Central vertical pathway


  1. Select a method

  2. Acquire and process the sample

  3. Dissolve the sample in a suitable solvent

  4. Measure a property of the analyte

  5. Calculate the results

  6. Estimate the reliability of the results
• Depending on the complexity of the sample and the chosen method, various other pathways may be necessary
• Picking a Method


  1. One of the first questions to be considered in the selection process is the level of accuracy required

  2. A second consideration related to economic factors is the number of samples to be analyzed

  3. The complexity of the sample and the number of components in the sample always influence the choice of method to some degree
• Acquiring the Sample


  1. Sampling involves obtaining a small mass of a material whose composition accurately represents the bulk of the material being sampled

  2. Sampling is frequently the most difficult step in an analysis and the source of greatest error. The final results of an analysis will never be any more reliable than the reliability of the sampling step

  3. A material is heterogeneous if its constituent parts can be distinguished visually or with the aid of a microscope

  4. An assay is the process of determining how much of a given sample is the material indicated by its name
• Processing the Sample


  1. Under certain circumstances, no sample processing is required prior to the measurement step

  2. Under most circumstances, we must process the sample in any of a variety of different ways

  3. The first step in processing the sample is often the preparation of a laboratory sample
• Preparing a Laboratory Sample

  1. A solid sample is ground to decrease particle size, mixed to ensure homogeneity, and stored for various lengths of time before analysis begins

  2. Because any loss or gain of water changes the chemical composition of solids, it is a good idea to dry samples just before starting an analysis

  3. Alternatively, the moisture content of the sample can be determined at the time of the analysis in a separate analytical procedure

  4. Liquid samples are subject to solvent evaporation

  5. If the analyte is a gas dissolved in a liquid, analyte must be kept inside a second sealed container to prevent contamination by atmospheric gases

  6. Extraordinary measures, including sample manipulation and measurement in an inert atmosphere, may be required to preserve the integrity of the sample
• Defining Replicate Samples


  1. Replicate samples, or replicates, are portions of a material of approximately the same size that are carried through an analytical procedure at the same time and in the same way

  2. Replication improves the quality of the results and provides a measure of their reliability

  3. Quantitative measurements on replicates are usually averaged, and various statistical tests are performed on the results to establish their reliability
• Preparing Solutions: Physical and Chemical Changes

  1. Ideally, the solvent should dissolve the entire sample, including the analyte, rapidly and completely

  2. The sample may require heating with aqueous solutions of strong acids
• Processing the Sample
• Preparing Solutions


  1. Physical and Chemical Changes

  2. The solvent should dissolve the entire sample, including the analyte, rapidly and completely

  3. The sample may require heating with aqueous solutions of strong acids, strong bases, oxidizing agents, reducing agents, or some combination of such reagents

  4. It may be necessary to ignite the sample in air or oxygen or perform a high-temperature fusion of the sample in the presence of various fluxes
• Eliminating Interferences
• Interference


  A species that causes an error in an analysis by enhancing or attenuating (making smaller) the quantity being measured
• Specific techniques or reactions

  • Work for only one analyte
• Selective techniques or reactions


  • Apply for only a few analytes
• Matrix


  All of the components in the sample containing an analyte
• Calibration and Measurement


  1. Ideally, the measurement of the property is directly proportional to the concentration

  2. Computing analyte concentrations are based on the raw experimental data collected in the measurement step, the characteristics of the measurement instruments, and the stoichiometry of the analytical reaction
• Calculating Results


  Computing analyte concentrations are based on the raw experimental data collected in the measurement step, the characteristics of the measurement instruments, and the stoichiometry of the analytical reaction
• Evaluating Results by Estimating Their Reliability

  Analytical results are incomplete without an estimate of their reliability
• Chemical analysis plays an integral role in feedback control systems
• Feedback control systems involve continuous measurement and control, often referred to as a feedback system
• Feedback control systems involve a cycle of measurement, comparison, and control called a feedback loop
• Volumetric titrations


  Involve measuring the volume of a solution of known concentration that is needed to react completely with the analyte
• Titration methods


  Are based on determining the quantity of a reagent of known concentration that is required to react completely with the analyte
• Reagent


  May be a standard solution of a chemical or an electric current of known magnitude
• Gravimetric titrations


  The mass of the reagent is measured instead of its volume
• Coulometric titrations


  The "reagent" is a constant direct electrical current of known magnitude that consumes the analyte. The time required (and thus the total charge) to complete the electrochemical reaction is measured.
• This lecture provides introductory material that applies to all the different types of titrations
• Typical setup for carrying out a titration


  1. The titrant is added to the flask with swirling until the color of the indicator persists

  2. The reference point on the meniscus and the proper position of the eye for reading are depicted

  3. Before the titration begins, indicator should be added
• Standard solution (or standard titrant)

  A reagent of known concentration that is used to carry out a volumetric titration