Analytical Chemistry






  


ANALYTICAL CHEMISTRY

WHAT IS ANAYTICAL CHEMISTRY?

I. Introduction

    A. Analytical chemistry deals with separating, identifying, and quantifying the relative amounts of the components of an analyte.

    B. Analyte = the thing to analyzed; the component(s) of a sample that are to be determined.

    C. There are several different areas of analytical chemistry:
     

      1. Clinical analysis - blood, urine, feces, cellular fluids, etc., for use in diagnosis.

      2. Pharmaceutical analysis - establish the physical properties, toxicity, metabolites, quality control, etc.

      3. Environmental analysis - pollutants, soil and water analysis, pesticides.

      4. Forensic analysis - analysis related to criminology; DNA finger printing, finger print detection; blood analysis.

      5. Industrial quality control - required by most companies to control product quality.

      6. Bioanalytical chemistry and analysis - detection and/or analysis of biological components (i.e., proteins, DNA, RNA, carbohydrates, metabolites, etc.).

        a. This often overlaps many areas.

        b. Develop new tools for basic and clinical research.
         

    D. The focus of the course is an introductory experience in the quantitative analysis with some methods of analytical separation.

    E. Four analytical methods are usually taught in an introductory course:
     

      1. Gravimetric methods - measure the mass of the analyte (or a compound chemically related to the analyte).

      2. Volumetric methods - measure the volume of a solution containing sufficient reagent to react with the analyte (i.e., titrations or gas analysis).

      3. Electroanalytic methods - measure an electrical property (i.e., potential, current, resistance, amperes, etc.) chemically related to the amount of analyte.

      4. Spectroscopic methods - measuring the interaction between the analyte and electromagnetic radiation (or the production of radiation by an analyte).
       

    F. Miscellaneous methods (that don't fit the classifications above):
     
      1. Mass spectrometry - mass-to-charge ratio of an analyte's decomposition products.

      2. Radiochemical methods - measuring rates of radioactive decay by an analyte.

      3. Kinetics - measuring reaction rates.

      4. Thermal conductivity.

      5. Optical activity - measuring the interactions of an analyte with plane-polarized light.

      6. Refractometry/Refractive index.

II. Steps in a Typical Quantitative Analysis
    A. Method selection. Factors to consider include:
     
      1. Accuracy.

      2. Reliability.

      3. Time.

      4. Cost/number of analyses.

      5. Complexity of sample.
       

    B. Sampling. A representative sample must be obtained.

    C. Preparing a laboratory sample.
     

      1. Converting the sample to a useful form.
       
        a. Solids are usually ground to a suitable particulate size to get a homogeneous sample.
         
      2. Absorption (or desorption) of water.

      3. Avoiding decomposition conditions. This is especially troublesome for biological samples.
       

    D. Defining replicate samples. Replicate samples are always performed unless the quantity of the analyte, expense or other factors prohibit.

    E. Preparing solutions of the sample.
     

      1. Most analyses are performed on solutions.

      2. A solvent is chosen that dissolves the whole sample without decomposing the analyte.
       

    F. Eliminating interferences. Interferences are substances that prevent direct measurement of the analyte and must be removed.

    G. Calibration and measurement.
     

      1. The physical or chemical property proportional to the analyte concentration is measured.

      2. Suitable standards must be measured to determine the relationship between analyte quantity and the physical/chemical property being measured (i.e., calibration).
       

    H. Calculating results.
     
      1. This requires using the raw data, stoichiometry of the reaction(s) and instrumental factors to calculate the analyte concentration.
       
    I. Evaluating the results and estimating their reliability. This requires appropriate use of statistics.