chem lec

• Analytical Chemistry

  It is a measurement science consisting of a set of powerful ideas and methods that are useful in all fields of science, engineering, and medicine.
• Gravimetric Methods – determine the mass of the analyte or some compound chemically related to it.
• Volumetric Method – measures the volume of a solution containing sufficient reagent to react completely with the analyte.
• Electroanalytical Methods – measure electrical properties such as potential, current, resistance, and quantity of electrical charge.
• Spectroscopic Methods – explore the interaction between EM radiation and analyte atoms or molecules or the emission of radiation by analytes.
• 1. Choose a Method

  Considerations: required accuracy level, number of samples, sample complexity/components

  Challenges: intuition-based, large investment time/money
• 2. Acquire Sample (rep. sample)

  Considerations: large/bulk and heterogenous - > great effort is required to get the representative sample

  Solution: Sampling (process of collecting a small mass of a material whose composition accurately represents the bulk of the material being sampled); Assay (process of determining how much of a given sample is the material by its indicated name)
• .3. Processing the Sample

  3.1 Preparing a Lab Sample

  solid samples must be ground to decrease size and ensure homogeneity and stored for various lengths of time before analysis begins. - dry sample before the start of analysis

  • If liquid/gas samples, keep in sealed containers to prevent contamination
• 3.2 Defining Replicate Samples

  • Replication improves the quality of the results and provides a measure of their reliability.
• 3.3 Preparing Solutions: Physical & Chemical Changes

  • Dissolution
• 4. Eliminating Interferences

  • Species other than the analyte that affect the final measurement are called interferences, or interferents.
• Matrix/sample matrix – is the collection of all the components in the sample containing an analyte.
• 4. Eliminating Interferences

  • Techniques or reactions that work for only one analyte are said to be specific. Techniques or reactions that apply to only a few analytes are selective.
• 5. Calibrating and Measuring

  Concentration

  All analytical results depend on the final measurement X of a physical or chemical property of the analyte.

  • The measurement of the property X is directly proportional to the concentration

  𝒄𝑨 = 𝒌𝑿
• 6. Calculating Results

  Computing analyte concentrations from experimental data is usually relatively easy, particularly with computers.

  • Computations are based on raw experimental data collected in the measurement step, characteristics of the measurement instruments, and the stoichiometry of the analytical reaction.
• 7. Evaluating Results by Estimating

  Reliability

  • Analytical results are complete only when their reliability has been estimated.
• Feedback Control System – refers to the process of continuous measurement and control.
• Feedback Loop – refers to the cycle of measurement, comparison, and control.