Introduction to Analytical Chemistry

Introduction to Analytical Chemistry

• Analytical chemistry plays a vital role in the development of science.
• The field plays a vital role in research areas of chemistry, biochemistry, biology, geology, physics and other sciences.
• All branches of chemistry draw on analytical chemistry ideas and techniques.
• The interdisciplinary nature of chemical analysis makes it a vital tool in medical, industrial, government and academic laboratories.

Quantitative vs Qualitative

• Analytical Chemistry deals with methods for determining the chemical composition of samples.
• Qualitative Analysis provides information about the identity of species or functional groups in the sample where an analyte can be identified.
• Quantitative Analysis provides numerical information of analyte.

Quantitative Analytical Methods

• Classical Methods include wet chemical methods like precipitation, extraction, distillation, boiling or melting points, gravimetric and titrimetric measurements.
• Instrumental Methods include analytical measurements like conductivity, electrode potential, light absorption or emission, mass-to-charge ratio, fluorescence etc.
• Gravimetric Methods determine the mass of the analyte or some compound chemically related to it.
• Volumetric Methods involve measuring the volume of a solution containing sufficient reagent to react completely with the analyte.
• Spectroscopic Methods are based on measurement of the interaction between electromagnetic radiation and analyte atoms or molecules.
• Chromatographic Methods are separation techniques for quantitation based on a calibration curve.
• Electroanalytical Methods involve the measurement of electrical properties such as voltage, current, resistance and quantity of electrical charge.

Typical Quantitative Analysis

• A typical quantitative analysis includes a sequence of steps shown in a flow diagram.
• In some instances, one or more of the steps can be omitted.
• The essential first step in any quantitative analysis includes method selection, sample acquisition, sample processing, sample solubility, assessment of measurable properties, interference elimination, measurement of property x, calculation of results and finally estimation of the reliability of results.

Classifying Chemicals

• Reagent Grade chemicals conform to the minimum standards set forth by the Reagent Chemical Committee of the American Chemical Society (ACS).
• Primary-Standard Grade reagents have been carefully analyzed by the supplier; the results are printed on the container label.
• Special-Purpose Reagent Chemicals of specific application include solvents for spectrophotometry and high-performance liquid chromatography.

Rules for Handling Reagents and Solutions

• Select the best grade of chemical available for analytical work and pick the smallest bottle sufficient to do the job.
• Hold the stoppers of reagent bottles between your fingers and never set a stopper on a desk top.
• Unless specifically directed otherwise, never return any excess reagent to a bottle.
• Never insert spatulas, spoons, or knives into a bottle that contains a solid chemical, but rather shake the capped bottle to break up an encrustation, then pour out the desired quantity.
• Keep the reagent shelf and the laboratory balance clean and neat and clean up any spills immediately.
• Follow local regulations concerning the disposal of surplus reagents and solutions.

Precautions in Using an Analytical Balance

• Center the load on the pan.
• Protect the balance from corrosion and limit objects to nonreactive metals, nonreactive plastics, and vitreous or glasslike materials.
• Consult your instructor if the balance appears to need adjustment.
• Keep the balance and its case scrupulously clean, using a camel's-hair brush for removing spilled material or dust.
• Always allow a heated object to return to room temperature before weighing it.
• Use tongs, finger pads, or a glassine paper strip to handle dried objects to prevent transferring moisture to them.

Weighing by Difference

• Weighing by difference is a method for determining a series of sample masses.
• First, the bottle and its contents are weighed. Then, a sample is transferred from the bottle to a container.
• Gentle tapping of the bottle with its top and slight rotation of the provide control over the amount of sample removed.
• Following transfer, the bottle and its residual contents are weighed; the mass of the sample is the difference between the two masses.
• Make sure all the solid removed from the weighing bottle be transferred without loss to the container.

Apparatus Measuring Volume

• Volume can be measured reliably with a pipet, buret, or volumetric flask.
• Pipets permit the transfer of accurately known volumes from one container to another.
• Burets make it possible to deliver volume up to the maximum capacity of the device.
• A buret consists of a calibrated tube to hold titrant plus a valve arrangement by which the flow of titrant is controlled.
• A buret equipped with a glass stopcock for a valve relies on a lubricant between the ground-glass surfaces of stopcock and barrel for a liquid-tight seal.

Safety in the laboratory

• Before any laboratory work, locate the nearest eye fountain, fire blanket, shower, and fire extinguisher.
• Wear eye protection at all times.
• Most of the chemicals in the laboratory are toxic and some such as concentrated solutions of acids and bases are highly corrosive.
• Never perform an unauthorized experiment or work alone in the laboratory.
• Never bring food or beverages into the laboratory, or drink from laboratory glassware.
• Use a bulb or other device to draw liquids into a pipet rather than pipetting by mouth.
• Wear adequate foot covering (no sandals) and confine long hair with a net.
• Be extremely tentative in touching objects that have been heated because hot glass looks like cold glass.
• Use fume hoods whenever toxic or noxious gases are likely to be evolved.
• Use hand to waft vapors above containers toward nose when testing for odors.
• Notify your instructor immediately in the event of an injury.
• Dispose of solutions and chemicals as instructed.