Untitled Essay Research Paper Analytical Chemistry

Untitled Essay, Research Paper

Analytical Chemistry Analytical Chemistry is the branch of chemistry principally concerned

with determining the chemical composition of materials, which may be solids, liquids,

gases, pure elements, compounds, or complex mixtures. In addition, chemical analysis can

characterize materials but determining their molecular structures and measuring such

physical properties as pH, color, and solubility. Wet analysis involves the studying of

substances that have been submerged in a solution and microanalysis uses substances in

very small amounts.

Qualitative chemical analysis is used to detect and identify one or

more constituents of a sample. This process involves a wide variety of tests. Ideally, the

tests should be simple, direct, and easily performed with available instruments and

chemicals. Test results may be an instrument reading, and observation of a physical

property, or a chemical reaction. Reactions used in qualitative analysis may attempt to

cause a characteristic color, odor, precipitate, or gas appear. Identification of an

unknown substance is accomplished when a known one is found with identical properties. If

none is found, the uknown substance must be a newly identified chemical. Tests should not

use up excessive amounts of a material to be identified. Most chemical methods of

qualitative analysis require a very small amount of the sample. Advance instrumental

techniques often use less than one millionth of a gram. An example of this is mass

spectrometry.

Quantitative chemical analysis is used to determine the amounts of

constituents. Most work in analytical chemistry is quantitative. It is also the most

difficult. In principle the analysis is simple. One measures the amount of sample. In

practice, however, the analysis is often complicated by interferences among sample

constituents and chemical separations are necessary to isolate tthe analyte or remove

interfering constituents.

The choice of method depends on a number of factors: Speed, Cost,

Accuracy, Convenience, Available equipment, Number of samples, Size of sample, Nature of

sample, and Expected concentration. Because these factors are interrelated any final

choice of analytical method involves compromises and it is impossible to specify a single

best method to carry out a given analysis in all laboratories under all conditions. Since

analyses are carried out under small amounts one must be careful when dealing with

heterogeneous materials. Carefullly designed sampling techniques must be used to obtan

representative samples.

Preparing solid samples for analysis usually involves grinding to

reduce particle size and ensure homogeneity and drying. Solid samples are weighed using an

accurate analytical balance. Liquid or gaseous samples are measureed by volume using

accurately calibrated glassware or flowmeters. Many, but not all, analyses are carried out

on solutions of the sample. Solid samples that are insoluble in water must be treated

chemically to dissolve them without any loss of analyte. Dissolving intractable substances

such as ores, plastics, or animal tisure is sometimes extremely difficult and time

consuming.

A most demanding step in many analytical procedures is isolating the

analyte or separating from it those sample constituents that otherwise would interfere

with its measurement. Most of the chemical and physical properties on which the final

measurement rests are not specific. Consequently, a variety of separation methods have

been developed to cope with the interference problem. Some common separation methods are

precipitation, distillation, extraction into an immiscible solvent, and various

chromatography procedures. Loss of analyte during separation procedures must be guarded

against. The purpose of all earlier steps in an analysis is to make the final measurement

a true indication of the quantity of analyte in the sample. Many types of final

measurement are possible, including gravimetric and volumetric analysis. Modern analysis

uses sophisticated instruments to measure a wide variety of optical, electrochemical, and

other physical properties of the analyte.

Methods of chemical analysis are frequently classified as classical and

instrumental, depending on the techniques and equipment used. Many of the methods

currently used are of relatively recent origin and employ sophisticated instruments to

measure physical properties of molecules, atoms, and ions. Such instruments have been made

possible by spectacular advances in electronics, including computer and microprocessor

development. Instrumental measurements can sometimes be carried out without separating the

constituents of interest from the rest of the sample, but often the instrumental

measurement is the final step following separation of the samples’s components, frequently

by means of one or another type of chromatography.

One of the best instrumental method is various types of spectroscopy.

All materials absorb or emit electromagnetic radiation to varying extents, depending of

their electronic structure. Therefore, studies of the electromagnetic spectrum of a

material yield scientific information. Many spectroscopic methods are based upon the

exposure of a sample substance to electromagnetic radiation. Measurements are then made of

how the intensity of radiation absorbed, emitted, or scattered by the sample changes as a

function of the energy, wave length, or frequency of the radiation. Other important

methods are based upon using beams of electrons or other particles to excite a sample to

emit radiation, or using radiation to induce a sample to emit electrons. In conjunction

with the related techniques of mass spectrometry and X-ray or neutron diffraction,

spectroscopy has almost completely replaced classical chemical analysis in studies of the

structure of materials.

Classical chemical procedures such as determination by volume as in

titrations is also used. A titration is a procedure for analyzing a sample solution by

gradually adding another solution and measuring the minimum volume required to react with

all of the analyte in the sample. The titrant contains a reagent whose concentration is

accurately known; it is added to the sample solution using a calibrated volumetric burette

to measure accurately the volume delivered.

When a precisely sufficient volume of titrant has been added, the

equivalence point, or endpoint, is reached. An endpoint can be located either visually,

using a suitable chemical indicator, or instrumentally, using an instrument to monitor

some appropriate physical property of the solution, such as pH or optical absorbance, that

changes during the titration. Ideally, the experimental endpoint coincides with the true

equivalence point, where an exactly equivalent amount of the titrant has been added, but

in practice some discrepancy exists. Proper choice of endpoint location system minimizes

this error.

Analytical chemistry has widespred useful applications. For example,

the problems of ascertaining the extent of pollution in the air or water involves

qualitative and quantitative chemical analysis to identify contaminants and to determine

their concentrations. Diagnosing human health problems in a clinical chemistry laboratory

is facilitated by quantitative analyses carried out on samples of the patient’s blood and

other fluids. Modern industrial chemical plants rely heavily on quantitative analyses of

raw materials, intermediates, and final products to ensure product quality and provide

information for process control. In addition, chemical analyses are essential to research

in all areas of chemistry as well as such related sciences as biology and geology.