Analytical Chemistry

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