The Analytica Proses

The general analytical process is shown in Figure l.l. The analytical chemist should

be involved in every step. The analyst is really a problem solver. a critical part of

the team deciding what, why, and how. The unit operations of analytical chemistry

that are common to most types of analyses are considered in more detail below.

DEFINING THE PROBLENI—WHAT DO WE REALLY NEED TO KNOW? (NOT NECESSARILY EVERYTHING)

Before the analyst can design an analysis procedure, he or she must know what in- The rr ay an analysis is perlornietl

formation is needed, by whom, for what purpose. and what type of sample is to depends on the inl`oi·nration needed.

be analyzed. As the analyst, you must have good communication with the client.

- This stage of an analysis is perhaps the most critical. The client may be the

Environmental Protection Agency (EPA), an industrial client. an engineer. or your

grandmother4each of which will have different criteria or needs. and each hav-

ing a different understanding of what a chemical analysis involves or means. lt is

important to communicate in language that is understandable by both sides. If someone puts a bottle on your desk and asks, "What is in here?" or “1s this safe?". you may have to explain that there are 10 million known compounds and sub· stances. A client who says, "1 want to know what elements are in here" needs to
understand that at perhaps $20 per analysis for 85 elements it will cost $1700 to test for them all. when perhaps only a few elements are of interest. 1 have often had laypersons come to me with cosmetics they wish to "revcrsc cngineer" so they can market them and make at fortune. When they realize it may cost a small fortune to determine the ingredients, requiring a number of sophisti- cated analyses, they always rethink their goals,
The concept of "safe" or "zero/nothing" is one that is hard to deiine or un-
derstand by many. Telling someone their water is safe is not for the analyst to say.
All you can do is present the analytical data (and give an indication of its range of
accuracy). The client must decide whether it is safe to drink, perhaps relying on
other experts. Also, never report an answer as "zero," but as less than the detec-
tion limit, which is based on the measurement device/instrument. We are limited
by our methodology and equipment. and that is all that can be reported. Some mod-
em instruments, though, can measure ridiculously small amounts or concentrations,
for example, parts per trillion. This presents a dilemma in making policy (often
political in nature). A law may be passed that there should be zero concentration
of a chemical effluent in water. ln practice, the acceptable level is defined by how
low a concentration can be detected; and the very low detectability may be far be-
low the natural occurrence of the chemical or below the levels to which it can be
reasonably reduced. We analysts and chemists need to be effective communicators
of what our measurements represent.
Once the problem is defined this will dictate how the sample is to be ob-
tained, how much is needed, how sensitive the method must be, how accurate and
precisel it must be, and what separations may be required to eliminate interfer-
ences. The determination of trace constituents will generally not have to be as pre-
cise as for major constituents. but greater care will be required to eliminate trace
contamination during the analysis.
Once the required measurement is known. the analytical method to be used
will depend on a number of factors, including the analysts skills and training in
different techniques and instruments; the facilities. equipment, and instruments
available; the sensitivity and precision required; the cost and the budget available
and the time for analysis and how soon results are needed. There are often one or
more standard procedures available in reference books for the determination of an
analyte (constituent to be determined) in a given sample type. This does not mean
that the method will necessarily be applicable to other sample types. For example,
a standard EPA method for groundwater samples may yield erroneous results when
applied to the analysis of sewage water. The chemical literature (joumals) contains
many specific descriptions of analyses.
published by the American Chemical Society. is a good place to begin a literature of literature.
search. It contains abstracts of all articles appearing in the major chemical jour-
nals of the world. Yearly and cumulative indices are available, and many libraries
have computer search facilities. The major analytical chemistry joumals may be
consulted separately. Some of these are: Analytica Chimicu Acta, Analytical Chem-
istry Analytical Letters, Analyst, Applied Spectr0sCOP)t Clirtica Chimica Acta, Clin-
ical Chemistry, Journal of the Association of Ojjicial Analytical Chemists, Journal
qfCltrm1tat0grz1phy, Spectroclzimictz Acta, and Ttzlcmta. While the specitic analysis
of interest may not be described, the analyst can often use literature information
on a given analyte to devise an appropriate analysis scheme. Finally, the analyst ·
may have to rely upon experience and knowledge to develop an analytical method
for a given sample. The literature references in Appendix A describe various pro-
cedures for the analysis of different substances.
Examples of the manner in which the analysis of particular types of samples
are made are given in Chapters 24 to 26. These chapters describe commonly per-
formed clinical, biochemical. and environmental analyses. The various techniques
described in this text are utilized for the specific analyses. Hence, it will be useful
for you to read through these applications chapters both now and after completing
the majority of this course to gain an appreciation of what goes into analyzing real
samples and why the analyses are made.
Once the problem has been defined, the following steps can be started.