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2 Modern Analytical Chemistry

1A What Is Analytical Chemistry?

“Analytical chemistry is what analytical chemists do.”*
We begin this section with a deceptively simple question. What is analytical chem-
istry? Like all fields of chemistry, analytical chemistry is too broad and active a disci-
pline for us to easily or completely define in an introductory textbook. Instead, we
will try to say a little about what analytical chemistry is, as well as a little about what
analytical chemistry is not.
Analytical chemistry is often described as the area of chemistry responsible for
characterizing the composition of matter, both qualitatively (what is present) and
quantitatively (how much is present). This description is misleading. After all, al-
most all chemists routinely make qualitative or quantitative measurements. The ar-
gument has been made that analytical chemistry is not a separate branch of chem-
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istry, but simply the application of chemical knowledge. In fact, you probably have
performed quantitative and qualitative analyses in other chemistry courses. For ex-
ample, many introductory courses in chemistry include qualitative schemes for
identifying inorganic ions and quantitative analyses involving titrations.
Unfortunately, this description ignores the unique perspective that analytical
chemists bring to the study of chemistry. The craft of analytical chemistry is not in
performing a routine analysis on a routine sample (which is more appropriately
called chemical analysis), but in improving established methods, extending existing
methods to new types of samples, and developing new methods for measuring
chemical phenomena. 2
Here’s one example of this distinction between analytical chemistry and chemi-
cal analysis. Mining engineers evaluate the economic feasibility of extracting an ore
by comparing the cost of removing the ore with the value of its contents. To esti-
mate its value they analyze a sample of the ore. The challenge of developing and val-
idating the method providing this information is the analytical chemist’s responsi-
bility. Once developed, the routine, daily application of the method becomes the
job of the chemical analyst.
Another distinction between analytical chemistry and chemical analysis is
that analytical chemists work to improve established methods. For example, sev-
eral factors complicate the quantitative analysis of Ni 2+ in ores, including the
presence of a complex heterogeneous mixture of silicates and oxides, the low con-
centration of Ni 2+ in ores, and the presence of other metals that may interfere in
the analysis. Figure 1.1 is a schematic outline of one standard method in use dur-
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ing the late nineteenth century. After dissolving a sample of the ore in a mixture
2+
of H 2 SO 4 and HNO 3 , trace metals that interfere with the analysis, such as Pb ,
3+
Cu 2+ and Fe , are removed by precipitation. Any cobalt and nickel in the sample
are reduced to Co and Ni, isolated by filtration and weighed (point A). After
dissolving the mixed solid, Co is isolated and weighed (point B). The amount
of nickel in the ore sample is determined from the difference in the masses at
points A and B.
mass point A – mass point B
%Ni = ´100
mass sample

*Attributed to C. N. Reilley (1925–1981) on receipt of the 1965 Fisher Award in Analytical Chemistry. Reilley, who was
a professor of chemistry at the University of North Carolina at Chapel Hill, was one of the most influential analytical
chemists of the last half of the twentieth century.