Page 21 - Modern Analytical Chemistry

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4 Modern Analytical Chemistry

Original sample

HNO 3 , HCl, heat

Residue Solution

20% NH 4 Cl
10% tartaric acid
take alkaline with 1:1 NH 3
take acid with HCl
10% tartaric acid
take alkaline with 1:1 NH 3 Is
Yes
solid
present?
Solid
Key No take acid with HCl
Solution 1% alcoholic DMG
take alkaline with 1:1 NH 3

2
Figure 1.2 A Ni(DMG) (s)
Analytical scheme outlined by Hillebrand and
4
Lundell for the gravimetric analysis of Ni in
ores (DMG = dimethylgloxime). The factor of
0.2031 in the equation for %Ni accounts for
the difference in the formula weights of %Ni = mass A ´ 0.2031 ´ 100
Ni(DMG) 2 and Ni; see Chapter 8 for more g sample
details.

The combination of determining the mass of Ni 2+ by difference, coupled with the
need for many reactions and filtrations makes this procedure both time-consuming
and difficult to perform accurately.
The development, in 1905, of dimethylgloxime (DMG), a reagent that selec-
2+
tively precipitates Ni 2+ and Pd , led to an improved analytical method for deter-
4
mining Ni 2+ in ores. As shown in Figure 1.2, the mass of Ni 2+ is measured directly,
requiring fewer manipulations and less time. By the 1970s, the standard method for
the analysis of Ni 2+ in ores progressed from precipitating Ni(DMG) 2 to flame
5
atomic absorption spectrophotometry, resulting in an even more rapid analysis.
Current interest is directed toward using inductively coupled plasmas for determin-
ing trace metals in ores.
In summary, a more appropriate description of analytical chemistry is “. . . the
science of inventing and applying the concepts, principles, and . . . strategies for
6
measuring the characteristics of chemical systems and species.” Analytical chemists
typically operate at the extreme edges of analysis, extending and improving the abil-
ity of all chemists to make meaningful measurements on smaller samples, on more
complex samples, on shorter time scales, and on species present at lower concentra-
tions. Throughout its history, analytical chemistry has provided many of the tools
and methods necessary for research in the other four traditional areas of chemistry,
as well as fostering multidisciplinary research in, to name a few, medicinal chem-
istry, clinical chemistry, toxicology, forensic chemistry, material science, geochem-
istry, and environmental chemistry.