Environmental Engineering Reference
In-Depth Information
chemicals suitable for colorimetric determinations. These methods offered some
advantages, but were still tedious and imprecise.
Soon, chromatographic methods made inroads into resolving separate
components from a mixed solution. Chromatography is a physical method of
separation that relies on the interaction of substances within a mixture when they are
exposed to both a stationary and a mobile phase. Early thin-layer chromatography
(TLC) and paper chromatography (PC) techniques used in the 1950s and 1960s
separated compounds that were detected by measuring their intensity using
ultraviolet and visible (UV-VIS) spectroscopy techniques.
Gas chromatography (GC) and high performance liquid chromatography
(HPLC) were developed in the 1960s, becoming the methods of choice for residue
analysis and replacing TLC and PC in the 1970s. GC and HPLC techniques
efficiently ''resolve'' individual components from a complex mixture and can
accurately quantify how much of an individual substance is present in the mixed
component sample. The primary difference between GC and HPLC is that the
former relies on resolution of substances being swept through a chromatography
column in the gas phase at elevated temperatures, while the latter relies on the
substance in a solution being chromatographically separated when in contact with a
solid stationary phase.
Mass spectroscopy (MS) developments in the 1980s dramatically enhanced the
scope of detection to include most semi- to nonpolar, and thermally-stable
compounds. The first generation combined GC-MS relied on electron impact (EI)
ionization to fragment the molecule into an array of positive mass ions. Continued
refinement in GC-MS and maturation of HPLC-mass spectrometry has resulted in
increasingly sensitive detections at even lower levels. Overall, the advances in
instrumentation and technology have provided analysts with powerful tools to
rapidly and accurately measure extremely low levels. Advanced analytical
instrumentations tend to detect small quantities of almost anything.
REFERENCES
B ERGER W, M C C ARTY H, S MITH R-K (1996), Environmental Laboratory Data Evaluation. Genium
Publishing Corporation Amsterdaan, NY, pp. 2-12-62; pp. 3-13-12.
C LEAVES KS (2005), Ancillaries and Analyzers: Balances, pH meters, and more were critical to the rise of
chemistry, Enterprise of the Chemical Sciences, 107-110 (http://pubs.acs.org/supplements/chemchro-
nical2/107.pdf).
*C LEAVES KS, L ESNEY MS (2005), Capitalizing on Chromatography: LC and GC have been key to the
central science, Enterprise of the Chemical Sciences, 75-82 (http://pubs.acs.org/supplements/chem-
chronical2/075.pdf).
*C RUMBLING DM, G ROENJES C, L ESNIK B, L YNCH K, S HOCKLEY J, V AN E E J, H OWE R, K EITH L, M C K ENNA
J (2001), Managing uncertainty in environmental decisions, Environ. Sci. Technol., 35(19):404A-409A.
D UNNIVANT FM (2004), Environmental Laboratory Excises for Instrumental Analysis and Environmental
Chemistry, John Wiley & Sons, Hoboken, NJ pp. xi-xii
* Suggested Readings
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