Environmental Engineering Reference
In-Depth Information
In Chapter 10, when environmental applications of GC and HPLC were
discussed, we have provided a list of EPA methods using GC and HPLC for the
analysis of chemicals in air (TO-series), water (500 and 600 series methods), and
waste (SW-846 8000 series methods). Of these methods approved by the U.S. EPA,
the number of GC-MS methods are too many to be listed here. In a significant contrast
is the fact that there are only a few LC-MS based standard methods listed in the EPA
method database. For a detailed list, interested reader can find such information at the
U.S. EPA's Web site: www.epa.gov/epahome/Standards.html. From this website,
there is a link to another important Web site: www.epa.gov/nerlcwww/methmans.
html, where a compendium called ''The Manual of Manuals'' can be found.
Readers can refer to Chapter 5 for specific methodologies of GC-MS and LC-
MS. Simply put, GC-MS methods for the analysis of toxic organic compounds in air
can be found in TO-series. These methods employ adsorbent tube, liquid impinger,
PUF cartridge, and SUMMA canisters as the sampling media. The standard GC-MS
methods for the analysis of VOCs can be found in 524 and 624 for drinking water
and wastewater, respectively. The equivalent GC-MS methods for SVOCs can be
found in 525 and 625 for drinking water and wastewater, respectively. The GC-MS
based waste methods in SW-846 include 8260B (VOCs), 8270C (SVOCs), and a
particular high resolution GC-MS method for the analysis of dioxin compounds. At
the time of writing, there are only two LC-MS methods (8231A and 8235) in the
SW-846 that are developed for solvent extractable nonvolatiles.
The readers should be aware that the number of publications in peer-reviewed
journals exploded in the last 10 years that explores the use of various mass
spectrometric methods. Many of these hyphenated methods are aimed at
contaminants of emerging environmental concerns with a low detection limit.
Table 5.5 in Chapter 5 is an example list of these emerging compounds, including
disinfection byproducts, pharmaceutical chemicals, endocrine disrupting chemicals,
chiral contaminants, algal toxin, natural organic mater, and many more. Richardson
(2001; 2002; 2003) gave several excellent reviews on the applications of mass
spectrometry in environmental sciences.
12.2 NUCLEAR MAGNETIC RESONANCE
SPECTROSCOPY (NMR)
12.2.1 NMR Spectrometers and the Origin
of NMR Signals
The term ''nuclear magnetic resonance (NMR)'' refers to a technique in which
nuclei in the presence of a magnetic field are in resonance with a radiation in the
radio frequency (rf) range (4-900 MHz). As shown in the schematic diagram of an
NMR spectrometer in Figure 12.10, the essential components are not hard to
understand. It consists of a sample probe, a superconducting magnet to align the
nuclear spins in the sample, a radiofrequency transmitter as a source of energy to
excite a nuclei from the low to the high energy states, a receiver to detect the
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